EPA-R3-73-021
February 1973 Ecological Research Series
Effects of Temperature on Growth
and Reproduction of Aquatic Snails
Office of Research and Monitoring
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ECOLOGICAL
RESEARCH series. This series describes research
on the effects of pollution on humans, plant and
animal species, and materials. Problems are
assessed for their long- and short-term
influences. Investigations include formation,
transport, and pathway studies to determine the
fate of pollutants and their effects. This work
provides the technical basis for setting standards
to minimize undesirable changes in living
organisms in the aquatic, terrestrial and
atmospheric environments.
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EPA-R3-73-021
February 1973
EFFECTS OF TEMPERATURE ON GROWTH AND
REPRODUCTION OF AQUATIC SNAILS
By
Henry van der Schalie
Elmer G. Berry
University of Michigan, Ann Arbor, MI
Contract No. 14-12-441
Project 18050 FOG
Project Officer
Dr. Donald I. Mount
National Water Quality Laboratory
6201 Congdon Boulevard
Duluth, Minnesota 55804
Prepared for
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.O. 20402
Price $2,36 domestic postpaid or $2.00 GPO Bookstore
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EPA Review Notice
This report has been reviewed by the Environmental Protection
Agency and approved for publication. Approval does not signify
that the contents necessarily reflect the views and policies of
the Environmental Protection Agency, nor does mention of trade
names or commercial products constitute endorsement or recommen-
dation for use.
ii
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ABSTRACT
The effects of temperature on the biology of freshwater snails were
studied using two lymnaeids (Lymnaea stagnalis and L. emarginata),
three planorbids (Helisoma trivolvisf ,~H. anceps and~"H. campanulatum),
and one physid (Physa gyrina) - all puEnonate "pond"~snails; only one
gill-breathing operculate (Amnicola limosa) was tested. Both growth
and egg-laying were measured in several temperatures ranging from 6°C
to 36°C. The gonad development was determined through serial paraffin
sections which were stained with haematoxylon and eosin; reproduction
was measured in terms of egg-laying. The data show that the lymnaeids
grow best at about 18°C, with egg production better but viability
reduced at 22°C and above. In contrast, the planorbids tend to grow
better under warmer conditions (about 25°C); however, when 30°C is
reached growth may appear better but reproduction is inhibited. The
physids tolerate the widest range, sometimes conditions warmer than
30°C, although at this temperature reproduction is also inhibited.
The one operculate, Amnicola limosa, studied showed a preference for
cool conditions and was more like the lymnaeids in temperature
responses.
Each of the seven species of animals studied was stressed in aquaria
with water maintained at 6°, 12°, 18°, 24°, 30°, and 34° or 36°C. The
range varied with the groups as indicated but none could be cultured
much below 12°C and none would reproduce when temperatures exceeded
30°C. Growth was usually better in "warm" water but advantages in
growth were generally offset by a lack of gonad development.
Mollusks, like other animals cited, are very sensitive to ambient
temperatures. Even small changes are shown to be important in their
influence on the environmental area affected. Studies are encouraged
to determine the effects of temperature changes well in advance of
projected developments such as the use of natural waters for cooling
reactors, e.g. - "improvements" that could adversely affect the flora
and fauna of the surrounding region.
iii
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CONTENTS
Section
I Conclusions
II Recommendations
III Introduction
IV Materials and Methods
V Pulmonate and Operculate
Snails Tested
VI Acknowledgments
VII References
VIII Selected Author Publications
Page
1
3
7
9
13
155
157
163
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FIGURES
PAGE
1 Equipment for maintaining constant temperatures 10
2 Growth of Lymnaea stagnalis at temperatures with
6°C intervals (Experiment 1) 19
3 Growth of Lymnaea stagnalis^ at 2°C intervals
(Experiment 3)24
4 The average number of egg cases produced per snail
per day by Lymnaea stagnalis at 2°C intervals
(Experiment 3)25
5 Estimated number of eggs laid by Lymnaea stagnalis
when calculated on 100% survival at 2°C~intervals
(Experiment 3) 26
6 Survival of Lymnaea stagnalis at 2°C intervals
(Experiment"!"} 27
7 Total number of eggs produced by Lymnaea stagnalis
at 2°C intervals (Experiment 3)28
8 The number of egg cases laid by Lymnaea stagnalis
in terms of the percentage of snails that survived
at 2°C intervals (Experiment 3) 29
9 Total number of egg cases of Lymnaea stagnalis at
2°C intervals (Experiment 3") 32
10 Data obtained from Experiments 1 and 3 as given in
Table 3 for Lymnaea stagnalis 37
11 Growth of Lymnaea stagnalis at four different
temperatures ("plop test") 40
12 Survival of Lymnaea stagnalis in "plop test" 41
13 Survival in percentage of Lymnaea stagnalis in
"plop test" shown in Figure 1241
14 Survival in percent of Lymnaea emarginata at 6°C
intervals (Experiment4)45
15 Growth and recovery of Lymnaea emarginata at 6°C
intervals (Experiment V) ~ 46
16 Egg cases laid (cumulative) by Lymnaea emarginata
at 6°C intervals (Experiment 4l"~ 47
VI
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FIGURES (Continued)
PAGE
17 Cumulative (adjusted to 100% survival) eggs
produced by Lymnaea emarginata at G°C intervals
(Experimental49,50,51
18 Eggs laid by Lymnaea emarginata at 6°C intervals
(Experiment^) 53
19 Growth of Lymnaea emarginata at 2°C intervals
(Experiment 5)55
20 Eggs produced by Lymnaea emarginata at 2°C intervals
(Experiment 5) 56
21 Cumulative (not adjusted to 100% survival) eggs
produced by Lymnaea emarginata at 2°C intervals
(Experiment ITJ~~ 57
22 Cumulative (adjusted to 100% survival) eggs produced
by Lymnaea emarginata at 2°C intervals (Experiment
5) 59
23 Data on "plop test" with Lymnaea emarginata at four
different temperatures 62
24 Growth of Helisoma trivolvis at 6°C intervals
(Experiment 2)70
25 Two sets of growth observations made on Helisoma
trivolvis (Experiments 2 and 6) 71
26 Egg production of Helisoma trivolvis at 6°C
intervals (Experiment 6) 73
27 Growth of Helisoma. trivolvis at 6°C intervals
(Experiment 6)74
28 Cumulative egg cases of Helisoma trivolvis at 6°C
intervals (Experiment 6~"575
29 Cumulative eggs produced by Helisoma trivolvis at
temperatures best for egg production (Experiment
6) 76
30 Mortality of Helisoma trivolvis at 6°C intervals
(Experiment~6)77
31 Growth of Helisoma trivolvis at 2°C intervals
(Experiment 12) 80
vi i
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FIGURES (Continued)
PAGE
32 Growth and recovery of Helisoma trivolvis at
2°C intervals (Experiment 12) 82
33 Growth and egg production of Helisoma trivolvis at
2°C intervals (Experiment 12~5 83
34 Egg production of Helisoma trivolvis on a weekly
basis after 4th week (Experiment 12) 84
35 Growth and survival of Helisoma anceps at 6°C
intervals (Experiment 10)~ 92
36 Growth of Helisoma anceps at 6°C intervals
(Experiment 10) 93
37 Growth and siorvival of Helisoma anceps at 2°C
intervals (Experiment 14)95
38 Growth of Helisoma anceps at 2°C intervals
(Experiment 14)97
39 Summary of "plop test" data for Helisoma anceps 99
40 Growth and reproduction of Helisoma campanulatum
at 6°C intervals (Experiment 9)104
41 Growth and survival of Helisoma campanulatum at
6°C intervals (Experiment 9)106
42 Growth and survival of Helisoma campanulatum at
2°C intervals (Experiment 1ST ~ 108
43 Survival of Helisoma campanulatum at 2°C intervals
(Experiment 15)~ 109
44 Growth, survival and cumulative number of eggs laid
(adjusted to 100% survival) of Physa gyrina at
6°C intervals (Experiment 7) 117
45 Curtailment of egg production of Physa gyrina due
to Chaetogaster infestation compared to normal
higher egg production (Experiment 7). 119
46 Eggs of Physa gyrina produced in the 30°C tank
(Experiment T)120
47 Comparison of Physa gyrina eggs produced in the 30°C
tank with the number (adjusted to 100% survival)
at room temperature (27°C) (Experiment 7) 121
Vlll
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FIGURES (Continued)
PAGE
48 Growth and survival of Physa gyrina at 2°C 124
49 Survival of Physa gyrina at 2°C intervals
(Experiment 137 125
50 Growth of Physa^ gyrina at 2°C intervals
(Experiment 13l126
51 Growth of Physa gyrina in the 14°C tank
(Experiment 13"5 129
52 Adjustment of temperature, dissolved oxygen and
growth of Physa gyrina in the 16°C tank
(Experiment 13) 130
53 Egg production by Physa gyrina at temperatures
ranging from 14°C to 34bC (Experiment 13) 131
54 Growth of Amnicola limosa. at 6°C intervals
(Experiment 8)137
55 Growth and survival of Amnicola limosa at 6°C
intervals (Experiment"!!!139
56 Growth of Amnicola limosa at 6°C intervals
(Experiment 11)
57 Diagrammatic comparison of growth and egg-laying
in Lymnaea stagnalis at 6° and 2°C intervals
(Experiments 1 and 3)
58 Diagrammatic comparison of growth and egg-laying
between Lymnaea stagnalis and Helisoma trivolvis 149
ix
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TABLES
PAGE
1 Summary of data for Lymnaea stagnails at 6°C
intervals (Experiment 1) 17
2 Summary of data for Lymnaea stagnalis at 2°C
intervals (Experiment 3) 22
3 Summary of data, Experiments 1 and 3, for
Lymnaea stagnalis 35
4 Summary of data for Lymnaea stagnalis "plop test" 38
5 Summary of data for Lymnaea emarginata at 6°C
intervals (Experiment 4)44
6 Summary of data for Lymnaea emarginata at 2°C
intervals (Experiment 5) 54
7 Summary of data for Lymnaea emarginata "plop test" 60
8 Summary of data for Helisoma trivolvis at 6°C
intervals (Experiment 2)68
9 Summary of data for Helisoma trivolvis at 6°C
intervals (Experiment 6)72
10 Summary of data for Helisoma trivolvis at 2°C
intervals (Experiment 12)78
11 Summary of data for Helisoma trivolvis "plop test" 85
12 Summary of data for Helisoma anceps at 6°C
intervals (Experiment 10) 91
13 Summary of data for Helisoma^ anceps at 2°C
intervals (Experiment 14)94
14 Summary of data for Helisoma anceps "plop test" 98
15 Summary of data for Helisoma campanulatum at 6°C
intervals (Experiment 9)103
16 Summary of data for Helisoma^ campanulatum^ at 2°C
intervals (Experiment 15) 107
17 Summary of data for Physa gyrina at 6°C intervals
(Experiment 7) 116
18 Summary of data for Physa gyrina at 2°C intervals
(Experiment 13) 122
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TABLES (Continued)
PAGE
19 Summary of data for Amnicola limosa at 6°C
intervals (Experiment 8)136
20 Summary of data for Amnicola limosa_at 6°C
intervals (Experiment 11) 138
XI
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MAPS
PAGE
1 Distribution of Lymnaea stagnalis (Say)
in the Great Lakes region20
2 Distribution of Lymnaea emarginata Say (L_.
catascopium Say) in the Great Lakes region H2
3 Distribution of Helisoma trivolvis (Say) in
the Great Lakes region 67
4 Distribution of Helisoma anceps (Menke) in
the Great Lakes region 90
5 Distribution of Helisoma campanulaturn (Say)
in the Great Lakes region102
6 Distribution of Physa gyrina Say in the Great
Lakes region 113
7 Distribution of Amnicola limosa (Say) in the
Great Lakes region134
XI1
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PLATES
PAGE
-i
I Figures 1-5 Gonad tissue sections from
Lymnaea stagnalis_ at different temperatures 34
II Figures 6-9 Gonad tissue sections from
Helisoma trivolvis at temperatures from
20° - 24°C 86
III Figures 10-13 Gonad tissue sections from
Helisoma trivolvis at temperatures from
26° - 34°C 87
IV Figures 14-19 Gonad tissue sections from
Helisoma trivolvis at temperatures from
6° - 30°C 88
V Figures 20-23 Gonad tissue sections from
Helisoma anceps at different temperatures 101
VI Figures 24-26 Gonad tissue sections from
Helisoma campanulatum at temperatures from
6° - 18°C 111
VII Figures 27-30 Gonad tissue sections from
Helisoma campanulatum at temperatures from
- 30°C 112
VIII Figures 31-33 Gonad tissue sections from
Physa gyrina at temperatures from 6° - 24°C 132
IX Figures 34-36 Gonad tissue sections from
Physa gyrina at temperatures from room - 34°C 133
X Figures 37-39 Gonad tissue sections from
Amnicola limosa at temperatures from 6° - 18°C 142
XI Figures 40-42 Gonad tissue sections from
Amnicola limosa at 24° C and room temperature 143
xiii
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SECTION I
CONCLUSIONS
1. Mollusks in nature make up much of the biomass; optimal temperatures
are shown to be important requisites both for reproduction and growth in
this group.
2. This temperature-stressing study demonstrated three reproductive
patterns among the seven species of aquatic snails tested:
(a) the lymnaeids reproduce and thrive best in cool (19° to 22°C)
conditions;
(b) the planorbids require warmer water (22° to 25°C);
(c) the physids are highly tolerant and can maintain themselves
in a much wider temperature range (12° to 30°C).
The gill-breathing operculate snail (as opposed to the pulmonates above),
Amnicola limosa, showed a preference for "cool" conditions similar to
that of Lymnaea stagnalis.
3. Sensitivity of aquatic mollusks to temperature is surprisingly
narrow. Although an increase in size might be interpreted as optimum for
the well-being of a given species, the present study demonstrated that
gonad development is arrested even in slightly higher temperatures.
Raising the optimum temperature as little as 5°C was demonstrated to
cause disastrous effects among the sensitive species.
M-. The circumpolar snail, Lymnaea stagnalis, no longer inhabits southern
Michigan lakes, but occurs 150 miles further north. Its disappearance is
probably due to the slightly higher temperatures in lakes in recent
decades, sufficient to cause critical breeding failures.
5. Physids showed wide tolerance to heat fluctuations. This capacity
explains their wide distribution and dominance under adverse conditions,
e.g., sewage disposal facilities (where they clog sieves), thermal
springs , etc.
6. In "plop tests" it appeared that pulmonate snails withstood sudden
changes of higher temperature better than sudden chilling. More studies
on behavior due to changing temperatures are projected.
7. Techniques for culturing these particular snails have been reasonably
well developed. The pulmonates, especially, could serve as important
tools for studying not only the role of temperature but other environmen-
tal factors as well. The cycle for Lymnaea stagnalis from egg to adult
is 4 months; for the other snails studied a 2-month period is required.
8. For most invertebrates studied, the normal functional range lies
somewhere between 12° and 30°C; environmental changes that fall to
either side of those limits are apt to be destructive to the fauna.
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SECTION II
RECOMMENDATIONS
Every effort should be made to maintain the original, normal and natural
situations in the environment and to preserve as much as possible the
existing ecological conditions. The dangers, as pointed out by Cairns
(1968) in his article, "We're in Hot Water," can no longer be ignored.
The recommendations that follow essentially substantiate what he has al-
ready stressed so well based on his wide field and laboratory experience.
After outlining the way power plants operate, he stated:
"At present we are throwing most of this heat away, as we do with
many other waste products, and it is capable of polluting our
environment just as surely as do sewage, industrial waste and
agricultural waste."
Figures given on the amounts of heated waste water that will return to a
river, estuary, ocean or lake are astounding. The elimination of species
will depend on their sensitivity, and we have now just begun to measure
how sensitive some of them are. The problem is compounded because the
higher temperatures in water make less dissolved oxygen available to the
aquatic animals. In view of these conditions, field survey work deserves
far more encouragement than it is receiving. Such studies should be
both qualitative and quantitative and should serve to predict the probable
changes heated waters would produce.
It is obvious that much more laboratory work is needed to assay the effects
of temperature on a variety of biotic groups that will be affected. The
prospective changes caused by elevated temperatures have also been out-
lined by Cairns (1968: 190) as: "death through direct effects of heat;
internal functional aberrations (reduced oxygen, disruption of food sup-
ply, decreased resistance to toxic substances); interference with spawn-
ing or other critical activities in the life cycle; competitive replace-
ment by more tolerant species as a result of the above physiological
effects." These several effects were clearly evident in the experiments
carried out and cited in this report. For example, while the snails grew
well in warmer than usual water, they often failed to reproduce. The
acclimatization shown could remove the normal occupants such as lymnaeids
and allow the establishment of conditions that might favor planorbids
like Biomphalaria, which can serve as intermediate hosts for schistosom-
iasis"More studies are needed especially with the operculate, gill-
breathing snails for which there was not sufficient time in this project.
When field conditions have been measured and the controlled laboratory
studies have been undertaken, sites should be monitored to assay the
changes in the "biological, chemical and physical effects" brought about
by the source of (in this case) heat pollution. Some groups lend them-
selves better for such monitoring studies, and mollusks, without question,
are among the best. Unfortunately, they have not had nearly the attention
they deserve. Not only are they widespread and common but, in terms of
biomass, they are far superior to insects which have been considered as
indices of that pollution. Yet, too little basic work has been done with
mollusks which are often ideal as tools for assaying environmental con-
ditions. It is now possible to maintain a number of the common species
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in culture. Some groups, such as the mussels, already are established
by M. M. Ellis (1937) as important in studies for the "detection and
measurement of stream pollution." The role of many mollusks for deter-
mining the ecology during the past, the present and the future deserves
far more attention than it has hitherto received. Studies of immediate
interest involve:
(1) the use of mussels as natural filtration agents in streams
where they may serve in programs designed to alleviate eutro-
phication;
(2) the potential use of mussels as monitors for measuring the
amount and the time of atomic fall-out, as was demonstrated
by Nelson (1964) at Oak Ridge;
(3) projecting tolerances to temperature, as well as other factors,
as determined in the laboratory better to understand conditions
during interglacial periods when mollusk deposits were among
the most prominent among the animals preserved.
Specific recommendations include:
1) More "plop" tests are needed to understand the levels of tolerance
to sudden temperature changes among such a large and prominent group
as the mollusks.
2) Too little is known, as yet, about the effects of temperature on
the gill-breathing operculate snails (such as the pleurocerids,
viviparids, amnicolids, etc.) that often pave the bottom of streams
and lakes. The success of such investigations will depend on the
ability to maintain these animals in culture to make the necessary
tests.
3) It has been established that trematode infections are often regulated
by the temperatures to which their mollusk hosts are subjected. These
factors directly control some of the serious human diseases such as
blood fluke (schistosomiasis) and "swimmer's itch" (schistosome
dermatitis). While studies have been initiated in our laboratory in
this field, more work is needed to determine the effects of tempera-
ture on the development of the parasites in their intermediate hosts.
4) If additional heat should enter rivers and lakes to produce "blooms"
of algae, such natural filtration agents as the freshwater mussels,
which often are found in large populations in the affected area,
should be tested to determine whether they could effectively serve
in this capacity.
5) Since it has been shown that certain species of mollusks are defin-
itely heat sensitive, it should be possible to use some of those
groups for testing tolerance in areas suspected of being subjected
to"heat pollution" or "calefaction."
6) More studies are needed on the "finger-nail clams" (Sphaeriidae),
a widespread and common group in the benthic fauna; they are also
important in the food chain (fish food, etc.). Their life histories
are virtually unknown, let alone their temperature tolerances.
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7) More detailed knowledge of the role of temperature on the biota should
be obtained to understand fully the nature of such problems today as
heat pollution. It also could provide the information needed by the
paleoecologist to help in interpreting the type of climate present in
various geological horizons. Most of the biogeographical interpreta-
tion of the Great Lakes region in its geologic past will depend on
some careful delineation of the temperature tolerances in several of
the widely distributed mollusk groups.
8) The behavior patterns of mollusks are closely related to ambient tem-
peratures; it is necessary, therefore, not only to ascertain their
ability to withstand sudden changes (as in the "plop" tests) but to
learn how they orient themselves under normal and abnormal temperature
stress. A neglected area of research is that of the effect of thermal
stress on behavior: on the rate of change of activity patterns (i.e.,
movement, respiration,feeding), alterations in copulatory and egg-
laying, and changes in horizontal and vertical migrations. Especially
needed are studies dealing with the effects'of short-term (i.e., hours)
and long-term (i.e., days) thermal stress on behavior, as well as
studies comparing the effects of fluctuating as opposed to constant
elevated temperatures.
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SECTION III
INTRODUCTION
While there are many references indicating that temperature plays an
important role in the biology of animals, it is often difficult to find
specific information dealing with its influence on species or species
groups. As pointed out by Cairns (1972: 831), many good references to
papers on the "effects of increased temperatures in the aquatic environ-
ment" are published in Raney and Menzel (1969) on fishes, and in Holda-
way, et al., (1969). While information relating to field situations is
of a rather general kind, there are several basic studies showing the
importance of temperature in nature. The earliest references were those
of Hogg (1854) and Semper (1881) who studied field conditions for Lymnaea
stagnalis. Both R. M. DeWitt (1954) in Michigan and W. F. DeWit (1955)
in the Netherlands recognized the importance of field temperatures in
their studies with species belonging to the Physidae. McNeil (1959, 1960,
1961 and 1963) studied winter survival of both Lymnaea and Physa snails
in the Columbia drainage system in the state of Washington.Shiff (1963,
1966), Sturrock (1966) and Jobin (1970) considered the role of temperature
in the bionomics of the planorbid snails that serve as intermediate hosts
to the blood parasite which causes the disease, schistosomiasis, in Africa
and Puerto Rico. It was clearly shown from their field studies of these
tropical species that there is a tendency for planorbids to thrive better
in warmer water.
