Abstract
Mating system, the tendency to reproduce via outcrossing or self-fertilization, varies widely across flowering plants. About a third of plant species both outcross and self-fertilize in mixed mating systems, which allows them to realize the benefits of both reproductive modes. Understanding the drivers of mating system evolution is important because mating system affects patterns of genetic diversity, floral traits, and the ability of populations to adapt. While the factors that influence the evolution of outcrossing and selfing, as well as their respective influence on floral phenotypes, are understood independently, less is known about the environments that select for mixed mating and its phenotypic consequences. In Chapter 1 of my dissertation, I tested the benefit of within-flower selfing in colonization of a mostly outcrossing herb, Campanula americana. Using experimental colonization experiments, I found a benefit of selfing in mate-limited environments through a decrease in pollen limitation. In Chapter 2, I characterized variation in the morphological structures, pollen-collecting hairs, involved in reproduction in C. americana to determine how outcrossing ability is maintained when selfing potential evolves. Pollen-collecting hairs hold pollen along the style and retract overtime to release pollen for pollination. I found that selfing ability was associated with an increased length of the hairs suggesting longer hairs aid in pollen retention and allow for pollen to remain for selfing. The longer hairs also retracted in a way that did not influence outcrossing potential, showing evidence for a stable mixed mating system. Finally, in Chapter 3 I stepped outside of mating-system variation to explore alternative hypotheses for variation in pollen-collecting hair traits across 39 species from the Campanulaceae family. I found that pollen-collecting hair length scaled allometrically across Campanulaceae and the variation in C. americana spanned a majority of the interspecific variation in the family, showing the strength of mating system as a selective agent. Taken together, the findings presented in my dissertation advance our understanding of the factors that select for mating system variation and in turn mating system variations effect on reproductive mechanisms and morphology.
