Clare Holleley (pictured, R), Kerensa McElroy (Australian National Wildlife Collection, CSIRO), Dan Rosauer, Craig Moritz (Research School of Biology, ANU), Arthur Georges (pictured, L) (Institute for Applied Ecology University of Canberra).
This project poses fundamental questions about how changes in the climate can rapidly alter the biology and genome of organisms. Specifically, how gene-environment interactions affect the rapid evolution of new sex determining modes.
Reptiles can switch from a sex determination mode that is predominantly genetic (using sex chromosomes) to a system where sex is determined by egg incubation temperature (without sex chromosomes). This is achieved through the occurrence of sex reversal in wild populations - where chromosomal males are feminised at high incubation temperature.
The bearded dragon (Pogona vitticeps) is the first terrestrial vertebrate species where environmental sex reversal has been identified in wild populations. Initial data suggests that in some populations, rates of sex reversal have been increasing over time (from 7% in 2003 to 22% in 2011). Populations experiencing high rates of reversal co-occur with geographical regions that have experienced a rapid increase in diurnal temperature range.
This study aims to more fully characterise temporal changes in sex reversal and to identify climatic variables that might impact on rates of sex reversal in the wild (e.g. mean temperatures, temperature variability, frequency of extreme high temperature events). Using historical climate data to identify biologically relevant climatic variables in this model system will ultimately allow us to generate a sophisticated spatially explicit predictive model, linking environmental change with rapid evolutionary responses.
This project will also develop new robust genomic approaches to interrogate historical specimens for evidence of sex reversal. We will develop a custom capture array that targets the recently characterised 219 genes on the Pogona Z chromosome. This whole-chromosome approach will be a much more sensitive and accurate approach to identify genotypic sex than the existing single-locus PCR based method and will facilitate the use of ancient and poor-quality DNA template. In the custom capture array we will also include a selection of fast and slow evolving autosomal regions to generate a fine resolution agamid phylogeny, and estimate population structure within Pogona vitticeps. Information about population connectivity is essential for future predictive modelling of the dynamics of W-chromosome loss.
This work addresses questions of broad scientific interest regarding our capacity to predict evolutionary responses to climate change and thus the impact on biodiversity globally.
Reptile sex goes wild in the outback