UBC Theses and Dissertations
Pollinator-mediated selection and diversity in flowering plants Sargent, Risa
This thesis examines the role pollinators have played in the diversification of flowering plants. The extent to which animal pollinators drive the formation of new angiosperm species remains unresolved. Animal pollinators may drive higher rates of diversification because they promote reproductive isolation via specialization on certain floral forms. In Chapter II, using sister group comparisons, I demonstrate that flowering plant lineages possessing monosymmetric (=bilaterally symmetrical) flowers, tend to be more species rich than their radially symmetrical sister lineages. This result supports an important role for pollinator-mediated speciation and indicates that floral morphology plays a key role in angiosperm speciation. The degree to which flowers should evolve to attract one type of pollinator or a suite of pollinators is unclear. In Chapter III, I develop a population genetics model that examines the effects of local species richness on the evolution of pollinator specialization. The model predicts that local species richness plays a role in determining whether or not plants evolve to specialize on one type of pollinator. This model connects the number of species competing for pollinator attention and the probability of a plant receiving conspecific pollen to show that generalist flowers are more likely to evolve when a species is numerically dominant. In addition to morphological diversity, angiosperm species also exhibit a wide diversity of mating strategies. In Chapter IV, I develop a population genetic model to explore the evolutionary forces that contribute to the evolution of dichogamy, a mating strategy whereby pollen dispersal and stigma receptivity are separated in time. The model suggests that factors such as anther-stigma interference and inbreeding depression tend to select for dichogamy, while factors such as the fitness advantage of selffertilization and selection to match the timing of ovule and pollen production tend to select against dichogamy. Lastly, In Chapter V, I test the hypothesis that pollination mode (i.e., wind or animal) is evolutionarily correlated with the form of dichogamy using a maximum likelihood program designed to detect correlated trait evolution on phylogenetic trees. The results suggest that protandry and protogyny have evolved in response to different modes of pollination; specifically, in animal-pollinated species flowers evolve protandry, while in wind-pollinated species flowers evolve protogyny.
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