THE EVOLUTION OF THE SELFING RATE IN FUNCTIONALLY HERMAPHRODITE PLANTS AND ANIMALS

Selfing, the fusion of male and female gametes from a single genetic individual or colony, is possible in many plants and also in hermaphrodite animals. We review the occurrence of selfing and mechanisms for its avoidance, in functionally hermaphrodite animal and plants. We discuss means by which selfing can be detected and briefly review techniques for estimation of selfing frequencies in natural populations. Although many functionally hemaphrodite species are probably almost complete outcrossers or inbreeders, mixed mating systems are also found in both plant and animal populations. We review theories for the advantages and disadvantages of selfing, and for the maintenance of mixed mating systems, together with empirical data showing that at least some of the factors involved in the theories (for instance, reproductive assurance, cost of mating, and inbreeding depression) are detectable in actually or potentially selfing organisms. More work is still needed on animal selfing and selfing avoidance and, for both animals and plants, on the evolutionary origins of selfing and on the effects of selfing on genetic diversity.