| This thesis examines components of mating-system evolution at several different levels. At a high taxonomic level, I examined current phylogenetic data to determine if self-fertilization is an evolutionary dead-end. Although we lack large-scale phylogenetic data to quantitatively assess the hypothesis, the observed pattern appears to support the hypothesis that selfing is a dead-end. At an individual level, I showed that a floral trait, separation between anther and stigma, influenced within-population variation in the selfing rate of an annual plant, Gilia achilleifolia. Theory predicts that when there is selfing-rate variation within a population, genetic associations will develop between genes controlling selfing rate and viability, and that such associations will influence the dynamics of mating-system evolution. This thesis reports evidence for the existence of an association between a floral trait influencing the selfing rate (anther-stigma distance) and inbreeding depression in G. achilleifolia. As predicted by theory, individuals with long anther-stigma distances (outcrossers) showed stronger inbreeding depression than individuals with short anther-stigma distance (selfers), suggesting that outcrossers carried more deleterious mutations than selfers. Finally, using a simulation model, I investigated the effects of polygenic inheritance of a trait controlling selfing rate on mating-system evolution. I found that under polygenic inheritance, the optimal selfing rate may not be realized if the population size is finite. As the number of loci controlling the selfing rate (modifier loci) increased, the strength of selection on each modifier locus decreased, allowing genetic drift to dominate the dynamics of mating-system evolution. I also found that under polygenic inheritance, deviations from the optimal selfing rates depended on the mapping function between the modifier genotype and the expressed selfing rate. |
