title: Contrasting patterns of genetic differentiation among Blackcaps (Sylvia atricapilla) with divergent migratory orientations in Europe.
abstract: Migratory divides are thought to facilitate behavioral, ecological, and genetic divergence among populations with different migratory routes. However, it is currently contentious how much genetic divergence is needed to maintain distinct migratory behavior across migratory divides. Here we investigate patterns of neutral genetic differentiation among Blackcap (Sylvia atricapilla) populations with different migratory strategies across Europe. We compare the level of genetic divergence of populations migrating to southwestern (SW) or southeastern (SE) wintering areas with birds wintering in the British Isles following a recently established northwesterly (NW) migration route. The migratory divide between SW and SE wintering areas can be interpreted as a result of a re-colonization process after the last glaciation. Thus we predicted greater levels of genetic differentiation among the SW/SE populations. However, a lack of genetic differentiation was found between SW and SE populations, suggesting that interbreeding likely occurs among Blackcaps with different migratory orientations across a large area; therefore the SW/SE migratory divide can be seen as diffuse, broad band and is, at best, a weak isolating barrier. Conversely, weak, albeit significant genetic differentiation was evident between NW and SW migrants breeding sympatrically in southern Germany, suggesting a stronger isolating mechanism may be acting in this population. Populations located within/near the SW/SE contact zone were the least genetically divergent from NW migrants, confirming NW migrants likely originated from within the contact zone. Significant isolation-by-distance was found among eastern Blackcap populations (i.e. SE migrants), but not among western populations (i.e. NW and SW migrants), revealing different patterns of genetic divergence among Blackcap populations in Europe. We discuss possible explanations for the genetic structure of European Blackcaps and how gene flow influences the persistence of divergent migratory behaviors.
authors.affiliation: Department of Evolutionary Biology and Animal Ecology, University of Freiburg, Freiburg, Germany.
authors.forename: Raeann
authors.initials: R
authors.lastname: Mettler
authors.forename: H Martin
authors.initials: HM
authors.lastname: Schaefer
authors.forename: Nikita
authors.initials: N
authors.lastname: Chernetsov
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Fiedler
authors.forename: Keith A
authors.initials: KA
authors.lastname: Hobson
authors.forename: Mihaela
authors.initials: M
authors.lastname: Ilieva
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Imhof
authors.forename: Arild
authors.initials: A
authors.lastname: Johnsen
authors.forename: Swen C
authors.initials: SC
authors.lastname: Renner
authors.forename: Gregor
authors.initials: G
authors.lastname: Rolshausen
authors.forename: David
authors.initials: D
authors.lastname: Serrano
authors.forename: Tomasz
authors.initials: T
authors.lastname: Wesołowski
authors.forename: Gernot
authors.initials: G
authors.lastname: Segelbacher
mesh_terms: D025041:Animal Migration; D000818:Animals; D005075:Biological Evolution; D005060:Europe; D005260:Female; D014644:Genetic Variation; D005828:Genetics, Population; D005843:Geography; D008297:Male; D046109:Passeriformes / Q000235:genetics*