title: Genomic evidence of geographically widespread effect of gene flow from polar bears into brown bears.
abstract: Polar bears are an arctic, marine adapted species that is closely related to brown bears. Genome analyses have shown that polar bears are distinct and genetically homogeneous in comparison to brown bears. However, these analyses have also revealed a remarkable episode of polar bear gene flow into the population of brown bears that colonized the Admiralty, Baranof and Chichagof islands (ABC islands) of Alaska. Here, we present an analysis of data from a large panel of polar bear and brown bear genomes that includes brown bears from the ABC islands, the Alaskan mainland and Europe. Our results provide clear evidence that gene flow between the two species had a geographically wide impact, with polar bear DNA found within the genomes of brown bears living both on the ABC islands and in the Alaskan mainland. Intriguingly, while brown bear genomes contain up to 8.8% polar bear ancestry, polar bear genomes appear to be devoid of brown bear ancestry, suggesting the presence of a barrier to gene flow in that direction.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA, 95064, USA.
authors.forename: James A
authors.initials: JA
authors.lastname: Cahill
authors.forename: Ian
authors.initials: I
authors.lastname: Stirling
authors.forename: Logan
authors.initials: L
authors.lastname: Kistler
authors.forename: Rauf
authors.initials: R
authors.lastname: Salamzade
authors.forename: Erik
authors.initials: E
authors.lastname: Ersmark
authors.forename: Tara L
authors.initials: TL
authors.lastname: Fulton
authors.forename: Mathias
authors.initials: M
authors.lastname: Stiller
authors.forename: Richard E
authors.initials: RE
authors.lastname: Green
authors.forename: Beth
authors.initials: B
authors.lastname: Shapiro
mesh_terms: D000413:Alaska; D000818:Animals; D001110:Arctic Regions; D005060:Europe; D019143:Evolution, Molecular; D005260:Female; D051456:Gene Flow; D005828:Genetics, Population; D008297:Male; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D001503:Ursidae / Q000145:classification / Q000235:genetics*; D014960:X Chromosome / Q000235:genetics
keywords: Ursus; brown bear; ecological genetics; genomics; hybridization; polar bear