Researchers at North Carolina State University discovered that rising water temperature renders water fleas (daphnia), a type of crustaceans found in plankton (drifting organisms that inhabit water column), more prone to hormones that induce gynandromorphism (hermaphrodism).

The exposure to the pesticide named pyriproxyfen, heavily employed in the fight against mosquitoes (it impedes them to breed), and which induces the same effect was also strengthened in warmer waters. "Reports of blue crabs exhibiting both male and female sex characteristics in the Chesapeake Bay and other water systems raise a red flag about the environment in which the crabs live," said Dr. Gerald A. LeBlanc, professor of environmental and molecular toxicology at North Carolina State University.

"Economically important animals - crab, lobster, shrimp and crayfish populations - have been affected by this phenomenon, albeit in low numbers. But if these confused animals produce fewer babies the impact could eventually be significant", he added.

The team had not found any individual exhibiting gynandromorphism in the birth records of about 9,000 daphnia kept in LeBlanc's lab over the course of 15 years.

Daphnia reproduce mainly through parthenogenesis: virgin females lay fertile eggs, and do not need males to produce offspring. The resulting offspring are usually females, who keep this asexual cycle.

Previous investigations made by the same team showed that females' exposure to high levels of methyl farnesoate, a hormone, induced them to produce males. They observed the same effect being induced by pyriproxyfen, but with a more powerful effect.

In the current research, exposure to moderate levels of the same hormone inflicted the emergence of some hermaphrodite daphnia, although not many. But when the water temperatures rose with some 10 degrees Celsius, the number of hermaphrodite daphnia boomed 46 times.

When the team combined pyriproxyfen with water temperature increase, the effect was similar: the number of hermaphrodite daphnia multiplied. "The incidence of gynandromorphism seen in the environment is too low to endanger crustacean populations, but something is going on when we see these sexually compromised animals," said LeBlanc. "It's a warning signal that something is happening in the environment. We're now focusing on the protein receptor that methyl farnesoate binds to in order to learn more about this phenomenon."