THE RELATIONSHIP BETWEEN MATING-SYSTEM CHARACTERS AND INBREEDING DEPRESSION IN MIMULUS-GUTTATUS

Several recent theoretical considerations of mating-sqstem evolution p redict within-population covariation between levels of inbreeding depr ession and genetically controlled mating-system characters. If inbreed ing depression is caused by deleterious recessive alleles, families wi th characters that promote self-pollination should show lower levels o f inbreeding depression than families with characters that promote out crossing. The converse is expected if inbreeding depression is due to overdominant allelic interactions. Whether these associations between mating-system and viability loci evolve will have important consequenc es for mating-system evolution. The evolution of selfing within the ge nus Mimulus is associated with a reduction in stigma-anther separation (i.e., a loss of herkogamy) and high autogamous seed set. In this stu dy we compared families from two M. guttatus populations that differed genetically in their degree of stigma-anther separation. In one of th ese populations we also compared families that differed genetically in the degree to which they autogamously set seed in a pollinator-free g reenhouse. Dams often differed significantly in levels of inbreeding d epression for aboveground biomass and flower production, but variation in inbreeding depression was never explained by herkogamy class or au togamy class. Several factors might account for why families with trai ts associated with selfing did not show lower inbreeding depression, a nd these are discussed. Our study also demonstrated significant variat ion among self progeny from a given female likely due to differences i n pollination date and position of fruit maturation. The detection of significant dam X sire interactions suggests biparental inbreeding or differences in combining ability for specific pairs of parents.