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Relationships between mitochondrial haplotypes of polar bears from the circumpolar range (15 subpopulations). a. Minimum evolution tree showing the relationships between 63 mitochondrial DNA control region haplotypes for polar bears from these subpopulations, the ancient Poolepynten (GenBank Accession No. GU573488) polar bear and haplotypes found within the three clades of Alaskan brown bears (GenBank Accession No. KM821364–KM821401). Numbers represent distances between deeper nodes, under the Tamura-Nei distance (I+G0.69) model. Filled circles indicate nodes with>70% bootstrap support, and arrows at nodes indicate 50–69% bootstrap support. b. Unrooted 95% parsimony network showing relationships of the 64 haplotypes. The size of the node corresponds to the frequency of each haplotype (numbered) with black squares representing unsampled haplotypes.
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We provide an expansive analysis of polar bear (Ursus maritimus) circumpolar genetic variation during the last two decades of decline in their sea-ice habitat. We sought to evaluate whether their genetic diversity and structure have changed over this period of habitat decline, how their current genetic patterns compare with past patterns, and how g...
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Source–sink dynamics affects population connectivity, spatial genetic structure and population viability for many species. We introduce a novel approach that uses individual-based genetic graphs to identify source–sink areas within a continuously distributed population of black bears (Ursus americanus) in the northern lower peninsula (NLP) of Michi...
Palaeogenomes provide the potential to study evolutionary processes in real time, but this potential is limited by our ability to recover genetic data over extended timescales. The Late Pleistocene currently represents the age-limit for temperate-zone palaeogenome retrieval. Consequently, large portions of the evolutionary histories of many organi...
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... Recently, the genetic structure of the global polar bear population has been reconsidered. Peacock et al. [7] identify three to four main genetic clusters: Canadian Arctic Archipelago, Southern Canada, and Polar Basin (the latter is divided into eastern and western subclusters). At the same time, in light of ongoing climate change a directed gene flow hypothesized. ...
... Malefant et al. [8] identify six genetic clusters of polar bears: Hudson Bay, the western and eastern parts of the Canadian Arctic Archipelago, the western and eastern Polar Basins, and the Norwegian Bay. Although the abundance, distribution, and population structure of polar bears are negatively impacted by the rapid loss of Arctic sea ice, Malefant et al. [8], unlike Peacock et al. [7], do not provide evidence for a strong directed gene flow in response to climate change. ...
We analyzed population genetic structure of polar bear (Ursus maritimus) in the Russian Arctic based on samples collected in 2010–2021. For 93 adult individuals, we report polymorphism of 17 nuclear DNA microsatellite loci and a 610 nucleotide long mtDNA D-loop fragment. High genetic diversity of nuclear DNA and low nucleotide diversity π for mitochondrial DNA was found. All genetic markers proved differentiation between bears of southern Barents Sea and northern Barents and Kara seas. These two groups differed by distribution of the mitochondrial marker (θst = 0.270) and, to less extent, by nuclear loci (Rst = 0.018).
... Introgression has also been observed in populations of Ursus maritimus -one of the species that is most susceptible to anthropogenic climate warming. Recent analyses of fossil records from interglacial refugia situated in Ireland and the Alexander Archipelago in Alaska have shown that modern Ursus maritimus originated as a result of several hybridisation events between Ursus maritimus and Ursus arctos co-occupying periglacial habitats during the late Pleistocene, approximately 32-28 ka BP in Europe and 26 ka BP in Alaska , Peacock et al. 2015. Fluctuations in Ursus maritimus population size have been consistent with climate changes; during Pleistocene cooling events, the population size of Ursus arctos decreased, while that of Ursus maritimus increased. ...
... Signals of admixture are consistent with overlapping geographic ranges and habitats of both species. Today, hybrids are also documented in the wild (Peacock et al. 2015, Pongracz et al. 2017. Contemporary populations of Ursus maritimus belong to a single Evolutionary Significant Unit, with high genetic homogeneity and low genetic diversity. ...
The historical biogeography of the terrestrial mammals in Europe has been widely studied on the basis of fossil records and molecular makers. However, to date, only one model of species' responses to glacial–interglacial cycles during the glacial episodes of the Quaternary, especially during the Last Glacial Maximum, has been proposed: the ‘expansion‐contraction model’.
The ‘expansion‐contraction model’ is more appropriate for thermophilous and temperate species than for Arctic species. We hypothesise that the responses of cold‐adapted species to the temperature fluctuations during glacial cycles cannot be explained by this model.
