Late-Quaternary biogeographic scenarios for the brown bear (Ursus arctos), a wild mammal model species |
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Authors: | John Davison Simon YW Ho Sarah C Bray Marju Korsten Egle Tammeleht Maris Hindrikson Kjartan Østbye Eivind Østbye Stein-Erik Lauritzen Jeremy Austin Alan Cooper Urmas Saarma |
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Institution: | 1. WA Conservation Science Institute, PO Box 494, Cashmere, WA 98815, USA;2. US Forest Service, Pacific Northwest Research Station, 1133 N Western Avenue, Wenatchee, WA, 98801, USA;3. US Fish and Wildlife Service, 385 Fish Hatchery Rd, Libby, MT, 59923, USA;4. BirchdaleEcologicalLtd, PO Box 606, Kaslo, BC, Canada V0G 1M0 |
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Abstract: | This review provides an up-to-date synthesis of the matrilineal phylogeography of a uniquely well-studied Holarctic mammal, the brown bear. We extend current knowledge by presenting a DNA sequence derived from one of the earliest known fossils of a polar bear (dated to 115 000 years before present), a species that shares a paraphyletic mitochondrial association with brown bears. A molecular clock analysis of 140 mitochondrial DNA sequences, including our new polar bear sequence, provides novel insights into the times of origin for different brown bear clades. We propose a number of regional biogeographic scenarios based on genetic data, divergence time estimates and paleontological records. The case of the brown bear provides an example for researchers working with less well-studied taxa: it shows clearly that phylogeographic models based on patterns of modern genetic variation alone can be substantially improved by including data on historical patterns of genetic diversity in the form of ancient DNA sequences derived from accurately dated samples and by using an approach to divergence-time estimation that suits the data under analysis. Using such approaches it has been possible to (i) establish that the processes shaping modern genetic diversity in brown bears acted recently, within the last three glacial cycles; (ii) distinguish among hypotheses concerning species’ responses to climatic oscillations in accordance with the lack of phylogeographic structure that existed in brown bears prior to the last glacial maximum (LGM); (iii) reassess theories linking monophyletic brown bear populations to particular LGM refuge areas; and (iv) identify vicariance events and track analogous patterns of migration by brown bears out of Eurasia to North America and Japan. |
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