Heat Triggers Sex Change in Lizards by "Turning Off" Key Gene

April 19, 2007

Too much sun may mean sexual inequality for an Australian desert lizard, with higher temperatures changing males into females while still in the egg.

The reptilian sex reversal was discovered by Australian researchers who say the finding shows that determination of sex in animals isn't nearly as clear-cut as most scientists thought.

Central bearded dragon lizards usually develop into males or females depending on the sex chromosomes they inherit. But the study team found that turning up the heat during incubation caused unborn lizards to switch sex inside their eggs.

It had previously been assumed that an animal's gender could be determined either by genes or by temperature as an embryo develops but not by both.

In the case of the central bearded dragon, it appears that temperature can override genes that trigger male development.

The study is reported in the current issue of the journal Science.

Heat Deactivates Sex Gene

Eggs incubated at higher than normal temperatures of 93.2 to 98.6 degrees Fahrenheit (34 to 37 degrees Celsius) produced a strong bias toward female hatchlings, which outnumbered males by about 16 to 1.

The researchers linked this gender bias to a sex-determining gene that was deactivated when the lizards' nests became unusually warm.

This process results in female offspring, because the key gene is on the so-called Z sex chromosome, of which male lizards have two and females only one.

Deactivation of the gene therefore turns a male (ZZ) into a female (WZ).

The findings could revolutionize thinking about how sex is determined in animals, said the research team, led by Alexander E. Quinn of the Institute for Applied Ecology at the University of Canberra.

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