title: Islands within an island: repeated adaptive divergence in a single population.
abstract: Physical barriers to gene flow were once viewed as prerequisites for adaptive evolutionary divergence. However, a growing body of theoretical and empirical work suggests that divergence can proceed within a single population. Here we document genetic structure and spatially replicated patterns of phenotypic divergence within a bird species endemic to 250 km(2) Santa Cruz Island, California, USA. Island scrub-jays (Aphelocoma insularis) in three separate stands of pine habitat had longer, shallower bills than jays in oak habitat, a pattern that mirrors adaptive differences between allopatric populations of the species' mainland congener. Variation in both bill measurements was heritable, and island scrub-jays mated nonrandomly with respect to bill morphology. The population was not panmictic; instead, we found a continuous pattern of isolation by distance across the east-west axis of the island, as well as a subtle genetic discontinuity across the boundary between the largest pine stand and adjacent oak habitat. The ecological factors that appear to have facilitated adaptive differentiation at such a fine scale--environmental heterogeneity and localized dispersal--are ubiquitous in nature. These findings support recent arguments that microgeographic patterns of adaptive divergence may be more common than currently appreciated, even in mobile taxonomic groups like birds.
authors: Department of Biology, Colorado State University, Fort Collins, Colorado, 80523; Graduate Degree Program in Ecology, Colorado State University, Fort Collins, Colorado, 80523; Fort Collins Science Center, U.S. Geological Survey, Fort Collins, Colorado, 80526. k.m.langin@gmail.com.
authors: Kathryn M
authors: KM
authors: Langin
authors: T Scott
authors: TS
authors: Sillett
authors: W Chris
authors: WC
authors: Funk
authors: Scott A
authors: SA
authors: Morrison
authors: Michelle A
authors: MA
authors: Desrosiers
authors: Cameron K
authors: CK
authors: Ghalambor
mesh_terms: D000220:Adaptation, Biological / Q000235:genetics*; D000818:Animals; D001502:Beak / Q000033:anatomy & histology*; D002140:California; D017753:Ecosystem; D005260:Female; D051456:Gene Flow; D005828:Genetics, Population; D005838:Genotype; D062312:Islands; D008297:Male; D018895:Microsatellite Repeats; D008957:Models, Genetic; D046109:Passeriformes / Q000033:anatomy & histology / Q000235:genetics*; D010641:Phenotype; D028223:Pinus; D029963:Quercus; D017422:Sequence Analysis, DNA
keywords: Adaptation; Aphelocoma; gene flow; morphological evolution; natural selection; population structure