MATE AVAILABILITY AND FECUNDITY SELECTION IN MULTI-ALLELIC SELF-INCOMPATIBILITY SYSTEMS IN PLANTS

We investigate mate availability in different models of multiallelic s elf-incompatibility systems in mutation-selection-drift balance in fin ite populations. Substantial differences among self-incompatibility sy stems occur in average mate availability, and in variances of mate ava ilability among individual plants. These differences are most pronounc ed in small populations in which low mate availability may reduce seed set in some types of sporophytic self-incompatibility. In cases where the pollination system causes a restriction in the number of pollen g enotypes available to an individual plant, the fecundity of that plant depends on the availability of compatible pollen, which is determined by its genotype at the incompatibility locus. This leads to an additi onal component of selection acting on self-incompatibility systems, wh ich we term ''fecundity selection.'' Fecundity selection increases the number of alleles maintained in finite populations and increases mate availability in small populations. The strength of fecundity selectio n is dependent on the type of self-incompatibility. In some cases, fec undity selection markedly alters the equilibrium dynamics of self-inco mpatibility alleles. We discuss the population genetic consequences of mate availability and fecundity selection in the contexts of conserva tion management of self-incompatible plant species and experimental in vestigations on self-incompatibility in natural populations.