Abstract
Environments are changing rapidly, with many species facing extinction. But some species have the evolutionary potential to adapt. Hence, quantifying genetic change and identifying the processes responsible is a focal point for better understanding species persistence in the face of human driven rapid environmental change. However, some environments are accustomed to rapid environmental change. The Simpson Desert, for example, is subject to episodic and irregular resource pulses triggered by heavy rain, showing some of the highest variability in rainfall across Australia. Resource pulses cause some small mammal populations to grow rapidly and subsequently crash – so-called ‘boom-bust’ population dynamics. While other species exhibit relatively stable population dynamics despite exposure to these large resource pulses. Thus, small mammal populations provide an excellent opportunity to examine how environmental change and ecological change drive genetic change in these dynamic systems.My thesis uses two study species with contrasting population dynamics, the sandy inland mouse (boom-bust), Pseudomys hermannsburgensis, and the lesser hairy-footed dunnart (stable), Sminthopsis youngsoni, to study temporal genetic patterns (over 15 years) and disentangle the underlying evolutionary processes responsible (using 1903 individuals and as many as 24,000 SNPs). First, I show that the boom-bust population dynamics of the mouse drives rapid genetic change, while the stable population dynamics of the dunnart are less responsive to the rainfall-driven resource pulses. Second, I disentangle drift and gene flow and their relative contribution to changes in genetic structure and reveal gene flow as a stronger predictor of genetic structure in both my study species. Third, I reveal how geographically restricted gene flow is determined by landscape productivity and is responsible for shaping spatiotemporal genetic patterns in the mouse, while the dunnart does not show signs of change in geographically restricted gene flow with changing landscape productivity. Lastly, I model my two study species’ population dynamics in response to two evolutionary processes (drift and gene flow), and in doing so identify signals of fluctuating selection in the boom-bust dynamics of the mouse, but not in the stable dynamics of the dunnart.
This thesis has revealed an intricate interplay between drift and gene flow and begun investigation into the dynamics of more subtle forms of selection that can utilise standing genetic variation to facilitate species adaption. Ultimately, I show the power of temporal sampling to better understand species’ genetic responses to our rapidly changing world.
| Date of Award | 2025 |
|---|---|
| Original language | English |
| Supervisor | Bernd GRUBER (Supervisor), Stephen SARRE (Supervisor) & Richard DUNCAN (Supervisor) |