We have used nucleotide sequence variation to reconstruct the evolutionary history of the Mimulus guttatus species complex, which consists of several closely related, often interfertile taxa that differ widely in floral morphology and degree of inbreeding. We sequenced portions of two floral development genes, CYCLOIDEA and APETALA3, to examine species-level relationships and to estimate levels of nucleotide diversity from populations of the self-fertilizing M. nasutus and of the outcrossing M. guttatus. Despite widespread geographic overlap, patterns of nucleotide diversity indicate that while local introgression between M. guttatus and M. nasutus may occur, these two species have remained broadly reproductively isolated since their divergence. To investigate whether highly inbreeding populations have low genetic variation relative to closely related outcrossing species, we examined nucleotide diversity for M. nasutus and M. guttatus. Though inter-population estimates of nucleotide diversity are similar between selfers and outcrossers, genetic variation is substantially reduced within populations of M. nasutus compared to that of M. guttatus.

Key words: inbreeding, mating system, Mimulus, nucleotide diversity