The most definitive and earliest basic temperature study in the laboratory
with a planorbid species, Biomphalaria (formerly Australorbis) glabrata,
was that of Standen (1952)"Mich els on (1961), also working with B_. gla-
brata, discovered that 30°C was the optimal temperature for maximum
growth, but in that range reproduction was inhabited. Shiff (1963,
1967) discovered that Bulinus (Physopsis) globosus , which also belongs
to the Planorbidae, can just maintain itself at 18°C but that its optimum
temperature is 25°C. Sturrock's (1966) laboratory investigations with
B. pfeifferi led him to the belief that the intermediate host snails for
S". mansoniVwhen exposed in nature to temperatures "in excess of 28-30°C
For several months on end" cannot persist in such habitats.
Chernin (1967) compared B. glabrata and Bulinus truncatus with Lymnaea
palustris in a thermal gFadient.Whereas the former "were generally
found in moderately warm loci, L. palustris tended to accumulate in the
relatively cool portions of the~gradient, and Bulinus truncatus distri-
buted themselves fairly uniformly throughout the gradient." Jobin (1970)
studied B_. glabrata living in three farm ponds in Puerto Rico and found
that optimum temperature for oviposition was 25°C "with oviposition
diminishing to zero as the temperatures approach 20°C and 30°C."
The best summary statement dealing with "acclimation in molluscs" appears
to be that by Segal (1961) who stated:
"We now know that growth rates, and other rate functions of poikilo-
therms from different environments, do not differ as much as expected
from the temperature differences between environments. Poikilo-
therms, which are passive conformers to the environmental temperature,
-------
show compensatory changes in growth rates and metabolic rates in
response to the temperatures encountered in different latitudes
(Fig. 1), seasons (Fig. 2), and microgeographic areas (Fig. 3)."
As indicated by the several references cited above, the majority of the
studies which have been made, particularly with species in the family
Planorbidae, are restricted to the tropics, e.g., Biomphalaria pfeifferi,
B_. glabrata, Bulinus truncatus, etc. Comparatively little is known re-
garding the effect of temperature in temperate regions in spite of the
fact that the planorbid species in the Great Lakes areas are more numer-
ous and diversified than those found in the tropics. These species are
of particular importance in that they consitute a major food item of
fish. Thermal pollution has become a most serious factor in the Great
Lakes region because of the number of thermal reactors installed in
lakes and rivers in order to generate electricity. More are being
planned for installation in the near future. What its effect will be on
the molluscan fauna has not been known.
The objective of the present study was to measure the influence of
temperature, ranging between 6°C and 36°C, on the growth and reproduction
of both pulmonate (pond) snails and operculate (gill-breathing) snails.
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SECTION IV
MATERIALS AND METHODS
All of the cultures were placed in 8-gallon aquaria filled with circu-
lating spring water at room temperature (about 25°C). Small chips of
crushed limestone were added to produce stronger shells. By means of a
continuous flow system coming from a chiller the water in each tank was
gradually heated to the desired temperature (ranging between 6°C and 34° or
36°C) with heat probes controlled by electronic monitors.
The equipment used for maintaining constant temperatures (Figure 1) con-
sisted of a large fiberglass storage tank holding 140 gallons of spring
water. This water was cooled to 4°C by a cooling unit or chiller inser-
ted in a 55-gallon, insulated drum. A submersible water pump in the
drum supplied a continuous supply of water to the figerglass storage
tank, with an "overflow" elbow to prevent flooding. The chilled water
ran as a continuous gravity flow into the several 8-gallon aquaria. The
enlarged section in the diagram (Figure 1) shows, a heat probe and the
thermo-regulator connected to the heat-regulating relay box; the drain-
hole at the rear of the aquarium to permit overflow water to return to
the chiller by a gravity drain pipe; the compressed air tube supplying
continuous bubbling of air to the aquarium; the floating C° thermometer;
and the protective plastic screens to prevent snails from "going down
the drain" at one end and from being burned by the heat probe at the
other end. The aquaria were encased in boxes made of styrofoam and
covered with glass lids, each with a corner cut to admit the several
tubes. Fluorescent lights were regulated to encourage algal growth
which could serve as supplemental snail food.
Oxygen determinations were made with Oxygen Meter Model 54 (Yellow
Springs Instrument Co., Inc.) as indicated in the tables; pH was measured
and tabulated (using a meter made by Analytical Measurements, Inc.). The
oxygen and pH were always at a sufficiently high level to maintain good
tolerance levels. The water kept in circulation was from the Arbor
Springs Water Company supply and was of a reasonably well-balanced grade
as shown in the following table:
Analysis of Arbor Springs Water
Parts per Grains
Million per gallon
Total Solids (Residue on evaporation) 481.0 28.13
Calcium (Ca) 110.0 6.43
Magnesium (Mg) 29.2 1.71
Normal Carbonate 11.7 0.68
Bicarbonate 289.2 16.91
Hardness in terms of CaCO 394,8 23.09
Chlorides (Cl) 40.0 2.34
Sulphates (SO ) 90.9 5.32
Iron (Fe) 0.06 0.003
Sodium (Na) 26.2 1.53
pH 7.95 (not in ppm)
-------
Fig. 1. Equipment for
maintaining constant
tern peratures.
/GLASS
INSULATING
LID
CHILLED
WATER
INSULATED
/ LID
!4OGal. FIBERGLASS XV
STORAGE TANK
GRAVITY FEED
WATER LINES
WATER
SUPPLY
PROTECTIVE
SCREEN
THERMOMETER
'STYROFOAM
INSULATION
FLUORESCENT LIGHTING
REGULATOR
HEAT PROBE
RELAY BOXES
mam nan
i i i i
locail Inaml
a
bag*
18"
24*
\
30'
36°
•oom
\ t /
INSULATED, REGULATED
INDIVIDUAL TANKS
~-WATER
PUMP
-------
A theoretically possible combination of the salts present is as
follows:
Sodium Chloride 65.9 3.85
Sodium Sulphate 0.9 0.053
Magnesium Sulphate 50.1 2.93
Calcium Sulphate 70.8 4.14
Magnesium Carbonate 66.2 3.87
Calcium Carbonate 222.7 13.02
The snails were laboratory reared and all shells smaller than 16 mm
were measured with ocular micrometers; larger snail sizes were deter-
mined with a ruler under the dissecting microscope. Data obtained was
not on growth alone but also on egg-laying (followed by serial section-
ing for cytological studies), sites of egg deposition, number of eggs
laid, size of clutches, and even viability when it was possible to
determine.
The first tests were usually made at 6°C intervals, namely: 6°, 12°,
18°, 24°, 30° and 3H°C, using room temperature as control; these were
followed by tests at 2°C intervals within what appeared to be the likely
tolerated ranges. In studying reproduction, adjustments were made to
determine the percentage of snails remaining (x%); the number of eggs
laid during the period was then multiplied by 100% - x% and added to
the sum.
In addition to the egg output, reproduction was studied using micro-
scopic gonad sections. At the end of an experiment the animals from
each aquarium were relaxed in sodium nembutal, killed and fixed in Bouin's
fluid, sectioned at 10 ju using the paraffin technique, and finally
.stained with Harris haematoxylon and an eosin counterstain. The micro-
photographs were made at X24, X70 and X400.
The oxygen figures in the tables are often too high in terms of what
would be expected at the given temperatures. This condition is undoubt-
edly due to the continuous bubbling of air in the tanks and the method
of sampling. It should be realized that the air content of the water is
not given to show accurate oxygen levels but rather to indicate that the
animals were maintained in conditions with sufficient oxygen so as not
to create special problems that might be brought about through poor
aeriation.
11
-------
SECTION V
J
PULMONATE AND OPERCULATE SNAILS TESTED
Lymnaea stagnalis Say
This large, circumpolar species is one of the most extensively studied
mollusks. It is not surprising that Hogg (1854), studying its develop-
ment and growth but a century ago, considered temperature only as it
related to the development of the eggs. Some basic and pioneering work
by Semper (1881) was concerned largely with the dwarfing or stunting of
these snails when raised under "crowded" conditions, but he did indicate
that temperature was decisive in its influence when it reached either of
its extremes. One of the first attempts to measure the influence of
temperature was a study by Bachrach and Cardot (1924), whose interests
were mainly along the lines of development. They observed growth in
temperatures between 7.5°C and 33°C in ten steps about 2°C apart. Their
optimum was 23°C, but since "development did not continue to completion"
they set the optimum at 21°C. In a series of studies on Lymnaea stagnalis
in Michigan, Crabb (1929) emphasized the effects on growth of crowding,"
food, pollution and "media", stating (1929: 52): "Temperature and light
are undoubtedly factors in the growth of this snail, but our preliminary
work does indicate the quantity or the quality which might be tolerated."
Cheatum (1934) published one of the most informative papers dealing with
the effects of temperature on snail behavior in nature. He indicated
that the 9 species of pulmonates (pond snails) inhabiting the shores of
Douglas Lake in northern Michigan near Cheboygan had an annual migratory
cycle which was seasonally regulated and showed that the animals (4 lym-
naeids, 3 planorbids and 2 physids) adjusted to the temperature changes
by moving to deeper water in the fall, remaining at deeper levels in the
winter, and coming back on the shores with the approach of spring and
summer. As shown by laboratory studies, this migration pattern appeared
to be regulated to the need for "breathing" surface air in the process
of filling the pulmonary chamber when, with increased metabolism at
higher temperatures , there was less oxygen available for cutaneous res-
piration. His laboratory data indicated that in water with 1.7 cc of
oxygen per liter, the animals used surface air three times oftener than
when the water contained 6.4 cc per liter.
A number of questions remain unanswered. Are there critical temperatures
that trigger migration? Do the several groups and species respond in
the same way? What are some of the depths to which the animals descend?
When the animals are said to be "active" in deeper water during the win-
ter periods, what is meant by active? Are there differences with respect
to movements depending on the size of the animals involved? Studies
have been made, and are now being prepared for publication, of observa-
tions on one of these snails, Lymnaea emarginata (also more recently
called L. catascopium) which has remained on the shoals of Lake Ann,
north oF Interlochen, Michigan. For the past two summers, Clampitt has
been studying the distribution and migration of the snails on the shores
of Douglas Lake. His studies will provide substantial information
13
-------
on the movements of those snails.
Forbes and Crampton (1942) studied Lymnaea palustris from two sites -
one at Croton, New York, and the other a mill-pond in Newton, Connecti-
cut. These animals were also studied experimentally in the laboratory.
They concluded that:
"Variation in Lymnaea palustri^s is exhibited in fertility, rate
of growth, size, and longevity. Individual, family and group
differences recur in successive generations in spite of the es-
sential uniformity of the laboratory conditions in culture;
hence their genetic causation seems probable."
In this study the role of temperature was not assessed although, as will
be noted later, it plays an important role in the dynamics of the snail
populations.
Cort, McMullen, Oliver and Brackett (1940), in a series of studies re-
lating to schistosome dermatitis (swimmer's itch) in northern Michigan,
especially in the vicinity of the University of Michigan Biological Sta-
tion, relate both the development of the key (then) snail host, Lymnaea
(called Stagnicola by them) emarginata angulata, as well as the occur-
rence of "the" in f e ci: i ous cercariae to seasonal conditions. Temperatures
are not given but it is evident from their observations that the heat
budgets in the region play an important part. They stated (1940: 64):
"Our records show that reports of dermatitis first begin to come
in late in June and that the worst outbreaks usually occur in
early July especially during and immediately after spells of
hot weather."
Both the development of the snail hosts and the fate of the trematode
parasites they carry are closely allied to the seasonal temperature
changes. The dynamics of these temperature-controlled patterns as ob-
served in nature are in need of far more study than hitherto given.
Fraser (1946) studied the embryology of the reproductive tract of Lymnaea
stagnalis. He was careful to maintain a temperature of 22°C to 25ttC in
the jars in which the eggs were developing. At temperatures that aver-
aged 23°C it took the eggs between 13 and 15 days to hatch. These tem-
peratures will be referred to later since they are close to the optimum
needed in the development of this snail. Vaughn (1953), who like Fraser
worked with L. E. Noland at the University of Wisconsin, studied the
effects of temperature on both growth and hatching. He discovered that
L. stagnalis eggs will hatch within a range of 9.9°C to 28°C; at 16°C it
takes the eggs 59 days to hatch. At the higher temperatures, particular-
ly when it reached 27.5°C, the egg masses exhibited unequal development,
and when the temperature reached 32°C, development was extremely unequal
and all the embryos "were dead in 10 days." Vaughn cites the work of
Imai (1937) on Lymnaea japonica in which the hatching time took about 8
days at 28°C and 16 days" alTTs^C. Imai observed that at lower tempera-
tures the snails tended to become large while in warm conditions larger
amounts of energy were expended and the snails tended to remain smaller.
The studies on growth undertaken by Vaughn (1953) were somewhat similar
to those reported here. He used the shell length as his measure. Nine
14
-------
cultures of 50 snails each (measuring between 6 and 15 mm at the begin-
ning of the experiment) were maintained at the following temperatures:
3.4°, 6.9°, 11.5°, 15.7°, 20.1°, 24.2°, 28.1°, 32° and 36°C. The control
was 24.1°C. Lettuce was given to them for food. Since Holm (1946) had
determined that snails 25-30 mm in length were sexually mature, Vaughn
terminated his experiments after 6 weeks when the snails had doubled in
size. After the first week the snails in the 23°C and 36°C tanks suc-
cumbed; those at or below 6.9°C failed to develop. He stated that "bio-
logical zero" for this snail was around 11°C. Vaughn (1953: 224) con-
cluded :
"Even though the growth was more rapid at 24.2°C than at lower
temperatures, it was evident in both jars run at that tempera-
ture that the mortality was somewhat higher than at 15.7° and
20.1°C. The mortality figures suggest that the optimum temper-
ature for the growth and development of Lymnaea stagnalis
appressa lies somewhere between 16° and 20°C""
It is also of interest to note that Belehradek (in Vaughn, 1953: 225)
listed 12°C as the biological zero of Lymnaea.
Studies on the life history and growth of a smaller Lymnaeid (Lymnaea
humulis) were published by McCraw (1961). His observations were largely
concerned with the animals in the field where he found that "little
growth occurred from the months of December to March when both the air
and water temperatures were below 10°C. Since the initiation of both
growth and oviposition was controlled by temperature there were no egg
masses "until April when the water and air temperatures were 13° and
20°C, respectively." Also, a study of field conditions undertaken by
McNeil (1963) to test the winter survival of Lymnaea palustris nuttal-
liana in irrigation canals of the Columbia Basin of Washington indicated
that about a fourth of them survived winter in the out-of-doors between
late October and late March; he also reported that "the large-sized
snails survived better than small snails."
For several years intensive studies of many kinds have been undertaken
with Lymnaea stagnalis in the biological laboratory of the Free Univer-
sity in Amsterdam. In" a study by Joosse (1964) on the dorsal bodies and
neurosecretory cells of the cerebral ganglia, he found (p. 95) that:
"The ovotestes showed a periodicity of the spermatogenetic activity
parallel with that of the dorsal cells and bodies. Starting in
March, spermatogenesis was most active in April. The majority of
the ripe sperm-cells appeared in the ovotestes in May. The percen-
tage distribution of the three types of female sex-cells (early
oocytes, oocytes and degenerating oocytes) showed no changes
throughout the year."
It is clear that there is an important temperature-controlling mechanism
at work in nature which determines the reproductive patterns and which
is under the control of annual heat budgets.
In a recent study, Foster (1971) observed the winter movements (vagili-
ty) of Lymnaea bulimoides, the intermediate host of Fasciola hepatica, in
Oregon. That this snail, like many Lymnaeids, is able to tolerate cold
temperatures was shown (p. 66) in its ability "to survive in the
15
-------
laboratory at a water temperature of 5°C for more than three months
with or even without food." The difficulties these animals experience,
as will be shown later, are greater with higher temperatures than with
lower since, as Segal (1961) has stressed, the animals can, under known
circumstances, become acclimated to their surroundings.
The first tests (see Table 1 and Figure 2) using Lymnaea stagnalis were
started in January, 1969, when 30 young laboratory^reared specimens
ranging in size from <4.4 mm to 8 mm were placed in each of 7 aquaria.
At this time the water in each tank was at room temperature; on each
successive day the temperature was changed by 6°C until the aquaria were
established at 6°s 12°, 18°, 24°, 30° and 36bC, respectively. The pH
ranged from 7.8 to 8.2; the dissolved oxygen was 6 ppm at the highest
temperature and 12.29 at the lowest, i.e., 6°C.
At the cold end (6°C), 13 of the 30 snails died while those remaining
frequented the lettuce but grew little, averaging only 0.7 mm in the
first month. In the 12°C aquarium, 20 (or 60%) survived and they doubled
their size (an average increase of H to 8 mm). The 18°C group had good
survival; in the first month their average size increase was between 5.8
and 11,1 mm. At this latter temperature the animals were also much more
active than in the colder tanks. In the aquarium kept at 2M-°C the snails
tended to crawl out of the water, indicating distress; they did grow bet-
ter and increased in size between 5.4 and 12.4 mm. Eight of the 30
snails disappeared during the first month in the 30°C; the snails
were frequently found out of water and growth was again somewhat inhibi-
ted with the increase in size between 5 and 9 mm. At 36°C all of the
snails died within a month; growth increase was about 1 mm and the snails
usually left the water. Since that temperature was critical, replicates
of the 36°C were undertaken.
Two replicate series were established in 8-gallon tanks maintained at
36°C; the 30 snails in one were between 6 and 8 mm in length when the
experiment began; those in the other were 5 to 7 mm in length. All 30
specimens in the latter tank died within 6 days; among those in the for-
mer, 3 of the 30 lasted for If days but grew only 1 mm im that two-week
period. It must be concluded that 36°C is above the critical maximum
temperature for |£|5naea_ stagnalis.
As previously stated, Vaughn also found, in the process of maintaining
this species, that 32°C and 36°C cannot be tolerated. The data compiled
here (Table 1 and Figure 2) indicate, as also shown by earlier investi-
gators , that the optimal temperature for maintaining Lymnaea stagnalis
is around 18°C or 20°C. The summary of the data in Experiment""! (from"
the series run for 84 days at 6°C intervals ranging from about 8° to
36°C) shows that growth was good at 18°C and 24°C. However, reproduc-
tion needs to be considered as well.
The distribution of Lymnaea stagnalis is circumpolar, Map 1 shows its
distribution in Michigan7~wnere the snails are subjected to prolonged
periods of freezing when they overwinter off the shoals and in the deeper
waters of the lakes or impoundments they inhabit. It was anticipated
that during cold-stressing they would survive very well. For example,
two-thirds of these animals cold-stressed at 6°C survived the ©ntii'e
16
-------
TABLE 1. Summary of data for Lymnaea stagnalis at 6°C intervals, studied for
84 days (1/6/69 - 3/31/69); 30 specimens per tank. (Experiment 1)
TEMPERATURE
°C
8.4 t 0.6
12.1 * 0.2
17.9 * 0.3
24.1 t 0.2
30.1 t 0.4
36.
22.2 * o.7
(room)
OXYGEN
ppm
9.8 * 0.7
9.1 t 0.6
8.1 t 0.7
7.1 * 0.5
6.1 * 0.2
no surviva
7.2 * 0.6
GROWTH
Total change -2s-
JC
in mm
4.1 t 0.9
10.1 t 1.3
21.4 t 1.5
20.2 t 4.5
5.8 (3)
L
17.8 ^ 2.2
Survival
63.3
60.0
73.3
16.7
10.0
86.7
REPRODUCTION
Number of days
to start of
egg- laying
--
--
58
--
--
68
Total cases
Total eggs
Number
--
--
29
758
--
-
1
30
Egg
Viability
--
--
--
--
3-4 weeks old at day 0; average length, 5.3 mm.
-------
Figure 2. Growth of Lymnaea stagnalis cultured for 84 days at
temperatures with 6°C intervals maintained at 6°, 12°,
18°, 24° and 30°C, respectively, with 30 specimens per
tank. Size at day 0 averaged 5.3 mm. Experiment 1.
18
-------
22
20
18
16
vO
£
E
e>
z
UJ
12
10
<
UJ p
S 8
6
4
30
i u. 1 r1
i
i
L
I
I
I
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85
DAYS
-------
NJ
O
Map 1. Lymnaea stagnalis (Say)
-------
84-day period (Figure 2). Although they were seen frequently on the
lettuce serving as food, they grew slowly and increased on an average
of about 4 mm only, while at 18°C they grew five times as fast. At this
optimum temperature the largest specimen measured 33 mm. Reproduction
occurred only in the 18°C tank (with the exception of the controls at
22°C) and the eggs first appeared when the animals were about 8 weeks
old. In the next four weeks 29 cases (758 eggs) were produced. At 18°C
about two weeks are required for the young to hatch.
The surviving snails from Experiment 1 were relaxed in sodium nembutal,
killed and fixed in Bouin's fluid, and sectioned at 10 ju. As can be ob-
served in Plate I, Figures 1-5, at 6°C and 12°C there was insufficient
gonad development; sperm or eggs had not appeared even at the 84th day.
The 18°C group had an abundance of normal sperm and eggs; at 24°C devel-
opment already showed some decline, and at 30°C the gonad again was un-
developed or perhaps "burned out." This functional relationship is also
shown graphically in the "reproduction" column of the 6°C interval table
(Table 1).
To determine more accurately the optimum temperature for the growth and
reproduction of Lymnaea stagnalis, another set of observations (Experi-
ment 3) were made. These tanks were maintained in the same way as those
at the 6°C intervals, but in this case a series of six aquaria were main-
tained at 2°C intervals, as follows: 14°, 16°, 18°, 20°, 22°, and 24°C;
the control was about 25°C. In this set (see Table 2; Figure 3) it ap-
pears that 20.4°C is somewhat closer to the optimum since 80% of the
snails survived the 111 days in culture at that temperature, while only
about half (47.7%) survived at 18°C in this series.
Data were also obtained on other aspects of the reproductive process.
The average number of egg cases produced, as well as the number of eggs,
was tallied. While this number varied considerably from day to day (Fig-
ure 4) it can be observed that the largest number appear between the 70th
and 110th day with peak production among the 18° to 22°C groups. When
viewed in a cumulative way (Figure 5), the 18° to 22°C again appear best;
the control, or room temperature, group may have been subject to somewhat
warmer conditions (about 26°C) and as a consequence produced fewer eggs.
