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Climate change turns male lizards into females

For the first time, scientists have confirmed that climate change affects the sex determination process of Australian bearded dragons in the wild.

A Central Bearded Dragon.Christopher Watson, CC BY-SA 3.0

A warming climate can now officially be considered emasculating. Australia's bearded dragon lizards can have their sex determined by climate change, a new study published in the journal Nature reveals -- with male dragons transitioning into female during incubation.

It's been known for some time that warmth has an effect on the gender of some reptiles. For Australian bearded dragons, temperatures greater than 34 to 37 degrees Celsius (93.2 to 98.6 degrees Fahrenheit) can cause male embryos to turn into females, resulting in a gender ratio of 16:1 female:male.

This new research demonstrates that not only does this happen in the wild, the sex-changed lizards are capable of reproducing -- and moreover that female lizards with male chromosomes produce more eggs.

"We had previously been able to demonstrate in the lab that when exposed to extreme temperatures, genetically male dragons turned into females," lead author Clare Holleley, a postdoctoral research fellow at the University of Canberra's Institute for Applied Ecology, explained in a statement.

"Now we have shown that these sex reversed individuals are fertile and that this is a natural occurring phenomenon," Holleley said.

The team used data from both controlled breeding experiments, as well as field data from 131 adult lizards. This data showed that some female lizards from warmer temperatures actually had male chromosomes -- and, moreover, those female lizards with male chromosomes produced more eggs.

"By breeding the sex reversed females with normal males, we could establish new breeding lines in which temperature alone determined sex," Holleley said. "In doing so, we discovered that these lizards could trigger a rapid transition from a genetically-dependent system to a temperature-dependent system."

The wild population is currently sitting at the red line. The black line indicates how little temperature needs to rise to effect change from genetic sex determination to temperature-based. Nature

At least one population of bearded dragons is at risk of making this transition in the wild, resulting in a heavily female-skewed population. A population studied by the team is on the precipice of making the change from genetic sex determination to temperature-based sex determination -- all that is required is for the climate to increase by just a fraction of a degree.

This could endanger the animals, the team said.

"Once they become temperature dependent, the risk is that if it keeps warming they'll produce 100 percent females and they'll be at risk of extinction, so this is a concerning finding," co-author Professor Arthur Georges told The Sydney Morning Herald.

However, it's also possible that the lizards could adapt to rising temperatures and produce more males. Going forward, the team will be trying to ascertain whether extinction or adaptation is more likely.

"The mechanisms that determine sex have a profound impact on the evolution and persistence of all sexually reproducing species," Georges said. "The more we learn about them, the better-equipped we'll be to predict evolutionary responses to climate change and the impact this can have on biodiversity globally."