title: Implications of the circumpolar genetic structure of polar bears for their conservation in a rapidly warming Arctic.
abstract: We provide an expansive analysis of polar bear (Ursus maritimus) circumpolar genetic variation during the last two decades of decline in their sea-ice habitat. We sought to evaluate whether their genetic diversity and structure have changed over this period of habitat decline, how their current genetic patterns compare with past patterns, and how genetic demography changed with ancient fluctuations in climate. Characterizing their circumpolar genetic structure using microsatellite data, we defined four clusters that largely correspond to current ecological and oceanographic factors: Eastern Polar Basin, Western Polar Basin, Canadian Archipelago and Southern Canada. We document evidence for recent (ca. last 1-3 generations) directional gene flow from Southern Canada and the Eastern Polar Basin towards the Canadian Archipelago, an area hypothesized to be a future refugium for polar bears as climate-induced habitat decline continues. Our data provide empirical evidence in support of this hypothesis. The direction of current gene flow differs from earlier patterns of gene flow in the Holocene. From analyses of mitochondrial DNA, the Canadian Archipelago cluster and the Barents Sea subpopulation within the Eastern Polar Basin cluster did not show signals of population expansion, suggesting these areas may have served also as past interglacial refugia. Mismatch analyses of mitochondrial DNA data from polar and the paraphyletic brown bear (U. arctos) uncovered offset signals in timing of population expansion between the two species, that are attributed to differential demographic responses to past climate cycling. Mitogenomic structure of polar bears was shallow and developed recently, in contrast to the multiple clades of brown bears. We found no genetic signatures of recent hybridization between the species in our large, circumpolar sample, suggesting that recently observed hybrids represent localized events. Documenting changes in subpopulation connectivity will allow polar nations to proactively adjust conservation actions to continuing decline in sea-ice habitat.
authors.affiliation: Alaska Science Center, US Geological Survey, Anchorage, Alaska, United States of America; Department of Environment, Government of Nunavut, Igloolik, Nunavut, Canada.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Peacock
authors.affiliation: Alaska Science Center, US Geological Survey, Anchorage, Alaska, United States of America.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Sonsthagen
authors.affiliation: Ontario Ministry of Natural Resources and Forestry, Peterborough, Ontario, Canada.
authors.forename: Martyn E
authors.initials: ME
authors.lastname: Obbard
authors.affiliation: All-Russian Research Institute for Nature Protection, Moscow, Russian Federation.
authors.forename: Andrei
authors.initials: A
authors.lastname: Boltunov
authors.affiliation: US Fish and Wildlife Service, Marine Mammals Management, Anchorage, Alaska, United States of America.
authors.forename: Eric V
authors.initials: EV
authors.lastname: Regehr
authors.affiliation: Wrangel Island State Nature Reserve, Moscow, Russian Federation.
authors.forename: Nikita
authors.initials: N
authors.lastname: Ovsyanikov
authors.affiliation: Norwegian Polar Institute, Tromsø, Norway.
authors.forename: Jon
authors.initials: J
authors.lastname: Aars
authors.affiliation: Department of Environment, Government of Nunavut, Igloolik, Nunavut, Canada.
authors.forename: Stephen N
authors.initials: SN
authors.lastname: Atkinson
authors.affiliation: Alaska Science Center, US Geological Survey, Anchorage, Alaska, United States of America.
authors.forename: George K
authors.initials: GK
authors.lastname: Sage
authors.affiliation: Alaska Science Center, US Geological Survey, Anchorage, Alaska, United States of America.
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Hope
authors.affiliation: Natural History Museum, University of Oslo, Oslo, Norway.
authors.forename: Eve
authors.initials: E
authors.lastname: Zeyl
authors.affiliation: Natural History Museum, University of Oslo, Oslo, Norway.
authors.forename: Lutz
authors.initials: L
authors.lastname: Bachmann
authors.affiliation: Natural History Museum, University of Oslo, Oslo, Norway.
authors.forename: Dorothee
authors.initials: D
authors.lastname: Ehrich
authors.affiliation: Department of Zoology, Michigan State University, East Lansing, Michigan, United States of America.
authors.forename: Kim T
authors.initials: KT
authors.lastname: Scribner
authors.affiliation: Polar Bears International, Bozeman, Montana, United States of America.
authors.forename: Steven C
authors.initials: SC
authors.lastname: Amstrup
authors.affiliation: All-Russian Research Institute for Nature Protection, Moscow, Russian Federation.
authors.forename: Stanislav
authors.initials: S
authors.lastname: Belikov
authors.affiliation: Greenland Institute of Natural Resources, Copenhagen, Denmark.
authors.forename: Erik W
authors.initials: EW
authors.lastname: Born
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Derocher
authors.affiliation: Science & Technology Branch, Environment Canada, Edmonton, Alberta, Canada.
authors.forename: Ian
authors.initials: I
authors.lastname: Stirling
authors.affiliation: Faculty of Science and Environmental Studies, Lakehead University, Thunder Bay, Ontario, Canada.
authors.forename: Mitchell K
authors.initials: MK
authors.lastname: Taylor
authors.affiliation: Natural History Museum, University of Oslo, Oslo, Norway.
authors.forename: Øystein
authors.initials: Ø
authors.lastname: Wiig
authors.affiliation: Wildlife Genetics International, Nelson, British Columbia, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Paetkau
authors.affiliation: Alaska Science Center, US Geological Survey, Anchorage, Alaska, United States of America.
authors.forename: Sandra L
authors.initials: SL
authors.lastname: Talbot
mesh_terms: D000818:Animals; D001110:Arctic Regions; D057231:Climate Change; D003247:Conservation of Natural Resources / Q000379:methods*; D004272:DNA, Mitochondrial / Q000737:chemistry / Q000235:genetics; D017753:Ecosystem; D051456:Gene Flow; D040342:Genetic Structures; D014644:Genetic Variation; D005838:Genotype; D005843:Geography; D006239:Haplotypes; D046448:Ice Cover; D018895:Microsatellite Repeats / Q000235:genetics; D010802:Phylogeny; D011156:Population Density; D011157:Population Dynamics; D017422:Sequence Analysis, DNA; D001503:Ursidae / Q000145:classification / Q000235:genetics* / Q000254:growth & development
chemical_list: D004272:DNA, Mitochondrial