Australian bearded dragons have the ability to swap genders during the egg stage in times of extreme climate. Source: Wikimedia Commons
Researchers at the University of Canberra have confirmed the first climate-induced change of male bearded dragons into females occurring in the wild.
Sex reversal has not evolved among mammals or birds, although it can happen in rarely in amphibians and in some fish. The Australian central bearded dragon was one of the first reptile species discovered to have a temperature override, as well as the first to demonstrate it genetically (1). High incubation temperatures experimentally feminize male chromosome individuals and produce sex-reversed offspring.
Researchers have previously been able to show in labs that when exposed to extreme temperatures, genetically male dragons shifted gender (2). New evidence, however, shows that depending on the climate’s temperature in the wild, baby males could alter gender while still developing in their eggs.
The researchers at the University of Canberra collected 131 wild adult bearded dragons from different locations in Queensland and New South Wales and took samples in the form of tail snips or blood. To identify sex-reversed females, researchers highlighted a molecular marker in the lizard’s genome that would only appear in sex-reversed lizards. Multiple generations of breeding occurred, and researchers then used genetic tests to trace the parentage of sex-reversed lizards in captivity.
Comparing wild-type individuals with specimens bred in the lab, researchers saw that many females matched the same chromosomal structure found in temperature driven female populations born in the lab. By breeding these sex-reversed females with normal males, researchers created new breeding lines in which incubation temperature solely determined the lizard’s sex. Sex-reversed females laid significantly more eggs per year than normal females of equivalent age (1).
As global temperatures rise, temperature-dependent sex determination in bearded dragons could occur more often than genotypic sex determination (1). This is a possible example of how a rapid change in climate can fundamentally alter the biology and genome of temperature sensitive reptiles (1). Reptiles may have greater potential to compensate for climate change than previously recognized.
References:
- Holleley, C., O’Meally, D., Sarre, S., Marshall Graves, J., Ezaz, T., & Matsubara, K. et al. (2015). Sex reversal triggers the rapid transition from genetic to temperature-dependent sex. Nature, 523(7558), 79-82. doi:10.1038/nature14574
- University of Canberra. (2015, July 4). Climate change is turning male dragon lizards into females. ScienceDaily. Retrieved July 10, 2015 from www.sciencedaily.com/releases/2015/07/150704082402.html