Female dragons are hot!

Unlike mammals, where the gender is determined by X and Y chromosomes, reptiles use a variety of strategies to determine the gender (with the X/Y system being just one of them). Some species of reptiles use Z and W chromosomes (similar to the X and Y chromosomes of mammals), where the female is the one with the different chromosomes (ZW) and the male the one with the same chromosomes (ZZ). More extreme are the species that don’t even have sex chromosomes, but where it’s the temperature that their eggs were incubated at that determines the sex of the hatchlings. Scientists had long believed that every species only uses one of these strategies, until they discovered that the central bearded dragon (picture) uses both these methods to determine the sex of individuals. Only when its eggs are incubated between 20 and 32 degrees Celsius, the Z/W sex genes determine whether the hatchlings are male (ZZ) or female (ZW), but when the eggs are incubated at higher temperatures, the sex chromosomes are ignored and all of the hatchlings are females, even if they are genetically male! With the temperature rising due to global warming, we can only hope that these reptiles aren’t all born as females, or the extinction of these amazing creatures will be inevitable…