The graph (Figure 6), showing survival as well as cumulative number of
eggs laid, indicates that this snail survives much better at 20°C and
tends to produce more offspring at that temperature. If the data are
graphed on a cumulative and adjusted basis (Figure 5) the 18°C and 22°C
totals look best, but the high zone in production is shown more clearly
(Figure 7) when the total number of eggs produced are tallied. As for
survival (Figure 8), it was best at 20°C, but was close to 50% in the
range between 14° and 25°C.
From these analyses it is evident that Lymnaea stagnalis is quite sensi-
tive to temperature, especially as it responds in its reproductive per-
iod to the higher range (above 24°C). The observations on the develop-
ment of egg cases were based on collections from each tank made once a
week. The eggs were measured under a dissecting microscope and their
size and development evaluated.
21
-------
TABLE 2. Summary of data for Lymnaea stagnalis at 2°C intervals,
studied for 111 days (6/10/69 through 9/29/69); 30
specimens per tank. (Experiment 3)
TEMPERATURE
°C
14.3 * 0.3
16.3 * 0.6
18.4 * 0.5
20.4 * 0.3
22.2 * 0.2
24.6 * 0.3
25.6 * 0.3
(room)
OXYGEN
ppm
7.5 * 0.1
7.1 * 0.1
6.8 t 0.2
6.3 t o.l
6.2 * 0.1
5.8 t 0.2
5.7 t 0.1
GROWTH*
Aver.
Size
Day 0
mm
2.8
2.8
2.8
3.0
2.6
2.7
2.9
Average
Size
Day 111
mm
28.9
30.6
32.9
30.3
31.4
31.6
30.5
Total Change
+ 2 s.
X
mm
26.1 * 0.9
27.8 ± 1.8
30.1 t 2.0
27.3 * 1.3
28.8 * 1.9
29.0 * 1.4
28.3 ± 1.2
No. of
Snails
on Day
111
12
19
14
24
13
21
22
Survi-
val
7.
40.0
63.3
47.7
80.0
43.3
70.0
73.0
REPRODUCTION
1st Day
of Egg-
Laying
No.
92
85
69
64
69
73
74
Aver .Size
Start of
Egg-Laying
mm
26.0
25.8
24.8
21.2
23.6
26.6
27.0
Total
Days of
Egg- Lay.
No.
19
26
42
47
42
38
37
Tot. Cases
Tot. Eggs
No.
10
314
46
1561
60
2402
90
3024
75
3166
75
2770
42
1405
Egg
Viabil-
ity
%
98.7
100.0
99.7
99.8
99.9
97.0
99.4
"6 days old at beginning of experiment.
-------
Figure 3. Growth of Lymnaea stagnalis cultured for 111 days
at temperatures with 2°C intervals; size at day 0
averaged 2.8 mm; 30 snails were cultured per tank
at 14°, 16°, 18°, 20°, 22° and 24°C. The control
was at room temperature - about 26°C. Experiment 3.
23
-------
• 20-
E
6
O)
c
5O 6O 7O
Da y s
8O 9O IOO NO I2O
-------
.24
.22-
.20
.18
.16
a -14
3 .12
o
E
.10
01 .08
.06
.04
.02
1
20°C
I8°C
Control
24°C
65
70
75
80 85 90
DAYS
95
100
105
110
Figure 4. The average number of egg cases produced per snail per day
by Lymnaea stagnalis during a culture period of 111 days;
30 snails per tank maintained in 7 aquaria at the following
temperatures: 14°, 16°, 18°, 20°, 22° and 24°C; the control
was at room temperature (about 26°C). Experiment 3,.
-------
Q
< 7000
§ 6000
LiJ
"2 50001-
3 4000
LU
> 3000
2000
£
i 1000
o
65 70 75
80 85 90 95 IOO 105 110 115
DAYS
Figure 5. Estimated number of eggs laid by Lymnaea stagnalis
when calculated on 1007,= survival with 30 snails per
tank maintained in aquaria at the following temper-
atures: 14°, 16°, 18°, 20°, 22°, and 24°C; controls
were at room temperature (about 26°C). Experiment 3.
-------
100
90-
80-
| 70-
1 6°
^ 50
z
LJ 40
u
o:
ol 30
20-
10-
I
I
14
16 18 20 22
TEMPERATURE fC
24 (25.55)
Control
Figure 6. Survival of Lymnaea stagnalis in aquaria maintained
at 2°C intervals ranging between 14° and about 26°C.
Experiment 3.
-------
3200
3000
2800
2600
2400
S 2200
e>
£ 2000
O
o: 1800
D
Z
O
1600
1400
1200
1000
800
600
400
200
14
I
Room
I
16
18 20 22 24
TEMPERATURE • C
26
Figure 7. Total number of eggs produced by Lymnaea stagnalis
cultured for 111 days in aquaria maintained at
intervals of 2°C ranging between 14° and 26°C.
(Experiment 3)
28
-------
I
1
E
o
3
V)
0
O
2
90
85
80
75
70
65
60
55
50
45
40
35
OD
30
25
20
15
10
5
/20°C
24°C
I
I
I
;
Control |6°C
j
/
i
22°C
i
[8°C
I
J L
i I I I I I I L
I4°C
I
L
IOO 92 88 84 80 76 72 60 64 60 56 52 48 44 40
PERCENT SURVIVAL
Figure 8. The number of egg cases laid by Lymnaea stagnalis in terms
of the percentage of snails that survived in tanks at the
following temperatures: 14°, 16°, 18°, 20°, 22°, 24°C;
the control was about 26°C. Experiment 3.
29
-------
In Experiment 3 (run at 2°C intervals) egg production in the 20°C tank
began on the 64th day when the animals were about 10 weeks old. In the
18° and 22°C tanks they appeared in 69 days, in the 24°C control group
after 73 days. In the 16° and 14°C groups eggs did not appear until the
85th and 92nd day, respectively (Figure 9). At the termination of the
experiment, the cumulative numbers (Figure 9), in the order of size from
largest to smallest, were as follows: 20°, 22°, 24° and 18°C. ^This rank-
ing occurred both in the adjusted graph (Figure 5) as well as in the
tanks when tabulated as growth progressed. To make the adjusted tabula-
tion, the percentage of the snails remaining (x%) was determined in terms
of the incremental laying period. The number of eggs laid during this
period was multiplied by 100% - x% and added to the sum which assumes
that the dead snails would have reproduced at the same rate as the live
ones. In the adjusted arrangement, the cumulative information indicated
that production decreased in the order shown:
Tank
22°C
20°
24°
18°
16°
Control
14°
Actual Number
of Eggs
3170
3030
2858
2409
1516
1413
318
Percent
Adjustment
29.9
17.1
21.9
36.5
26.4
- 4.6
41.7
Adjusted Number
of Eggs
4118
3548
3484
3288
1973
1349
451
In making these adjustments it was noted that the average number of eggs
per case did increase slightly as the snails became older although with
this rise there were fluctuations in number per case.
Viability in all tanks remained high. It is possible that in early stages
viability may not always be determined accurately and that embryo mortal-
ity may come at later stages. However, as shown in Figure 8, there was
a very high rate (almost 90%) of survival of the embryos.
Egg cases were found in all parts of the tanks.
best be summarized in the following table:
Their distribution can
Tank Float Side Bottom Filter Lettuce Hose Screen Dish Wrong Wrong Shell
Side Bottom
Control 14
24°C 21
22°
20°
18°
16°
14°
TOTAL
23
35
37
15
145
9
25
22
14
3
1
1
75
16
12
10
18
8
4
4
72
10
6
14
5
10
2
72
5
7
5
3
12
3
35
1
—
1
1
2
—
5
—
2
—
1
__
1
4
—
1
1
1
1
—
4
—
__
1
— _
1
2
1
__ _t _
1
— — __
1 1
30
-------
Figure 9. Total number of egg cases of Lymnaea stagnalis
produced in 111 days when aquaria, each with
30 snails, were maintained at 2°C intervals, as
follows: 14°, 16°, 18°, 20°, 22° and 24°C. The
control was room temperature estimated at 26°C.
The data on which the cumulative figures were
based are: (Experiment 3)
Control 737= 22 snails
24°C 70% 21
22°C 43% 13
20°C 80% 24 "
18°C 47% 14
16°C 63% 19
14°C 40% 12
31
-------
6465
70
75
80 85 90
DAYS
-------
It is ^ evident that the floats used to hold the thermometers and the
aquaria sides and bottoms were used most as sites for egg deposition.
Gonad development of Lymnaea stagnalis is shown in Plate I, Figures 1-5,
This species has approximately' a 1-month cycle and the figures represent
the condition of the gonads at the end of that time. At 6°C (Plate I,
Figure 1) there was practically no development; the gonad is visible but
without sexual differentiation. At 12°C it is better developed but no
appearance of eggs or sperm. When temperature is maintained at the 18°C
level this species approaches its best reproductive level as shown in the
development of sperm and eggs (plate I; Figures 3a (X24) and 3b (X400).
The high production of viable eggs at this temperature is also quite evi-
dent in the data given for reproduction (Table 3). At 2M-°C the tissue
shown (Plate I, Figure 4) is that of an active gonad with both sperm and
egg development, but it is not as well developed as the tissue was at 18°C.
This temperature relation to egg production is again shown in the cultures
maintained at 2°C intervals (Table 2), which indicate that optimum repro-
ductive potential was found between 18° and 2H°C. At 30°C the gonad re-
mained undeveloped (Plate I, Figure 5) which was also shown by the failure
of any eggs to appear in the cultures maintained in that comparatively
warm water (Table 3).
These observations on the relation of temperature to gonad development
have a ready application to the history of the distribution of Lymnaea
stagnalis in Michigan. The distribution map (Map 1) shows clearly that
—' S'tagnalis is present is found about 200 miles north of the Ann Arbor
—
region. Yet, some 40 or 50 years ago this snail was common in lakes of
southern Michigan. Studies by investigators in Ann Arbor (including
George R. LaRue and E. D. Crabb) used this snail from stocks common in
local lakes (Third Sister Lake and others) for studies in parasitology ,
genetics and functional anatomy. The studies on the sensitivity of this
snail to temperatures above 25°C serve to emphasize that increasing the
heat budgets, whether by natural or artificial means, can have a profound
effect on the ecology and distribution of this snail.
The sensitivity of L. stagnalis to temperature is shown in Figure 10 and
Table 3 in which tHe data from Experiments 1 and 3 have been combined so
as to indicate the maximum size and egg-laying expressed percentage-wise.
The data when graphed indicate again that growth is best at a cool tem-
perature (about 18°C) and the largest number of eggs appear at somewhat
warmer temperatures (about 24°C). While the significance of these rela-
tionships with respect to distribution of this snail in a region like
Michigan is not at all clearly related to the possible changes in heat
budgets during the reproductive periods in the spring in southern Michi-
gan, the disappearance of this snail from the southern part of Michigan
would appear more than a coincidence in view of the need for "cool" con-
ditions during the critical breeding periods.
"Plop Tests." In the other tests to determine growth and reproduction
at several temperatures , the animals were acclimatized gradually to the
temperature at which they were to be evaluated. In this experiment the
young were taken from the stock ranks at room temperature and placed
directly in the water at the test temperatures. The results (Table M-;
33
-------
PLATE I. Gonad tissue sections from Lymnaea stagnalis
cultured for 84 days at different temperatures.
Fig. 1. 6°C (X70)
Fig. 2. 12°C (X70)
Fig. 3a. 18°C (X24.5)
Fig. 3b. 18°C (X400)
Fig. 4. 24°C (X70)
Fig. 5. 30°C (X70)
34
-------
TABLE 3 . Summary of data, Experiments 1 and 3, for Lymnaea stagnalis;
30 specimens per tank.
1/6/69-3/3L/69 by 6°C intervals - 84 days
Experiment 1
Aver .
Temp .
°C
9.3
14.4
18.3
24.1
29.3
30.0
22.2
(room
Growth"
Final
Size
mm
9.2
14.8
27.2
25.6
10.8
no
23.4
Total Growth
- 2S-
X
mm
4.1 t o.9 .,
U9)*1
10.1 * 1.3
(18)
21.4 ± 1.5
(22)
20.2 t 4.5
( 5)
5.8 (3)
survivors
17.8 * 2.2
(26)
Reproduction
# Day
Laying
Began
58
68
Laying
Size
mm
19.7
21.8
Tot. Cases
Tot. Eggs
#
29
758
1
30
Survival
Snail
%
63.3
60.0
73.3
16.7
10.0
86.7
Egg
%
--
6/10/69-9/29/69 by 2°C intervals - 111 days
Experiment 3
Aver.
Temp.
°C
13.8
16.5
18.5
20.4
22.1
24.7
25.6
(room)
Growth*
Final
Size
mm
28.9
30.6
32.9
30.3
31.4
31.6
30.5
Total Growth
- 2S-
X
mm
26.1 + 0.9
(12)
9 "7 Q 1 C
z/.o - J. • o
(19)
30.1 ± 2.0
(14)
27.3 * 1.3
(24)
28.8 * 1.9
(13)
29.0 t 1.4
(21)
28.3 * 1.2
(22)
Reproduction
# Day
Laying
Began
92
85
69
64
69
73
74
Laying
Size
mm
26.0
25.8
24.8
20.5
24.8
26.6
27.0
Tot. Cases
Tot. Eggs
#
10
314
46
1561
60
2402
90
3024
75
3166
75
2770
42
1405
Survival
Snail
7o
40.0
63.3
47.7
80.0
43.3
70.0
73.0
Egg
%
9a9
LOO.
99.7
99.8
99.9
97.0
99.4
u>
Ul
Beginning ages: 6°C interval - 3 to 4 weeks;
Number of snails al end of experiment.
2°C intervals - 1 week.
-------
Figure 10. Data obtained from Experiments 1 and 3, as given
in Table 3, for Lymnaea stagnalis and plotted to
show overlapping areas. Optimum temperature is
between 18°C and 24°C with better survival in
colder temperatures.
36
-------
-------
TABLE 4. Summary of data for Lymnaea stagnalis "plop test" (animals subjected to
sudden changes of temperature in tanks from room temperature), studied
for 21 days (4/1/71 to 4/22/71), 30 specimens per tank.
TEMPERATURE
°C
6.35 t 0.03
12.45 * 0.14
20.64 t 0.39
30.98 * 0.07
NUMBER OF SNAILS
AT DAY 21
25
25
28
0
SURVIVAL
83 . 3%
83.3%
93.3%
**
,0.0%
AVERAGE SIZE''"
AT DAY 0
mm
2.76 mm
2 . 82 mm
2.64 mm
2 . 67 mm
AVERAGE SIZE
AT DAY 21
mm
3 . 06 mm
5 . 47 mm
8.11 mm
__**
CHANGE IN SIZE
FROM DAY 0
mm
0.30 mm
2.65 mm
5. 47 mm
__**
OXYGEN
ppm
17.42 * 0.33
14.44 * 0.13
11.50 * 0.49
8.12 t o.Ol
OO
Age at Day 0: 3-14 days.
31°C tank: 3 snails (107,) alive at day 14, with average size of 3.85 mm (change in size 1.18 mm).
-------
Figures 11, 12 and 13), when Lymnaea stagnalis were maintained at 6°, 12°,
20° and 30°C, indicate good tolerance at colder and the normal, natural
temperatures; they rapidly disappeared in the warm (30°C) water. Again
it is^evident that L_. stagnalis cannot tolerate warm conditions, and that
its distribution (as shown in Map 1) in northern Michigan is probably
conditioned by the annual heat budgets in that region.
Lymnaea emarginata Say
Lymnaea emarginata Say (recently called Lymnaea catascopium Say by H. J.
Walter, 1969) was studied quite intensively 30 years ago in northern Mich-
igan at the University of Michigan Biological Station by those interested
in its role as one of the most important intermediate hosts of schisto-
some dermatitis, or "swimmer's itch." Based on the need for controlling
infestations on beaches inhabited by this snail, the Michigan Stream
Control Commission published a bulletin in 1939 entitled "Water Itch"
that has been widely used in the Great Lakes Region. At that time, L.
emarginata was considered the most harmful of the snails which carry~~the
several non-human schistose-roes (mostly bird blood flukes) in the northern
lakes. Its prevalence in these lakes earned for it the common name "beach
snail." H. J. Walter made a study of its ecology and recently published
a detailed topographic anatomy of its several organ systems, thus provid-
ing one of the most thorough morphological studies available on any pul-
monate snail. This work provided the basis for changing the name to
Lymnaea catascopium, but these names will remain uncertain until more com-
parative studies of related lymnaeids have been undertaken.
As shown in Map 2, L. emarginata (L_. catascopium) has a decidedly northern
distribution in the~Great Lakes regiorHIt tends to inhabit the open,
wind-swept beaches where the bottom is sandy and weed-free - often the
kind of beach preferred by bathers. Stony regions are also favorite sites
for this snail; their white shells and light animal coloration camouflage
them so well in such surroundings that, although often present in large
numbers, they may not readily be seen by even the most experienced col-
lector.
This species was tested using two experiments; in Experiment H the animals
were stressed for 121 days at temperatures with 6°C intervals between; in
Experiment 5 they were maintained at 2°C intervals over a period of 77
days. As confirmed by the data obtained in these studies, it is evident
that Lymnaea emarginata, like L. stagnalis (also a northern snail) prefers
temperatures ranging between 18* and 24~°C, definitely on the cool side.
The first test (Experiment 4) with Lymnaea emarginata was started July 3,
1969, and involved 6 tanks each containing 30 specimens which were main-
tained at 6°, 12°, 18°, 24°, 30° and 36°C, respectively. A control was
kept at room temperature (about 25°C). The snails used were about two
weeks old, and their shell length was measured just prior to being put in
the tanks, using a dissecting microscope and an ocular micrometer. When
the animals grew beyond 16 mm they were measured by ruler under a lens.
At the beginning of the tests the shell lengths ranged from 1.9 to 3.5 mm.
To avoid damage to the shells they were not measured again until they
39
-------
5.5-
5.0-
4.5
4.0
£
£ 3.5
B3.0
^2.5
2.0
1.5
1.0
0.5
0.0
I2°C
30°C
(all dead at day 21)
r ....... T ....... r ...... t ...... i ....... 1
6°C
0246
8 10 12 14 16 18 20
DAYS
Figure 11. Growth of 30 Lymnaea stagnalis placed directly
into tanks with water at four different temper-
atures ("plop test"): 6°, 12°, 22° and 30°C.
Those at 30°C survived only 21 days compared to
the normal life span of at least 4 months.
40
-------
100
22°C
6°ond I2°C
468
10 12 14 16 18 20 22
DAYS
Figure 12. Survival of Lymnaea stagnalis in "plop test" when
30 specimens were maintained for 21 days in tanks
at 6°, 12°, 22° and 30°C.
100
6° 12° 22° 30°
TEMPERATURE,°C
Figure 13. Survival in percentage of Lymnaea stagnalis in
"plop test" shown in Figure 12.
41
-------
Map 2. Lymnaeo emarginata Say (L.cataicoplurn Say)
-------
were approximately 4-5 weeks old; after that measurements were made at
weekly intervals.
The data are summarized in tables and graphs. The information obtained
when the animals were maintained at constant temperatures with intervals
of 6°C over a period of 110 days (about 4 months) gave a measure both of
their growth and their reproduction at the several maintenance tempera-
tures. Table 5 shows that at 6°C (actually averaging 8.7°C) some 24
specimens (77%) survived but the animals did not grow larger than 11 mm;
also, as expected, no eggs were produced at that temperature. At the
other extreme, the animals in the 36°C tank did not survive more than 18
days, as indicated by two separate tests. Good survival was recorde^ at
the 12°C level but reproduction was curtailed so that only a few eggs
were produced when the snails did start laying after the 63rd day in
culture. In the tanks maintained at 18°C and 24°C survival was not good
but the snails that did live grew to normal size, averaging 15 mm and
17 mm, respectively. Figure 14, which plots survival in the form of a
graph, shows that survival tends to be best in the co6ler ranges (12° to
18°C). From Figure 15, which graphs growth and recovery for each of the
tanks, it is clear that growth and survival are best in the cool range
(roughly 18°C). Two graphs (Figures 16 and 17) are used to plot the egg
cases produced during culture at the four temperatures the animals were
maintained; Figure 16 gives the total number of cases produced by the
surviving snails; Figure 17a, b, c, d and e is the "adjusted" total when
the production is calculated as though all of the snails survived and
produced the potential number. In both instances the temperatures in
the range of 18° to 24°C appeared to be the most productive. The total
number of eggs laid in the 110 days was more than 16,000, as is shown in
Figure 18.
In the studies (Experiment 4) in which the snails were stressed at 6°C
intervals it was indicated that the optimum temperature for maintaining
and culturing L. emarginata was roughly between 18° and 25°C. It seemed
desirable to stress the animals at 2°C intervals also, and these tests -
using a range between 18° and 28°C - are represented in the data provided
in Experiment 5. The specimens used were 7-10 days old; their delicate
shells kept us from measuring them again until they were three weeks old.
The general information obtained indicated that egg-laying began in the
22° and 24°C tanks when the snails were 28 days old. In the warmer water
(26° and 28°C) mortality was comparatively high with almost half of the
30 snails decimated. These data are shown in Table 6 and they are more
graphically indicated in the figures. Growth was not really very differ-
ent between 18° and 28°C (Figure 19). Egg production was best around
24°C (Figure 20). When egg production is viewed first merely on a cumu-
lative basis (Figure 21) the room temperature (25°C) and the 24°C temper-
atures look best, but if they are calculated on the basis of 100% survival
(Figure 22) the 26°C temperature is better.
With Lymnaea emarginata, a "plop test" was undertaken by placing 30 young
(about 2 mm long) specimens in tanks with temperatures maintained at 6°,
12°, 22° and 30°C. The animals were 4-14 days old at the beginning of
the test and remained in culture about 3 weeks (Table 7). In growth
(Figure 23a) those at the warmer temperatures grew best; the survival
(Figure 23b) in the 6° and 30°C tanks was poor with only half of those
tested alive after 3 weeks.
43
-------
TABLE 5. Summary of data for Lymnaea emarginata at 6°C intervals,
studied for 121 days (7/2/69 through 10/29/69), 30 speci-
mens per tank. Experiment 4.
TEMPERATURE
°C
8.7 + 0.5
13.0 + l.O*2
18.2 +o.7*2
24.6 t 0.4
29.8 * 0.1
*5
34.6
25.4 i" 0.8
(room)
OXYGEN
ppm
*1
9.0
8.1
7.5
6.4
5.9
--
6.3
GROWTH" REPRODUCTION
Aver .
