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Urquhart-Cronish, Mackenzie

University of British Columbia

Species range expansions exist at the interface of ecology and evolutionary biology and the iterative interactions between eco-evolutionary theory and observational and experimental tests in nature. Understanding the demographic pathways and genetic consequences of range expansion has important implications for interpreting spatial patterns in biodiversity in the context of historical processes, managing invasive species, and forecasting species range shifts. Range expansion theory makes robust predictions about how genetic diversity, fitness, and traits should change over space and time due to serial founder events characterizing the demographic pathways underlying the history of colonization, but empirical results do not always match theoretical expectations. In this thesis, I use a combination of theoretical and empirical work to investigate the demographic pathways and genetic consequences of post-glacial species range expansions. First, I investigate whether density-dependent selection on loci underlying relevant life-history traits at the low-density range edge may be an important factor explaining discrepancies between theoretical and empirical studies of the predicted negative genetic consequences of range expansion. I find expressed genetic load is dependent on the population density in which fitness is measured. Next, I investigate patterns of genetic diversity through space and time in the context of colonization following alpine glacier recession to understand whether dispersal limitation (i.e., serial founder events) also characterizes expansions across this relatively understudied smaller spatiotemporal scale. I find that shorter spatiotemporal scales of range expansion do not appear to be limited by dispersal at the range edge, suggesting levels of population genetic diversity are not reduced post-expansion. Finally, I investigate how mating system diversity is maintained within a species, specifically testing how historical range expansion can influence contemporary biogeographic patterns in species traits. I detect, on average, a pattern of increased probability of selfing and clonal propagation with increased distance from putative historical refugia. This pattern suggests selection for both sexual and asexual reproductive assurance occurred in colonizing populations during range expansion. Together, these studies provide a better understanding for how range expansion in ecologically complex simulated and natural environments can shape spatial patterns in biodiversity we see today.

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2024-08-27

10.14288/1.0445168

Doctor of Philosophy - PhD

Science, Faculty of; Botany, Department of

2024-11

Graduate