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When It Gets Hot Out There, These Lizards Turn Into Ladies

ByAnna LiebNOVA NextNOVA Next

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A sex-reversed dragon sounds like something you’ll find in a racier corner of the science fiction section—but in fact you might stumble across one in central Australia, according to a recent study published in the journal Nature . Researchers studying Pogona vitticeps , a two-foot long, vaguely brown Australian lizard also known called a “bearded dragon”, observed that in the wild, high temperatures override genetics to produce a surfeit of lady lizards.

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In some reptiles, the sex of a hatchling is can be determined by genetics, but it’s not necessarily hardwired like it is in mammals. In mammals, DNA decides whether a baby develops male or female reproductive parts. The so-called sex chromosomes make the call: two X chromosomes mandate ovaries; an X and a Y chromosome form a coalition for testes. Bearded dragons also have a pair of sex chromosomes called Z and W. Males have two Z chromosomes; females have one of each.

But unlike mammals, bearded dragons also exhibit a “temperature override” switch. Eggs incubated in very warm nests end up female—even if they have two Z chromosomes. Thus environmental conditions can produce “sex-reversed” lizards. These fellows develop with female naughty bits, and can actually lay eggs. The researchers at the University of Canberra who authored the Nature study observed sex reversal in the wild for the first time, finding that more than one out of five of wild females is genetically male.

The researchers found that the override switch starts to kick in at about 90˚ F. Above 97˚ F, just one out of 25 eggs hatches as a male. In other words, at sufficiently steamy temperatures, every night will be ladies night for bearded dragons.

The warm-weather proliferation of lady bearded dragons could cause the population to die out as the climate changes. Or it may help the dragons flourish: When sex-reversed females lay eggs, the sex of the baby lizards depends only on temperature. (The sex-reversed females have two Z chromosomes, like the male lizards, so their offspring will only have Z chromosomes. Thus at low temperatures, all the babies come out male, and at higher temperatures, all end up female.)

This scenario could mean the population goes extinct for lack of eligible males to make babies, the researchers note. But temperature-dependent sex could be an asset, allowing the dragons to change their population structure quickly in order to adapt.

“A high degree of flexibility in sex-determination mode could be a powerful and, until now, unappreciated weapon in the arsenal of evolutionary responses to an unpredictable climate,” the authors wrote.