On the Evolution of Self-fertilization in a Metapopulation

The loss of morphological and physiological mechanisms that prevent self-fertilization is perhaps the most common evolutionary trend in the flowering plants. It is generally acknowledged that self-fertilization may often be favored by selection at the individual level, principally by providing reproductive assurance when conditions for vector-mediated pollination are poor and also because mating system modifiers that reduce the rate of outcrossing bias their own transmission. Inbreeding depression is accepted as the principal factor opposing the selection of selfing at the individual level, though this barrier may be transient because of purging of inbreeding load from natural populations. Here we explore the possibility that the selection of selfing may occur not only at the individual level but also at the group level. Accordingly, we model the selection of mating system modifier genes within and among populations and suggest that both levels of selection play a role in the evolution of the mating system. We find that selection among populations can maintain outcrossing through higher extinction rates of selfing groups and through reduced transition rates from outcrossing to selfing.