HOW DOES SELF-POLLINATION EVOLVE - INFERENCES FROM FLORAL ECOLOGY ANDMOLECULAR-GENETIC VARIATION

The automatic selection and reproductive assurance hypotheses provide the two most general explanations for the evolution of self-pollinatio n. Under automatic selection, self-pollination is mediated by pollen v ectors and the mating system modifier experiences a transmission bias through the pollen chat leads to its selection. Under reproductive ass urance, 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 f loral traits influencing several modes of selfing simultaneously. Infe rences from these models suggest that reproductive assurance may be mo re important than has been appreciated. Additional insight into the im portance of automatic selection versus reproductive assurance may be g ained by considering the distribution of neutral genetic diversity amo ng populations within selfing species. A number of approaches are outl ined for analysing patterns of neutral diversity as they pertain to th e mechanism of the evolution of selfing.