BUFFALO, N.Y. -- Male water fleas that scientists have never
seen have made their debut in a University at Buffalo laboratory,
providing biologists with their first glimpse of these elusive
The UB research, published last month in Proceedings of the
Royal Society: Biological Sciences, opens a new window on the
biological diversity of several species of water fleas, including
those in the genus Daphnia and the genus Bosmina,
that play major roles in freshwater food webs.
It also demonstrates that pesticides that mimic the hormone used
in the UB experiments may have much broader effects than initially
believed, and could damage populations of fish and other organisms
higher up in the food chain.
"Most freshwater fish eat water fleas at some point in their
lives," said Derek J. Taylor, Ph.D., associate professor of
biological sciences in UB's College of Arts and Sciences and
co-author on the paper. "They are an important food source for
Water fleas are nearly microscopic organisms with transparent
bodies. Found in lakes, ponds and other bodies of fresh water, they
are crustaceans like lobsters and not insects, as their name
"People use water fleas as aquatic 'coal-mine canaries,'" said
Taylor. "They are good indicators of environmental change."
In stable environments, female water fleas generally reproduce
asexually, essentially cloning themselves and resulting in
populations of females that are practically impossible to tell
Water flea populations grow much faster when they reproduce
asexually than when they do so sexually, Taylor explained.
He added that the practice of rarely producing males has likely
been conserved for 100 million years or more in a large group of
In the UB experiments, four distantly related species of water
fleas were exposed to methyl farnesoate (MF), a crustacean juvenile
hormone that is known to determine sex in some species that
regularly produce males.
The researchers found that the MF exposure caused the production
of males in different families of water fleas, despite the fact
that they were only distantly related to each other and despite the
fact that laboratory conditions were designed to be unfavorable to
the production of males.
"Because the same MF hormone affects a broad range of
crustaceans, any insecticide that mimics MF also may affect a large
number of species in freshwater communities," said Taylor.
"In other words, MF-based insecticides are not insect-specific,
and if you affect a non-target species that's a major player in
these freshwater food webs, then it will affect things higher up
the food chain," he said.
The increased production of males after exposure to these
insecticides could reduce water flea populations significantly,
adversely affecting freshwater fish populations, he said.
The induction of males in the lab comes at an important time,
Taylor explained, since the Daphnia genome is expected to be
published next year. Taylor is a member of the consortium based at
Indiana University that is working on the genome.
"Breeding studies with both males and females often are
necessary to identify candidate genes responsible for certain
genetic traits," Taylor said. "If we want to understand, for
example, the genetic basis for why some clones of Daphnia
from lakes are more resistant to pollution, then having males could
help to find the genes in the genome."
Male water fleas, Taylor explained, are assigned more readily to
a species than are females, but males are only rarely produced and
for many species, have never been seen.
"We need to know the species identities in order to understand
how freshwater communities are changing over time, as a response to
climate change, pollution or invasive species," said Taylor. "We're
hoping that by studying the biology of the rare males, we can learn
more about species diversity and freshwater ecosystem changes."
The male-inducing tool now will be used to understand water flea
species diversity on a global scale.
Co-authors on the paper are Keonho Kim, doctoral candidate in
the UB Department of Biological Sciences, and Alexey A. Kotov,
Ph.D., scientist at the A. N. Severtsov Institute of Ecology and
Evolution, Russian Academy of Sciences in Moscow.
The research was supported by a grant from the National Science
Foundation, "Partnership for Enhancing Expertise in Taxonomy."
The University at Buffalo is a premier research-intensive
public university, the largest and most comprehensive campus in the
State University of New York.