United States
Environmental Protection
Agency
Environmental Monitoring and
Support Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S4-86/032 Jan. 1987
SEPA Project Summary
Taxonomy of Ceriodaphnia
(Crustacea: Cladocera) in
U.S. Environmental Protection
Agency Cultures
Dorothy B. Berner
This study investigated the taxonomy of
three groups of the cladoceran genus
Ceriodaphnia in cultures being used by the
U.S. Environmental Protection Agency.
One taxonomic group was identified as C.
reticulata. The second group was identi-
fied as C. dub/a. The third group was tax-
onomically nearly identical to C. dubla but
was determined to be a hitherto undescrib-
ed phenotypic variant of C. dubla, and is
designated as C, dubla, toothed-pecten
variety. Specimens of this form have been
found in populations of C. dubla collected
west of the Mississippi River.
Similarities in the general morphology,
postabdomens, and ephippia of C. reti-
culata and C. dubia suggest that they are
evolutionary closely related and might be
able to hybridize and produce offspring
having an ovate-toothed pecten like that
of the C. dubia variant. Experiments
designed to test this possibility were in-
conclusive although two successful inter-
specific matings were observed. It is sug-
gested that the relationship between these
two Ceriodaphnia could be further eluci-
dated by study of more extensive field
samples, and by interspecific breeding
experiments that include hatching of
hybrid young from ephippia and study of
their taxonomy and fertility.
This Project Summary was developed
by EPA's Environmental Monitoring and
Support Laboratory, Cincinnati, OH, to
announce key findings of the research pro-
ject that is fully documented in a separate
report of the same title (see Project Report
ordering information at back).
Introduction
The U.S. Environmental Protection
Agency (EPA) Environmental Research
Laboratory-Duluth, the Environmental
Monitoring and Support Laboratory-
Cincinnati, and other EPA and private
laboratories have been exploring the
suitability of Ceriodaphnia for short-term
(7 day) toxicity testing for several years.
Initial Ceriodaphnia stock cultures
established during 1969 in the Duluth
laboratory with animals obtained from fish
ponds at EPA's Fish Toxicology Station,
Newtown, OH, were identified as Cerio-
daphnia reticulata. In 1982-83, subtle dif-
ferences in the appearance of the cultured
animals suggested that the stocks com-
prised more than one species. Subsequent
microscopic examination revealed that
their cultures contained two, possibly
three, species of Ceriodaphnia. Two were
tentatively identified as C. reticulata and
C. dubia (or C. affinis because a problem
in synonomy exists), but the third was
unidentifiable and appeared to have
characteristics of both the other two.
The goals of the study reported herein
were to verify the identification of Cerio-
daphnia in culture at the EMSL-Cincinnati
Facility, Newtown and at other EPA
laboratories, and to try to determine, by
taxonomic comparison and by interspe-
cific matings, if the unidentifiable animals
were hybrids of the two former species,
a morph of one of those species, or a new
species.
Materials and Methods
EPA's Ceriodaphnia were compared with
specimens from other sources, including
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specimens from the U.S. Natural History
Museum (Smithsonian), Washington, DC,
the British Museum of Natural History,
London; and the Lilljeborg Collection,
Uppsala, Sweden, using optical and scan-
ning electron microscopy.
Conclusions
1. Nearly all Ceriodaphnia cultures at
the EPA Newtown Facility and Duluth lab-
oratories, and other cultures derived from
them, were C. reticulata or C. dub/a.
2. A third Ceriodaphnia found in a few
EPA cultures, particularly those from EPA's
Athens, GA, laboratory, was a morpholog-
ical variant of C. dubia, which it resembles
almost completely. The morph was rever-
sibly altered to the dubia form when the
animals were cultured in reconstituted,
rather than well water. The males are indis-
tinguishable from C. dubia males,
regardless of culture medium. Specimens
of this variant have been found in natural
populations of C. dubia west of the
Mississippi River. It is designated in the full
report as C. dubia, toothed-pecten variety.
3. Experiments attempting to hybridize
C. reticulata and C. dubia were incon-
clusive, although two successful inter-
specific matings occurred. Taxonomically,
these species appear to be closely enough
related that males might mistake a female
of the other species as their own. To ascer-
tain whether hybridization is possible,
more experiments of the kind attempted
in this study would have to be carried out.
Lastly, the morphology of such hybrids
should be compared with specimens from
field populations in which C. reticulata and
C. dubia coexist, to see if hybrid forms
occur naturally.
4. Comparison of the EPA C. dubia with
N. American and European populations
designated C. dubia or C. affinis revealed
no significant differences among them.
This study therefore supports earlier con-
clusions that the two names are synon-
omous, and that C. dubia takes prece-
dence over C. affinis. It is likely, however,
that other species of Ceriodaphnia exist
that have characteristics similar to that of
dubia, that should not be used to identify
animals found in natural populations.
Recommendations
As an outcome of this study, the follow-
ing recommendations were made:
1. There needs to be a nationally organ-
ized and funded program for sampling
freshwaters, accompanied by support for
systematic studies, development of refer-
ence collections, and the publication of
adequate taxonomic keys. Difficulties en-
countered by EPA personnel in identifying
the species in their cultures reflect the in-
adequacy of the keys commonly used in
N. America to identify zooplankton. Fur-
thermore, original species' descriptions are
frequently in Latin, German, or French, are
not readily available, and may not be ap-
plicable to N. America because they are
of taxa from other continents. As the need
to monitor freshwaters increases, so does
the need for contemporary, comprehen-
sive reference collections and taxonomic
information.
2. It is suggested that some of the key
characteristics in C. dubia are under nutri-
tional control. This could possibly be
tested by rearing them in defined medium
and feeding them algae also grown in de-
fined medium. This would make it possible
to manipulate the presence and concentra-
tions of micronutrients, which seem likely
candidates for such control. Such studies
might contribute to the knowledge of
some of the factors affecting polymorph-
ism in the Daphniidae.
Dorothy B. Berner is with Temple University, Philadelphia. PA 19122.
William J. Horning, II, is the EPA Project Officer (see below).
The complete report, entitled "Taxonomy of Ceriodaphnia (Crustacea:Cladocera)
in U.S. Environmental Protection Agency Cultures." (Order No. PB 87-110
508/AS; Cost: $11.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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