Sex in the reptile world is full of surprises — like lizards that change sex in response to the climate.
That’s right: In warm environments, a type of lizard known as the Australian bearded dragon can switch from having its sex determined by genes to having it determined by temperature.
Some types of fish can reverse their sex — for example, parrotfish start life as females and change to males. In rare cases, some amphibians like the common reed frog and crested newt larvae can too.
But this case, described in a study published Wednesday, July 1, is the very first time scientists have documented wild reptiles changing their sex in response to the temperature.
It was a shocking discovery, even to the researchers:
“We thought we knew it all about sex,” study researcher and University of Canberra in Australia ecologist Arthur Georges told Business Insider. “But along came our little dragon.”
Typically, bearded dragons inherit two sex chromosomes — one from each of their parents — just like humans. (Instead of an X and a Y chromosome, they get a Z and a W chromosome; boy lizards are ZZ and girl lizards are ZW.)
For their study, Georges and his colleagues captured 131 wild adult bearded dragons from different parts of Australia and brought them back to their lab in Canberra to breed them. The researchers could tell what sex the lizards were based on the presence or absence of male sex organs called hemipenes.
After the females laid eggs, the researchers moved them to a separate container to incubate them until they hatched.
They sequenced the lizards’ sex chromosomes to determine their genetic sex. Curiously, 11 of the lizards (the ones from the warmest areas they sampled)
had a male set of chromosomes (ZZ), but in all other ways were
Even more surprisingly, the offspring of the sex-changing lizzards had a sex that was determined by temperature alone. Within one generation, the W chromosome was completely eliminated from that population. And “once that chromosome is gone, it’s really hard to flip back, because once you’ve thrown that machinery away, to reinvent it takes a long time,” Georges said.
The sex-reversed females also tended to lay about twice as many eggs as normal girl lizards, so over time, this resulted in a largely female population.
Scientists aren’t sure why the lizards evolved this ability to change sex, but one possibility is that is gives them more flexibility to live in different environments. But it could also mean the lizards may be more susceptible to the effects of climate change, because their population could end up becoming 100% female.
“If the climate kept on warming four to five degrees, it could be quite catastrophic, and could drive the lizards to extinction,” Georges said.