Self-incompatibility and Biosystematics in the Wild Chilean Tomato Group (Solanum sect. Lycopersicum)

Understanding the forces that influence the patterns of plant reproduction is a shared con- cern of plant evolutionary biology. Self-incompatibility (SI), the molecular rejection of self- pollen by an otherwise fertile hermaphroditic plant, is a widespread mechanism that promotes outcrossing (de Nettancourt, 1977). SI is found in over 100 plant families (Igic et al., 2008). The descriptions of the patterns of phylogenetic distribution of SI, as well as its strength in natural populations, and geographic distribution, have lead many to proclaim the importance of SI in the development and maintenance of plant species diversity (Whitehouse, 1950; Stebbins, 1957; Bateman, 1952). The transition from SI to self-compatibility (SC) in plant lineages is one of the most common pathways in plant evolution (Stebbins, 1974). The loss of enforced outcrossing leads to a reduction of genetic diversity and increased linkage disequilibrium within species. This has lead many to conclude that habitual self-fertilization is an evolutionary dead- end (Stebbins, 1957; Stebbins, 1974; Takebayashi and Morrell, 2001; Goldberg et al., 2010). Despite longstanding interest in patterns of SI occurrence and its maintenance and loss, rel- atively few empirical details are known about the evolution of SI and its relationship with realized mating patterns in natural populations. This thesis provides results from three research projects that relate to SI. First, the largest collection of reports of the strength of SI across flowering plants and its relationship with outcrossing rate are discussed. Second, variation in the strength of SI is quantified across populations of a wild tomato species. Results from controlled crosses to investigate the genetic basis of variation in SI and the effect of SI variation on outcrossing rate are reported. Lastly, results from an integrative biosystematic study, motivated by observed unique relationships between alleles involved in SI, suggest that species are not properly described in a group of wild tomatoes. The distribution of morphological and genetic variation and patterns of reproductive isolation across populations are provided as evidence of multiple species within a currently described single species. Together, the chapters synthesize novel insights into the evolution of a common plant breeding system.