Male crustaceans can "lock down" their maleness to avoid being completely feminised by seawater contaminated by feminising pollutants, according to scientists.
New research at the University of Portsmouth has shown that crustaceans turned partially into females retain a core of masculinity, and they may have learned how to do it after evolutionary battles with parasites.
The researchers have also published the entire genetic code for the amphipod crustacean they studied, which they hope will lead to even better understanding of their biology.
Dr Alex Ford said: "We've known for some time that fish change sex if they're subjected to even small amounts of oestrogen in the water, but until now we didn't know what was happening to crustaceans.
"What we found is that once a crustacean has decided to be male, it can lock down its maleness. It will still become feminised in many respects, but at its core, it will remain male. This has important implications for how we study the effects of potential feminising pollutants on these creatures."
Fish and some other aquatic creatures are increasingly changing sex because the rivers and oceans are receiving a steady stream of feminising pollutants in sewage and industrial effluent.
The research was part of a four-year project that looked at the effects of parasites and pollution on crustaceans.