Genomic Evidence of Widespread Admixture from Polar Bears into Brown Bears during the Last Ice Age

James A. Cahill, Peter D. Heintzman, Kelley Harris, Matthew D. Teasdale, Joshua Kapp, Andre E.R. Soares, Ian Stirling, Daniel G. Bradley, Ceiridwen J. Edwards, Kiley Graim, Aliaksandr A. Kisleika, Alexander V. Malev, Nigel Monaghan, Richard E. Green, Beth Shapiro

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

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, whereas 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.
Original languageEnglish
Pages (from-to)1120-1129
Number of pages10
JournalMolecular Biology and Evolution
Volume35
Issue number5
Early online date20 Feb 2018
DOIs
Publication statusPublished - 1 May 2018

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Ursidae
Ursus maritimus
Ursus arctos
Ice
bear
genomics
ice
Pleistocene
climate change
Climate Change
introgression
ancestry
gene flow
extinction
fossil
Population
DNA
Gene Flow
history
fossils

Cite this

Cahill, J. A., Heintzman, P. D., Harris, K., Teasdale, M. D., Kapp, J., Soares, A. E. R., ... Shapiro, B. (2018). Genomic Evidence of Widespread Admixture from Polar Bears into Brown Bears during the Last Ice Age. Molecular Biology and Evolution, 35(5), 1120-1129. https://doi.org/10.1093/molbev/msy018
Cahill, James A. ; Heintzman, Peter D. ; Harris, Kelley ; Teasdale, Matthew D. ; Kapp, Joshua ; Soares, Andre E.R. ; Stirling, Ian ; Bradley, Daniel G. ; Edwards, Ceiridwen J. ; Graim, Kiley ; Kisleika, Aliaksandr A. ; Malev, Alexander V. ; Monaghan, Nigel ; Green, Richard E. ; Shapiro, Beth. / Genomic Evidence of Widespread Admixture from Polar Bears into Brown Bears during the Last Ice Age. In: Molecular Biology and Evolution. 2018 ; Vol. 35, No. 5. pp. 1120-1129.
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Cahill, JA, Heintzman, PD, Harris, K, Teasdale, MD, Kapp, J, Soares, AER, Stirling, I, Bradley, DG, Edwards, CJ, Graim, K, Kisleika, AA, Malev, AV, Monaghan, N, Green, RE & Shapiro, B 2018, 'Genomic Evidence of Widespread Admixture from Polar Bears into Brown Bears during the Last Ice Age', Molecular Biology and Evolution, vol. 35, no. 5, pp. 1120-1129. https://doi.org/10.1093/molbev/msy018

Genomic Evidence of Widespread Admixture from Polar Bears into Brown Bears during the Last Ice Age. / Cahill, James A.; Heintzman, Peter D.; Harris, Kelley; Teasdale, Matthew D.; Kapp, Joshua; Soares, Andre E.R.; Stirling, Ian; Bradley, Daniel G.; Edwards, Ceiridwen J.; Graim, Kiley; Kisleika, Aliaksandr A.; Malev, Alexander V.; Monaghan, Nigel; Green, Richard E.; Shapiro, Beth.

In: Molecular Biology and Evolution, Vol. 35, No. 5, 01.05.2018, p. 1120-1129.

Research output: Contribution to journalArticle

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T1 - Genomic Evidence of Widespread Admixture from Polar Bears into Brown Bears during the Last Ice Age

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AU - Soares, Andre E.R.

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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 - This is a pre-copyedited, author-produced version of an article accepted for publication in Molecular Biology and Evolution following peer review. The version of record James A Cahill, Peter D Heintzman, Kelley Harris, Matthew D Teasdale, Joshua Kapp, Andre E R Soares, Ian Stirling, Daniel Bradley, Ceiridwen J Edwards, Kiley Graim, Aliaksandr A Kisleika, Alexander V Malev, Nigel Monaghan, Richard E Green, Beth Shapiro; Genomic Evidence of Widespread Admixture from Polar Bears into Brown Bears during the Last Ice Age, Molecular Biology and Evolution, Volume 35, Issue 5, 1 May 2018, Pages 1120–1129 is available online at: https://doi.org/10.1093/molbev/msy018

PY - 2018/5/1

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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, whereas 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, whereas 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 - genomics

KW - hybridization

KW - ancient DNA

KW - ursus

KW - paleogenomics

KW - admixture

U2 - 10.1093/molbev/msy018

DO - 10.1093/molbev/msy018

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JO - Molecular Biology and Evolution

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