MICROSATELLITE VARIATION AND EVOLUTION IN THE MIMULUS-GUTTATUS SPECIES COMPLEX WITH CONTRASTING MATING SYSTEMS

Mutational variability at microsatellite loci is shaped by both popula tion history and the mating system. In turn, alternate mating systems in flowering plants can resolve aspects of microsatellite loci evoluti on. Five species of yellow monkeyflowers (Mimulus sect. Simiolis) diff ering for historical rates of inbreeding were surveyed for variation a t six microsatellite loci. High levels of diversity at these loci were found in both outcrossing and selfing taxa. In line with allozyme stu dies, inbreeders showed more partitioning of diversity among populatio ns, and diversity in selfing taxa was lower than expected from reducti ons in effective population size due to selfing alone, suggesting the presence of either population bottlenecks or background selection in s elfers. Evaluation of the stepwise mutation model (a model of DNA repl ication slippage) suggests that these loci evolve in a stepwise fashio n. Inferred coalescent times of microsatellite alleles indicate that p ast bottlenecks of population size or colonization events were importa nt in reducing diversity in the inbreeding taxon.