title: Spatial Isolation and Temporal Variation in Fitness and Condition Facilitate Divergence in a Migratory Divide.
abstract: A novel migratory polymorphism evolved within the last 60 years in blackcaps (Sylvia atricapilla) breeding sympatrically in southwestern Germany. While most individuals winter in the traditional areas in the Mediterranean, a growing number of blackcaps started migrating to Britain instead. The rapid microevolution of this new strategy has been attributed to assortative mating and better physical condition of birds wintering in Britain. However, the isolating barriers as well as the physical condition of birds are not well known. In our study, we examined whether spatial isolation occurred among individuals with distinct migratory behaviour and birds with different arrival dates also differed in physical and genetic condition. We caught blackcaps in six consecutive years upon arrival on the breeding grounds and assigned them via stable isotope analysis to their wintering areas. Analysis of the vegetation structure within blackcap territories revealed different microhabitat preferences of birds migrating to distinct wintering areas. Blackcaps arriving early on the breeding grounds had higher survival rates, better body condition and higher multilocus heterozygosities than later arriving birds. We did however not find an effect of parasite infection status on arrival time. Our results suggest that early arriving birds have disproportionate effects on population dynamics. Allochrony and habitat isolation may thus act together to facilitate ongoing divergence in hybrid zones, and migratory divides in particular.
authors.affiliation: Department of Evolutionary Biology and Animal Ecology, Faculty of Biology, University of Freiburg, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Hermes
authors.affiliation: Department of Evolutionary Biology and Animal Ecology, Faculty of Biology, University of Freiburg, Germany.
authors.forename: Raeann
authors.initials: R
authors.lastname: Mettler
authors.affiliation: Department of Evolutionary Biology and Animal Ecology, Faculty of Biology, University of Freiburg, Germany.|Biología y Conservación de Vertebrados, Instituto de Ecología A.C., Xalapa, Mexico.
authors.forename: Diego
authors.initials: D
authors.lastname: Santiago-Alarcon
authors.affiliation: Department of Wildlife Ecology and Management, Faculty of Environment and Natural Resources, University of Freiburg, Germany.
authors.forename: Gernot
authors.initials: G
authors.lastname: Segelbacher
authors.affiliation: Department of Evolutionary Biology and Animal Ecology, Faculty of Biology, University of Freiburg, Germany.
authors.forename: H Martin
authors.initials: HM
authors.lastname: Schaefer
mesh_terms: D025041:Animal Migration / Q000502:physiology*; D000818:Animals; D005075:Biological Evolution; D001947:Breeding; D005858:Germany; D007553:Isotope Labeling; D019083:Mediterranean Region; D046109:Passeriformes / Q000235:genetics* / Q000502:physiology; D010805:Physical Conditioning, Animal; D011157:Population Dynamics; D060047:Reproductive Isolation; D012621:Seasons; D065854:Spatial Navigation / Q000502:physiology*; D006113:United Kingdom