Genomic evidence of widespread admixture from polar bears into brown bears during the last ice age

TY - JOUR

T1 - Genomic evidence of widespread admixture from polar bears into brown bears during the last ice age

AU - Cahill, James A

AU - Heintzman, Peter D

AU - Harris, Kelley

AU - Teasdale, Matthew D

AU - Kapp, Joshua

AU - Soares, André E Rodrigues

AU - Stirling, Ian

AU - Bradley, Daniel

AU - Edwards, Ceiridwen J

AU - Graim, Kiley

AU - Kisleika, Aliaksandr A

AU - Malev, Alexander V

AU - Monaghan, Nigel

AU - Green, Richard E.

AU - Shapiro, Beth

N1 - © The Author 2018. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details

PY - 2018/2/20

Y1 - 2018/2/20

N2 - Recent genomic analyses have provided substantial evidence for past periods of gene flow from polar bears (Ursus maritimus) into Alaskan brown bears (Ursus arctos), with some analyses suggesting a link between climate change and genomic introgression. However, because it has mainly been possible to sample bears from the present day, the timing, frequency, and evolutionary significance of this admixture remains unknown. Here, we analyze genomic DNA from three additional and geographically distinct brown bear populations, including two that lived temporally close to the peak of the last ice age. We find evidence of admixture in all three populations, suggesting that admixture between these species has been common in their recent evolutionary history. In addition, analyses of ten fossil bears from the now-extinct Irish population indicate that admixture peaked during the last ice age, when brown bear and polar bear ranges overlapped. Following this peak, the proportion of polar bear ancestry in Irish brown bears declined rapidly until their extinction. Our results support a model in which ice age climate change created geographically widespread conditions conducive to admixture between polar bears and brown bears, as is again occurring today. We postulate that this model will be informative for many admixing species pairs impacted by climate change. Our results highlight the power of paleogenomics to reveal patterns of evolutionary change that are otherwise masked in contemporary data.

AB - Recent genomic analyses have provided substantial evidence for past periods of gene flow from polar bears (Ursus maritimus) into Alaskan brown bears (Ursus arctos), with some analyses suggesting a link between climate change and genomic introgression. However, because it has mainly been possible to sample bears from the present day, the timing, frequency, and evolutionary significance of this admixture remains unknown. Here, we analyze genomic DNA from three additional and geographically distinct brown bear populations, including two that lived temporally close to the peak of the last ice age. We find evidence of admixture in all three populations, suggesting that admixture between these species has been common in their recent evolutionary history. In addition, analyses of ten fossil bears from the now-extinct Irish population indicate that admixture peaked during the last ice age, when brown bear and polar bear ranges overlapped. Following this peak, the proportion of polar bear ancestry in Irish brown bears declined rapidly until their extinction. Our results support a model in which ice age climate change created geographically widespread conditions conducive to admixture between polar bears and brown bears, as is again occurring today. We postulate that this model will be informative for many admixing species pairs impacted by climate change. Our results highlight the power of paleogenomics to reveal patterns of evolutionary change that are otherwise masked in contemporary data.

KW - Journal Article

U2 - 10.1093/molbev/msy018

DO - 10.1093/molbev/msy018

M3 - Article

C2 - 29471451

SN - 0737-4038

JO - Molecular Biology and Evolution

JF - Molecular Biology and Evolution

ER -