Though switching sexes isn't unheard of in the animal kingdom, it's also not all that common. That's why researchers from the National Oceanography Center were surprised to learn that Antarctic molluscs are capable of changing their sex.
Researchers studying the bivalves, known as Lissarca miliaris, published their findings in the most recent volume of Polar Biology. Their research suggests the molluscs switch between sexes in order to efficiently reproduce in the extreme cold.
Previous reproductive research focused solely on the brooding -- incubation -- habits of females, according to Adam Reed, Ph.D student and lead study author. Reed's research, on the other hand, looked at males, and found something entirely unexpected.
"Curiously, we found huge numbers of very small eggs in functional males, which appear to be far higher in number than an individual could brood throughout the life of the animal," Reed told BBC Nature.
According to the findings, the antarctic molluscs tend to reproduce as males in the "small" stages of development, before switching to female organs in later stages in order to bear a larger number of eggs.
The hermaphroditic behavior is unusual for Antarctic bivalves, however it could become more common in the next decade as the species evolves, Reed told BBC. After all, it appears the molluscs may be attempting to maximize their reproductive efficiency.
"Perhaps they may alternate their sex so they can continue to reproduce as males while brooding their young for 18 months," Reed proposed.
Brooding is fairly common among Antarctic bivalves because it "reduces the need for long periods of feeding," Reed explained. The act also increases the likelihood of the egg's survival, lowering the mortality rate. So if Reed's findings hold true, the Antarctic molluscs' act of switching sexes may be an evolutionary response to the need to ensure successful reproduction in the Antarctic climate.
Recently, scientists pinpointed a specific parasite as the cause of sex swaps in shrimp. But, unlike shrimp, the Antarctic molluscs are able to actively switch between the two sexes, even though male reproductive tissue persists after the change.
While the findings present a significant discovery the work is far from over. However, scientists will have to wait until they return to the remote British Antarctic Survey research station.