Understanding the role behaviours and reproductive strategies have on sex-reversal in lizards

The sex of vertebrates is generally determined genetically; however, in reptiles, sex determination systems can be rather flexible being determined by genetics (Genetic Sex Determination: GSD) or by temperature (Temperature-dependent Sex Determination: TSD). Even more strangely, laboratory experiments in some reptiles have shown that temperature can interact with chromosomal sex determination to cause sex reversal such that genotypic males resemble phenotypic females and vice versa (depending on the chromosomal system).

The sex chromosome system of the Central Bearded Dragon (Pogona vitticeps) has been shown in the laboratory to be overridden by hot temperatures, resulting in reversal of chromosomally male embryos to females. These females are functionally and anatomically female but in captivity, exhibit behaviours similar to those of males. Sex reversed females have been found in parts of Queensland, NSW, and South Australia so if those male-like behaviours occur in nature, then sex reversal could have profound implications for reproductive success and even the way in which populations, sex chromosomes and sex determination mechanisms evolve. Despite that potential significance, nothing is known about the behaviour and ecology of these sex reversed females in nature and how they might compare to their normal (non sex-reversed) female counterparts. The main objective of the work proposed here is to determine the specific roles that behaviour and reproductive strategies play in shaping the success of sex-reversal in the wild. In particular, this phenomenon could affect individual fitness by altering behavioural phenotypes and reproductive strategies leading to evolutionary change and increasing the risk of negative impacts from climate change.

The first year of this project (establishment of a field site and testing of radio-telemetry methods) has been completed. In the remaining two years, I aim to determine the physiological consequence of sex-reversal in Pogona vitticeps by investigating how behaviours and reproductive strategies differ among the sexes (males, females and sex reversed females). With the requested funding, my aim is to use accelerometers to test for behavioural differences among the sexes and to inject doubly labeled water to estimate the field metabolic rates associated with these different behaviours. This combination of approaches will enable me to address the question: do behavioural differences associated with sex reversal increase the metabolic requirements of sex reversed females? This particular aspect of my PhD work is not covered by my current project funding but would provide critical insight into the short and long-term impacts of sex reversal on lizards.