Sea ice reduction drives genetic differentiation among Barents Sea polar bears

Maduna, Simo N.; Aars, Jon; Fløystad, Ida; Klütsch, Cornelya F. C.; Fiskebeck, Eve Zeyl; Wiig, Øystein; Ehrich, Dorothée; Andersen, Magnus; Bachmann, Lutz; Derocher, Andrew E.; Nyman, Tommi; Eiken, Hans Geir; Hagen, Snorre B.

doi:10.1098/rspb.2021.1741

Cited by 21 publications

(12 citation statements)

References 64 publications

(96 reference statements)

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“…In some cases, they merely indicated close relationships (population sharing) between the target C and one of the sources, because the presence of segments that are identical by descent will inflict a downward deviation in the f 3 -statistic estimators (for the exact derivation of the deviation on the level of single individuals see SI Appendix , section S15 ). Such cases included polar bear individuals from the Svalbard Archipelago (PB3/PB8, PB5/PB14, and PB7/PB9), where the highly significantly negative f 3 values may indicate familial relationships or inbreeding among Svalbard Archipelago polar bears ( 36 ). West Greenland polar bears also appeared to be close relatives of one another, particularly BGI-PB47/BGI-PB10, although less so compared to the aforementioned Svalbard individuals.…”

Section: Resultsmentioning

confidence: 99%

Insights into bear evolution from a Pleistocene polar bear genome

Lan

Leppälä

Tomlin

et al. 2022

Proc. Natl. Acad. Sci. U.S.A.

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The polar bear ( Ursus maritimus ) has become a symbol of the threat to biodiversity from climate change. Understanding polar bear evolutionary history may provide insights into apex carnivore responses and prospects during periods of extreme environmental perturbations. In recent years, genomic studies have examined bear speciation and population history, including evidence for ancient admixture between polar bears and brown bears ( Ursus arctos ). Here, we extend our earlier studies of a 130,000- to 115,000-y-old polar bear from the Svalbard Archipelago using a 10× coverage genome sequence and 10 new genomes of polar and brown bears from contemporary zones of overlap in northern Alaska. We demonstrate a dramatic decline in effective population size for this ancient polar bear’s lineage, followed by a modest increase just before its demise. A slightly higher genetic diversity in the ancient polar bear suggests a severe genetic erosion over a prolonged bottleneck in modern polar bears. Statistical fitting of data to alternative admixture graph scenarios favors at least one ancient introgression event from brown bears into the ancestor of polar bears, possibly dating back over 150,000 y. Gene flow was likely bidirectional, but allelic transfer from brown into polar bear is the strongest detected signal, which contrasts with other published work. These findings may have implications for our understanding of climate change impacts: Polar bears, a specialist Arctic lineage, may not only have undergone severe genetic bottlenecks but also been the recipient of generalist, boreal genetic variants from brown bears during critical phases of Northern Hemisphere glacial oscillations.

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Section: Resultsmentioning

confidence: 99%

Insights into bear evolution from a Pleistocene polar bear genome

Lan

Leppälä

Tomlin

et al. 2022

Proc. Natl. Acad. Sci. U.S.A.

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show abstract

“…In some cases, they merely indicated close relationships (population sharing) between the target C and one of the sources, because the presence of segments that are identical by descent will inflict a downwards deviation in the f 3 -statistic estimators (for the exact derivation of the deviation on the level of single individuals, see SI Appendix , Text S15). Such cases included polar bear individuals from the Svalbard Archipelago (PB3/PB8, PB5/PB14, and PB7/PB9), where the highly significantly negative f 3 values may indicate familial relationships or inbreeding among Svalbard Archipelago polar bears (35). West Greenland polar bears also appeared to be close relatives of one another, particularly BGI-PB47/BGI-PB10, although less so compared to the aforementioned Svalbard individuals.…”

Section: Resultsmentioning

confidence: 99%

“…Importantly, however, the selective pressures incurred by habitat loss and other climate-related impacts will most likely outweigh any potential for adaptive evolutionary change catalyzed by hybridization. The current fragmentation of sea ice habitat is predicted to reduce gene flow among polar bear populations, resulting in increased local inbreeding and overall diversity loss (35). The marked differences between brown and polar bear population histories and genetic diversities, wherein polar bears show the signature of an ancient steep decline in population size with adverse effects to their genetic diversity, may be a testament to the impact of similar responses in the past.…”

