Population Genetics, Natural Selection and Genetic Architecture of the Selfing Syndrome in the Morning Glory Ipomoea lacunosa

The evolutionary transition from outcrossing to self-pollination occurs frequently in flowering plants and has direct and indirect effects on genomics, life history and floral morphology. The life history and floral traits common to selfing plants are collectively called the "selfing syndrome." This dissertation uses the highly selfing morning glory Ipomoea lacunosa to address three major questions in the evolution of highly selfing plants: what are the genomic consequences of selfing, do the morphological changes associated with the transition to self-pollination result from natural selection or genetic drift, and how does the genetic architecture of those morphological traits affect their evolution? In the first chapter, we analyze genetic data from I. lacunosa and its outcrossing sister species I. cordatotriloba to compare the genomic consequences of selfing in I. lacunosa to theoretical predictions. We find that the reduction in genetic diversity is greater than that predicted by theory, suggesting a population bottleneck in I. lacunosa's history. There is also evidence for the relaxation of natural selection. The second chapter combines these genetic data with phenotypic measurements in a Qst-Fst comparison to determine whether natural selection is responsible for life history and floral morphology differences between I. lacunosa and its outcrossing relative I. cordatotriloba. Our analyses reveal that several component traits in the selfing syndrome diverged in response to natural selection. Chapter Three uses a quantitative trait locus (QTL) mapping approach to characterize the genetic architecture of the selfing syndrome and investigate how genetic correlations between traits affected its evolution. We find generally lower levels of genetic correlation between selfing syndrome traits than previous QTL studies of the selfing syndrome. The low level of genetic correlation indicates that independent selection on selfing syndrome traits is responsible for the evolution of the syndrome as a whole.