Changing sex with changing climate: mechanisms and consequences of divergence in sex determination across a glaciated landscape (APSF 17-8)

APSF 17-8 | Amount: $ 44,400 | Project Leader: E Wapstra | Project Period: Jul 2017 - Jul 2020

A project undertaken at the University of Tasmania in conjunction with the University of Canberra and led by Erik Wapstra, Chris Burridge and Tariq Ezaz

The prevailing paradigm is that sex determination in vertebrates is fixed within lineages. For example, eutherian mammals and birds have alternative but fixed states of genetic sex determination (GSD: XY and ZW heterogamety respectively) while within reptiles, most lineages have GSD, while others (predominantly crocodiles and turtles) have temperature dependent sex determination (TSD). A series of recent papers in the past two decades have challenged this paradigm and we now understand that sex determination is highly labile in reptiles with evidence of multiple transitions between GSD and TSD throughout its evolutionary history. Understanding these transitions remains a major challenge within evolutionary biology. Importantly, this is also an important ecological and conservation question – species with TSD have very different responses to climate variation and change to species with GSD. Our previous studies which span over two decades have established Tasmanian endemic snow skink Niveoscincus ocellatus as the model species to understand evolutionary transitions between GSD and TSD as well as the ecological divergence in response to climate change.

Figure 1. Niveoscincus ocellatus (the spotted snow skink) exhibits population divergence in sex determination. Credit: Peta Hill.
Figure 2. PhD student Peta Hill performing field work in Tasmania. Credit: George Cunningham.
Figure 3. Niveoscincus ocellatus: Maternal basking behaviour determines offspring sex in lowland but not highland populations. Credit: Geoff While.
Figure 4.Niveoscincus ocellatus: An ideal taxon for understanding the mechanisms involved in evolutionary transitions in sex determination across vertebrates. Credit: Peta Hill

The first objective of this project is to document the phylogenetic patterns of transitions and mechanisms in sex determination among snow skink species and populations.
The second objective of this project is to model the links between sex determination systems, climate drivers and the consequences of climate change on populations.
The third objective of this project is to test the reproductive compatibility of highland (GSD) and lowland (TSD) snow skink populations (within species) and the viability of their offspring to reveal whether local adaptation to differences in climate will inhibit gene flow among populations and potentially promote the loss of genetic variation through reproductive isolation.

The fourth objective of this project is to sequence the N. ocellatus genome to identify genes associated with differences in sex determination mechanism, to (i) understand the mechanisms of transition between systems, and (ii) to assess of homology with sex determining regions in other amniotes.