How Does Self-Pollination Evolve? Inferences from Floral Ecology and Molecular Genetic Variation

The automatic selection and reproductive assurance hypotheses provide the two most general explanations for the evolution of self-pollination. Under automatic selection, self-pollination is mediated by pollen vectors and the mating system modifier experiences a transmission bias through the pollen that leads to its selection. Under reproductive assurance, self-pollination is autonomous and the mating system modifier is selected as it allows seed production when pollinators are scarce. We present phenotypic selection models that examine the selection of floral traits influencing several modes of selling simultaneously. Inferences from these models suggest that reproductive assurance may be more important than has been appreciated. Additional insight into the importance of automatic selection versus reproductive assurance may be gained by considering the distribution of neutral genetic diversity among populations within selfing species. A number of approaches are outlined for analysing patterns of neutral diversity as they pertain to the mechanism of the evolution of selfing.