The central bearded dragon, a bold little beast from Australia, has a fairly unusual time when it's developing in the egg.
Much like a handful of other reptiles, central bearded dragons determine their sex by the temperature of their egg during incubation. If the egg is buried at a higher temperature, around 36°C (96.8°F), then genetically male individuals will turn into functional females. Although genetically male, these dragons are fertile and capable of laying eggs. That's different from humans and most vertebrates whose sex is purely determined by their chromosomes at the time of conception.
Australian scientists at the University of Queensland, the University of Canberra, and CSIRO have recently been looking at this phenomenon only to discover something even more, in their words, “decidedly weird”. Their study was recently published in the journal EvoDevo.
It turns out, the genetically female individuals also do something fairly unusual. As a female develops in its egg, it temporarily grows a pair of hemipenes, the lizard equivalent of a penis, during development.
"Our team incubated 265 bearded dragon eggs at two temperatures – either at 28 or 36°C [82.4 or 96.8°F], the latter of which causes genetically male dragons to reverse their sex,” researcher Dr Vera Weisbecker said in a statement. "The way these females grew hemipenes, the equivalent of a mammalian penis, was decidedly weird."
Dr Weisbecker's Honors student Sarah Whiteley added: "I noticed that female embryos first grew a pair of hemipenes, just like male embryos, and only lost them closer to hatching.”
Scientists actually know very little about the process of temperature-dependent sex determination. Nevertheless, widening our understanding of this could help shed light on the evolution of female genitalia among humans and other vertebrates, something we know equally little about.
"While sex determination is a major switch in individual development, we know little about the differences between the two developmental modes," said Whiteley. "Understanding these might give us some insights into the evolution of our own, genetically determined sexes."
Dr Weisbecker concluded: "One of the biggest barriers for broader understanding is that there is scant knowledge on the female genitalia of reptiles, compared to a relatively large body of literature on male genital development and diversity."
"Understanding these might give us some insights into the evolution of our own, genetically determined sexes."