Section: Discussionmentioning

confidence: 99%

Insights into bear evolution from a Pleistocene polar bear genome

Lan

Leppälä

Tomlin³

et al. 2021

Preprint

Self Cite

View full text Add to dashboard Cite

The polar bear (Ursus maritimus) has become a symbol of the threat to biodiversity from climate change. Understanding polar bear evolutionary history may provide insights into apex carnivore responses and prospects during periods of extreme environmental perturbations. In recent years, genomic studies have examined bear speciation and population history, including evidence for ancient admixture between polar bears and brown bears (Ursus arctos). Here, we extend our earlier studies of a 130,000-115,000-year-old polar bear from the Svalbard Archipelago using 10X coverage genome sequence and ten new genomes of polar and brown bears from contemporary zones of overlap in northern Alaska. We demonstrate a dramatic decline in effective population size for this ancient polar bear's lineage, followed by a modest increase just before its demise. A slightly higher genetic diversity in the ancient polar bear suggests a severe genetic erosion over a prolonged bottleneck in modern polar bears. Statistical fitting of data to alternative admixture graph scenarios favors at least one ancient introgression event from brown bears into the ancestor of polar bears, possibly dating back over 150,000 years. Gene flow was likely bidirectional, but allelic transfer from brown into polar bear is the strongest detected signal, which contrasts with other published works. These findings have implications for our understanding of climate change impacts: polar bears, a specialist Arctic lineage, may not only have undergone severe genetic bottlenecks, but also been the recipient of generalist, boreal genetic variants from brown bear during critical phases of Northern Hemisphere glacial oscillations.

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“…But loss of denning areas does present a form of habitat fragmentation that might result in reduced connectivity across the population if it persists over a longer period. This is supported by the exhibited high degree of site fidelity in Barents Sea polar bears in terms of denning areas as well as year-round area use, which is even visible across generations (Zeyl et al 2009;Lone et al 2013;Brun et al 2021), and a recent increased genetic structure between different areas within Svalbard that best may be explained by less gene flow from the bears living offshore (Maduna et al 2021).…”

Section: Discussionmentioning

confidence: 90%

Shifting polar bear Ursus maritimus denning habitat availability in the European Arctic

Merkel

Aars

2022

Polar Biol

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Climate warming has resulted in extensive sea ice loss across the Arctic. Polar bears (Ursus maritimus) rely on sea ice for hunting, resting, travelling and in some parts of the Arctic also maternity denning. In the European Arctic, polar bears rely on snow drifts on land to den and give birth. Consequently, timely arrival of sea ice around land masses during autumn is important for pregnant females to reach their denning habitat from their sea ice hunting grounds. We defined denning habitat as landforms necessary to accumulate snow to a depth sufficient for dens. We quantified availability of terrestrial denning habitat across the three European Arctic archipelagos throughout the last four (1979–2020) and the next eight decades (until 2100) using arrival of autumn sea ice around these islands. Across the study area, a clear trend was visible towards later sea ice arrival, varying up to 102 days. Female polar bears in the European Arctic now have 33% denning habitat available compared to the 1980's as many areas became inaccessible in time to start maternity denning. By the 2090's, all areas were projected to be inaccessible to pregnant bears. This decline was unequally distributed, with most reduction in Svalbard and Novaya Zemlya until 2020, whilst denning habitat availability in Franz Josef Land remained unchanged until 2020 but is predicted to become inaccessible by the end of the century. This work emphasizes the importance of the temporal dimension of sea ice dynamics for the persistence of polar bear populations.

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Sea ice reduction drives genetic differentiation among Barents Sea polar bears

Cited by 21 publications

References 64 publications

Insights into bear evolution from a Pleistocene polar bear genome

Insights into bear evolution from a Pleistocene polar bear genome

Insights into bear evolution from a Pleistocene polar bear genome

Shifting polar bear Ursus maritimus denning habitat availability in the European Arctic

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