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60 results for “polar bear”
Data from: Genetic relationships of extant brown bears (Ursus arctos) and polar bears (Ursus maritimus)
Polar bears (Ursus maritimus) and brown bears (Ursus arctos) are closely related species for which extensive mitochondrial and nuclear phylogenetic genetic comparisons have been made. We used previously-published genotype data for 8 microsatellite DNA loci from 930 brown bears in 19 populations and 473 polar bears in 16 populations to compare the population genetic relationships of extant populations of the species. Genetic distances (Nei standard distance = 1.157), the proportion of private alleles (52% of alleles are not shared by the species), and Bayesian cluster analysis are consistent with morphological and life history characteristics that distinguish polar bears and brown bears as different species with little or no gene flow among extant populations.
Polar Bear Skull
Laser scan of a Polar Bear skull and jaw. Faro laser arm. Source: Objaverse 1.0 / Sketchfab
Stable isotope differences of polar bears in the Southern Beaufort Sea and Chukchi Sea
<p>The life history, genetic, and habitat use differences between the 2 polar bear<strong> </strong>(Ursus maritimus) subpopulations in Alaska have been used to determine the geographic border separating them, but it has sparked a debate of the correct placement of the border for several years. Recently, the Southern Beaufort Sea (SBS) polar bear subpopulation has declined due to sea ice loss, while the Chukchi Sea (CS) subpopulation appears stable. To provide additional information about potential differences between the SBS and CS subpopulations, such as differences in prey sources, we used stable isotope analysis of carbon and nitrogen from bone collagen of polar bears in these 2 neighboring subpopulations. We analyzed polar bear bones (1954–2019) from 112 individuals. Our purpose was to determine if the SBS and CS subpopulations could be distinguished based on the stable isotope signatures of bone collagen. A difference greater than 1‰ in δ<sup>13</sup>C values suggests a change in carbon sources, such as nearshore to offshore, while a 3‰ change in δ<sup>15</sup>N values equates to a change of about 1 trophic level. Our study showed a significant difference in δ<sup>13</sup>C values (P ≤ 0.001), but not δ<sup>15</sup>N values (P = 0.654) between the CS (−13.0±0.3‰ and 22.0±0.9‰, respectively) and SBS bears (−14.7±1.3‰ and 22.2±1.0‰, respectively). Our findings indicate that the 2 subpopulations are consuming similar high trophic level prey, while feeding in ecosystems with different δ<sup>13</sup>C baselines. We performed a logistic regression analysis (LR) using δ<sup>13</sup>C and δ<sup>15</sup>N values of the polar bears to predict their placement into these 2 subpopulations. Using Icy Cape, AK as the geographical boundary, the LR correctly placed polar bears in their respective subpopulations 82% of the time. Overall accuracy of placement changed to 84% when using the current geographical boundary at Utqiaġvik, AK. Samples collected from the Wainwright, AK region were predicted as 58% CS and 42% SBS polar bears. This suggests that the area between Wainwright and Icy Cape is a polar bear mixing zone that includes bears from both subpopulations. Bone collagen has a long-term, potentially life-long, stable isotope turnover rate, and our findings could be used to determine the association of harvested polar bears to Alaska subpopulations, thus aiding in transboundary harvest quota management.</p>
Data from: Heritability of body size in the polar bears of Western Hudson Bay
Among polar bears (Ursus maritimus), fitness is dependent on body size through males' abilities to win mates, females' abilities to provide for their young, and all bears' abilities to survive increasingly longer fasting periods caused by climate change. In the Western Hudson Bay subpopulation (near Churchill, Manitoba, Canada), polar bears have declined in body size and condition, but nothing is known about the genetic underpinnings of body size variation, which may be subject to natural selection. Here, we combine a 4449-individual pedigree and an array of 5433 single-nucleotide polymorphisms (SNPs) to provide the first quantitative genetics study of polar bears. We used animal models to estimate heritability (h2) among polar bears handled between 1966 and 2011, obtaining h2 estimates of 0.34-0.48 for strictly skeletal traits and 0.18 for axillary girth (which is also dependent on fatness). We genotyped 859 individuals with the SNP array to test for marker-trait association and combined p-values over genetic pathways using gene-set analysis. Variation in all traits appeared to be polygenic, but we detected one region of moderately large effect size in body length near a putative noncoding RNA in an unannotated region of the genome. Gene-set analysis suggested that variation in body length was associated with genes in the regulatory cascade of cyclin expression, which has previously been associated with body size in mice. A greater understanding of the genetic architecture of body size variation will be valuable in understanding the potential for adaptation in polar bear populations challenged by climate change.