Size
Day 0
2.4
2.6
2.4
2.7
2.7
--
2.4
Aver .
Size
Day 111
11.0
13.6
15.1
17.4
13.8
--
20.2
Total Change
1 2 g
X
mm
8.6 * 0.7
11.0 * 0.7
12.7 * 0.9
14.7 * 2.3
11.1 O)*4
--
17.8 * 1.2
Survi-
val
7o
76.6
90.0
60.0
16.7
10.0
--
56.7
Start of Laying
Day
No.
__
63
42
36
63
—
34
Snails
No.
__
27
23
5
4
--
21
Size
mm
__
12.0
10.0
10.4
13.4
--
10.3
Day 121
Total Cases
Total Eggs
No.
32*3
525
178
1957
154
3694
20
0
--
522
11,582
Cases/
Day
No.
__
0.68
2.3
1.8
0.43
—
6.0
Eggs/
Case
No.
__
16.4
11.0
24.0
0
—
22.2
Eggs/
Day
No.
-_
11.2
24.8
43.5
0
--
133. 0
Egg
Viability
7.
__
99.6
97.4
97.9
0
--
94.3
-e-
-O
*
*3
*4
*5
At beginning of experiment, animals were 3-4 weeks old.
Only one reading for dissolved oxygen - meter not working.
Difficulties encountered with heaters, relay boxes and controls.
No more eggs laid after Day 110.
Number of snails left at end of experiment too few for calculation of standard deviations.
Started two different groups: (1) all dead before measuring at 18 days;
(2) 2 snails alive at 7 days and all dead at 14 days.
-------
TEMPERATURE,
Control
(25.44)
°C
Figure 14. Survival in percent of Lymnaea emarginata maintained
at 6° temperature intervals between 0° and 36°C. The
trend is toward fewer surviving at the warmer temper-
atures. Experiment 4.
45
-------
Percent Recovery of Snails at Each
Time of Measuring
Change in Size of Snails from Day 0
o ^0
I2°C Tank no. 2 -
1 I I
24°C Tank no. 4 -
-i 20
16
12
8
4
0
20
CO
Room Temp. Tank no. 7
j I I I
20 40 60 80
100 120 20
DAYS
60 80 100 I2O
4
O
20
16
12
8
4
0
-------
35
40 45 50 55 60 65 70
75 80
DAYS
85 90 95 100 105 110 115
120 125
Figure 16. Egg cases laid (cumulative) by Lymnaea emarginata maintained at 12C
18°, 24C
and 30°C, and
the control temperature; egg-laying between 18° and 24°C extended over a 90-day period.
both cold and warm conditions it began late and was greatly reduced. Experiment 4.
In
-------
Figure 17. Cumulative (adjusted to 1007o survival) eggs
produced by Lymnaea emarginata maintained at
6°C intervals of temperature plotted for each
of the aquaria and showing number of days eggs
were laid, the number produced, and the numbers
at the periods (days) during the egg-laying
period. Experiment 4.
(A) - 18°C
(B) - 12°C
(C) - 30°C
(D) - 24°C
(E) - Room Temperature
48
-------
4000
3000-
FIG. 17(A)-18°C
IU
40 50
60
70 80
(B)-12°C
90 100
200
(C)-30°C
1000
60
70
80 90 100
DAYS
200
0
800
600
-4QO
200
LU
LJ
£
N.
-------
18,000
Ln
O
FIG. 17(D)- 24°C
Q
< 12,000
_i
en
LU
>
< 8000
O
2000h
7O SO
DAYS
-------
FIG.17(E)
ROOM TEMPERATURE
70 80
DAYS
-------
Figure L8. Eggs laid by Lymnaea emarginata maintained at 12°C,
18°C, 24°C and 30°C; room temperature (about 25°C)
served as control. Between Day 35 and 110 (75 days)
in Experiment 4 more than 16,000 eggs were produced
(these figures are adjusted to 100%, i.e., they are
the number of eggs that would be produced if all of
the snails survived).
52
-------
Ln
Co
18,000
16,000-
14,000 -
9 12,000 ~
§ 10,000
m
UJ
>
h- 8000
6000-
4000-
200O-
0
55 65 75 85 95 105 115
35 45
-------
TABLE 6. Summary of data for Lymnaea emarginata at 2° intervals, studied for
77 days (12/9/69 through 2/24/70), 30 specimens per tank. (Experiment 5)
TEMPERATURE
°C
18.6 * 0.4
20.4 * 0.2
22.2 * 0.3
23.9 t o.2
26.0 ± o.9
27.9 + 0.3
26.9 t 0.4
(Control)
OXYGEN
ppm
9.0 * 0.2
8.3 t 0.2
8.1 ^ 0.2
7.6 t 0.2
7.3 * 0.2
6.6 t l.l
6.9 * 0.4
GROWTH""'
Total change -2s-
X
in mm
11.9 + 0.8
13.0 * 0.5
12.2 * 0.9
13.1 t 0.5
14.8 t 1.2
16.3 ± 1.1
15.3 ^ 0.5
.Survival
7o
70.0
73.3
53.3
76.6
23.3
33.3
86.7
REPRODUCTION
Number of days
to start of
egg- laying
35
28
28
28
28
28
21
Total cases
Total eggs
Number
105
1137
184
1744
288
3162
335
4343
182
2907
76
560
308
2953
Egg
Viability
%
98.7
98.4
97.1
97.4
93.5
83.4
80.1
At beginning of experiment, animals were 7-10 old, 2..7 mm average length.
-------
20
E 16
E
O
I'2
O
Si 8
IX
0
10
20
30
40
DAYS
50
60
70
80
Figure 19. Growth of Lymnaea emarginata maintained at 2°C intervals
for 70 days. Experiment 5.
-------
4000 -
28 27
(Control)
TEMPERATURE, °C
Figure 20. Eggs produced by Lymnaea emarginata at 2° intervals
between 18° and 28°C; peak production appeared at
24°C. Experiment 5.
56
-------
4000
3600 -
3200-
o 2800 h
(A)
g 2400
u
UJ
2000
D
1 1600
o
1200-
8OO-
400-
Figure 21.
DA T E S
Cumulative (not adjusted to 10070 survival) eggs produced by
Lymnaea emarginata maintained at 2°C intervals between 18°
and 28°C; room temperature (about 25°C) served as control.
Experiment 5.
57
-------
Figure 22. Cumulative (adjusted to 10070 snail survival)
number of eggs produced by Lymnaea emarginata
maintained at 2° intervals between 18° and
28°C; room temperature (about 25°C) served as
control. Experiment 5.
58
-------
I2,OOO
10,000
8000
en
e>
LJ
UJ
> 6000
I-
_i
ID
5
^ 4000
2000
20
/26C
i i i i i i i i
80
-------
TABLE 7. Summary of data for Lymnaea emarginata "plop test" (animals subjected to
sudden changes of temperature in tanks from room temperature), studied
for 21 days (5/6/71 to 5/27/71), 30 specimens per tank.
TEMPERATURE
°C
6.63 * 0.10
12.31 * 0.10
21.88 * 0.06
30.50 ^ 0.02
OXYGEN
ppm
15.30 * 0.34
14.56 * 0.07
10.14 t 0.04
8.00 t 0.06
NUMBER ALIVE .
AT .DAY 21
14
25
24
18
SURVIVAL
46 . 7%
83.3%
80.0%
60.0%
AVERAGE SIZE
AT DAY 0
2.29 mm
2.18 mm
2.19 mm
2.27 mm
AVERAGE SIZE
AT DAY 21
3.28 mm
4. 55 mm
7 . 46 mm
5.99 mm
CHANGE IN SIZE
FROM DAY 0
0.99 mm
2.38 mm
5. 27 mm
3.72 mm
A.
Age at Day 0: 4-14 days.
-------
Figure 23. Data on "plop test" with Lymnaea emarginata showing
growth (23a) and survival (23b) in a 3-week period
at different temperatures.
61
-------
I I I I I I
(2 3 a)
(23b)
-------
Since ^rather comprehensive information on the reproduction of Lymnaea
emarginata was given in terms of egg-laying, gonad sections were not
made. Data on eggs produced and reproductive potential are found in
Table 5 (Experiment 4) in which the tanks were maintained at 6°C inter-
vals between 8.7° and 34.6°C; another series (Table 6) shows egg output
when these snails were cultured at 2°C intervals (Experiment 5) between 18°
and 28°C. Reproduction, as shown for both series, indicates that L^. emar-
is similar to L_. stagnalis in that even at 13°C, although it" too"
_
more than 60 days to produce eggs, a surprising number of egg-cases were
deposited in this cool water and the eggs had an unusually high viability.
At 18°C production was better, as it was also in the 24°C tanks. Beyond
that, i.e., at 30° and 34°C, conditions were too warm and no eggs were pro-
duced. In the series run at 2°C intervals (Table 6) a more comprehensive
survey of egg-laying appears when the range was between 18° and 28°C, again,
the best cultures appeared in the 18° to 26°C range; above the latter tem-
perature fewer egg masses were produced and the eggs are shown to be less
viable . For all practical purposes , L_. emarginata and L_. stagnalis are
very similar in their northern distribution pattern and~their preference
for waters on the cooler side, i.e., below 26°C and even as low as 14°C.
Although the tissues were prepared for cutting and staining, there was
not sufficient time allotted in this project to prepare gonad sections.
This work will be done later; hopefully, these and other studies can be
continued.
Helisoma trivolvis (Say)
Planorbid snails are abundant and widely distributed. The group is es-
pecially important since species of Biomphalaria (in the Americas and
Africa) and Bulinus , or Physopsis, (in Africa) serve as the intermediate
hosts of human blood fluke (Bilharziasis or schistosomiasis). Conse-
quently, some useful basic studies have been undertaken to learn more
about the role of temperature in the growth and reproduction of some of
the more important planorbid snail intermediate hosts. The investiga-
tions referred to in this report will concern mainly those that have a
bearing on the role of temperature as studied both in the laboratory and
in the field.
Standen (1952: 48), working with an Egyptian strain of Schistosoma man-
soni, cited several references to indicate that there is a "relationship
of season and temperature to the incidence and intensity of schistosome
infection in snails." In some studies designed to ascertain the optimum
temperature for culturing the snails (now called Biomphalaria glabrata)
he found that the optimum temperature for that planorbid was between 26°
and 28°C; the minimum necessary for adequately developing the parasite
(sporocysts) was 26°C. Stirewalt (1954), using the Puerto Rican strain
of S. mansoni, also studied the effects of temperature on this snail and
its~~parasite. Some of her conclusions are important in that they clearly
indicate the tolerance of B. glabrata to comparatively warm temperatures.
Her results can best be summarized in the following statement (1954: 507-
08):
"Even under these conditions the influence of temperature changes is
63
-------
obvious: at 23 to 25°C, 28% of exposed snails developed infections,
32% of the survivors. Further temperature increase to 31 to 33°C
increased the number of snails which died, but of those which
survived 52% developed infections. At 33° to 35°C, the death rate
was prohibitive, and at 36° to 38°C all the snails died within
three days."
Stirewalt (Ibid: 515), in discussing the effects of temperature on the
snail host and its parasite, made the following statement:
"The responsible mechanism is not known. An attractive hypothesis
is that the low temperature, transferred from the environment to
the exposed poikilothermous molluscan hosts, retards the metabolism
of the parasite as well as the host. Growth and cell division of
the schistosomes, then, may be so inhibited that (1) the infection
is completely suppressed, giving the lowered' infection rate recorded;
(2) the development of the schistosomes from miracidia to cercariae
is retarded, resulting in the long pre-patent period described; and
(3) the duration of those infections which do mature is limited as
cercariae develop within the retarded sporocysts, until the latter
are exhausted, terminating many of the infections, as reported. It
is tempting further to surmise that perhaps the cercariae which
emerge from these sporocysts are less mature in some way, in their
sensory or muscular or enzymatic development, for example, and
therefore they produced fewer adult worms in susceptible mouse
hosts.
"With temperature such an important environmental factor, its further
effects should be investigated both in the laboratory and in the
field. The results of such work should contribute to a better con-
ception of optimal conditions for maintenance of snail and parasite
in the laboratory, to a more intelligent evaluation of ecological
data relative to the dissemination of human schistosomes, and to
more economical application of controls of this parasite in the
field."
With regard to the temperatures to which the planorbids that serve as in-
termediate hosts are subjected in nature, Abdel Malek (1958) considered
both the hydrographic and hydrogeological factors. He'indicated that in
the Nile basin seasonal variations were greater in the north than in the
south. The temperatures varied considerably depending on rainfall; his
recorded range in various parts of the Nile (1958: 698) was between 24°C
in November at Kosti to 31°C in May at Khartoum.
Michelson (1961) studied the effects of temperature on the growth and
reproduction of Biomphalaria (formerly Australorbis) glabrata in the
laboratory. He exposed 15 snails in 3-liter pyrex battery jars to tem-
peratures of 5°, 15°, 20°, 25°, 30° and 35°C, with 25°C as controls. He
found that on the higher levels (30°C) the reproductive process failed
and few eggs were produced. Dissected specimens in this "hyperthermal"
group had "the albumin glands atrophied, abnormal in color, or entirely
absent. Sections of the ovotestis in these snails showed that the female
elements were poorly developed although the male elements appeared normal."
He stated (1961: 72): "Thus, although maintenance at 30°C appeared to be
-------
optimal for maximum growth, reproduction was inhibited." At the 35°C
level all the snails died within 15 days. When his snails were main-
tained at lower temperatures (the "hypothermal" groups), growth and repro-
duction were inhibited but, since no serious tissue alterations occurred,
those processes carried on in a normal way when the animals were trans-
ferred to optimal temperatures.
Shiff (1963) published a series of three papers on the biology
sian Bulinus (Physopsis) globosus in which he discussed: I. 11
of Rhode-
The influecne
of temperature on the intrinsic rate of natural increase; II. Factors in-
fluencing the relationship between age and growth; and III. Bionomics of
a natural population existing in a temporary pool. In his summary (1963:
104) he reported that his life tables used for determining the influence
of temperature on "the intrinsic rate of natural increase" indicated that
the optimal temperature was 25°C; he also reported (1963: 115) that "the
snails grew most rapidly at 25°C; and when he studied a natural popula-
tion that temperature also was the one at which "egg-production is high-
est." Later Shiff (1966: 214), in a study of the influence of tempera-
ture on vertical movement of this snail both in the laboratory and in
the field, stated: "It has been shown that for both Biomphalaria pfeif-
feri and Bulinus globosus in the laboratory, the intrinsic rate of
natural increase rises considerably with temperature from 18° to 22°C.
Any movement of snails from cold to warmth will result in a higher rate
of increase at a time of the year when the size of the population may be
critical for enabling the species to survive the possible drying out of
the habitat during early summer."
Sturrock (1966) studied the influence of temperature on Biomphalaria
pfeifferi, the intermediate host for Schistosoma mansoni. He observed
that these snails were usually not found in the low, hot regions along
the coasts of Kenya, Mozambique, the Red Sea and those of West Africa.
His thesis is that temperature may be a controlling factor in the dis-
tribution of this snail. He emphasized the role played by temperature,
as follows:
"Nevertheless, where water bodies may be expected to have tempera-
tures in excess of 28-30°C for several months on end, as on the
coastal plain of Tanzania, it is unlikely that any suitable natural
habitats will be successfully colonized by B_. pfeifferi^, and it is
therefore reasonable to assume that high temperatures have been,
and will remain, a major barrier to the colonization of such
habitats."
He found that the optimum temperature was 25°C; survival was good at
19°C but it was poor at 30°C. The maximum heat tolerated was 32°C, and
under field conditions he doubted that this species of snail could sur-
vive for any extended period at temperatures much above 28°C.
Chernin (1967) studied the reaction of Biomphalaria glabrata, Bulinus
truncatus and Lymnaea palustris in a thermal gradient established in a
shallow water trough. He found that B. glabrata avoided thermal extremes
but tended to select "zones proximating 27° to 32°C." When food was
placed in a "cool" zone these snails "congregated" there. His observa-
tions (1967: 1233), as will be shown later, tend to corroborate those
65
-------
reported here in that the three species studied "differed in their distri-
butional responses to the thermal gradient; thus, B_. glabrata were gener-
ally found in moderately warm loci; L. palustris tended to accumulate in
the relatively cool portions of the gradient, and B_. t run cat us distributed
themselves fairly uniformly throughout the gradient. The general findings
may contribute to a better understanding of some of the influences under-
lying the localization of discontinuity of natural colonies of snails."
Jobin (1970) studied Biomphalaria glabrata in three farm ponds in Puerto
Rico. Temperature was an important factor in the dynamics of the popula-
tions there and he stated (1970: 1046) as follows: "Specifically, the
population declines of B. glabrata in Ponds B and C were related to
extreme water temperatuFes that limited reproduction; in Pond A the tem-
perature was 25°C to 28°C, optimum for reproduction, when the B_. glabrata
disappeared...;". He also observed that: "Optimum temperature for ovi^
position diminished to zero as the temperatures approach 20°C or 30°C.
Since the temperatures in the three ponds reached and even surpassed the
extreme limits during winter and summer, temperature plays an important
part in controlling the pattern of reproduction of the snail populations,
although it was ignored in previous field studies. ''" These observations
are essentially similar to those reported by others and they will be
shown later to affirm the data obtained in the following studies. When
temperatures go above 30°C, as they did in Ponds B and C in Puerto Rico,
reproduction is adversely affected. It is important to have more such
field data to corroborate the information obtained in laboratory experi-
ments .
Helisoma trivolvis (Say) is among the most widespread of the freshwater
pulmonates in North America (see Map 3). It is a more tolerant species
of heat and pollution, so that it is not uncommon to find it in areas
where heat and eutrophication may have eliminated Lymnaeid snails. In
the tests used in stressing this snail it is clear that as a planorbid
it tolerates warm conditions better than most lymnaeid snails do. Its
range from Alaska to Georgia and Maine to California implies that it
lives under conditions that subject it to a wide range of tolerance.
Experiment 2. The snails used were cultured from stocks obtained from
Bass Lake, Livingston County, Michigan; several generations were cul-
tured before the animals were subjected to the different temperatures
used in the experiments. The first tests were conducted with young spec-
imens stressed at six temperatures between 9.9° and 25°C (Table 8) with
the aquaria maintained at 10°, 12°, 18°, 24°, 30° and 35.5°C, respec-
tively; the control was at room temperature - about 25°C. Thirty young
snails averaging 3.6 mm were cultured in each of the seven aquaria. The
animals were given small amounts of fish food ground to a powder and
mixed with equal portions of calcium carbonate. This mixture supplied
the young snails with protein and also gave a source of calcium for
shell growth. As the snails grew larger they were given pieces of ro-
maine lettuce for food. Lettuce not eaten was removed when there were
signs of decomposition. This experiment ran for 51 days. The pH and
dissolved oxygen were recorded three times per week; the pH remained
between 8.1 and 8.4, while the dissolved oxygen averaged 7.7 ppm at the
lower scale (i.e., 6°C) to 5.1 ppm at the maximum (36°C). Both the
66
-------
Map 3. Helisoma trivolvis (Say)
-------
TABLE 8. Summary of data for Helisoma trivolvis at 6° intervals, studied for
51 days (4/8/69 through 5/29/69), 30 specimens per tank. (Experiment 2)
TEMPERATURE
°C
9.9 * 0.7
12.1 t o.l
18.2 i"
24.0 * 0.5
29.9 * 0.1
35.5 ± 0.5
,25.2,.* 1.0
(room)
OXYGEN
ppm
8.0 (6)*
7.7 (5)*
7.0 (3)*
6.2 + 0.5
5.6 + 0.3
5.5 (4)*
5.5 + 0.3
GROWTH
Total change -2s-
in mm
1.0 + 0.3
1.4 *• 0.3
2.0 + 0.5
5.0 + 0.9
6.5 * 0.8
2.2
4.6 * 1.0
Survival
90.0
76.7
76.6 (31)"
80.0
60.0
0.0(36)**
96.7
REPRODUCTION
Number of days
to start of
egg-laying
--
__
--
42
28
--
31
Total cases
Total eggs
Number
__
__
__
15
212
21
240
19
295
Egg
Viability
__
--
—
94.6
97.6
__
93.6
00
"Number insufficient for calculating standard deviation, i.e., less than 8.
^Number of days at termination of tank.
-------
table (Table 8) and the graph (Figure 24) indicate that Helisoma trivolvis
grows best at higher temperatures (24° to 30°C) and that it does rather
poorly at lower temperatures at which the Lymnaea stagnalis and L. emar-
ginata did best (18° and 20°C). ~
The relation of growth to temperature in Helisoma trivolvis is striking
(Figure 24) in that this animal does not grow well in colder conditions.
Little growth occurred in the aquarium at 6°C. Survival was good (27
out of 30 survived) but their growth in 51 days was only 1 mm; also, in
the aquarium with a temperature that averaged 12°C, growth was hardly
much better. At 18°C there was a slight increase which averaged about
2 mm in four weeks. It was unfortunate that in this tank a monitoring
relay burned out and the temperature rose to 42°C which killed all of
those specimens. At 24°C the animals doubled their size in 11 weeks,
going from an average of 4.1 mm to 8.6 mm; 25 snails survived. It is
quite evident that warmer conditions enhance the possibilities for cul-
turing this snail. If data are graphed (Figure 25), comparing two sets
of cultures run in January and in May (heavy lines versus light lines on
the graph), the pattern is essentially the same although the profiles
are different; i.e., growth is poor at low temperatures, good in the warm
range (24° to 30°C) but above 30°C conditions become intolerable. These
results are also shown to be similar in Experiment 6.
Experiment 6_. In the previous tests (Experiment 2) the 28°C tank over-
heated due to a faulty instrument. The results in this experiment with
the temperatures at 6°C intervals are similar to those in Experiment 2 but
they are more complete. As can be observed (Table 9), only half (53.3%)
of the snails survived in the cold (7.6°C) water and those in the 12°C
and 18°C tanks grew poorly. It was also seen that no reproduction oc-
curred until the animals were maintained in temperatures at 24°C or above.
