title: Chromosomal variation segregates within incipient species and correlates with reproductive isolation.
abstract: Reproductive isolation is a critical step in the process of speciation. Among the most important factors driving reproductive isolation are genetic incompatibilities. Whether these incompatibilities are already present before extrinsic factors prevent gene flow between incipient species remains largely unresolved in natural systems. This question is particularly challenging because it requires that we catch speciating populations in the act before they reach the full-fledged species status. We measured the extent of intrinsic postzygotic isolation within and between phenotypically and genetically divergent lineages of the wild yeast Saccharomyces paradoxus that have partially overlapping geographical distributions. We find that hybrid viability between lineages progressively decreases with genetic divergence. A large proportion of postzygotic inviability within lineages is associated with chromosomal rearrangements, suggesting that chromosomal differences substantially contribute to the early steps of reproductive isolation within lineages before reaching fixation. Our observations show that polymorphic intrinsic factors may segregate within incipient species before they contribute to their full reproductive isolation and highlight the role of chromosomal rearrangements in speciation. We propose different hypotheses based on adaptation, biogeographical events and life history evolution that could explain these observations.
authors.affiliation: Département de Biologie, Institut de Biologie Intégrative et des Systèmes, PROTEO, Université Laval, Québec, QC, G1V 0A6, Canada.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Charron
authors.forename: Jean-Baptiste
authors.initials: JB
authors.lastname: Leducq
authors.forename: Christian R
authors.initials: CR
authors.lastname: Landry
mesh_terms: D015825:Chromosomes, Fungal; D015321:Gene Rearrangement; D049810:Genetic Speciation; D006824:Hybridization, Genetic; D059785:Karyotype; D009656:North America; D010641:Phenotype; D060047:Reproductive Isolation; D012440:Saccharomyces / Q000235:genetics*
keywords: Saccharomyces paradoxus; chromosomal rearrangements; genetic incompatibilities; reproductive isolation; speciation