EVOLUTION OF THE MATING SYSTEM IN A PARTIALLY SELF-INCOMPATIBLE SPECIES: REPRODUCTIVE ASSURANCE AND POLLEN LIMITATION IN POPULATIONS THAT DIFFER IN THE TIMING OF SELF-COMPATIBILITY

Self-fertilization can provide reproductive assurance during periods of low or unreliable pollinator visitation. Therefore, periods of low pollen receipt may favor evolutionary shifts from cross-fertilization to self-fertilization. Although reproductive assurance is hypothesized to be important in mating system evolution, it has been quantified in relatively few species. Leptosiphon jepsonii shows variation in the mode of selfing, with transient self-incompatibility conferring delayed selfing seen in some individuals and early self-compatibility present in others. Autofertility, reproductive assurance, and pollen limitation were quantified in three populations of L. jepsonii that vary in the timing of self-compatibility and rate of self-fertilization. Plants in all three populations were capable of high seed set through autonomous self-fertilization, and selfing provided significant reproductive assurance in two populations, including one with the highest frequency of delayed selfing. Confidence intervals revealed no difference in reproductive assurance among populations. We conclude that both early and delayed self-compatibility can confer reproductive assurance and alleviate pollen limitation in this species. Results from this study are integrated with previous studies on the same three populations. We synthesize data on inbreeding depression, outcrossing rates, and floral biology for a comprehensive evaluation of the factors affecting the evolution of mixed mating in L. jepsonii.