ena-STUDY-BIK-F-17-12-2013-16:28:58:878-170
Brown and polar bear Y chromosomes reveal extensive male-biased gene flow within brother lineages
Brown and polar bears have become prominent model organisms in phylogeography, but previous phylogeographic studies were geographically restricted, or relied largely on maternally inherited mitochondrial DNA (mtDNA). The male-specific Y chromosome, a natural counterpart to mtDNA, has remained under-explored. Although this paternally inherited chromosome is indispensible for integrative analyses of phylogeographic patterns, technical difficulties have hampered its application in most mammals. We developed novel Y-chromosomal 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 fragment from published male ursine genomes. Contrary to well-established mtDNA patterns, we found (i) brown and polar bears to be reciprocally monophyletic sister (or rather brother) lineages, without signals of introgression, (ii) male-biased gene flow across continents and on phylogeographic time scales, and (iii) male dispersal that links the enigmatic Alaskan ABC-islands population to mainland brown bears. MtDNA-based studies have thus overestimated population structuring, due to female philopatry and the homogenizing effect of male-biased gene flow Our findings highlight the importance of analysing both maternally and paternally inherited loci for a comprehensive view of phylogeographic history and that mtDNA-based phylogeographic studies of many mammals should be re-evaluated.
Brown and polar bears have become prominent model organisms in phylogeography, but previous phylogeographic studies were geographically restricted, or relied largely on maternally inherited mitochondrial DNA (mtDNA). The male-specific Y chromosome, a natural counterpart to mtDNA, has remained under-explored. Although this paternally inherited chromosome is indispensible for integrative analyses of phylogeographic patterns, technical difficulties have hampered its application in most mammals. We developed novel Y-chromosomal 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 fragment from published male ursine genomes. Contrary to well-established mtDNA patterns, we found (i) brown and polar bears to be reciprocally monophyletic sister (or rather brother) lineages, without signals of introgression, (ii) male-biased gene flow across continents and on phylogeographic time scales, and (iii) male dispersal that links the enigmatic Alaskan ABC-islands population to mainland brown bears. MtDNA-based studies have thus overestimated population structuring, due to female philopatry and the homogenizing effect of male-biased gene flow Our findings highlight the importance of analysing both maternally and paternally inherited loci for a comprehensive view of phylogeographic history and that mtDNA-based phylogeographic studies of many mammals should be re-evaluated.