The sex of newborns of an Australian species of lizard changes as temperatures increase, and global warming could put the species at risk by creating a female-only population, researchers say.

The findings of a study conducted by the University of Canberra on the lizards known as Australian bearded dragons is the first confirmation of climate change triggering sex changes in the wild, the authors say.

Within the eggs of the cold-blooded lizards, genetically male embryos with two Z chromosomes - equivalent to human X chromosomes - can instead develop as females if the egg is incubated at warmer temperatures, they explain.

Such temperature-affected sex changes, previously only produced in laboratories, raise questions about the future of some species, says study lead author Clare Holleley.

"What we have found is that temperature does potentially affect the evolution of the species," she says. "If they are going to be exposed to higher temperatures more frequently, that is potentially going to affect their biology."

In bearded dragons, sex is determined both by chromosomes and by the temperature at which eggs are incubated, the researchers report in their study published in the journal Nature.

However, global warming with climate change has pushed entire populations of the lizard to the point where sex determination by temperature may completely replace the genetic signals of chromosomes, they say.

Animal species that transition from using genetic triggers to determine sex to temperature determination become much more vulnerable to extinction because they now possess fewer evolutionary options if they need to adapt, study co-author Arthur Georges explains.

"Once [bearded dragons] 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," he says.

Field studies of adult lizards showed a number of individuals from the warmer regions of the species' range possessed a set of male chromosomes and yet were actually females.

When some of those sex-reversed females were mated with normal males, the offspring were entirely without sex chromosomes - meaning their sex was entirely determined by the incubation temperature of their eggs, the researchers say.

"They've completely lost a whole chromosome in one generation," says Holleley.

Sex reversal was widespread, with such individuals found across nearly 15,000 square miles in remote semi-arid Australia, the study reported.

And the proportion of sex-reversed females within lizard populations has been increasing, the researchers say, from 6.7 percent in 2003 to 22.2 percent in 2011.

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