Strange news out of Australia these days: It appears that a third gender of sex-reversed bearded dragons are developing into functional "superfemales" and laying eggs all over the place. In the realm of biology, some sentences are just fun to type.
Julian Huguet gets into the specifics in today's DNews report, which addresses the odd phenomenon of temperature-dependent sex, and the worrisome role that global warming may be playing in recent years.
The central bearded dragon, a large lizard found in eastern Australia, is similar to other reptiles in that the species' male-to-female ratio is partly dependent on environment. Eggs incubated at a certain temperatures produce males, while eggs incubated at another temperature produce females. The phenomenon has been observed in turtles, crocodiles and some species of fish.
Nature tends to balance things out, but the Australian bearded dragon is gumming up the works, it seems. Scientists have discovered that the species is capable of producing a kind of third gender. Embryos that are otherwise genetically male are being born as functional females when the eggs are heated to a certain temperature at a certain time of development.
RELATED: Science Says There Are More Than Two Genders
It works like this: Instead of X and Y chromosomes, the bearded dragon have what are called Z and W chromosomes. If an unborn dragon has one of each, no matter what the temperature, it will be a female. However, if the embryo is homogametic and has two Z chromosomes, then it could wind up either male or female -- depending on temperature.
The problem that has biologists worried is that certain double-Z lizards are exhibiting both male and female characteristics. These superfemales can lay eggs while retaining the male chromosomal makeup and, evidently, temperament. They're more aggressive and, according to the recent studies, are behaviorally even more "male-like" than the regular males.
As such, the double-Z females are crowding out the other gals and dominating the lizards' territories. That's not great for genetic diversity and in fact could lead to all-female populations, which is clearly not a sustainable model. Making matters worse, there's a growing body of empirical evidence that suggests global warming may be playing a part in this and other reptilian gender crises. Uh-oh.
-- Glenn McDonald
Science: 'Third Sex' Lizards Could Outcompete Their Normal Female Cousins
Science Daily: Fish With Temperature-Dependent Sex Determination: How Common Are They?
NCBI: Climate Change And Temperature-Dependent Sex Determination In Reptiles