Data from: Intrapopulation differences in polar bear movement and step selection patterns
<p><strong>Background</strong>: The spatial ecology of individuals often varies within a population or species. Identifying how individuals in different classes interact with their environment can lead to a better understanding of population responses to human activities and environmental change and improve population estimates. Most inferences about polar bear (<em>Ursus maritimus</em>) spatial ecology are based on data from adult females due to morphological constraints on applying satellite radio collars to other classes of bears. Recent studies, however, have provided limited movement data for adult males and sub-adults of both sexes using ear-mounted and glue-on tags. We evaluated class-specific movements and step selection patterns for polar bears in the Chukchi Sea subpopulation during spring.</p> <p><strong>Methods</strong>: We developed hierarchical Bayesian models to evaluate polar bear movement (i.e., step length and directional persistence) and step selection at the scale of 4-day step lengths. We assessed differences in movement and step selection parameters among the three classes of polar bears (i.e., adult males, sub-adults, and adult females without cubs-of-the-year).</p> <p><strong>Results</strong>: Adult males had larger step lengths and less directed movements than adult females. Sub-adult movement parameters did not differ from the other classes but point estimates were most similar to adult females. We did not detect differences among polar bear classes in step selection parameters and parameter estimates were consistent with previous studies.</p> <p><strong>Conclusions</strong>: Our findings support the use of estimated step selection patterns from adult females as a proxy for other classes of polar bears during spring. Conversely, movement analyses indicated that using data from adult females as a proxy for the movements of adult males is likely inappropriate. We recommend that researchers consider whether it is valid to extend inference derived from adult female movements to other classes, based on the questions being asked and the spatial and temporal scope of the data. Because our data were specific to spring, these findings highlight the need to evaluate differences in movement and step selection during other periods of the year, for which data from ear-mounted and glue-on tags are currently lacking.</p>
Data from: Icing-related injuries in polar bears (Ursus maritimus) at high latitudes
<p>Climate change has broad ecological implications for wildlife, especially for species that rely on temperature-sensitive habitats. For polar bears (<em>Ursus maritimus</em>), loss of Arctic sea ice reduces access to prey and lengthens seasonal fasting periods leading to behavioral, nutritional, and reproductive impacts that may result in population declines. Secondary factors, such as disease and contaminants can exacerbate primary stressors and new health-related conditions are likely to emerge. For example, once unusual but now increasingly frequent warming cycles are creating unprecedented icing conditions that have demographic consequences for cold-adapted mammals.</p> <p>We report on icing-related lesions observed in wild polar bears during live-capture research in two high-latitude subpopulations, Kane Basin (KB) and East Greenland (EG), between 2012 and 2022. We observed ice build-up, hair loss (alopecia), and skin ulcerations primarily affecting the feet of adult bears as well as other parts of the body. The most severely affected individuals had blocks of ice up to 30 cm in diameter adhered to the foot pads, deep, bleeding ulcerations of foot pads and exhibited lameness. These injuries have not been observed during previous research in these areas or reported in the scientific literature, suggesting this may be a new phenomenon. To provide context for our observations, we conducted interviews with Indigenous polar bear subsistence hunters in West and East Greenland and Nunavut to document Indigenous knowledge about the potential causes and frequency of these injuries.</p>
Fig. 3 in Den phenology and reproductive success of polar bears in a changing climate
Fig. 3.—Den locations for female polar bears (Ursus maritimus) that were observed with (dens that produced cubs) or without cubs (dens that did not produce cubs) following den emergence. Females were observed on average 37 days after emergence from dens.
Fig. 2 in Den phenology and reproductive success of polar bears in a changing climate
Fig. 2.—Examples of control charts with temperature data measured by thermistors onboard satellite collars fitted to adult female polar bears (Ursus maritimus) used to identify denning and to estimate entrance into and emergence from dens. Entrance and emergence dates were estimated as the median date between observations within and above control limits at the start and end of a denning event (shown as horizontal dashed lines).
Fig. 1 in Den phenology and reproductive success of polar bears in a changing climate
Fig. 1.—Locations of maternal dens of polar bears (Ursus maritimus) identified using temperature-sensor data collected from satellite radiocollars deployed on adult female polar bears in the Chukchi Sea and Beaufort Sea subpopulations. Red lines indicate IUCN Polar Bear Specialist Group identified subpopulation boundaries.
Data from: Assessing polar bear (Ursus maritimus) population structure in the Hudson Bay region using SNPs
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Data from: Heritability of body size in the polar bears of Western Hudson Bay
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Data from: Brown and polar bear Y chromosomes reveal extensive male-biased gene flow within brother lineages
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Data from: "Polar bear (Ursus maritimus) transcriptome assembly and SNP discovery" in Genomic Resources Notes accepted 1 August 2013-30 September 2013
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Data from: Integrated population modeling provides the first empirical estimates of vital rates and abundance for polar bears in the Chukchi Sea
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Data from: Range contraction and increasing isolation of a polar bear subpopulation in an era of sea-ice loss
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Data from: Design of a 9K SNP chip for polar bears (Ursus maritimus) from RAD and transcriptome sequencing
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Data from: Harvesting wildlife affected by climate change: a modelling and management approach for polar bears
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Data from: Intrapopulation differences in polar bear movement and step selection patterns
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Data from: Projected polar bear sea ice habitat in the Canadian Arctic Archipelago
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Canadian polar bear population structure using genome-wide markers
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