title: Brown and polar bear Y chromosomes reveal extensive male-biased gene flow within brother lineages.
abstract: Brown and polar bears have become prominent examples in phylogeography, but previous phylogeographic studies relied largely on maternally inherited mitochondrial DNA (mtDNA) or were geographically restricted. The male-specific Y chromosome, a natural counterpart to mtDNA, has remained underexplored. Although this paternally inherited chromosome is indispensable for comprehensive analyses of phylogeographic patterns, technical difficulties and low variability have hampered its application in most mammals. We developed 13 novel Y-chromosomal sequence and microsatellite markers from the polar bear genome and screened these in a broad geographic sample of 130 brown and polar bears. We also analyzed a 390-kb-long Y-chromosomal scaffold using sequencing data from published male ursine genomes. Y chromosome evidence support the emerging understanding that brown and polar bears started to diverge no later than the Middle Pleistocene. Contrary to mtDNA patterns, we found 1) brown and polar bears to be reciprocally monophyletic sister (or rather brother) lineages, without signals of introgression, 2) male-biased gene flow across continents and on phylogeographic time scales, and 3) male dispersal that links the Alaskan ABC islands population to mainland brown bears. Due to female philopatry, mtDNA provides a highly structured estimate of population differentiation, while male-biased gene flow is a homogenizing force for nuclear genetic variation. Our findings highlight the importance of analyzing both maternally and paternally inherited loci for a comprehensive view of phylogeographic history, and that mtDNA-based phylogeographic studies of many mammals should be reevaluated. Recent advances in sequencing technology render the analysis of Y-chromosomal variation feasible, even in nonmodel organisms.
authors.affiliation: Biodiversity and Climate Research Centre (BiK-F), Frankfurt am Main, Germany tobias.bidon@senckenberg.de frashai@gmx.net.
authors.forename: Tobias
authors.initials: T
authors.lastname: Bidon
authors.affiliation: Biodiversity and Climate Research Centre (BiK-F), Frankfurt am Main, GermanyGoethe University Frankfurt, Institute for Ecology, Evolution & Diversity, Frankfurt am Main, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Janke
authors.affiliation: National Fish and Wildlife Forensic Laboratory, Ashland, OR.
authors.forename: Steven R
authors.initials: SR
authors.lastname: Fain
authors.affiliation: Bioforsk, Norwegian Institute for Agricultural and Environmental Research, Svanvik, Norway.
authors.forename: Hans Geir
authors.initials: HG
authors.lastname: Eiken
authors.affiliation: Bioforsk, Norwegian Institute for Agricultural and Environmental Research, Svanvik, Norway.
authors.forename: Snorre B
authors.initials: SB
authors.lastname: Hagen
authors.affiliation: Department of Zoology, Institute of Ecology and Earth Sciences, University of Tartu, Tartu, Estonia.
authors.forename: Urmas
authors.initials: U
authors.lastname: Saarma
authors.affiliation: Biodiversity and Climate Research Centre (BiK-F), Frankfurt am Main, GermanyScience for Life Laboratory, School of Biotechnology, KTH, Stockholm, Sweden.
authors.forename: Björn M
authors.initials: BM
authors.lastname: Hallström
authors.affiliation: Canada Research Chair in Polar and Boreal Ecology, Department of Biology, University of Moncton, Moncton, Canada.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Lecomte
authors.affiliation: Biodiversity and Climate Research Centre (BiK-F), Frankfurt am Main, Germany tobias.bidon@senckenberg.de frashai@gmx.net.
authors.forename: Frank
authors.initials: F
authors.lastname: Hailer
mesh_terms: D000818:Animals; D033481:Chromosomes, Mammalian; D004247:DNA / Q000032:analysis*; D019143:Evolution, Molecular; D005260:Female; D051456:Gene Flow; D049810:Genetic Speciation; D014644:Genetic Variation; D006239:Haplotypes; D008297:Male; D018895:Microsatellite Repeats; D010802:Phylogeny; D058974:Phylogeography; D020641:Polymorphism, Single Nucleotide; D017422:Sequence Analysis, DNA; D012737:Sex Factors; D035781:Siblings; D001503:Ursidae / Q000145:classification / Q000235:genetics*; D014998:Y Chromosome
chemical_list: D004247:DNA
keywords: SNP; Y chromosome; bears; introgression; microsatellite; phylogeography