An Ice Age Refugium for Large Mammals in the Alexander Archipelago, Southeastern Alaska

Genetic and paleontological evidence are combining to provide a new and surprising picture of mammalian biogeography in southeastern Alaska. Prior to our study, the brown and black bears of the Alexander Archipelago were considered postglacial immigrants that never had overlapping ranges. Vertebrate fossils from caves on Prince of Wales Island now demonstrate that brown and black bears coexisted there (and even inhabited the same caves) both before and after the last glaciation. Differences in mtDNA sequences suggest that living brown bears of the Alexander Archipelago comprise a distinct clade and are more closely related to polar bears than to their mainland conspecifics. We conclude that brown bears, and perhaps other large mammals, have continuously inhabited the archipelago for at least 40,000 yr and that habitable refugia were therefore available throughout the last glaciation.

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Interspecific and intraspecific mitochondrial DNA variation in North American bears (Ursus)

Canadian Journal of Zoology ◽

10.1139/z91-421 ◽

1991 ◽

Vol 69 (12) ◽

pp. 2985-2992 ◽

Cited By ~ 60

Author(s):

Matthew A. Cronin ◽

Steven C. Amstrup ◽

Gerald W. Garner ◽

Ernest R. Vyse

Keyword(s):

Mitochondrial Dna ◽

North American ◽

Ursus Arctos ◽

Phylogenetic Analyses ◽

Sequence Divergence ◽

Black Bears ◽

Polar Bears ◽

Brown Bears ◽

Dna Variation ◽

Base Substitutions

We assessed mitochondrial DNA variation in North American black bears (Ursus americanus), brown bears (Ursus arctos), and polar bears (Ursus maritimus). Divergent mitochondrial DNA haplotypes (0.05 base substitutions per nucleotide) were identified in populations of black bears from Montana and Oregon. In contrast, very similar haplotypes occur in black bears across North America. This discordance of haplotype phylogeny and geographic distribution indicates that there has been maintenance of polymorphism and considerable gene flow throughout the history of the species. Intraspecific mitochondrial DNA sequence divergence in brown bears and polar bears is lower than in black bears. The two morphological forms of U. arctos, grizzly and coastal brown bears, are not in distinct mtDNA lineages. Interspecific comparisons indicate that brown bears and polar bears share similar mitochondrial DNA (0.023 base substitutions per nucleotide) which is quite divergent (0.078 base substitutions per nucleotide) from that of black bears. High mitochondrial DNA divergence within black bears and paraphyletic relationships of brown and polar bear mitochondrial DNA indicate that intraspecific variation across species' ranges should be considered in phylogenetic analyses of mitochondrial DNA.

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Genetic relationships of North American bears (Ursus) inferred from amplified fragment length polymorphisms and mitochondrial DNA sequences

Canadian Journal of Zoology ◽

10.1139/cjz-2013-0078 ◽

2013 ◽

Vol 91 (9) ◽

pp. 626-634 ◽

Cited By ~ 12

Author(s):

M.A. Cronin ◽

M.M. McDonough ◽

H.M. Huynh ◽

R.J. Baker

Keyword(s):

Mitochondrial Dna ◽

Fragment Length ◽

Genetic Relationships ◽

Black Bears ◽

Gene Pools ◽

Polar Bears ◽

Brown Bears ◽

Southeast Alaska ◽

Length Polymorphisms ◽

Amplified Fragment Length Polymorphisms

The three species of bears in North America, polar bears (Ursus maritimus Phipps, 1774), brown bears (Ursus arctos L., 1758), and black bears (Ursus americanus Pallas, 1780), have differentiated morphologies and nuclear and mitochondrial genomes. An exception is a paraphyletic mitochondrial DNA relationship and some nuclear gene lineages common to polar bears and a population of brown bears from islands in southeast Alaska. In this study, we quantified the genetic relationships of extant brown bears and black bears from Alaska and Montana, and polar bears from Alaska, with amplified fragment length polymorphisms (AFLP) and mtDNA cytochrome-b sequences. Bayesian cluster analyses of the AFLP data show each species is distinct. All brown bears, including those from the islands in southeast Alaska, cluster separately from polar bears, and black bears cluster separately from brown bears and polar bears. The mtDNA of polar bears and southeast Alaska island brown bears is paraphyletic as reported previously, but the species have different haplotypes. These data indicate that extant populations of brown bears and polar bears have separate nuclear and mitochondrial gene pools and are supported as species under the genetic species concept.