In this review, we synthesise and describe, for the first time, the historical biogeography of various cold‐adapted terrestrial mammalian taxa (small mammals, herbivores, and carnivores) in Eurasia during the last glaciation (especially during the Last Glacial Maximum), and identify mechanisms underlying their response to glacier pulsation and severe climate fluctuations.
We formulate the paradigm for the biogeography of cold‐adapted mammalian taxa in Europe, and identified three response models to glacial–interglacial cycles: 1) ‘extinction and genetic diminution’ for Lasiopodomys gregalis , Dicrostonyx spp. and Lemmus lemmus , 2) ‘extinction and replacement’ for Alopex lagopus , Gulo gulo and Rangifer tarandus , and 3) ‘contraction and gene transfer’ for Lepus timidus and Martes zibellina .
Knowledge of past biogeography is essential for understanding how cold‐adapted taxa are responding to anthropogenic climate warming, and for on‐going biodiversity and habitat conservation in the Anthropocene. There is no doubt that cold‐adapted, Arctic species are suffering the most from global warming.
... These findings suggested that although the evolutionary importance of breakdown of species barriers should not be underestimated, recent hybridization between the two species could merely be caused by uncommon and atypical mating preferences of select individuals. In keeping with this hypothesis, an expansive genetic analysis of a large, circumpolar sample of polar bear subpopulations failed to find genetic signatures of recent hybridization between the two species, suggesting that recently observed hybrids represent localized events (58). ...
SignificanceInterspecific hybridization is a widespread phenomenon, but measuring its extent, directionality, and adaptive importance remains challenging. Ancient genomes, however, can help illuminate the history of modern organisms. Here, we present a genome retrieved from a 130,000- to 115,000-y-old polar bear and perform genome analyses of modern polar and brown bears throughout their geographic ranges. We find that the principal direction of ancient allele sharing was from brown bear into polar bear, although gene flow between them has likely been bidirectional. This partially inverts the current paradigm of unidirectional gene flow from polar into brown bear, and it suggests that polar bears were recipients of external genetic variation prior to their extensive population decline.
... Polar bears are distributed over ∼24 million km 2 across the Arctic, from about 51 • N in Canada, north to the North Pole, within 19 subpopulations (Figure 1; Polar Bear Specialist Group, 2010). The delineation of polar bear subpopulations is based on telemetry data, recapture of tagged bears, and returns of tags from bears harvested by Inuit hunters, genetics, sea ice, and geographic barriers to movement (Bethke et al., 1996;Paetkau et al., 1999;Mauritzen et al., 2002;Peacock et al., 2015). The term "subpopulation" is the term used by the International Union for Conservation of Nature (IUCN) Species Survival Commission for "geographically and otherwise distinct groups in the population between which there is little demographic or genetic exchange" (IUCN, 2012). ...
Wildlife harvest remains a conservation concern for many species and assessing patterns of harvest can provide insights on sustainability and inform management. Polar bears (Ursus maritimus) are harvested over a large part of their range by local people. The species has a history of unsustainable harvest that was largely rectified by an international agreement that required science-based management. The objective of our study was to examine the temporal patterns in the number of polar bears harvested, harvest sex ratios, and harvest rates from 1970 to 2018. We analyzed data from 39,049 harvested polar bears (annual mean 797 bears) collected from 1970 to 2018. Harvest varied across populations and times that reflect varying management objectives, episodic events, and changes based on new population estimates. More males than females were harvested with an overall M:F sex ratio of 1.84. Harvest varied by jurisdiction with 68.0% of bears harvested in Canada, 18.0% in Greenland, 11.8% in the USA, and 2.2% in Norway. Harvest rate was often near the 4.5% target rate. Where data allowed harvest rate estimation, the target rate was exceeded in 11 of 13 populations with 1–5 populations per year above the target since 1978. Harvest rates at times were up to 15.9% of the estimated population size suggesting rare episodes of severe over-harvest. Harvest rate was unrelated to a proxy for ecosystem productivity (area of continental shelf within each population) but was correlated with prey diversity. In the last 5–10 years, monitored populations all had harvest rates near sustainable limits, suggesting improvements in management. Polar bear harvest management has reduced the threat it once posed to the species. However, infrequent estimates of abundance, new management objectives, and climate change have raised new concerns about the effects of harvest.
