The central bearded dragon, a large lizard of eastern Australia, is a complicated creature when it comes to sex. While their embryos can be–as expected–either male or female, the male of the species can transform into a female while still in the egg. And, researchers have discovered, this creates a ‘superfemale’ lizard–a third sex that could wipe out their conventional female cousins.
The ‘sex-reversal’ of male dragons occurs when the eggs are incubated in a nest above 32ºC, causing eggs that are genetically coded to be male develop into females with female reproductive systems. And this is when it gets really strange.
The resulting females retain some male characteristics–tail length, for instance. Additionally, both their male and female traits are hypercharged; they produce more eggs than their female cousins, and can be bolder and more active than even their male cousins. In effect, they represent a third sex super-dragon that is neither male nor female.
A team of scientists from Australia and China studied 100 central bearded dragons, including 20 sex-revered dragons, and have published their findings in the Proceedings of the Royal Society, where they explain:
Although functionally female (i.e. capable of producing viable eggs), the only phenotypic trait in which sex-reversed females resembled normal females was in body condition.
With the ‘third sex’ dragons proving to be bolder, more social and more fertile, the researchers believe that they could, in theory, rapidly cause the demise of their female cousins.
A single period of high incubation temperatures (generating thermally induced sex reversal) can produce functionally female individuals with male-like (or novel) traits that enhance individual fitness, allowing the new temperature-dependent sex-determining system to rapidly replace the previous genetically based one.
At present this change has only happened in the lab–the researchers are still attempting to determine if it can happen in the wild, and if the superfemale dragons retain their traits throughout their life.