title: Lineages of Silene nutans developed rapid, strong, asymmetric postzygotic reproductive isolation in allopatry.
abstract: Reproductive isolation can rise either as a consequence of genomic divergence in allopatry or as a byproduct of divergent selection in parapatry. To determine whether reproductive isolation in gynodioecious Silene nutans results from allopatric divergence or from ecological adaptation following secondary contact, we investigated the pattern of postzygotic reproductive isolation and hybridization in natural populations using two phylogeographic lineages, western (W1) and eastern (E1). Experimental crosses between the lineages identified strong, asymmetric postzygotic isolation between the W1 and the E1 lineages, independent of geographic overlap. The proportion of ovules fertilized, seeds aborted, and seeds germinated revealed relatively little effect on the fitness of hybrids. In contrast, hybrid mortality was high and asymmetric: while half of the hybrid seedlings with western lineage mothers died, nearly all hybrid seedlings with E1 mothers died. This asymmetric mortality mirrored the proportion of chlorotic seedlings, and is congruent with cytonuclear incompatibility. We found no evidence of hybridization between the lineages in regions of co-occurrence using nuclear and plastid markers. Together, our results are consistent with the hypothesis that strong postzygotic reproductive isolation involving cytonuclear incompatibilities arose in allopatry. We argue that the dynamics of cytonuclear gynodioecy could facilitate the evolution of reproductive isolation.
authors.affiliation: Unité Évolution, Écologie, Paléontologie, UMR CNRS 8198, Université de Lille 1-Sciences et Technologies, F-59655, Villeneuve d'Ascq, France.
authors.forename: Hélène
authors.initials: H
authors.lastname: Martin
authors.affiliation: Unité Évolution, Écologie, Paléontologie, UMR CNRS 8198, Université de Lille 1-Sciences et Technologies, F-59655, Villeneuve d'Ascq, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Touzet
authors.affiliation: Unité Évolution, Écologie, Paléontologie, UMR CNRS 8198, Université de Lille 1-Sciences et Technologies, F-59655, Villeneuve d'Ascq, France.
authors.forename: Mathilde
authors.initials: M
authors.lastname: Dufay
authors.affiliation: Unité Évolution, Écologie, Paléontologie, UMR CNRS 8198, Université de Lille 1-Sciences et Technologies, F-59655, Villeneuve d'Ascq, France.
authors.forename: Cécile
authors.initials: C
authors.lastname: Godé
authors.affiliation: Unité Évolution, Écologie, Paléontologie, UMR CNRS 8198, Université de Lille 1-Sciences et Technologies, F-59655, Villeneuve d'Ascq, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Schmitt
authors.affiliation: Unité Évolution, Écologie, Paléontologie, UMR CNRS 8198, Université de Lille 1-Sciences et Technologies, F-59655, Villeneuve d'Ascq, France.
authors.forename: Emna
authors.initials: E
authors.lastname: Lahiani
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana, 47405.
authors.forename: Lynda F
authors.initials: LF
authors.lastname: Delph
authors.affiliation: Meise Botanic Garden (formerly National Botanic Garden of Belgium), Nieuwelaan 38, BE-1860, Meise, Belgium.|Écologie végétale et Biogéochimie, Université Libre de Bruxelles, CP244, Boulevard du Triomphe, BE-1050, Brussels, Belgium.|Fédération Wallonie-Bruxelles, rue A. Lavallée 1, BE-1080, Brussels, Belgium.
authors.forename: Fabienne
authors.initials: F
authors.lastname: Van Rossum
mesh_terms: D000222:Adaptation, Physiological; D006824:Hybridization, Genetic; D058974:Phylogeography; D060047:Reproductive Isolation; D029751:Silene / Q000235:genetics*
keywords: Asymmetric reproductive isolation; chlorosis; cytonuclear incompatibility; microsatellites; postzygotic reproductive isolation