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UBC Theses and Dissertations

Studies investigating evolutionary transitions in plant reproduction Jordan, Crispin Yves


In this thesis I explore several topics related to the evolution of plant reproductive characters. First, I consider mating system evolution at a single locus that simultaneously affects multiple fitness components, including pollen export, selfing rate, and viability (i.e., survival or a similar change in male and female function). I use two approaches. First, I assume frequency-independent mating, so the model characterizes prior selfing (Chapter 2). Second, I assume that selfing rates are determined by a "mass action" process, which characterizes several additional modes of selfing (Chapter 3). For both approaches, pleiotropy between increased viability and selfing rate reduces opportunities for the evolution of pure outcrossing, can favor complete selfing despite high inbreeding depression, and notably, can cause the evolution of mixed mating despite very high inbreeding depression. These results suggest that selection by non-pollinating agents may help explain mixed mating, particularly in species with very high inbreeding depression. Second, I analyze the potential for different genome regions to harbor intra-locus sexually-antagonistic polymorphism. Such polymorphism, involving one allele that benefits fitness in males but decreases fitness in females, and a second allele with opposite effects, is believed to influence the evolution of sexual dimorphism and sex chromosome evolution; both have evolved repeatedly among plant lineages, so understanding the potential for sexually-antagonistic variation informs the evolution of dioecy. Numerical analyses confirm the previous major conclusion that sexually-antagonistic polymorphisms are generally maintained in a larger region of parameter space if the locus is in the pseudo-autosomal region than if it is autosomal. Finally, I consider the effect of two stressors on time to flowering to address hypotheses regarding the evolution of flowering time in heterogeneous environments. A greenhouse experiment using Mimulus guttatus revealed that low water and herbivory had opposite effects on time to flowering, although these effects were weak. These stressors had stronger influences on plant height and the number of flowers produced. These data, combined with previously published results, suggest that a stressor's effect on non-phenological traits may influence the evolution of flowering time through mechanisms not considered by previously published theoretical studies.

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