Egg-production was good (Figure 26) among animals maintained at 30°C but
the viability of the eggs at that temperature was considerably lower than
that of eggs maintained at 24°C. The graph (Figure 27) also indicates
that some specimens survived as long as 42 days in the very warm water
(36°C), but in that temperature extreme no reproduction took place. Data
shown in Figures 28 and 29 again indicate that the optimum temperature
appears to be between 24° and 30°C. When mortality was plotted on a per-
centage basis (Figure 30) it is apparent that Helisoma trivolvis does
not survive either in the extreme cold (6°C) nor in the hot (36°C) range;
however, between 12° and 30°C mortality is shown to be relatively low
tending to be better under warm conditions. Since H. trivolvis appears
to prefer warm conditions, tests were undertaken to" maintain them at 2°C
intervals ranging between 20° and 34°C to determine optimum conditions,
maximum growth and egg production (see Experiment 12).
Experiment 12. In the course of the studies involved with stressing the
Helisoma trivolvis at 6°C intervals (Experiments 2 and 6), growth and egg
production were found to be best in the range between 24° and 30°C. As
a consequence, another set of observations were made with the range
between 20° and 32°C, using tanks maintained at 2°C intervals. A tube
failure in the control of the 28°C tank ended that one on the 27th day
due to overheating. The data on growth and survival are summarized in
Table 10 and Figure 31. It can be seen that growth and survival within
the normal ranges, i.e., between 20° and 30°C, were reasonably good
69
-------
M 11 i i i
15 17 21 24
APRIL
2 579 12 14 86 19 20 28 27 29
MAY
DATE
Figure 24. Growth of Helisoma trivolvis maintained for 51 days in tanks
at 6°C intervals ranging from 6° to 36°C. Development is
best in the warmer water (24° - 30°C). Experiment 2.
-------
12
10
8
i
cc
u.
IX
<
0
•30«
-Control Jan
• Pd.®
10
20
30 40
DAYS
50
60
Figure 25. Two sets of growth observations made on Helisoma trivolvis
are compared to indicate that the basic pattern is the
same but the growth patterns differ. The optimum in each
(January - heavy lines; May - light lines) is still between
24° and 30°C. Experiments 2 and 6.
71
-------
TABLE 9. Summary of data for Helisoma trivolvis at 6° intervals, studied for .
77 days (12/15/69 through 3/2/70), 30 specimens per tank. (Experiment 6)'
TEMPERATURE
°C
7.6 t 0.3
12.7 - 0.5
18.3 t 0.4
24.0 * 0.3
29.9 * o.l
35.6 t 0.2
24.5 t 0.5
OXYGEN
ppm
11.7 t 0.3
9.8 ± 0.3
8.9 t 0.3
7.5 t 0.3
6.5 ^ 0.2
5.7 t 0.4
7.3 t 0.3
GROWTH"'*
Total change -2s-
in mm
1.1 * 0.2
5.2 t 0.6
6.4 ± 0.8
9.2 * 0.9
11.2 * 0.5
6.6 * 1.0
9.6 * 0.6
Survival
7.
53.3
76.7
60.0
46.7
60.0
(all dead, 42
days)
73.3
REPRODUCTION
Number of days
to start of
egg- laying
__
__
—
35
21
35
Total cases
Total eggs
Number
—
--
__
50
799
209
3109
202
3361
Egg
Viability
7.
--
--
—
93.5
86.2
94.0
Repeat of Experiment 2 because of insufficient data.
!r
At beginning of experiment, animals were 7-10 days old, 0.9 mm average diameter.
-------
12
18° 24° 30°
TEMPERATURE, °C
Room
Figure 26. Egg production of Helisoma trivolvis maintained in
six tanks at temperatures ranging between 7° and
36°C. Highest production occurred between 24° and
30°C. Experiment 6.
73
-------
16
E
E
o
12
8
Room
^"HH^-— • —'l^^^=:
"— 24°
•*••••»•»••••»•••**•*«**
12*
10 2O 30 4O
DAYS
50
60
70
8O
Figure 27. Growth of He1isoma trivolvis maintained for 77 days
in 6 tanks at 6° intervals; room temperature (25°C)
was used as a control. Note that growth was best
between 24° and 30°C; survival in hot water (36°C)
was surprisingly good. Experiment 6.
-------
22
20
ui 18
UJ 16
O 14
o
{3 l2
en
< IO
o
O
J_
I
I
28
30
32
34
36
38
40 42
DAYS
44
46
48
50
52
54
Figure 28. Helisoma trivolvis; cumulative egg-cases collected when snails
were maintained in tanks at 6°C intervals between 6° and 36°C.
The three temperatures represented show that warm conditions
not only cause laying to begin early (the 28th day) but also
stimulate the largest amount. Control temperature about 25°C.
Experiment 6.
-------
5500
5000
4500
4000h
o
2 3500
u
> 3000
I-
^ 2500
g 2000
1500
1000
500
21
28 35
DAYS
Figure 29. Cumulative eggs produced by Helisoma trivolvis from those
tanks out of the six ranging in temperature from 6° to 36°C
that had the best egg production. The control at room
temperature was about 26°C. The warmer conditions favor
high egg production. Experiment 6.
76
-------
100
80
OC
o
UJ
o
-------
TABLE 10. Summary of data for Helisoma trivolvis at 2° intervals, studied for
77 days (6/24/70 - 9/9/70), 30 specimens per tank. (Experiment 12)
TEMPERATURE
°C
20.7 -* 0., 4
23.0 * 0.4
24.4 t 0.4
25.7 * 0.2
27.1 * 0.8
29.6 t 0.4
30.6 * 0.6
32.4 * 0.8
23.6 t 0.5
(room)
OXYGEN
ppm
10.3 * 0.5
10.0 * 0.5
9.4 t 0.5
8.7 t 0.7
9.0
7.9 t 0.5
7.5 t 0.6
7.5 t 0.5
9.3 * o.4
GROWTH"
Total change- 2 S-
in mm
-L -'-^t
9.3 - 0.5 (25)"
9.7 t 0.2 (24)
9.7 * 0.3 (22)
10.6 t o.3 (28)
5.3 t 0.8 (28)***
11.2 t 0.3 (26)
11.6 * 0.6 (19)
14.0 (6)
11.0 t 0.3 (26)
Survival
%
83.3
80.0
73.3
93.3
0
86.7
63.3
20.0
86.7
F
Number of days
to start of
egg-laying
42
49
35
28
_ —
35
28
--
28
.EPRODUCTION
Total cases
Total eggs
Number
98
2193
228
5163
261
4561
353
6671
--
250
4246
158
2252
--
199
4055
Egg
Viability
78.0
83.8
83.9
75.8
--
60.0
62.9
--
84.8
00
***
At beginning of experiment, animals were 1-8 days old.
.1-
Number of snails surviving at end of experiment.
Number of snails on 21st day; all died on 27th day from overheating.
-------
Figure 31. Growth of Helisoma trivolvis maintained for 77 days in
tanks at 2°C intervals ranging from 20° through 34°C.
Development was best at the warmer temperatures; the
28°C was lost due to overheating of a faulty probe.
Experiment 12.
79
-------
00
O
-------
(Figure 32). In reproductive potential (Figure 33) the greatest egg out-
put occurs around 26°C. When growth and reproduction, in terms of eggs
laid, are compared as between the snails that reproduced and those that
may^have produced eggs on a cumulative basis the results are similar.
Again, growth is best in warm conditions and maximum egg production oc-
curred in the 26°C range. It was determined that eggs appeared after
the 4th week and that viability was highest in the warmer water (26° to
30°C) (see Figure 34).
A "plop test" was carried out with Helisoma trivolvis to test the effect
of a sudden change in temperature on the growth of th~e snails. Ninety
young snails between 1 and 14 days old were measured and placed in aquaria
at 6°, 12° and 30°C temperatures. Thirty snails were placed in each test
aquarium and they were taken from a stock supply at room temperature
(about 25°C) without any previous acclimatization. Since excessive hand-
ling interferes with growth and survival, these snails were not measured
until the 14th day. By the 7th day the number of snails surviving was
already less than half the number started. On the 14th day only 3 snails
remained alive (see Table 11) in the 6° and 30°C aquaria; no live speci-
mens were found in the 12°C aquarium. In growth, the 30°C group increased
by only 3.7 mm. More tests of this kind are needed and they have been
projected for the future.
Gonad development in Helisoma trivolvis was studied in two series in which:
(1) the snails were stressed in cultures for 77 days with a temperature
range between 20°C and 34°C and maintained at 2°C intervals; and (2) these
snails were cultured for 51 days between 6°C and 30°C at 6°C intervals.
In the first set normal egg and sperm development appeared (Plate II,
Figures 6a and 6b) in the 20°C tank; also, at 22°C gonad differentiation
(Plate II, Figure 7) was good. The control at room temperature (Figure 8)
(about 25°C) was similar to that of 24°C (Plate II, Figures 9a and 9b).
Some of the best tissue development and highest egg production appeared
at 26°C (Plate III, Figures lOa and lOb). At 30°C it is evident that the
warm conditions tended to speed up the gonad development (Plate III,
Figures lla and lib) but the egg production was poor. In both the 32°C
cultures (Figure 12) and in the 34°C (Plate III, Figure 13), development
was not normal and the animals failed to reach the egg-laying stage.
At 6°C (which actually ran about 10°C) there was hardly any gonad develop-
ment (Plate IV), (Figure 14) and only a small mass of darkly staining tis-
sue was observed where the gonad should appear. When the tissues of an
animal maintained at 12°C were enlarged (X400) early development (Plate
IV, Figure 15) is seen but with little differentiation. Also, at 18°C
the tissues remained poorly developed (Plate Iv, Figure 16) and eggs and
sperm did not appear. The first good differentiation appeared in the
24°C culture (Plate IV, Figure 17) and in the room temperature tank
(Plate Iv» Figure 18); these animals also did well in egg production as
shown in Table 8. In the warm water at 30°C the gonad was reasonably well
developed (Plate Iv, Figure 19) but there was no egg-laying as seen
again in Table 8.
81
-------
100
80
60
40
20
100
80
v 60
QC
u> 4O
8 20
UJ
K n
r- 20"C Tank no. 1 -
- £~^ . 1
24°C Tank no. 3 -
Recovery only
I i i
^*^»« • m •.— j ^
30"C Tank no. 6
^•^
*' i t i
- \ 34°C Tank no. 8 -
B^^-^-^^^^
x-
,' \ i i
24°C Tank no. 3 -
Size only
xT^^T""
- >*. 32°C Tank no. 7 -
**+*-*
~—- o-TT""
: x^* :
S i i i
Tank no. 9
Room Temp. -
:/***^":
Xlii
20
16
12
8
4 i
0 (J
N
20 in
16 <
8
4
° 20 40 60 80 2O 40 60 80 20 40 60 80
DAYS
Figure 32. Growth and recovery of Helisoma trivolvis
maintained for 77 days at 2°C intervals
between 20° and 34°C; the control was at
room temperature (about 25°C). Note that
survival is good up to 30°C; also, that
throughout the series growth was fairly
uniform in all of the tanks. Experiment 12.
82
-------
100
Snails that
Reproduced
80
UJ
60
00
U)
X
5
h-
UJ
o
a:
UJ
CL
40
Snails
20
IOO
CO
o
UJ
80 u.
O
o:
UJ
flD
60 o
D
40 x
20 o
ct
UJ
a.
20
22
26
28
30
32
TEMPERATURE. °C
Figure 33. Growth and egg production of Helisoma trivolvis maintained in tanks at
2°C intervals ranging from 20° to 32°C. Growth tended to be better in
the warmer water and egg production was best at 26°C. Experiment 12.
-------
UJ
LU
CO
o
o
800
700
600
500
400
300
200
100
0
Room
I
100
80
60
2O
GO
40 ^
UJ
o
QC
111
CL
10 20 30
DAYS
40
50
Figure 34. Egg production of Helisoma trivolvis on a weekly basis
(after the 4th week). Largest yields were in warm water
(room temperature or about 25°C to 30°C). Experiment 12,
84
-------
TABLE 11. Summary of data for Helisoma trivolvis "Plop test" (animals subjected to
sudden changes of temperature in tanks from room temperature), studied for
14 days (1/29/71 to 2/12/71), 30 specimens per tank.
TEMPERATURE
°C
7.59 * 0.52
12.49 + 2.05
29.40 * 1.09
NUMBER OF SNAILS
AT DAY 14
3
0
3
SURVIVAL
7.
--107.
07.
10%
A/ERAGE SIZE*
AT DAY 0
0.8420 mm
0.7663 mm
0.7793 mm
AVERAGE SIZE
AT DAY 14
1.2766 mm
--
4.4500 mm
CHANGE IN SIZE
FROM DAY 0
0.4340
--
3.6710
OXYGEN
ppm
17.20
14.50
8.53
00
Ln
Age at Day 0: 1-14 days.
-------
SljSv?-* \£% ?*X*
^ i
."
- *<•+
.':»* ''
* * ^^
O
9a
"
-------
12
PLATE III. Gonad tissue sections from Helisoma trivolvis cultured tor
77 days at different temperatures.
Figure lOa. 26°C (X70)
Figure lOb. 26°C (X400)
Figure lla. 30°C (X70)
Figure lib. 30°C (X400)
Figure 12. 32°C (X400)
Figure 13. 34°C (X400)
87
-------
14
16
18
PLATE IV. Gonad tissue sections from Helisoma trivolvis cultured for
51 days at different temperatures.
Figure 14. 6°C (X70)
Figure 15. 12°C (X400)
Figure 16. 18°C (X70)
Figure 17. 24°C (X400)
Figure 18. Room temp. (X400)
Figure 19. 30°C (X400)
88
-------
Helisoma anceps (Menke)
In older books this species will appear under the name Helisoma antrosum.
It is a snail with a wide distribution (see Map 4) and can usually be
differentiated from the common and widely distributed Helisoma trivolvis
by the depression in, the upper surface. It may occur in the same^ habitat
with H_. trivolvis . It tends to become acutely keeled, and the pit on top
may be deeper or more shallow; as a consequence, some seven subspecies
have been recognized in Michigan (Goodrich, 1932: 63). The animals tend
to be most numerous in lakes or in the quiet , ponded regions of creeks
and rivers .
This species was subjected to two sets of experiments to measure its
growth and reproductive possibilities . One set of observations (Experi-
ment 10) covered a period of 77 days and the animals were maintained in
temperatures ranging from 6° to 36° at 6°C intervals. The data are
shown in Table 12 and Figures 35 and 36. In the 34°C tank all of the
snails died by the 27th day and before the desired 36°C temperature could
be attained. In this series some difficulties arose in controlling both
leeches and chironomids (the 2t*°C tank). Maximum growth but with poor
survival (20%) took place in the 29°C tank; however, in the 24°C tank the
snails showed maximum survival as well as maximum egg production. At
18.7°C, eggs showed a cloudy appearance, perhaps due to a fungus. The
single egg case produced at 13. 6° C had only 3 of the 7 eggs viable. The
fact that any eggs at all were produced was attributed to a heater mal-
function which permitted a rise in temperature of from .1° to 3.4°C for
a few days. It was of interest to find that egg production was reasonably
good at 18°C, reflecting, perhaps, an innate ability in this snail which
is widespread in the northern parts of Michigan to adjust to relatively
cold conditions. Additional tests are reported in Experiment 14 which
measured responses to temperatures at 2°C intervals between 16° and 28°C.
The information obtained in this 2°C interval study (see Table 13,
Figures 37 and 38) indicates that H_. anceps grows better in the warmer
conditions (26° and 28°C) and that~it produces young better in that same
range. The animals in this series (as well as those in the stock tanks)
showed poor survival, presumably due to the presence of chironomids.
While the greatest change in growth occurred at room temperature (8.63mm),
only 3 snails were alive at the end of the experiment. Growth was 7 mm
in the warmer conditions , which is in keeping with the results obtained
in the 6°C set of observations.
"Plop test" with Helisoma anceps (Table 1H). That this species is more
tolerant of warm conditions than of cold is shown in the results when
animals living in room temperature tanks (2H°C approximately) were sud-
denly introduced to tanks maintained at 6°, 12°, 22° and 30° C, respec-
tively. At the lower ranges (6° and 12° C) there was virtually no growth
during the 21 days of stressing (Figure 39), but at 12°C survival was
reasonably good. In the 22°C tank the survival was very good and growth
was best. At 30° C growth was good but at that temperature the survival
was again not encouraging and reflected the poor maintenance experienced
in the 12° C group.
89
-------
Map 4- He I j ionic anceps (Menke)
-------
TABLE 1.2. Summary of data for Helisoma anceps at 6°C intervals, studied
for 77 days (4/1/70 - 6/16/70); 30 specimens per tank.
(Experiment 10)
TEMPERATURE
°C
7.3 t 0.2
13.6 t 0.5
18.7 * 0.4
24.1 * 0.3
29.3 t o.3
34.0 t i.o
24.9 * 0.4
(room)
OXYGEN
ppm
14.6 * 0.3
12.7 * 0.4
10.7 t 0.2
9.3 t 0.2
7.7 t 0.4
7.0 * 0.4
8.3 * 0.4
GROWTH*
Total change- 2 S-
X
in mm
0.85 t 0.33U3)*1
4.86 * 0.67(12)
4.92 t 0.52(14)
4.87 * 0.46(16)
6.91 t 1.12( 6)
3.04 t Q.49( 7)
5.77 - 0.30(24)
Survival
7»
43.3
40.0
46.7
53.3
20.0
(all dead,
27 days)
80.0
REPRODUCTION
Number of days
to start of
egg- laying
—
70
70
56
--
56
Total cases
Total eggs
Number
--
1
7
33
211
70
444
--
119
1,064
Egg
Viability
--
42.9
80.1
87.8
--
77.2
1-14 days old at day 0; average diameter 1.16 mm.
1
Number of snails surviving at end of experiment.
-------
Percent Recovery of Snails at
Each Time of Measuring
0---0 Change in Size of Snails from
Day 0
>-
-------
8
Q 4
O
u.
00
0
Room
10
20
30 40
DAYS
50
60
70
Figure 36. Growth of Helisoma anceps maintained for 63 of 77 days in tanks
at 6°C intervals ranging from 6° to 36°C; growth was best in the
warmer water with a fairly wide spread between 18° and 30°C.
Egg-laying (squares) took place only at 24° and 26°C.
Experiment 10.
-------
TABLE 13. Summary of data for Helisoma anceps at 2°C intervals, studied for
84 days (11/17/70 - 2/9/71); 30 specimens per tank. (Experiment 14)
TEMPERATURE
°C
16.8 t 0.5
18.7 t 0.4
20.2 t 0.3
21.9 * 0.05
24.1 t o.Ol
25.8 t o.Ol
27.7 t o.l
26.0 t 0.04
(room)
OXYGEN
ppm
13.4 t 0.4
12.6 t 0.3
11.99* 0.3
11. 36* 0.03
10.52* 0.01
9.7 * 0.02
9.4 * o.Ol
9.8 * 0.01
GROWTH"
Total change- 2 S-
in mm
6.25 * 0.17
6.34 * 0.02
5.19 t 0.75
7.07 t 0.72
6.83 t o.ll
6.41 ^ 0.07
7.24 ± 0.26
8.63 ^ 0.28
Survival
%
26.7
13.3
13.3
13.3
13.3
46.7
23.3
10.0
REPRODUCTION
Number of days
to start of
egg- laying
77
--
--
--
70
70
--
70
Total cases
Total eggs
Number
3
33
--
--
--
9
82
2
19
--
2
7
Egg
Viability
%
100
--
--
--
95.12
68.42
--
100
1-8 days old at day 0.
-------
• • Percent Recovery of Snails at Each
Time of Measuring
o—o Change in Size of Snails from Day 0
-i8
I6°C Tank no. I "
--O _
24°C Tank no. 5
I8°C Tank no. 2
26°C Tank no. 6 -
28°C Tank
20°C Tank no. 3
22°C Tank no. 4_
Room Temp. -
Tank no. 8
2 E
DAYS
Figure 37. The growth and survival of Helisoma anceps maintained
for 84 days in tanks with 2°C intervals of temperature
ranging between 16° and 28°C; room temperature (26°C)
served as control. Experiment 14.
95
-------
Figure 38. Growth of Helisoma anceps maintained for 84 days in
tanks at 2°C intervals from 16° to 28°C; the control
was at room temperature (26°C). Experiment 14.
96
-------
9.0
8.5
8.0
7.5
7.0
6.5
6.0
£5.5
! 5.0
UJ
N 4.5
< 4.0
3.5
3.0
2.5
2.0
1.5
i.O
0.5
Room
Tempy
^18° y. •••
.--'/
.•• / s
\ ! 1 ! I I I I i i
O 5 10 1.5 20 25 30 35 40 45 50 55 60 65 70 75 8O 85 90
DAYS
-------
TABLE 14. Summary of data for Helisoma anceps "Plop test" (animals subjected to
00
sudden changes of temperature in tanks, from room temperature), studied
for 21 days (4/14/71 to 5/5/71), 30 specimens per tank initially.
TEMPERATURE OXYGEN
°C ppm
6.39 * 0.09 16.64 * 0.06
12.26 t 0.67 14.68 t 0.30
21.86 t 0.34 10.62 ± 0.12
30.50 t 0.04 7.82 * 0.01
AVERAGE SIZE"
AT DAY 0
mm
1.33
1.46
1.42
1.41
AVERAGE SIZE CHANGE IN SIZE NUMBER ALIVE SURVIVAL
AT DAY 21 FROM DAY 0 AT DAY 21
mm ram
1.43 0.10 12 40%
2.02 0.56 21 70%
3.88 2.46 26 86.7%
3.29 1.88 21 70%
Age at day 0: 3-14 days.
-------
£
E
3.0
2.5
LJ
.2.0
1.0
0.5
0
246
8 10 12 14 16 18 20 22
DAYS
Figure 39. Summary of "Plop test" data for Helisoma anceps
maintained for 22 days, indicating growth and
survival; 30 specimens per tank initially.
