Data from: Postzygotic barriers persist despite ongoing introgression in hybridizing Mimulus species

The evolution of postzygotic isolation is thought to be a key step in
maintaining species boundaries upon secondary contact, yet the dynamics
and persistence of hybrid incompatibilities in naturally hybridizing
species are not well understood. Here, we explore these issues using
genetic mapping in three independent populations of recombinant inbred
lines between naturally hybridizing monkeyflowers Mimulus guttatus and M.
nasutus from the sympatric Catherine Creek population. We discover that
the three M. guttatus founders differ dramatically in admixture history,
with nearly a quarter of one founder’s genome introgressed from M.
nasutus. Comparative genetic mapping in the three RIL populations reveals
three new putative inversions, each one segregating among the M. guttatus
founders, two due to admixture. We find strong, genome-wide transmission
ratio distortion in all RILs, but patterns are highly variable among the
three populations. At least some of this distortion appears to be
explained by epistatic selection favoring parental genotypes, but tests of
inter-chromosomal linkage disequilibrium also reveal multiple candidate
Dobzhansky-Muller incompatibilities. We also map several genetic loci for
hybrid pollen viability, including two interacting pairs that coincide
with peaks of distortion. Remarkably, even with this limited sample of
three M. guttatus lines, we discover abundant segregating variation for
hybrid incompatibilities with M. nasutus, suggesting this population
harbors diverse contributors to postzygotic isolation. Moreover, even with
substantial admixture, hybrid incompatibilities between Mimulus species
persist, suggesting postzygotic isolation might be a potent force in
maintaining species barriers in this system.