... Scharf et al. (2019) expanded methods for subpopulation delineation into a Bayesian framework that accounted for selection by bears of dynamic sea-ice habitats. Both ST and genetic methods (Paetkau et al., 1999;Peacock et al., 2015;Viengkone et al., 2016) have been used to understand the degree to which individual subpopulations are isolated (Bethke et al., 1996;Mauritzen et al., 2001;Taylor et al., 2001), which can affect population viability (e.g., via source-sink dynamics or smallpopulation effects). ...
Satellite telemetry (ST) has played a critical role in the management and conservation of polar bears (Ursus maritimus) over the last 50 years. ST data provide biological information relevant to subpopulation delineation, movements, habitat use, maternal denning, health, human-bear interactions, and accurate estimates of vital rates and abundance. Given that polar bears are distributed at low densities over vast and remote habitats, much of the information provided by ST data cannot be collected by other means. Obtaining ST data for polar bears requires chemical immobilization and application of a tracking device. Although immobilization has not been found to have negative effects beyond a several-day reduction in activity, over the last few decades opposition to immobilization and deployment of satellite-linked radio collars has resulted in a lack of current ST data in many of the 19 recognized polar bear subpopulations. Here, we review the uses of ST data for polar bears and evaluate its role in addressing 21st century conservation and management challenges, which include estimation of sustainable harvest rates, understanding the impacts of climate warming, delineating critical habitat, and assessing potential anthropogenic impacts from tourism, resource development and extraction. We found that in subpopulations where ST data have been consistently collected, information was available to estimate vital rates and subpopulation density, document the effects of sea-ice loss, and inform management related to subsistence harvest and regulatory requirements. In contrast, a lack of ST data in some subpopulations resulted in increased bias and uncertainty in ecological and demographic parameters, which has a range of negative consequences. As sea-ice loss due to climate warming continues, there is a greater need to monitor polar bear distribution, habitat use, abundance, and subpopulation connectivity. We conclude that continued collection of ST data will be critically important for polar bear management and conservation in the 21st century and that the benefits of immobilizing small numbers of individual polar bears in order to deploy ST devices significantly outweigh the risks.
... These findings suggested that although the evolutionary importance of breakdown of species barriers should not be underestimated, recent hybridization between the two species could merely be caused by uncommon and atypical mating preferences of select individuals. In keeping with this hypothesis, an expansive genetic analysis of a large, circumpolar sample of polar bear subpopulations failed to find genetic signatures of recent hybridization between the two species, suggesting that recently observed hybrids represent localized events (55). ...
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.
Significance
Interspecific hybridization is a widespread phenomenon but measuring its extent, directionality, and adaptive importance remains challenging. Ancient genomes, however, can help illuminate the history of modern organisms. Here, we present a genome retrieved from a ~120,000-year-old polar bear and perform genome analyses of modern polar and brown bears throughout their geographic range. We find that principal direction of ancient allele sharing was from brown bear into polar bear, although gene flow between them has likely been bidirectional. This inverts the current paradigm of unidirectional gene flow from polar into brown bear. Allele sharing facilitated by variants from boreal brown bear generalists may have helped facilitate the ability of the polar bear lineage to endure warming periods and mitigate genetic erosion from prolonged population bottlenecks.
... Movement data of satellite-collared bears (Taylor et al. 2001), genetic analyses (e.g. Paetkau et al. 1999, Peacock et al. 2015, recaptures, and harvest recoveries of research-marked bears (Taylor & Lee 1995) have been used to delineate the boundaries of the BB subpopulation. Although some interchange occurs among BB and adjacent subpopulations, including Davis Strait to the south, Lancaster Sound to the northwest, and Kane Basin to the north, the BB subpopulation is considered a distinct demographic unit for management purposes (Taylor et al. 2001, Laidre et al. 2018a. ...