99
-------
Gonad tissues of Helisoma anceps maintained at 6°C intervals (Experiment
10) were sectioned to determine the degree of development after remaining
in cultures at temperatures ranging between 6° and 34° C for 77 days. The
12°C tank actually was held closer to 15°C (see Table 12) but did show
good egg and sperm development (Plate V, Figure 20). A few eggs were
even produced after 70 days in culture but only half of them were viable
(Table 12). Unfortunately, the tissues from the 18°C tank were not
available for sectioning but the egg-laying was good, starting at the
70th day, with relatively high (80%) viability. The 24°C cultures, both
the control (Plate V; Figure 21) and the 24° C test cultures (Plate V;
Figures 22a and 22b) showed good egg and sperm production as well as
large numbers of viable eggs. When the culture was maintained at 30°C,
growth (Table 12) was better than usual but the gonads (Plate V; Figures
23a and 23b) do not appear to be normal, nor were any viable eggs pro-
duced. At 34°C all of these snails were dead by the 27th day. In sum-
mary, H_. anceps developed best in cultures around 24°C and they tend to
do best" in cool rather than warm (approaching 30°C) water. Since this
species tends to be common in the northern regions of the Great Lakes
area, the tendency to do better in moderately warm water is reflected
by these tests .
Helisoma campanulatum (Say)
This is one of the most common snails in the thousands of lakes through-
out the Great Lakes region , yet very little information of a basic nature
has been published relating to it. It is always amazing to find a vir-
tual mat of dead shells of this snail covering the windswept parts of
the beaches , but it is often difficult to find the live animals when sur-
veying areas of the lake itself. Out stock came from a small lake
(Crooked Lake) in southern Michigan where they were collected in shallow
water under an extended dock. More studies are needed on the ecology of
this snail in the lake habitats. Within its very wide distribution
range (Map_ 5) at least a half dozen varieties have been recognized. An
evaluation of this variation in nature is long overdue.
Studies to measure growth and reproduction (Experiment 9) were first
made at 6°C intervals over a period of 99 days (Table 15 and Figure 40).
It will be noted that the data are similar to those for Helisoma trivolvis
which grew and reproduced best in the temperature range between 24° and
30°C. Egg-laying started first in the control tank (room temperature or
25°C). While culture may have been somewhat influenced by the presence
of chironomids , the pattern is nevertheless reasonably definite and the
information from the 2°C interval study (Experiment 15) collaborates
this data. Also, as in the case of other planorbids studied, maximum
growth occurred under warmer conditions (about 30°C) while survival was
better around 24°C (Figure
When H_. campanulatum was stressed to 84 days at 2°C intervals between
18° and 34°C, survival was relatively poor (Table 16 and Figures 42 and
43). It was difficult to determine the reason for the high mortality
but the tanks that showed poor survival developed what may have been a
noxious algal growth. For example, when a new tank was established at
100
-------
I
- 2v
!-V.Uj*.
j » j ***
,.;. • f- • . '
PLATE V.
Gonad tissue sections from Helisoma anceps cultured for
77 days at different temperatures.
Figure 20. 15°C (X70)
Figure 21. Room temperature (X400)
Figure 22a. 24°C (X70)
Figure 22b. 24°C (X400)
Figure 23a. 30°C (X70)
Figure 23b. 30°C (X400)
101
-------
Map 5. Helisoma campan u latum (Say)
-------
TABLE 15. Summary of data for Helisoma campanulaturn at 6°C intervals,
studied for 99 days (3/4/70 - 6/10/70); 30 specimens per
tank. (Experiment 9)
TEMPERATURE
°C
6.6 t 0.2
12.9 t 0.3
18.1 t 0.4
23.5 t 0.7
29.2 * 0.2
34.5 * 0.9
24.9 t 0.4
(room)
OXYGEN
ppm
13.7 * 0.4
11.8 * 0.3
9.8 t 0.4
8.7 t 0.2
7.7 ± 0.2
6.5 t 0.4
8.1 t 0.3
GROWTH*
Total change - 2 S-
in mm
0.67 t 0.21 (13)*1
5.87 ^ 0.53 (14)
(all dead, 56 days)
6.77 t 0.31 (19)
7.58 ^ 0.68 ( 9)
(all dead, 28 days)
7.93 ^ 0.27 (14)
Survival
43.3
46.7
0
63.3
30.0
0
46.6
REPRODUCTION
Number of days
to start of
egg- laying
--
--
--
98
77
--
56
Total cases
Total eggs
Number
--
--
--
7
44
3
11
--
97
835
Egg
Viability
--
--
--
90.0
54.5
--
95.7
o
Lo
1-3 weeks old at day 0; average diameter 1.47 mm.
H
Number of snails surviving at end of experiment.
-------
Beginning of
1 Eggfaying RT
Spinning of
S~*~^r~^ I Egglaying.3Q°.
/ S<^'~!' 1 -• 20°
90 100
FIGURE 40. Growth and reproduction of Helisoma campanulaturn maintained for 99 days in tanks
ranging from 6°C to 36°C at 6°C intervals; egg-laying started on 77th day at 30°C
but survival was better at 24°C.
-------
Figure 41, Growth and survival o£ Helisoma campa-qulatum
maintained for 99 days in tanks at temperatures
ranging between 6* and 36°C at 6°C intervals;
room temperature (25°C) was used as control.
105
-------
tu
>
O
O
g
g
-------
TABLE 16.Summary of data for Helisoma campanulaturn at 2°C intervals, studied
for 84 days (1/13/71 - 4/7/71); 30 specimens per tank. (Experiment 15)
TEMPERATURE
°C
18.88 * 0.17
20.41 t 0.06
22.27 * 0.17
24.02 * 0.02
25.74 t 0.02
27.62 t 0.03
29.31 t 0.01
31.22 t 0.02
26.24 * o.04
(Room temp. )
OXYGEN
ppm
11.57 t 0.11
11.32 t 0.05
11.11 t 0.9
9.86 t o.Ol
9.47 t o.Ol
8.73 * 0.02
8.54 * 0.01
7.81 * 0.04
9.43 * 0.04
GROWTH*
Total change - 2 S-
X.
in mm
__*!
8.34 t 0.04
5.99 t 0.08
7.32 ^ 0.17
7.54 t 3.5
7.13 ^ 0.10
7.69 * 0.02
7.40 t 0.76
8.56 t 0.52
Survival
0
13.3
40.0
16.7
10.0
40.0
30.0
13.3
16.7
REPRODUCTION
Number of days
to start of
egg- laying
--
77
--
--
84
--
--
--
70
Total cases
Total eggs
Number
--
5
72
--
--
2
16
--
--
--
11
125
Egg
Viability
--
94.4
--
--
100.0
--
--
--
85.6
•7-18 days old
*1
at day 0
18°C tank: 1 alive at day 70 (3.37. survival); 8.55 ^ 0.00 mm total change.
-------
100
75
50
25
0
• • Percent Recovery of Snails at Each
Time of Measuring
o—o Change in Size of Snails from Day 0
I8°C Tank no. I J
24 °C
Tank no. 4
(Trial 2)
30°C -\
o
00
100
75
ui 25
o
32 °C J
8
2 1
100
75
50
25
22°C Tank no. 3
(Trial 2)
Room Temperature "j
• • •
20
40
60
80
20
40 60
DAYS
80
20
40
60
80
Figure 42. Growth and survival of Helisoma campanulaturn maintained in tanks for 84 days in
temperatures of 2°C intervals ranging between 18° and 32°C; 26°C was the control.
Experiment 15.
-------
100
90
80
70
60
50
I-
g 40
o
OC
20
10
18° 20° 22° 24° 26° 28° 30° 32° Room
Temp.
TEMPERATURE. °C
18* 3.3% SURVIVAL AT 70 DAYS,
ALL DEAD AT 84 DAYS
22* TRIAL 2, IN TRIAL 1 2/30
ALIVE AT DAY 14
24° TRIAL 2; IN TRIAL 1 1/30
ALIVE AT DAY 35
Figure 43. Survival of Helisoma campanulatum maintained for 84 days
in tanks at temperatures ranging between 18° and 32°C at
2°C intervals; this indicates relatively low survival in
culture. (Experiment 15)
109
-------
22°C to replace the one in which only 2 snails were alive after the first
14 days, there was less difficulty and almost half of the snails survived.
Again, in the 24°C tank on day 35 only one snail was living (see Figure
42) and a replicate was established. The losses remain unexplained, but
when the work was re-done the tests were successful.
Whether viewed in terms of the 6°C series of tests or the 2°C series, the
pattern is similar to that of the other species of planorbid snails
tested, i.e., growth in the warmer range is reasonably good but survival
is poor; reproduction appears limited with a range between 20°C and the
mid-twenties. The optimum temperature both for growth and reproduction
usually is around 25°C.
At 6°C only an undifferentiated mass of tissue (Plate VI; Figures 24a
and 24b) was seen. At 12°C the oogenesis was in an early stage, but well
developed sperm were in evidence (Plate VI; Figures 25a and 25b). How-
ever, no egg-laying took place (see Table 15). At 18°C both eggs and
sperm (Plate VI; Figures 26a and 26b) were well developed but the snails
failed to survive and there were no eggs. In a subsequent series eggs
did appear (Table 16) in the 20°C tank, which indicates a normal pattern
in that temperature range. At 24°C, gonad production (Plate VII;
Figures 27a and 27b) was good, and viable egg production (Table 15)
appeared to be at its best. At 30°C there was also evidence of normal
gonad activity, but fewer eggs were laid and viability was only half as
good as in the 24°C range. The tank maintained as a control at room
temperature (about 24°C) proved to be the best in gonad development
(Plate VII; Figures 28 and 29) as well as in the high production of eggs
that were viable.
Physa gyrina Say
Physid Snails. While Physa as a group ranks among the most common and
widespread of all freshwater snails (Map 6), it is difficult to find data
on their tolerances to the temperature extremes which they experience in
nature. DeWit (1955), studying the life history of Physa fontinalis near
Amsterdam, Netherlands, measured the influence of temperature on the rate
of growth arid noted especially how temperature influenced hatching and
the mortality of young. He also found that when the animals failed to
feed and grow in the winter the mean temperature was usually less than
6°C; this was shown in our laboratory tests undertaken later as well.
He correlated the growth and reproductive patterns with the seasons but
the definite ranges of temperature were not given.
In the Ann Arbor region, another DeWitt (1955) compared the ecology and
life history of a local American pond snail, Physa gyrina, in widely
separated colonies - those in southern Michigan with ones 300 miles north
at the University of Michigan Biological Station on Douglas Lake. He
observed (1955: 41) ovipositing "in April when the water had risen to at
least 10°C." Again, these data can be compared with our laboratory tests.
While the pattern in the life cycle of this snail in its various tempor-
ary and permanent habitats is now established, it is evident from these
studies, as well as our own, that the physids tolerate a far wider range of
110
-------
24a
l$p^i; '^fr%*?iS&
^»vt| %-. ^Hp^W^'
m v,t
,'/'" ••••-« •'*
'ZSa-;
PLATE VI.
Gonad tissue sections from Helisoma campanulatum
cultured for 99 days at different temperatures.
Figure 24a. 6«C (X70) Figure 25b. 12«C (X400)
Figure 24b. 6«>C (X400 Figure 26a. 188C X70)
Figure 25a. 12°C (X70) Figure 26b. 18°C (X400)
111
-------
f »- f
V *v«s
;' '•"' Av".
*
X
27b
28
30a
PLATE VII. Gonad tissue sections from Helisoma campanulatum
cultured for 99 days at different temperatures.
Figure 27a. 24°C (X70) Figure 29. 24°C (X400)
Figure 27b. 24°C (X400) Figure 30a. 30°C (X70)
Figure 28. Room temp. (X70) Figure 30b. 30°C (X400)
112
-------
Physa gyrina Soy
-------
temperatures than other pulmonate groups. This tolerance will also be
indicated in the data obtained from studies reported here.
The physid snails are often abundant in polluted waters. Wurtz (1956),
in his study of the relation of freshwater mollusks to stream pollution,
stated: "Physa heterostropha is the most tolerant species that has been
found." He did not pursue the effects of the physical and chemical pol-
lution on them because their effects are "usually direct, and usually
absolute." Working with this same snail, Cairns and Scheier (1962)
stated:
"The experimental data suggest that temperature had great effect
upon the toxicity of Naphtenic acids to snails in soft water..."
"These results indicate that the response of snails is less con-
sistent than that of the fish, and that, therefore, a greater
number of tests are required for comparable statistical signifi-
cance ."
Along similar lines, Cooley and Nelson (1970) indicated that temperature
plays an important part in physiological responses involving the "effects
of chronic irradiation and temperature on populations of the aquatic
snail Physa heterostropha." They found that:
"A temperature of 25°C, as compared with 15°C, significantly
increased capsule production by a factor of 2.04 and egg pro-
duction by a factor of 2.50. The increased temperature had
no significant effect on the average number of eggs/capsule
and percent of eggs hatched. No adverse effect on laboratory
populations was demonstrated to result from 10°C temperature
increase."
Another physid snail, Aplexa hypnorum L. , common to woods pools, has a
circumpolar range and is known to exist under extremely rigorous cold
climates. Den Hartog (1963) contributed to what he called the "Aplexa
hypnorum coenosis" and analyzed the associated mollusk assemblages in
relation to soil type and salinity; information on temperature was
largely in terms of seasons. Recently, Vlasblom (1971) carried out a
series of experiments with this snail and he (1971: 102) "concluded that
optimum temperatures are between 10 and 17°C. Figs. 3 and 4 even indi-
cate that the optimum temperature must be higher than 15°C."
In view of their wide range of temperature tolerance, the physids hold a
unique position among mollusk studied. Beames and Lindeborg (1967) cite
Precht (1958) in Prosser's book on physiology, where adaptation to tem-
perature among the poikilotherms may be (1) "resistance adaptation" or
(2) "capacity adaptation" and that the former is more common in nature
than the latter. As for capacity adaptation, the Physa anatina studied
in spring-fed, hot water pools near Montezuma, New Mexico, had become
adapted to the point where they withstood temperatures for one hour as
high as 43°C. Beames and Lindeborg (1967: 14) observed:
"In summary, P_. anatina is capable of 'capacity and resistance
adaptation1 to changes in its environmental temperature. The
animal should be a very useful experimental animal for deter-
mination of the mechanisms of temperature adaptation in poikilo-
therms ."
114
-------
As will be shown later, the physid snails do show far greater plasticity
both in their growth and reproduction when subjected to a wide range of
temperatures.
A more deinite study on the tolerances of heat of two common and wide-
spread American species of Physa was undertaken by Clampitt (1970) in
his work on the comparative ecology of Physa gyrina and Physa integra.
He acclimatized both species to average room temperatures (23° - 25°C)
and then heated their aquaria in a 4-hour period to 40°C; in a second
set he heated the water to 35°C. He found (1970: 144; Figure 14):
"In both sets of experiments, P_. gyrina consistently tolerated the
high temperature conditions for a longer period than did P_. integra.
At 40°C (Fig. 14a), the range for the former species, until 50%
mortality occurred, was 7-16 hours; for the latter species, only
5-10 hours. Considering the results of each experiment as a unit,
the difference between species is significant (P< .01). At 35°C
(Fig. 14b), both species survived many times longer than at 40°C;
50% mortality was reached by 11-13 days (264-312 hours) in P_.
gyrina and in 5.7 - 8.7 days (136-208 hours) in P_. integra.~ Again
the difference between species is significant (PC .005). Differen-
tial tolerance to high temperatures may therefore be a factor helping
to explain the presence of P_. gyrina in ponds and the absence of P_.
integra from such habitats."
The snails used in our study (Experiment 7) were somewhat older (3-4
weeks of age) than generally used for stocking test tanks. A slump in
production of young necessitated the mustering of these animals. The
temperatures in the six experimental aquaria again were maintained at
6°C intervals between 6° and 36°C. Since these Physa were somewhat
older at the start of the tests it was not surprising that egg-laying
began on the 14th day (Table 17; Figures 44, 45, 46, 47) in both the 24°
and 30°C tanks. The snails in the control tank (about 27°C) showed the
greatest growth and the best survival. It is clearly shown that Physa
gyrina has an unusually wp'de range of tolerance with exceptional ability
to survive; reproduction, as well as egg viability, was normal between
18° and 30°C with an optimum at 24°C. An experiment to measure growth
and egg production at 2°C intervals within a range between 14° and 34°C
was also made (see Experiment 13).
The experimental tanks in Experiment 7 became infested with chaetogasters.
While they are usually considered to be commensals, they appear to have
caused a decrease in egg production. This hindrance was especially
noticeable in the 18°C and 24°C tanks and became acute two to three weeks
after egg-laying started. Their presence in the stock aquaria may also
have caused the slump in production of young previously mentioned.
Growth and egg production of Physa gyrina were measured in tanks at 2°C
intervals (Figure 50) in a range from 14° to 34°C (Experiment 13). The
tests were fortunately free of the chaetogasters that adversely influenced
the tanks previously maintained at 6°C intervals. On the whole, survival
was good and varied from 33% in the 14°C tank to 66% in both the 24°C
and 30°C tanks (Table 18; Figures 48 and 49). Adjustment to temperature
115
-------
TABLE 17. Summary of data for Physa gyrina at 6°C intervals, studied for
70 days (1/9/70 - 3/20/70); 30 specimens per tank (Experiment 7).
TEMPERATURE
°C
6.7 * 0.2
12.2 * 0.4
18.1 * 0.4
24.1 ^ 0.2
30.2 t o.l
36.0 + Q.3*1
27.8 ^ 0.5
(room)
OXYGEN
ppm
12.4 * 0.3
10.8 * 0.4
9.7 t 0.3
8.3 ± 0.2
7.4 * o.l
6.6 * 0.3
7.0 t 0.4
..u
GROWTH"
Total change -2s-
in mm
5.4 * 0.6
5.9 ^ 0.6
6.7 t 0.5
6.6 t 0.3
6.7 ^ 0.6
5.8+Q.4*2
7.0 t 0.5
Survival
76.7
76.7
70.0
86.7
66.7
0
100.0
REPRODUCTION
Number of days
to start of
egg- laying
--
--
22
14
14
21
Total cases
Total eggs
Number
--
--
14
293
16
204
42
537
71
1175
Egg
Viability
--
--
98.0
98.0
99.4
100.0
3-4 weeks old at day 0.
j, 1
Only one snail left at 59 days; used for sectioning.
"'2
8 snails at 42 days - last date for statistical use.
Note: Chaetogasters present at varying times in 12°, 18° and 24°C tanks.
-------
*Chaetogaster Infestations
Percent Recovery of Snails at Each
Time of Measuring
°—° Change in Size of Snails from Day O
Cumulative Number of Eggs Laid (In
hundreds) (Adjusted to IOO% Snail
Survival)
30°C Tank no. 5 ~|
8
6
4
2
0
12
9
6
3
0
25
24°C Tank no. 4
...•c\~& &"A
I I I
r-/5
/
Room Temp.
Tank no. 7
2
0
8
6
4
2
12
9
6
3
20
40
60
80
DAYS
20
40
60
80
Figure 44. Growth, survival and cumulative number of eggs laid
(adjusted to 1007= snail survival) of Physa gyrina,
maintained in tanks with temperatures set at 6°C
intervals between 6° and 36°C for 70 days; room
temperature (27°C) served as control. Experiment 7.
117
-------
Figure 45. Egg production of Physa gyrina at 24°C (a) and
18°C (b), showing curtailment due to Chaetogaster
infestation; for comparison, the more normal and
high production at room temperature (27°C) is
also given (c). Experiment 7.
118
-------
to
0300
LU
LU
> 200
- 24° C
(a)
IOO
o
jChaetogosters
15 22
43
50
o
300 g
u.
200 °
cc.
LU
100 CD
57
(c)
Room Temperature
36 43
DAYS
L19
-------
8001- 3O°C Egg Production
700-
n800
57
Figure 46. Eggs of Physa gyrina produced in the 30°C tank over a 6-week
period showing the fluctuations in the number pr-oduced from
week to week. Experiment 7.
-------
V *
O
O
U
1200
1100
1000
900
800
LU
> 700
^ 600
3 500
400
300
200
100
Cumulative Eggs Laid
(adjusted to 100% snail
survival)
Room Temp.
(Chaetogasters) ..<
18
(Chaetogasters)--
24*
1
Figure
15 22 29 36 43 50 57
DAYS
47. Comparison of Physa gyrina eggs produced in the 30°C tank with
the number (adjusted to 1007,, survival) at room temperature (27°C)
over a 6-week period. The 18° and 24°C tanks were infested with
Chaetogasters and egg production was not normal. Experiment 7.
121
-------
TABLE 18. Summary of data for Physa gyrina at 2°C intervals, studied for
77 days (10/22/70 - 1/7/71); 30 specimens per tank (Experiment 13).
TEMPERATURE
°C
15.0 t 0.3
17.0 t 0.5
18.3 t 0.3
20.4 t 0.3
22.1 * 0.3
24.1 t o.l
25.9 ± o.l
27.9 t o.l
29.8 t o.l
31.6 t 0.3
33.3 * 0.4
25.2 ± o.2
(room)
OXYGEN
ppm
13.9 t 0.4
13.1 t 0.3
12.9 t 0.2
11.6 t 0.3
11.3 t 0.3
10.3 t o.2
9.9 * 0.1
9.3 t 0.2
8.7 * 0.1
8.5 t 0.2
8.2 t 0.2
10.1 * 0.2
GROWTH"
Total change -2s-
X
in mm
11.2 ± 0.8 (lOf1
9.9 t 0.6 (17)
10.9 * 0.6 (12)
9.8 t 0.5 (18)
9.0 t 0.5 (17)
9.3 ± 0.4 (20)
10.6 ^ 0.8 (11)
8.9 t o.7 (16)
8.6 t o.5 (20)
11.6 * 0.9 (11)
7.0 ^ 0.7 ( 3)
10.0 t 0.4 (16)
Survival
%
33.3
56.7
40.0
60.0
56.7
66.7
36.7
53.3
66.7
36.7
0
(day 49)
53.3
REPRODUCTION
Number of days
to start of
egg- laying
34
34
28
21
28
21
28
21
40
28
28
28
Total cases
Total eggs
Number
60
2353
45
1116
146
4313
3198
3780
47
816
133
2396
67
1482
109
2022
42
647
42
743
2
7
113
1839
Egg
Viability
7o
97.5
99.7
97.5
99.0
98.9
99.5
97.4
99.2
95.8
56.5
85.7
98.9
^Age at Day 0: 1-14 days.
Number of snails surviving at end of experiment.
