Heat Triggers Sex Change in Lizards by Turning Off Genes

A new study out this week has shown for the first time that heat causes lizard eggs to change sex by switching off a key gene.While that may not sound especially revolutionary, it actually means that biologists will now have to think completely differently about the way sex is determined in animals.

Previously it was thought that sex is determined in one of two ways.  For humans, and other mammals as well as birds and some amphibians, an individual animal is male or female depending on the sex chromosomes it inherited from its parents.  Human females have two X chromosomes, while males have one X and one Y.

For other animals, sex is controlled without the help of sex chromosomes - but instead is governed by temperature.  so, in some reptiles, like crocs and turtles, the number of male and female young hatching from a clutch of eggs depends on the temperature that the eggs were kept at while they were being incubated.

Now researchers from the Institute for Applied Ecology at the University of Canberra in Australia have discovered that one of their native lizards, the central bearded dragon lizard, not only have sex chromosomes but they are also affected by temperature - if eggs are incubated at higher temperatures then ones that would develop into males based on their chromosomes, instead turn into females.

The researchers think that temperature is effectively switching off the affect of the male gene - the presence of which makes an individual a male, a bit like the Y chromosome in humans. By switching off that gene, the unborn lizard becomes female.

As well as rocking our understanding of how sex is determined, this latest piece of research might also have important implications for the survival of species in the face of climate change.  If there are too many females being produced and not enough males for them to partner with, it can spell serious problems for the survival of species, since an increasingly warm world could be an increasingly female world, at least as far as lizards go...