Changes in sea-ice dynamics are affecting polar bears Ursus maritimus across their circumpolar range, which highlights the importance of periodic demographic assessments to inform management and conservation. We used genetic mark-recapture-recovery to derive estimates of abundance and survival for the Baffin Bay (BB) polar bear subpopulation—the first time this method has been used successfully for this species. Genetic data from tissue samples we collected via biopsy darting were combined with historical physical capture and harvest recovery data. The combined data set consisted of 1410 genetic samples (2011-2013), 914 physical captures (1993-1995, 1997), and 234 harvest returns of marked bears (1993-2013). The estimate of mean subpopulation abundance was 2826 (95% CI = 2284-3367) in 2012-2013. Estimates of annual survival (mean ± SE) were 0.90 ± 0.05 and 0.78 ± 0.06 for females and males age ≥2 yr, respectively. The proportion of total mortality of adult females and males that was attributed to legal harvest was 0.16 ± 0.05 and 0.26 ± 0.06, respectively. Remote sensing sea-ice data, telemetry data, and spatial distribution of onshore sampling indicated that polar bears were more likely to use offshore sea-ice habitat during the 1990s sampling period compared to the 2010s. Furthermore, in the 1990s, sampling of deep fjords and inland areas was limited, and no offshore sampling occurred in either time period, which precluded comparisons of abundance between the 1993-1997 and 2011-2013 study periods. Our findings demonstrate that genetic sampling can be a practical method for demographic assessment of polar bears over large spatial and temporal scales.
... Over time, such erosion of genetic diversity may reduce the fitness of individuals and cause an elevated risk of extinction [19,46]. The magnitude and rate of loss of genetic diversity and gene flow that we observed is alarming considering that polar bears have historically shown relatively little genetic differentiation even on a global scale [47][48][49], but now are facing increasingly strong climatic selective pressure. The results of simulations suggested that further loss of sea ice will lead to the continued erosion of local genetic diversity in polar bears of the Svalbard Archipelago and to increased isolation between local areas, especially if there is a concurrent decrease in the number of bears. ...
Loss of Arctic sea ice owing to climate change is predicted to reduce both genetic diversity and gene flow in ice-dependent species, with potentially negative consequences for their long-term viability. Here, we tested for the population-genetic impacts of reduced sea ice cover on the polar bear (Ursus maritimus) sampled across two decades (1995-2016) from the Svalbard Archipelago, Norway, an area that is affected by rapid sea ice loss in the Arctic Barents Sea. We analysed genetic variation at 22 micro-satellite loci for 626 polar bears from four sampling areas within the archipelago. Our results revealed a 3-10% loss of genetic diversity across the study period, accompanied by a near 200% increase in genetic differentiation across regions. These effects may best be explained by a decrease in gene flow caused by habitat fragmentation owing to the loss of sea ice coverage , resulting in increased inbreeding of local polar bears within the focal sampling areas in the Svalbard Archipelago. This study illustrates the importance of genetic monitoring for developing adaptive management strategies for polar bears and other ice-dependent species.
... Nineteen recognized polar bear subpopulations: WH: Western Hudson Bay, SH: Southern Hudson Bay, DS: Davis Strait, BB: Baffin Bay, FB: Foxe Basin, KB: Kane Basin, NW: Norwegian Bay, LS: Lancaster Sound, GB: Gulf of Boothia, MC: McClintock Channel, VM: Viscount Melville Sound, NB: Northern Beaufort Sea, SB: Southern Beaufort Sea, CS: Chukchi Sea, LP: Laptev Sea, KS: Kara Sea, BS: Barents Sea, EG: East Greenland(Peacock et al., 2015). The size of the points indicates the sample size of the data sampled at that specific location. ...
POP levels remain high in Arctic predators like polar bears, despite banning of POPs. • Studies focused on individual effects, disregarding population-level effects. • We modelled potential polar bear population decline using SSDs for endother-mic species. • PCB concentrations posed the largest threat to subpopulations, yielding population decline. • Modelled growth rates increased over time: decreasing effect of PCBs, DDTs, and mercury. Although atmospheric concentrations of many conventional persistent organic pollutants (POPs) have decreased in the Arctic over the past few decades, levels of most POPs and mercury remain high since the 1990s or start to increase again in Arctic areas, especially polar bears. So far, studies generally focused on individual effects of POPs, and do not directly link POP concentrations in prey species to population-specific parameters. In this study we therefore aimed to estimate the effect of legacy POPs and mercury on population growth rate of nineteen polar bear subpopulations. We modelled population development in three scenarios, based on species sensitivity distributions (SSDs) derived for POPs based on ecotoxicity data for endothermic species. In the first scenario, ecotoxicity data for polar bears were based on the HC 50 (the concentration at which 50% of the species is affected). The other two scenarios were based on the HC 5 and HC 95. Considerable variation in effects of POPs could be observed among the scenarios. In our intermediate scenario, we predicted subpopulation decline for ten out of 15 polar bear subpopulations. The estimated population growth rate was least reduced in Gulf of Boothia and Foxe Basin. On average, PCB concentrations in prey (in μg/g toxic equivalency (TEQ)) posed the largest threat to polar bear subpopulations, with negative modelled population growth rates for the majority of sub-populations. We did not find a correlation between modelled population changes and monitored population trends for the majority of chemical-subpopulation combinations. Modelled population growth rates increased over time, implying a decreasing effect of PCBs, DDTs, and mercury. Polar bear subpopulations are reportedly still declining in four out of the seven subpopulations for which sufficient long-term monitoring data is available, as reported by the IUCN-PBSG. This implies that other emerging pollutants or other anthropogenic stressors may affect polar bear subpopulations.