-------
Figure 48. Growth and survival of Physa gyrina maintained for
77 days in tanks with 2°C temperature intervals
ranging from 14° to 34°C; room temperature (25°C)
served as control. The lower temperatures are
tolerated better than the highest (34°C).
Experiment 13.
123
-------
e—-o
Change in Size of Snails from Day 0
Percent Recovery of Snails at Each
Time of Measuring
22°C Tank no. 5 -
I
ui
I
UJ
a:
o
lit
00
75
50
25
O
V j;
*s it /b-**'?"""t) ur *
*>'"
~ X•— * — m a A ur, ft-Q — 5 — ^*
"^-
>t*
XX 32°C Tank no. 10
XII 1
12
9
6
3 I
n uT
N
Room Temp: _
Tank no. 12
20°C Tank no. 4 -
28 °C Tank no. 8 -
60 80
o-
-------
100
90
_i 80
I 70
^ 60
K 50
z
LU 40
o
BJ 30
Q_
20
10
14° 16° 18° 20° 22° 24° 26° 28° 30* 32° 34° Room
Temp.
TEMPERATURE
*AII snails dead at day 49
Figure 49. Survival of Physa gyrina maintained in tanks at 2°C
temperature intervals between 14° and 34°C for 77 days.
Except for the extreme 34°C temperature, survival
throughout this range was relatively good. Experiment 13.
125
-------
• _• , . « .
. • ' ' / 24°
70
80
Growth of Physa gyrina maintained in tanks with temperatures set at 2°C intervals
between 14° and 34°C; room temperature (25°C) served-as control. J?. gyrina, in
contrast to the lymnaeids and planorbids tested, can maintain itself in an
unusually wide range of temperatures. Experiment 13.
-------
and dissolved oxygen are shown for the 14°C tank (Figure 51) and for the
16 C tank (Figure 52). In this experiment, reproduction was high (Fig-
ure 53) with an average of 15.4 eggs per case produced in the 30°C tank
and 39.2 eggs per case in the 14°C tank. It is evident that egg produc-
tion was better in the colder temperatures where viability was 98% in the
three coldest tanks and 24.9 eggs or more per case were produced. While
30°C was about the upper limit for all of the other pulmonate snails
tested, some of the Physa gyrina in the 34°C tank remained alive for 49
days; however, only a few eggs were produced at such a high temperature.
In growth the greatest amount was 11.6 mm in the 32°C tank, indicating
that the x^arm water induces growth but hinders reproduction. In decreas-
ing order showing greatest change in size, the other temperatures were
14°C, 18°C, 26°C and room temperature; these data are summarized in
Table 18.
In the sections made of the gonads of Physa gyrina (Plate VIII; Figures
31-36), it was surprising but interesting to observe that this species
could reproduce and maintain itself under a wider range of temperatures
than any of the other species or groups tested. Even at 6°C, while no
eggs were laid (see Table 17), there was already good gonad development.
This 6°C interval experiment was concluded after 70 days but from the
appearance of the gonad tissues (Plate VIII; Figures 31a and 31b) it
could be presumed that egg and sperm development, as xrell as egg-laying,
may have come later and still be normal. In the 12°C culture the tissues
(Plate VIII; Figures 32a and 32b) with eggs and sperm look healthy and
normal but again it is possible that there was not enough time allowed
for egg-laying. The 18°C tank specimens were inadvertently lost so tis-
sues for that series are not available. At 24°C (Plate VIII; Figures 33a
and 33b) the gonads appear fully functional and, as Table 18 (Experiment
13) shows, large quantities of viable eggs were produced at this tempera-
ture. The same situation prevailed in the room temperature tank (about
25°C) where the gonad structure is healthy in appearance and egg-laying
was high (Plate IX; Figures 34a and 34b). Hoxrever, as Table 18 indicates,
there appears to be slightly better production in*the cooler water. At
30°C, normal tissue development (Plate IX; Figures 35a and 35b) is appar-
ent and again eggs and sperm produce a good egg-laying potential. Even
at 36°C, a temperature too high for most of the other snails tested.
there was normal gonad tissue development, but the extreme in the high
temperature range is reflected in the very low incidence of eggs laid
(see Table 1C).
Amnicpla limosa (Say)
As noted in a study by E. G. Berry (1943), these small operculates are
among the most common of aquatic gastropods. Amnicola limosa has the
widest distribution of all the Hex7 World amnicolas and also produces lar-
ger colonies than, the other species in the genus. Its wide distribution
in the Great Lakes region is shown in Hap 7; its general range east-west
extends from the Atlantic to Utah and north-south from Labrador to Florida.
A. limp_sa_ occupies a diversity of habitats such as creeks, rivers and most
Takes. It is often present in large numbers on aquatic vegetation - Chara,
12?
-------
Figure 51- Growth of Physa jgyrjLna in the 14°C tank showing
the fluctuations in temperature and dissolved
oxygen during the 77 days of observations.
(Experiment 13)
128
-------
£
e
IX
0
-25
20
30
40
DAYS
50
60
70
80
-------
E
E
IX
12
10
8
0
• •
ttemp/time
pprn D.O.
I8H
/D.O./time
X/time
10
20
TIME
30
14-
10-
O —
--20
LxJ
o:
ID
cr
o.
5
UJ
I-
-10
40
Figure 52. The adjustment of temperature, dissolved oxygen
and growth of Physa gyrina over a 35-day period
in the 16°C tank. Experiment 13.
130
-------
4500
15° 17° 18° 20° 22° 24° 26° 28° 30° 32° 33° 25°
(Room)
TEMPERATURE, °C
Figure 53. Egg production by Physa gyrina maintained for
77 days at temperatures ranging from 14°C to
34°C; room temperature (25°C) served as con-
trol. Production is highest in the colder
ranges. Experiment 13.
131
-------
a '•-;
V
*r~S
& *
JP1T*
r^^Jj r^
^ rli*%%v: ^'^'
i8?iMs^2 gfec*
-; *
W?^«?';
ri3Su-«^!
t
»M^5
-t,
33b
^.>.
PLATE VIII. Gonad tissue sections from Physa gyrina cultured
for 70 days at different temperatures.
Figure 31a. 6°C (X27.5) Figure 32b. 12°C (X400)
Figure 31b. 6°C (X400) Figure 33a. 24°C (X70)
Figure 32a. 12°C (X27.5) Figure 33b. 24°C (X400)
132
-------
*'*+ . * ^VL%P, X*
ite^^A
f^SSPSv' -w' ;V f w
^L/T^At, A T .r .
•^•<
'-» ^* <* »tT-
•^^S«-'M
«?.«
ir Jft^T
V %>
*" ^
m^f-
36,
PLATE
\* •;
*'. ' --
^*
<
Gonad tissue sections from Physa ^rrina cultured
for 70 days at different temperatures.
Figure 34a. Room temp. (X70) Figure 35b. 30«C (X400)
Figure 34b. Room temp. (X400) Figure 36a. 34 C (X70)
Figure 35a. 30«C (X70) Figure 36b. 34'C (X400)
133
-------
Map 7. Amnicola limosa (Say)
-------
Potamogejtonj Vallisnerig and Elodea, for example, The snails brox^se on
the rich supply of diatoms and algae that cover these plants.
Culturing Amnicola and maintaining them in tanks for study purposes has
problems not encountered with the pulmonates previously considered. Adult
animals are only 4.5 mm long, so they were maintained in small trays that
floated in the larger standard aquaria. Young snails from eggs (laid
singly) in the stock aquaria were placed in trays of the 7 experimental
tanks (30 per tank). Since the animals were so smalls the age-range at
the beginning of the experiment was wider (1-4 weeks of age) than pre-
ferred. Survival (Table 19; Experiment 8) was poor with less than 50%
alive in the 6°G tank after 105 days; in the room temperature tank (24°C)
only 8 snails (2&.77o) survived the tests. Excess algal growth and chiro-
nomid flies were probably in part responsible for this poor maintenance.
Growth as measured (Figure 54) indicated that 18°, 24" and room temperar
ture (24°C) were best; in 30°G all were dead by the 21st day. i
In contrast to Experiment 8, a more successful experiment (Experiment 11)
with Amnicola limosa was completed (Table 20). The snails were maiiitained
for 84 days. To compensate for poor survival the tanks were stocked with
40 rather than 30 snails at the start of the experiment. Ages of snails
used were better, being 1 to 2 weeks old rather than 1 to 4 as in the
previous test. These snails also were maintained in small plastic con-
tainers within the regular 8-gallon tanks. Precautions were taken to
retain the snails and small petri dishes with algae were placed with them
to serve as food.
As in Experiment 8, no eggs were produced and survival again was relatively
poor. The young in this test were from eggs of snails recently brought
to the laboratory from the field. In Experiment 8 the snails x\rere second
generation young. However, the cold (7,2°C) tank over the 84-day period
had a survival of only 307,5 in the 13.6°C and 18.7°C tanks it was even
less (25%). An unexpected cracked heater in the 24°C tank electrocuted
some snails to reduce the number from 34 to 19 at day 42; only one sur-
vived until day 70. In the 29.6°C tank, 9 were left at day 70 and they
died before day 84. At 36°C only 25 lasted 2 treeks but by day 28 all were
dead. The 35.3°C temperature started at 25.2°C and rose to 34°C by day 13;
hence, the 2-week survival (Figures 55 and 56) was to be expected. Even
in the room temperature (or control) tank survival was poor aiid only half
of the original 40 specimens were alive at day 28; only 2 were left at
the last day of the experiment. These tanks were also infested with chir-
onomids.
The data from these experiments do indicate that these small operculate
snails survive better in cold water and that they do not manage to toler-
ate the warmer (30°C or higher) temperatures. Both with Amnicola and
the common stream operculate, Goniobasis, much remains to be accomplished
in learning how best to maintain them in the laboratory. Because these
groups are so widespread and abundant, additional studies are needed, and
information on their adjustment to temperatures in natural waters is of
importance.
The development of the gonads in Amnicola limosa, as xrell as the data on
growth (Tables 19 and 20), indicate that this snail can maintain itself
135
-------
.TABLE 19. Summary of data for Amnicola 1imosa at 6°C intervals,
studied for 105 days (2/26/70 - 6/11/70); 30 specimens
per tank. Terminated without reproduction.(Experiment 8)
TEMPERATURE
°C
6.7 + 0.3
13.5 t 0.4
18.6 t 0.3
24.1 t 0.2
29.6 * 0.3
35.0 t 0.3
23.9 t 0.4
OXYGEN
ppm
13.7 t 0.4
11.5 * 0.4
10.9 t 0.3
8.6 t 0.3
6,9 t o.5
6.2 t 0.3
8.9 t 0.3
GROWTH"
Total change - 2S-
in mm
_i_ juj,
0.56 - 0.33 (14)""
0.52 (3)
2.04 t 0.37 (11)
3.55 (4)
(all dead, 34 days)
(all dead, 21 days)
2.72 t 0.25 (8)
^Survival
7.
46.7
10.0
36.7
13.3
0
0
26.7
™l-4 weeks old at day 0; average length, 1.02 mm.
'Number of snails surviving at end of experiment.
-------
?3
o
I
§2
a:
u_
i
IX
<3
24°C
I2°C
'6°C
30°C,(olldeod bygldoy)
0
10
20
30
50
DAYS
60
70
80
90
100
Figure 54. Growth of Amnicola limosa maintained in tanks at 6°C intervals of temperature
between 6° and 30°C; room temperature (24°C) served as control; 30 specimens
per tank were used. Survival in all tanks was relatively poor. Experiment 8.
-------
TABLE 20. Summary of data for Anmicola limosa at 6°C intervals, studied
for 84 days (6/23/70 - 9/10/70); 40 specimens per tank.
(Experiment 11)
00
TEMPERATURE
°C
7.2 * 0.6
13.6 * 0.5
18.7 * 0.6
I
24.1 - 0.7
.
29.6 - 0.3
32.1 t 1.8
23.0 t 0.5
(room)
OXYGEN
ppm
15.3 t 0.7
13.1 t 0.6
11.3 * 0.2
.
10.1 - 0.2
i
8.6 - 0.3
8.4
10.0 * 0.5
GROWTH*
Total change -
in mm
0.27 + 0.07
0.55 * 0.08
2.3 ± o.l
1.3
i
3.0 - 0.3
2.0
2 S-
X
U2)*1
(10)
(10)
*?
( 1) ^
*3
( 9)*J
( o)*4
( 2)
Survival
30.0
25.0
25.0
0
0
0
5.0
*2
*3
1-2 weeks old at day 0
""Number of snails surviving at end of experiment.
On day 42, electrical shock; 1 alive at day 70.
On day 70, 9 alive, but none alive at day 84.
On day 28, none alive.
-------
100
75
50
25
0
o. ._ 2.
^ • ° „
;/ 6°c tank no.
Percent Recovery of Snails
o- o Change in Size from Day 0
75
50
8
ui 0
(£
/ I2°c tank no. 2
1 I » I i L
30°C
' tanK no. 5
3.0
2.5
2.0
1.5
1.0
0.5
I 10
(£
S 75
50
25
0
100
75
50
25
0
- X I8°c tank no.3
'x. i . i . i i i
36°C
tank no. 6
e
£
ui
0.2
O.I
room temp.£.._—
- 0.5
20 40 60 80
DAYS
Figure 55. Growth and survival of Amnicola limosa maintained
in tanks at 6°C intervals between 6° and 36°C, with
room temperature (about 23°C) as control. Experiment
11.
139
-------
-A-—
••••*••••••• •••*••^ *" *
'~""24°C \
90
100
Figure 56. Growth of Amnicola limosa maintained in tanks at 6°C intervals of temperature
between 6° and 30°C; room temperature (24°C) served as control; 40 specimens
per tank were used. Growth was best between 18°C and 24°C. Survival in all
tanks was poor. Experiment 11.
-------
^n temperatures on the cool side, i.e., between 7°C and 24°C. In
sections of the gonad of a female (Plate X; Figures 37a and 37b) some
differentiation is shown at the end of 84 days in culture, but spermato-
genesis was incomplete. The male at 18°C (Plate X; Figures 38a and 38b)
had good spermatogenesis development but no mature sperm. Whether or
not these tissues would develop completely over a more extended period
in that relatively cool temperature remains an open question. At that
same temperature the female (Plate X; Figures 39a and 39b) had well-
developed ^ eggs. It is possible that reproduction could take place at
18°C but in the cultures no eggs were laid. The section of a male gonad
maintained at 24°C (Plate XI; Figures 40a and 40b) had an abundance of
well-developed eggs. Another male (the control at 24°C) had a normal
and productive gonad with an abundance of sperm (Plate XI; Figures 42a
and 42b). As also shown in the growth studies, Amnicola limosa appears
to be quite sensitive to warm water to the point where its optimum range
would be on the cool side and in the 18° to 24°C range. Its small size
and its usual failure to produce eggs when cultured suggest that this
snail will need more intensive work to establish good culture methods.
Discussion
From the data given both in the tables and the graphs, one can see that
the snails tested do have definite patterns ,of behavior in their growth
and in their reproductive processes. While some of these patterns were
known for a few of the species previously studied, it has now been estab-
lished that there are definite restrictions, even for the families, in
relation to temperature stress. In a few instances these relationships
were studied, e.g., the investigation by Vaughn (1953) working with Lymnaea
stagnalis. He maintained them in a range, as follows: 3.4, 6.9, 11.5~j
15.7, 20.1, 24.2, 28.1, 32.0 and 36.C°C; the control was 24.1°C. His
tests ran for 6 weeks; ours were maintained for 4 months or the time to
run a complete life cycle with this species. In essence, besides discov-
ering the range (between 11° and 32°C) at which this species can be main-
tained, Vaughn established that growth was best at 24°C, but at that tem-
perature mortality was higher than when the snails were kept at 16° to
20°C, which range appears to be the best for their maintenance. This
work essentially substantiates the observations of Noland and Carriker
(1946), in their very definitive study on the biology of Lymnaea stagnalis.
Temperature conditions in nature have a profound effect on the pulmonate
snails as shown in limnological investigations undertaken by Cheatum^(1934).
The pulmonates he studied in nature at Douglas Lake in northern Michigan
were for the most part the same as those stressed in these laboratory
tests. Since temperature has a profound effect on the amount of oxygen
available to the pulmonates in nature, several lake-inhabiting species^
have an annual migratory cycle which brings them into deeper water during
the winter and back on the shoals with the advent of spring. As the
water warms, the number of trips which snails make to the surface for
filling their pulmonary cavity with air increases markedly. Cheatum
showed that at 1.7 cc of oxygen per liter the pulmonates he studied came
to the surface for air three times more often than when the amount was
141
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37
38*,^
-'--. ' ^
x ,
PLATE X. Gonad tissue sections from Amnicola limosa cultured for
84 days at different temperatures.
Figure 37a. 6°C (X70)
Figure 37b. 6°C (X400)
Figure 38a. 18°C (X70), male
Figure 38b. 18°C (X400), male
Figure 39a. 18°C (X70), female
Figure 39b. 18°C (X400), female
142
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40
PLATE XI. Gonad tissue sections from Amnicola limosa cultured for
84 days at different temperatures.
Figure 40a. 24°C (X70), male Figure 41b. Room temp. (X400),
Figure 40b. 24°C (X400), male female
Figure 41a. Room temp. (X70), Figure 42a. Room temp. (X70), male
female Figure 42b. Room temp. (X400),male
143
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6.4 cc per liter. With regard to respiratory acclimatization to tempera-
ture, Kaj Berg (1953), in testing an hypothesis by August Krogh, found:
"The oxygen consumption increases 1.9 times tfhen the temperature of
the experimental animals increases from 11°C to 18°C. The 'reversed
acclimatization' found for Ancylus f luviatilis is about 1.4. It
means that the observed respiration of the warm-water animals in
relation to that of the cold-water animals is about 1.4 times greater
than would be implied from the temperature difference between their
habitats."
Hurst (1927), in his studies of Physa occidentalis, found that those
snails needed twice as much oxygen at 21°C as compared to the amount .they
used at 4°C.
The migration cycle among the 16 species of pulmonate snails studied by
Cheatum appeared to be prompted in the autumn by the lowering water tem-
peratures, with the reverse trend as the waters became warmer in the
spring. Several critical questions remain unanswered, such as: What are
the temperatures that stimulate this movement; do all of the species
respond in the same way; what is the "deeper" part of the lake; what is
meant by "active" in the "deeper" areas; when the snails spend 3 to 4
months in an inactive state in "deep" water under the ice, what determines
the extent of the time they spend there? More recent studies indicate
there is a question whether some of the pulmonates assumed to have such a
migration pattern actually remain on the shoals throughout the winter.
Both Wall, working in our laboratory, and Clampitt, currently studying
migration patterns of these snails in Douglas Lake, have reservations
about the extent and nature of these migrations. Wall (paper being sub-
mitted for publication) has data taken over a three-year period in Lake
Ann, north of Interlochen, Michigan, indicating Lymnaea emarginata did not
migrate to deeper water during any of the winter periods under investiga-
tion.
Among the snails tested in our experiments, two - Helisoma trivolvis and
Physa gyrina - were frozen in ice by Cheatum and living specimens recovered
later. It has been known that the circumpolar physid, Aplexa hypnorum,
annually survives through severe frigid conditions in Siberia. The crux
of the matter appears to be related to the suddenness with which the
changes occur. Cheatum found that many snails do not survive if they are
suddenly transferred from warm water (29°C) to cold (5.5°C). The same
animals would survive if they were cooled gradually over a 24-hour period.
More studies on the adjustment of animals to sudden changes in temperature
are needed and this introduces the obvious need for "plop tests" which
were not possible in the time allotted for our studies. W. Russell
Hunter (in Wilbur and Yonge, 1964) indicated that: "In environments
provided by fresh waters, physical, chemical, and biotic- trophic con-
ditions vary more widely than in the sea. The temperature range within
which some fresh-water molluscs can live practically corresponds to
the absolute limits for metabolism in metazoan tissues..." In his
studies of the life cycles and intraspecif ic variation of four snails in
Loch Lomond, W. Russell Hunter (1961) stated: "Variations in breeding
are dependent both on environmental factors, water temperature being most
important, and on endogenous causes involving the growth of the snails;..."
144
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ere are exceptions, perhaps more than realized, to the rule that lymnaeid
snails often thrive better under "cool" conditions. In the region of Aus-
ralia, Boray (1964) studied Lymnaea tormentosa both in the field and in
the laboratory. He discovered that the optimum temperature for that wide-
spread host of fascioliasis was 26°C; the snails were able to survive
6 weeks in water at 36°C and "they remained alive for 3 years at 2-5°C."
More recently Foster (1971), working on Fasciola hepatica in Oregon and
studying the movement (sometimes called "vagility") of Lymnaea bulimoides,
noted its tolerance to cold is indicated by its ability to survive in
the laboratory at a water temperature of 5°C for more than 3 months with
or even without food. Movement is slowed considerably at this temperature."
Dean Arnold (1969) wrote about the development of problems that relate to
thermal pollution and nuclear power in the Great Lakes. He stressed that
temperature is very important both in relation to physical as well as
biological processes. Such problems are apt to increase since it has
been predicted that electric power demands will double every 8 years! He
stated (1969: 134): "Probably the most likely effect of heated discharges
is an increase in biological production in the local surrounding area.
This may take the form of "blooms' of weeds or of blue-green and green
algae, which are already a problem in Lakes Ontario and Erie and some
areas of Lake Michigan." One could add that the altering of temperature
conditions would also undoubtedly eliminate or alter the mollusks that
inhabit the lakes. These changes are not of small proportions since, in
bio-mass, this group far outweighs many of the other invertebrate animals.
For example, at one time thousands of Lymnaea auricularia introduced from
Europe thrived on the dense emergent aquatic vegetation in western Lake
Erie. Today the species is absent. If one were to add the mussel fauna,
there would be no other group of animals that would be represented so much
in bio-mass!
Mackenthum and Keup (1969) also stressed that "temperature is a prime reg-
ulator of natural processes within the water environment...depending on
the extend of environmental temperature change, organisms can be activated,
depressed, restricted, or killed." Later, they state: "Because of its
capacity to determine metabolic rate, temperature may be the most impor-
tant single environmental entity to life and life processes."
