Data from: Hybrid speciation by sorting of parental incompatibilities in Italian sparrows

Speciation by hybridization is emerging as a significant contributor to
biological diversification. Yet, little is known about the relative
contributions of (i) evolutionary novelty and (ii) sorting of preexisting
parental incompatibilities to the build-up of reproductive isolation under
this mode of speciation. Few studies have addressed empirically whether
hybrid animal taxa are intrinsically isolated from their parents, and no
study has so far investigated by which of the two aforementioned routes
intrinsic barriers evolve. Here, we show that sorting of preexisting
parental incompatibilities contributes to intrinsic isolation of a hybrid
animal taxon. Using a genomic cline framework, we demonstrate that the
sex-linked and mito-nuclear incompatibilities isolating the homoploid
hybrid Italian sparrow at its two geographically separated hybrid-parent
boundaries represent a subset of those contributing to reproductive
isolation between its parent species, house and Spanish sparrows. Should
such a sorting mechanism prove to be pervasive, the circumstances
promoting homoploid hybrid speciation may be broader than currently
thought, and indeed there may be many cryptic hybrid taxa separated from
their parent species by sorted, inherited incompatibilities.