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Title: Polar and brown bear genomes reveal ancient admixture and demographic footprints of past climate change
Authors: Bedoya-Reina, Oscar C.
Ibarra-Laclette, Enrique
Herrera-Estrella, Luis
Schuster, Stephan C.
Welch, Andreanna J.
Miller, Webb
Ratan, Aakrosh
Zhao, Fangqing
Kim, Hie Lim
Burhans, Richard C.
Drautz, Daniela I.
Wittekindt, Nicola E.
Tomsho, Lynn P.
Peacock, Elizabeth
Farley, Sean
Sage, George K.
Rode, Karyn
Obbard, Martyn
Montiel, Rafael
Bachmann, Lutz
Ingolfsson, Olafur
Aars, Jon
Mailund, Thomas
Wiig, Oystein
Talbot, Sandra L.
Lindqvist, Charlotte
Issue Date: 2012
Source: Miller, W., Schuster, S. C., Welch, A. J., Ratan, A., Bedoya-Reina, O. C., Zhao, F., et al. (2012). Polar and brown bear genomes reveal ancient admixture and demographic footprints of past climate change. Proceedings of the National Academy of Sciences, 109(36), E2382-E2390.
Series/Report no.: Proceedings of the national academy of sciences
Abstract: Polar bears (PBs) are superbly adapted to the extreme Arctic environment and have become emblematic of the threat to biodiversity from global climate change. Their divergence from the lower-latitude brown bear provides a textbook example of rapid evolution of distinct phenotypes. However, limited mitochondrial and nuclear DNA evidence conflicts in the timing of PB origin as well as placement of the species within versus sister to the brown bear lineage. We gathered extensive genomic sequence data from contemporary polar, brown, and American black bear samples, in addition to a 130,000- to 110,000-y old PB, to examine this problem from a genome-wide perspective. Nuclear DNA markers reflect a species tree consistent with expectation, showing polar and brown bears to be sister species. However, for the enigmatic brown bears native to Alaska's Alexander Archipelago, we estimate that not only their mitochondrial genome, but also 5–10% of their nuclear genome, is most closely related to PBs, indicating ancient admixture between the two species. Explicit admixture analyses are consistent with ancient splits among PBs, brown bears and black bears that were later followed by occasional admixture. We also provide paleodemographic estimates that suggest bear evolution has tracked key climate events, and that PB in particular experienced a prolonged and dramatic decline in its effective population size during the last ca. 500,000 years. We demonstrate that brown bears and PBs have had sufficiently independent evolutionary histories over the last 4–5 million years to leave imprints in the PB nuclear genome that likely are associated with ecological adaptation to the Arctic environment.
DOI: 10.1073/pnas.1210506109
Rights: © 2012 National Academy of Sciences. This paper was published in Proceedings of the National Academy of Sciences and is made available as an electronic reprint (preprint) with permission of National Academy of Sciences. The paper can be found at the following official DOI: []. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper is prohibited and is subject to penalties under law.
Fulltext Permission: open
Fulltext Availability: With Fulltext
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