Comparative Evidence for the Correlated Evolution of Polyploidy and Self-compatibility in Solanaceae

Whole genome duplication, or polyploidy, is especially common among flowering plants and has numerous phenotypic and genotypic consequences (Ramsey and Schemske, 1998; Otto and Whitton, 2000). Of particular importance is the effect of polyploidy on plant reproductive systems, which directly influence the genetic structure of individuals, populations (Hamrick and Godt, 1996), and the rate at which lineages diversify (Goldberg et al., 2010). Early in- vestigations of polyploidy frequently used the chemical colchicine, which inhibits microtubule formation and creates polyploid seeds or polyploid branches in diploid plants. Among the phe- notypic changes caused by polyploidy were increased leaf and flower size, and unexpectedly, in some plants, the novel ability to self-fertilize (Stout and Chandler, 1942; Pandey, 1968). A number of mutational studies have shown that polyploidy directly causes self-fertility in species with a specific mode of reproduction (where self-sterility is mediated by S-RNases), yet the prevalence of this phenomenon in natural populations and at larger phylogenetic scales is not well characterized (Stone, 2002). In the first chapter of this thesis, “Polyploidy and Self-compatibility: An Introduction”, background information is presented on self-incompatibility and polyploidy. In the second chapter, “Comparative Evidence for Correlated Evolution of Self-compatibility and Polyploidy in Solanaceae”, analyses are presented that determine the extent of correlated evolution, the relative magnitude of evolutionary pathways to self-compatibility caused by polyploidy, and the evolutionary pathways by which self-compatible polyploids arise. As the evolutionary transitions causing changes in ploidy and mode of reproduction are thought to be two of the most important processes in angiosperm evolution (Stebbins, 1950; Levin, 1983), the research presented in this thesis contributes, in part, to our understanding of the patterns and processes by which this remarkably diverse group of organisms evolves.