... Our current understanding of polar bear (Ursus maritimus) population structure has emerged over time through population genetic studies based on mitochondrial sequences and microsatellite genotypic data (Malenfant, Davis, Cullingham, & Coltman, 2016;Paetkau et al., 1999;Paetkau, Calvert, Stirling, & Strobeck, 1995;Peacock et al., 2015). A recently developed SNP chip for polar bears (Malenfant, Coltman, & Davis, 2015), used for a preliminary population structure analysis, revealed four genetic clusters in the Canadian Arctic; however, other than this no large-scale study has yet been published using genome-wide markers, although there are focused studies at more local levels (Malenfant, Davis, Richardson, Lunn, & Coltman, 2018;Viengkone et al., 2016). ...
... In this study, we used thousands of genome-wide SNP markers to assess population structure across the range of polar bears in Canada. Our results clearly show differentiation within Canada, and the membership patterns and geographic ranges of the "Hudson Complex," "Arctic Archipelago," and "Polar Basin" genetic groups match closely with the results of previous studies using microsatellite loci Paetkau et al., 1999;Peacock et al., 2015) and a preliminary analysis using ~3,000 SNPs and 78 individuals (Malenfant et al., 2015). The previous studies included the global range of polar bears, and found that the genetic cluster of the Beaufort Sea continues around the arctic coast of Asia and Europe to the eastern side of Greenland Paetkau et al., 1999;Peacock et al., 2015), which is why we have chosen to refer to this cluster in our study as the Polar Basin. ...
... Our results clearly show differentiation within Canada, and the membership patterns and geographic ranges of the "Hudson Complex," "Arctic Archipelago," and "Polar Basin" genetic groups match closely with the results of previous studies using microsatellite loci Paetkau et al., 1999;Peacock et al., 2015) and a preliminary analysis using ~3,000 SNPs and 78 individuals (Malenfant et al., 2015). The previous studies included the global range of polar bears, and found that the genetic cluster of the Beaufort Sea continues around the arctic coast of Asia and Europe to the eastern side of Greenland Paetkau et al., 1999;Peacock et al., 2015), which is why we have chosen to refer to this cluster in our study as the Polar Basin. A fourth genetic cluster has been identified by previous authors (Malenfant et al., 2015Paetkau et al., 1999) coincident with the Norwegian Bay subpopulation, but due to our very small sample size (n = 1), we cannot confirm its existence. ...
Predicting the consequences of environmental changes, including human‐mediated climate change on species, requires that we quantify range‐wide patterns of genetic diversity and identify the ecological, environmental, and historical factors that have contributed to it. Here, we generate baseline data on polar bear population structure across most Canadian subpopulations (n = 358) using 13,488 genome‐wide single nucleotide polymorphisms (SNPs) identified with double‐digest restriction site‐associated DNA sequencing (ddRAD). Our ddRAD dataset showed three genetic clusters in the sampled Canadian range, congruent with previous studies based on microsatellites across the same regions; however, due to a lack of sampling in Norwegian Bay, we were unable to confirm the existence of a unique cluster in that subpopulation. These data on the genetic structure of polar bears using SNPs provide a detailed baseline against which future shifts in population structure can be assessed, and opportunities to develop new noninvasive tools for monitoring polar bears across their range. With ongoing rapid sea ice loss and environmental change in the Arctic, there is the potential for rapid changes in polar bear population structure. Here, we generated baseline data on polar bear population structure across 12 of 13 Canadian subpopulations using genome‐wide SNPs. These data on the genetic structure of polar bears using SNPs provide a detailed baseline against which future shifts in population structure can be assessed, and opportunities to develop new noninvasive tools for monitoring polar bears across their range.
