title: Hybrid speciation through sorting of parental incompatibilities in Italian sparrows.
abstract: 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 pre-existing 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 pre-existing parental incompatibilities contributes to intrinsic isolation of a hybrid animal taxon. Using a genomic cline framework, we demonstrate that the sex-linked and mitonuclear 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.
authors.affiliation: Department of Biosciences, Centre for Ecological and Evolutionary Synthesis, University of Oslo, PO Box 1066, Blindern, N-0316, Oslo, Norway.
authors.forename: Jo S
authors.initials: JS
authors.lastname: Hermansen
authors.forename: Fredrik
authors.initials: F
authors.lastname: Haas
authors.forename: Cassandra N
authors.initials: CN
authors.lastname: Trier
authors.forename: Richard I
authors.initials: RI
authors.lastname: Bailey
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Nederbragt
authors.forename: Alfonso
authors.initials: A
authors.lastname: Marzal
authors.forename: Glenn-Peter
authors.initials: GP
authors.lastname: Saetre
mesh_terms: D000818:Animals; D001499:Bayes Theorem; D005260:Female; D049810:Genetic Speciation; D006824:Hybridization, Genetic; D007558:Italy; D008297:Male; D020641:Polymorphism, Single Nucleotide; D060047:Reproductive Isolation; D017422:Sequence Analysis, DNA; D013030:Spain; D046370:Sparrows / Q000235:genetics*; D061350:Sympatry
keywords: Passer; birds; hybridization; introgression; reproductive barriers; speciation