Hybrid seed inviability maintains species barriers in Diplacus (Mimulus) sect. Eunanus
Authors: Matthew Farnitano; Andrea Sweigart
Affiliation: University of Georgia
Keywords: Speciation & hybridization
Postzygotic reproductive barriers are important in the maintenance of species barriers over long time scales, though their role as a driver of speciation is controversial. Comparing across a larger number of taxa helps us to better understand which postzygotic barriers act at what stages of divergence, and how their distribution might influence patterns of speciation. Mimulus monkeyflowers are a model genus for studies of speciation, but most work focuses on a few well-known clades. I have conducted crosses between populations of four sympatric species in Diplacus sect. Eunanus, an understudied clade of Mimulus, to determine the distribution of postzygotic crossing barriers in this group. In addition, I generated the first genome-scale SNP dataset for these species. I find considerable genetic divergence between morphologically similar taxa and limited signatures of historical introgression between groups. Seed inviability is a near-complete hybrid barrier in all but one comparison (D. fremontii x D. brevipes, which in turn has reduced pollen fertility in viable hybrids). Seed phenotypes show parent-of-origin effects, suggesting a possible role for parental conflict in seed inviability. Three of the studied species have remarkably similar floral morphology, suggesting seed inviability may be more important than pollinator-mediated barriers in reducing gene flow. In total, these data suggest an important role for post-zygotic barriers in explaining the diversity of the Mimulus radiation.