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Molecular Phylogeny and SNP Variation of Polar Bears (Ursus maritimus), Brown Bears (U. arctos), and Black Bears (U. americanus) Derived from Genome Sequences

Journal of Heredity ◽

10.1093/jhered/est133 ◽

2014 ◽

Vol 105 (3) ◽

pp. 312-323 ◽

Cited By ~ 14

Author(s):

Matthew A. Cronin ◽

Gonzalo Rincon ◽

Robert W. Meredith ◽

Michael D. MacNeil ◽

Alma Islas-Trejo ◽

...

Keyword(s):

Molecular Phylogeny ◽

Ursus Maritimus ◽

Black Bears ◽

Polar Bears ◽

Genome Sequences ◽

Brown Bears

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

Molecular Biology and Evolution ◽

10.1093/molbev/msy018 ◽

2018 ◽

Vol 35 (5) ◽

pp. 1120-1129 ◽

Cited By ~ 18

Author(s):

James A Cahill ◽

Peter D Heintzman ◽

Kelley Harris ◽

Matthew D Teasdale ◽

Joshua Kapp ◽

...

Keyword(s):

Ice Age ◽

Polar Bears ◽

Brown Bears ◽

Last Ice Age

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

10.1101/154773 ◽

2017 ◽

Author(s):

James A. Cahill ◽

Peter D. Heintzman ◽

Kelley Harris ◽

Matthew Teasdale ◽

Joshua Kapp ◽

...

Keyword(s):

Climate Change ◽

Polar Bear ◽

Ursus Arctos ◽

Brown Bear ◽

Ice Age ◽

Evolutionary Significance ◽

Polar Bears ◽

Brown Bears ◽

Last Ice Age ◽

Genomic Introgression

AbstractRecent 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 only 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 paleogenomes to reveal patterns of evolutionary change that are otherwise masked with only contemporary data.

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New insights into dietary management of polar bears ( Ursus maritimus ) and brown bears ( U. arctos )

Zoo Biology ◽

10.1002/zoo.21658 ◽

2021 ◽

Author(s):

Charles T. Robbins ◽

Troy N. Tollefson ◽

Karyn D. Rode ◽

Joy A. Erlenbach ◽

Amanda J. Ardente

Keyword(s):

Ursus Maritimus ◽

Dietary Management ◽

Polar Bears ◽

Brown Bears

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Phylogeography of Mitochondrial DNA Variation in Brown Bears and Polar Bears

Molecular Phylogenetics and Evolution ◽

10.1006/mpev.1999.0730 ◽

2000 ◽

Vol 15 (2) ◽

pp. 319-326 ◽

Cited By ~ 20

Author(s):

Gerald F. Shields ◽

Deborah Adams ◽

Gerald Garner ◽

Martine Labelle ◽

Jacy Pietsch ◽

...

Keyword(s):

Mitochondrial Dna ◽

Polar Bears ◽

Brown Bears ◽

Dna Variation

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Heart rate during hyperphagia differs between two bear species

Biology Letters ◽

10.1098/rsbl.2018.0681 ◽

2019 ◽

Vol 15 (1) ◽

pp. 20180681 ◽

Cited By ~ 2

Author(s):

Boris Fuchs ◽

Koji Yamazaki ◽

Alina L. Evans ◽

Toshio Tsubota ◽

Shinsuke Koike ◽

...

Keyword(s):

Heart Rate ◽

Ursus Arctos ◽

Brown Bear ◽

Black Bear ◽

Black Bears ◽

Brown Bears ◽

Fat Reserves ◽

Generalized Additive Mixed Models ◽

Additive Mixed Models ◽

Increased Activity

Hyperphagia is a critical part of the yearly cycle of bears when they gain fat reserves before entering hibernation. We used heart rate as a proxy to compare the metabolic rate between the Asian black bear ( Ursus thibetanus ) in Japan and the Eurasian brown bear ( Ursus arctos ) in Sweden from summer into hibernation. In the hyperphagic period, black bears feed on fat- and carbohydrate-rich hard masts whereas brown bears feed on sugar-rich berries. Availability of hard masts has quantitative and spatial annual fluctuations, which might require increased activity and result in intraspecific stress. Using generalized additive mixed models we analysed the differences in heart rate between the two species. Black bears had decreased heart rates during summer but had doubled heart rate values throughout the hyperphagic period compared to brown bears. This letter illustrates the different physiological consequences of seasonal differences in food availability in two species of the same genus dealing with the same phenological challenge.

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