Merriman (1970) studied the "calefaction" (also known as "thermal pollu-
tion") at the site of the nuclear power plant near the mouth of the Con-
necticut River. While the results have not been published, the point was
made that (1970: 52): "Where the calefaction of streams, rivers and
lakes is concerned, what must be done is not only to squarely face the
ecological problems that the rising demand for power are creating but
also to accompany programs of construction with programs of environmental
research so that the most favorable possible conditions are achieved."
Naylor (1965) wrote a very sound and comprehensive paper on "Effects of
Heated Effluents upon Marine and Estuarine Organisms." He gave one of
the best summary statements indicating the relatively narrow temperature
range (roughly 12°C to 32°C) within which freshwater organisms must live.
His succinct statement (1965: 77) is as follows:
"For freshwater organisms in general the normal population structure
is maintained only up to a tolerance limit of about 32°C and
145
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extensive loss in numbers and diversity of organisms occurs above
that temperature (Coutant, 1962). Some genera were shown to be
more tolerant than others of temperatures higher than 32°C, but
all species were limited by temperatures of 40-43°C (Coutant, 1962).
Cairns (1956) concluded that to maintain survival in temperate
streams large areas should not be heated above 30°C for long
periods. This conclusion is also supported by the results of work
by Alabaster (1963) who showed that though coarse fish are attracted
into water heated to about 26°C., temperatures above 30°C are
avoided."
The sensitivity of animals to temperature was reviewed by Stauber (1950)
in a study to determine whether there were physiological species partic-
ularly among oysters and oyster drills. He also refers to Runnstrom
(1929; 1936) who worked industriously to show that among marine animals
of Europe there were physiological races which were noticeable through
their spawning periods in which one group spawned only during the winter
while forms in another group spawned throughout the year. In summary,
Stauber (1950: 117) stated:
"The evidence for physiological species of oysters and oyster drills
has been presented. The probability has been raised that other
marine inshore invertebrates may also be shown to contain physiolog-
ical varieties within the designation of the usually accepted morpho-
logical species. Finally, the practical importance of such informa-
tion has been cited to demonstrate the need for additional observa-
tions and to stimulate the interest of others in this problem."
The existence of physiologically different races of oysters, Crassostrea
virginica, was again established later by Loosanoff and Nomejko (1952).
Mollusks have been important in the interpretation of former ecological
conditions and this relationship was reviewed by F. C. Baker (1937).
Snails are recognized as having "northern1 or "southern" patterns of dis-
tribution; they are also understood to have sensitivity to degrees of
moisture for interpreting whether conditions were moist or dry, as shown
by studies of such operculate species as Pomatiopsis or Hendersonia. More
recent applications involve the effects of the removal of the forest cover
and the changes that occur when rivers are impounded. Wurtz (1969) indi-
cated that the removal of vegetation over extended areas exposed large
drainages to increased solar radiation and brought about a warming of
natural waters. He cited conditions in Lake Erie which had a mean annual
temperature of 40°F between 1918 and 1928, but that mean increased by 2°F
between 1929 and 1930. While the animals were already subjected to wide
ranges in temperature, it is known that during growth and reproduction
such temperature changes may become critical.
Just as Wurtz (Ibid.) indicated that there was evidence for increased tem-
perature in Lake Erie, an interesting correlary also appears in the lake
region of Ann Arbor where about a half century ago it was relatively easy
to obtain Lymnaea stagnalis in large quantities. In those days such in-
vestigators as E. D. Crabb (1929 - in studies of genetics and embryology)
and George R. LaRue, sponsoring parasitological work with his students,
were finding L_. stagnalis in several of the local lakes (Third Sister,
Frains, etc.) within the lower part of the Southern Peninsula. It is no
longer possible to find this snail anywhere in this region; the nearest
146
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good collecting grounds are some 200 miles north, starting at about the
level of Houghton Lake (see Map 1). A likely explanation is indicated
graphically in a diagram (Figure 57) and in a tabulted form below:
Lymnaea stagnalis - First experiment, using 6°C intervals
Tank
Temperature
18.3
24.1
22.2 (control)
14.4
29.3
9.3
36.0
7° of Maximum
Size Change
100.0
94.4
83.2
47.2
27.1
19.2
0
7o Maximum
Eggs
100.0
0
4.0
0
0
0
0
Lymnaea stagnalis - Second experiment, using 2°C intervals
Tank
Temperature
18.5
24.7
22.1
25.6 (control)
16.5
20.4
13.8
7o of Maximum
Size Change
100.0
96.3
95.7
94.0
92.4
90.7
86.7
Tank
Temperature
22.1
20.4
24.7
18.5
16.5
25.6 (control)
13.8
7o Maximum
Eggs
100.0
95.6
90.2
76.0
47.8
44.6
10.0
The' data from two experiments (1 and 3), when plotted on a percentage
basis, indicate, as previously shown, that growth of L_. stagnalis is best
around 20°C, with the optimum for egg-laying only slightly higher. While
the data given for the two experiments are on a percentage basis and may
not be statistically valid, the diagram, nevertheless, gives a true indi-
cation of the relation of growth and reproduction to temperatures. In
contrast to the relatively low optimal temperatures best suited for
Lymnaea stagnalis, the tendency for Helisoma trivolvis (and, for that
matter, some of the other large planorbids) to show preference for rela-
tively warm conditions is shown in a similar and superimposed graph
(Figure 58) and in the following tabulation:
147
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LYMNAEA STAGNALIS
100r
80
CO
60
40
20
0
•....1ST. EXPT. BY 6
0....2NP-EXPT. BY 2'
GROWTH
EGGS
Figure 57 . Diagrammatic comparison of growth and egg-laying among
Lymnaea stagnalis snails in Experiment 1 (6°C intervals)
and Experiment 3 (2°C intervals), indicating the sensi-
tivity of this species to critical temperatures (18°C for
growth and around 24°C for egg-laying).
148
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GROWTH
EGG-LAYING
100
lymnoeo
stognolis
UJ
N
80
60
X
5
h-
z
UJ
o
QC
UJ
QL
40
20
10 22 30 40
TEMPERATURE, °C
50
Figure 58. Diagrammatic comparison of growth and egg-laying,
showing that Lymnaea stagnalis requires "cool"
conditions while Helisoma trivolvis thrives in
"warm" water.
149
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Helisoma trivolvis - Experiment using 6°C intervals
Tank
Temperature
30.0
24.8 (control)
24.0
18.0
12.0
6.0
36.0
7o of Maximum
Size Change
100.0
86.0
82.2
57.2
48.9
9.9
0
7o Maximum
Eggs
100.0
85.3
24.1
0
0
0
0
While, as yet, there is little basic information to substantiate the ob-
servation, it is possible that both the warmer waters and some eutrophi-
cation will tend to favor the Helisoma group so that they may become
dominant species while the lymnaeids would disappear with the advent of
an increasing amount of warmth in the heat budgets of bodies of water
subjected to sources of increased solar or other radiation.
The tests designed to measure the sensitivity of animals to various tem-
peratures during developmental stages may also be useful for interpreting
the role temperature played during the glacial periods. Kearney (1968),
in assessing post-glacial climatic conditions based on pollen analyses,
indicated that there were three periods: (1) increasing; (2) maximum; and
(3) decreasing warmth. He was concerned about the land snails and indi-
cated that "very little comparative work has yet been done on the thermal
tolerances of mollusca." He also stressed the need for precise geographic
ranges, experimental and observational work on thermal tolerances, and
much more careful paleontological work. The use of mollusks as time
markers and for measuring ecological conditions has been recognized by
Pleistocene geologists, among them F. C. Baker (1937), Deevey (1949),
Hibbard (1960), D. W. Taylor (1966) and others.
According to D. W. Taylor (1966: 9) the extinct snail, Biomphalaria kan-
sasensis Berry, is "one of the most significant fossil occurrences in
southwestern Kansas." As a generally recognized tropical or subtropical
snail, it became extinct in that region in early Pleistocene. With the
more precise information provided by the tests used here showing the need
for warm conditions for growth and reproduction, the climatic conditions
that must have existed can most certainly be assessed in a more positive
way. Hibbard (1960) dealt with this problem in an article giving a better
appreciation of North American climates during the Pliocene and Pleisto-
cene. His speculations were based on extrapolations of climates that
would account for the presence of giant land tortoises and crocodiles.
With more detailed information on tolerance as provided by experimental
studies, similar temperature requirements can be postulated for many mol-
lusks found so abundantly in a large number of the interglacial fossil beds,
Crisp (1957) also considered the limits of temperature within which marine
animals could breed. He emphasized that, as a function, breeding differed
according to the "variation in temperature at different latitudes." His
150
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studies on arctic barnacles indicated that they did not reach a breeding
condition if they were subjected to high temperature for prolonged periods.
Essentially these observations substantiate those given here in which
freshwater pulmonate snails grow better in "warm" water (around 30°C)
but often fail to show a normal reproductive potential. As already shown
for some of the species of lymnaeids, Crisp found that among marine bar-
nacles "a prolonged period of high temperature prevents the animals from
reaching the breeding condition." The problem is accentuated if the heat
is applied during the breeding period, a condition which appears complex
as was indicated by Joosse (1964: 95) who found in Lymnaea stagnalis "a
clear annual periodicity in the activity of the neurosecretory cells and
of the C-cells." Acclimated responses do occur but, as stated by Segal
(1961): "Seasonal acclimation is particularly difficult to demonstrate."
Where it is known to occur, it would be emphasized in Physa which seem
to tolerate a far wider range of temperatures than any other mollusk so
far tested.
In an attempt to measure the effects of the extremes of temperature on the
cold side, McNeil (1963) studied Lymnaea (Stagnicola) palustris and Physa
propinqua through several winters (1958 to 1961). He found that the former
survived better "attached to the cement lining of culvert walls and formed
an epiphragm when the water receded in late October." The Physa survived
best "chiefly in the water of the culvert and at the bottom of the larger
ditches." The problem of survival of pulmonate snails in areas where
winters are severe and where the mollusk groups are widely diverse needs
far more attention than hitherto given it. In some cases the animals
migrate, as indicated in studies by Cheatum (1934), Chernin (1967), Wall
(in press) and Clampitt (in press).
Abrahamson (1972) also gave a broad and basic discourse on some of the
ecological hazards produced by power plants. He stated: "Over two-thirds
of the total heat generated by a nuclear power station is discharged
as waste into the local environment. Should this heat be introduced into
lakes, rivers, or estuaries, serious and widespread changes can be expected,
In the same volume (The Careless Technology), Cairns presented data of
studies designed to assay the effects of heated effluents both in the
Savannah River basin and in the Potomac drainage. While his data include
a large number of species (including mollusks) found at different seasons,
the monitoring showed all stations remained healthy in the Savannah study.
He did state that "all stations remained in the 'healthy1 range from 1951
to 1960 according to the system proposed by Patrick (1949)." Perhaps the
importance of the experience by this limnological team is best summarized
in the following statement by Cairns (1972: 845):
"These situations are not dramatic - no rivers were grossly damaged
with accompanying fish kills; there were no spectacular confronta-
tions between the various groups involved; and although the com-
munities of aquatic organisms changed, the successional pattern
appeared to be similar for the areas studied in each of the rivers
(of course, there were considerable differences between the Savan-
nah and Potomac rivers). The two factors that are of interest are
(1) that a truly multidisciplinary group of administrators, plant
waste disposal engineers, and ecologists from state regulatory
151
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agencies and a research organization worked successfully towards
the common goal of preserving the river, and (2) the extensive
use of river water was made over a number of years without inter- •
fering with other beneficial uses or degrading the aquatic com-
munity inhabiting the receiving waters."
The problems relating to "thermal pollution" or "calefaction" were well
defined by Cairns (1972) and he clearly stated the alternatives to those
interested in maintaining a reasonable balance of conditions in natural
ecosystems. It is not possible here to do justice to his thought-
provoking analysis, but the following quotation seems appropriate as ap-
plied to the results of these snail-stressing studies:
"The rapidly increasing warming of surface waters by industrial
uses of water is an example of the urgent need for basic social
and policy changes so that proper management of the environment
may occur. (Detailed discussions are given of present problems
and techniques of observing and analyzing changes in ecological
patterns in heated waters). Electric power companies and all
others using the environment for waste disposal have two alter-
natives; either to continue to increase stress on the environ-
ment and regard the resulting damage as a necessary product of
civilization, or manage the environment so it serves the greatest
number of beneficial uses. If we don"t choose the second of
these, we may soon have no choices at all. If we agree to manage
the environment we must set up institutions to coordinate and
implement the complex decisions on environmental uses and safe-
guards which must be made."
In terms of the studies reported here with regard to the sensitivity to
growth and reproduction of the snails studied, the degree of change the
animals can tolerate is not great. Any change that would add as much as
10°C to the normal heat budgets these snails tolerate could be disastrous
to the fauna. There are those who would argue that the added heat in
the environment might be temporary and adjustments could be made later.
Unfortunately, most natural conditions were established only over long
periods of time, and significant changes in the number and composition
of a fauna usually cannot be "fixed up" regardless of how well the promise
is intended.
Another factor in the data obtained by stressing these snails relates to
the fact that in warmer water the animals invariably grow better and
appear to be huskier specimens. From such observations it would seem
reasonable to argue that adding heat to the habitat obviously produces
more robust specimens. Unfortunately, what calipers show in larger size
is countermanded by the accompanying failure by these same animals to
produce offspring. The level, as shown previously, varies definitely
with the groups studied so that lymnaeids tolerate warm conditions poorly,
planorbids show a preference for warm water, and the physids seem most
tolerant with a tendency to do better toward the cooler side.
An aspect of change that might bear watching relates to the shifts that
can and often do take place when environmental conditions are altered.
Many of the current problems in regions of the world plagued with human
152
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blood fluke (schistosomiasis) are directly related to discouraging and
eliminating the appearance of the intermediate host snails which, for two
of the most serious schistosomes, are planorbid snails. The Biomphalaria
found as a fossil in Kansas (members of the group that make Schistosoma
mansoni a serious disease in Puerto Rico, in other islands of the Greater
Antilles and in South America) might get established in the United States
if more semi-tropical conditions were available to those intermediate host
snails. In this connection, there is also ample evidence - but not enough
good data - to indicate important shifts in faunal assemblages at sites
where temperature, eutrophication, industrial pollutants, etc. have changed
the habitat conditions. In those situations, the less tolerant species
disappear and some of the more resistant ones remain and may even multiply.
Such changes are well documented in places where Physa became a nuisance
in clogging sieves, gumming up intake pipes, etc. The data given for
Physa as compared with those obtained for Lymnaea and Helisoma, even in
this one factor of temperature tolerance, shows that its widespread occur-
rence is directly related to its wider range of tolerance.
A further aspect relating to Public Health interests may be cited in con-
nection with maintaining snails in culture; some intensive studies have
already been undertaken with the genus Pomatiopsis in Michigan and its
close oriental relative, the genus Oncomelania, that serves as host for the
Oriental Blood Fluke (Schistosoma japonicum). Responses of four Oncome-
lania (nosophora, formosana, hupensis and quadrasi) and two Pomatiopsis
(cincinnatiensis and lapidaria) were measured both for their tolerances
and their movements by H. van der Schalie and Lowell L. Getz (1963). Their
observations (1963: 82) were summarized, as follows: "when subjected to
a temperature gradient ranging from 6°C to 36°C, the mean temperatures pre-
ferred by the 6 species tested varied from 21°C for ]?. cincinnatiensis and
0_. hupensis to 26°C for 0_. quadrasi. The range of selection was between
12°C and 30°C."
Movement was studied in relation to temperature (at 5, 10, 15, 30, 25, 30
and 35°C). In all species except one, little movement occurred before
20°C was reached; most movement occurred at 25°C. The exception, P_. cin-
cinnatiensis, displayed considerable movement at temperatures as low as
10°C and it was still very active at 30°C and 35°C. This adaptation is
a necessity for a snail subject to wide extremes of temperature in the
late fall when it must find its way to the top of the river bank where it
hibernates.
***
These studies of growth and reproduction produced what may, in the aggre-
gate, appear to be a confusing amount of temperature information. It
would, perhaps, be useful to indicate for each of the species tested our
results in terms of the optimum temperature for growth and survival, as
well as for highest egg production. Such information could provide quick
reference in situations, for example, where changes are suddenly brought
about in nature by various development projects. It is summarized as
follows:
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OPTIMAL TEMPERATURES FOR THE SNAILS STUDIED
Family
Genus - Species
Optimal Temperatures
Growth and Survival Egg-Laying
Lymnaeidae:
Planorbidae:
Physidae:
Amnicolidae:
Lymnaea stagnalis
Lymnaea emarginata
Helisoma trivolvis
Helisoma anceps
Helisoma campanulaturn
Physa gyrina
Amnicola limosa
20°C
18°
28°
26°
24°
26°
24°
22°C
24°
30°
26°
26°
20°
18°
154
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SECTION VI
ACKNOWLEDGEMENTS
During the three years devoted to these studies, we were fortunate
to have expert laboratory assistance from the following people: we are
especially grateful to Dr. Peter Colby for recommending suitable appara-
tus for carrying out these studies; his expertise was indispensable;
Tani Hale assisted in the early stages of the program; the most sustained
effort, especially the statistical aspects, were carried out by Mrs.
Shirley Johnson; William Kovalak reviewed the statistical methods; William
Collier, Ellen Knight and Gwendolyn Klingler cultured the snails, measured
growth and kept the apparatus in proper order throughout the course of the
experiments; Linda Murtfeldt prepared the gonad sections. We would like
to acknowledge the assistance of Sharon McDonald, who at present is con-
ducting basic behaviour studies with Lymnaea stagnalis using some of this
apparatus.
We appreciate the sustained efforts of the following who worked
industriously in the process of assembling the data and preparing the
report: Annette van der Schalie and Elizabeth Huber; Sally Everhardus made
the final copies of the graphs. Special recognition must go to Mr. Aubrey
Hart who helped build the apparatus and was always ready to assist in
emergencies.
Grateful acknowledgement is made for the support of the Water Quality
Office, Environmental Protection Agency, and the constructive advice and
encouragement provided by Dr. Donald Mount, the Grant Project Officer.
155
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SECTION VII
REFERENCES
Abrahamson, D. H. 1972. Ecological hazards from nuclear power plants.
The Careless Technology, Doubleday/Natural History Press, Garden
City, New York, pp. 795-811.
Ansell, A. B., K. F. Lander, J. Coughlan and F. A. Loosmore 1964.
Studies on the hard-shell clam, Venus mercenaria, in British
waters. I. Growth and reproduction in natural and experimental
colonies. J. Appl. Ecol. _!, 63-82, May 1964.
Arnold, Dean E. 1969. Thermal pollution, nuclear power, and the Great
Lakes. Reprinted from Limnos, Vol. 2(1), 1969, pp. 20-24, in Great
Lakes Research Div., Collected Reprints, Vol. 3 (1969-1970) 1971.
Bachrack, E. and H. Cardot 1924. Developpement des limaces et des lim-
nees a differentes temperatures. Soc. Biol., Tome XCI, no. 23, 1924.
Baker, Frank Collins 1937. Pleistocene land and freshwater Mollusca as
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***
Note: The following pertinent and timely article appeared after this report
was prepared. This article and its references would be indispensable to
anyone interested in problems relating to heat and waste water discharges:
Cairns, J., Jr. 1972. Coping with heated waste water discharges from
steam-electric power plants. BioScience, Vol. 22, No. 7, pp. 411-419-
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162
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SECTION VIII
SELECTED AUTHOR PUBLICATIONS
Berry, E. G. and A. L. Crawford 1932. Preliminary notes on the
Mollusca of Lake Bonneville. Ut. Acad. Sci., Vol. IX, 1932,
pp. 53-54.
Berry- Elmer G. 1943. The Amnicolidae of Michigan: distribution,
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van der Schalie, Henry and Calvin Goodrich 1938. The naiad fauna of
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van der Schalie, Henry and Calvin Goodrich 1939. Aquatic mollusks of
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Midi. Nat., 50: 511-512.
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1963. People and their snail borne diseases. Mich. Quarterly
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1968. Culturing Oncomelania snails for studies of oriental
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163
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1969. The control of Schistosome Dermatitis in the Great
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April, 1972; 10-12.
•1-64 HU.S. GOVERNMENT PRINTING OFFICE: 1973-514-154/269
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1 Accession Number
W
2 Subject Field £ Group
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
5 Organization
Museum of Zoology
University of Michigan
Ann Arbor, Michigan
Title
The Effects of Temperature on Growth and Reproduction
of Aquatic Snails
10 Author (s)
van der Schalie, Henry
Berry, Elmer G.
16 Project Designation
21
22 Citation
Environmental Protection Agency report
number. EPA-R3-73-021. February 1973.
23 Descriptors (Starred First)
Aquatic pulmonate and operculate snails
25 Identifiers (Starred First)
Heat Pollution or "Calefaction"
27 Abstract : The effects of temperature on the following freshwater snails were
studied: Lymnaea stagnalis, L_. emarginata, Helisoma trivolvis, H_. anceps, H_. campanula turn
and Physa gyrina - all pulmonate "pond" snails; one gill-breathing operculate (Amnicola
limosa) was also tested. Both growth and egg-laying were measured in temperatures ranging
from 6° to 36°C. Gonad development was determined through serial paraffin sections; repro-
duction was measured in terms of egg-laying. The lymnaeids grow best at 18°C; egg produc-
tion is better at 22°C. In contrast, the planorbids grow better under warmer conditions
(about 25°C); however, when 30°C is reached growth may appear better but reproduction is
inhibited. The physids tolerate the widest range, sometimes conditions warmer than 30°C,
although at this temperature reproduction is also inhibited. The one operculate, Amnicola
limosa, studied had a preference for cool conditions; i.e., it was like the lymnaeids in
temperature responses. The groups varied in response to temperature as indicated, but none
could be cultured much below 12°C and none would reproduce at temperatures above 30°C.
Mollusks are very sensitive to ambient temperatures; even small changes are important in
their influence on the environmental area affected. Studies are encouraged to determine
the effects of temperature changes well in advance of projected developments.
Abstractor
Henry van der Schalie
Institution
University of Michigan
WR:102 (rev. July 1969)
WRSIC
Send, with Copy of
Qocument to:
Water Resources Scientific Inf. Center
U.S. Department of the Interior
Washington, D.C. 202UO
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