Molecular evidence that the Channel Islands populations of the orange-crowned warbler (Oreothlypis celata; Aves: Passeriformes: Parulidae) represent a distinct evolutionary lineage

Abstract

We used molecular data to assess the degree of genetic divergence across the breeding range of the orange-crowned warbler (Oreothlypis celata) in western North America with particular focus on characterizing the divergence betweenO. celatapopulations on the mainland of southern California and on the Channel Islands. We obtained sequences of the mitochondrial geneND2and genotypes at ten microsatellite data for 192O. celatafrom populations spanning all four recognized subspecies. We recovered shallow, but significant, levels of divergence amongO. celatapopulations across the species range. Our results suggest that island isolation, subspecies (delineation by morphology, ecological, and life-history characteristics), and isolation-by-distance, in that order, are the variables that best explain the geographic structure detected across the range ofO. celata. Populations on the Channel Islands were genetically divergent from those on the mainland. We found evidence for greater gene flow from the Channel Islands population to mainland southern California than from the mainland to the islands. We discuss these data in the context of differentiation in phenotypic and ecological characters.