title: The role of selection and historical factors in driving population differentiation along an elevational gradient in an island bird.
abstract: Adaptation to local environmental conditions and the range dynamics of populations can influence evolutionary divergence along environmental gradients. Thus, it is important to investigate patterns of both phenotypic and genetic variations among populations to reveal the respective roles of these two types of factors in driving population differentiation. Here, we test for evidence of phenotypic and genetic structure across populations of a passerine bird (Zosterops borbonicus) distributed along a steep elevational gradient on the island of Réunion. Using 11 microsatellite loci screened in 401 individuals from 18 localities distributed along the gradient, we found that genetic differentiation occurred at two spatial levels: (i) between two main population groups corresponding to highland and lowland areas, respectively, and (ii) within each of these two groups. In contrast, several morphological traits varied gradually along the gradient. Comparison of neutral genetic differentiation (FST ) and phenotypic differentiation (PST ) showed that PST largely exceeds FST at several morphological traits, which is consistent with a role for local adaptation in driving morphological divergence along the gradient. Overall, our results revealed an area of secondary contact midway up the gradient between two major, cryptic, population groups likely diverged in allopatry. Remarkably, local adaptation has shaped phenotypic differentiation irrespective of population history, resulting in different patterns of variation along the elevational gradient. Our findings underscore the importance of understanding both historical and selective factors when trying to explain variation along environmental gradients.
authors.affiliation: Laboratoire Évolution et Diversité Biologique, UMR 5174, Université Paul Sabatier, Toulouse 3 - Centre National de la Recherche Scientifique (CNRS) - École Nationale de Formation Agronomique (ENFA), Toulouse Cedex 9, France.
authors.forename: J A M
authors.initials: JA
authors.lastname: Bertrand
authors.affiliation: Laboratoire Évolution et Diversité Biologique, UMR 5174, Université Paul Sabatier, Toulouse 3 - Centre National de la Recherche Scientifique (CNRS) - École Nationale de Formation Agronomique (ENFA), Toulouse Cedex 9, France.
authors.forename: B
authors.initials: B
authors.lastname: Delahaie
authors.affiliation: Laboratoire Évolution et Diversité Biologique, UMR 5174, Université Paul Sabatier, Toulouse 3 - Centre National de la Recherche Scientifique (CNRS) - École Nationale de Formation Agronomique (ENFA), Toulouse Cedex 9, France.
authors.forename: Y X C
authors.initials: YX
authors.lastname: Bourgeois
authors.affiliation: Hémisphères, Poindimié, New Caledonia.
authors.forename: T
authors.initials: T
authors.lastname: Duval
authors.affiliation: National Museum of Natural Sciences, Spanish National Research Council (CSIC), Madrid, Spain.
authors.forename: R
authors.initials: R
authors.lastname: García-Jiménez
authors.affiliation: Laboratoire Évolution et Diversité Biologique, UMR 5174, Université Paul Sabatier, Toulouse 3 - Centre National de la Recherche Scientifique (CNRS) - École Nationale de Formation Agronomique (ENFA), Toulouse Cedex 9, France.
authors.forename: J
authors.initials: J
authors.lastname: Cornuault
authors.affiliation: Laboratoire Évolution et Diversité Biologique, UMR 5174, Université Paul Sabatier, Toulouse 3 - Centre National de la Recherche Scientifique (CNRS) - École Nationale de Formation Agronomique (ENFA), Toulouse Cedex 9, France.
authors.forename: B
authors.initials: B
authors.lastname: Pujol
authors.affiliation: Laboratoire Évolution et Diversité Biologique, UMR 5174, Université Paul Sabatier, Toulouse 3 - Centre National de la Recherche Scientifique (CNRS) - École Nationale de Formation Agronomique (ENFA), Toulouse Cedex 9, France.
authors.forename: C
authors.initials: C
authors.lastname: Thébaud
authors.affiliation: National Museum of Natural Sciences, Spanish National Research Council (CSIC), Madrid, Spain.
authors.forename: B
authors.initials: B
authors.lastname: Milá
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D000531:Altitude; D000818:Animals; D005075:Biological Evolution; D014644:Genetic Variation; D062312:Islands; D018895:Microsatellite Repeats / Q000235:genetics; D046109:Passeriformes / Q000235:genetics / Q000502:physiology*; D010641:Phenotype; D012641:Selection, Genetic
keywords: Mascarene Islands; PST/FST comparisons; Réunion grey white-eye; Zosterops borbonicus; altitudinal gradient; local adaptation; microsatellites; natural selection; population history; secondary contact