UBC Theses and Dissertations
Diversification and evolution of Townsend's daisies (Townsendia-Asteraceae) : a phylogenetic and niche modelling perspective Lee, Christopher
Townsendia is a genus of the sunflower family (Asteraceae) flush with species that frequently specialize in marginal habitats limited by various abiotic factors (e.g., soil, temperature, precipitation), particularly in higher elevation habitats. Although species are well defined geographically and morphologically, the evolutionary relationships in the genus remain unclear. This thesis investigates the evolutionary relationships of Townsendia species through phylogenetic inference, and also uses an ecological niche modelling (ENM) approach to better understand the processes that have lead to inter- and intra-specific variation of the genus. Phylogenetic analysis of plastid DNA regions and the internal transcribed spacer (ITS) establishes the monophyly of the group, and also recovers a large core polytomy in Townsendia and two clades sister to the rest of the genus. The presence of this core polytomy suggests that the diversity in Townsendia may be the result of a recent and rapid process of adaptive radiation. Further evidence for an adaptive radiation in the genus may appear as greater rates of ecological niche divergence between related species, relative to expectations based on a process of random diversification under background environmental conditions. Looking at interspecific variation, ENMs presented varying levels of niche divergence between related species, suggesting that a combination of niche conservatism and divergence played a role in the evolutionary history of the genus. Niche modelling is also used to better understand the variation present within one species, particularly one with discrete population subsets such as diploid sexuals and polyploid asexuals. Polyploid asexual populations of T. hookeri tend to have a wider and more northerly distribution than their diploid counterparts, though the role of this pattern on the speciation of Townsendia is unclear. Such unequal distributions may arise from differences in dispersal ability, or in abiotic preferences between reproductive types. Comparisons of ENMs between these groups find evidence for intraspecific niche variation, and also predict the role of competitive exclusion, as factors that drive and maintain this distributional pattern. Overall, the combined use of phylogenetic analysis and ecological niche modelling in this thesis improves our understanding regarding the distribution patterns, evolutionary history and speciation pathways of Townsendia.
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