Late Pleistocene and early Holocene sea-level history and glacial retreat interpreted from shell-bearing marine deposits of southeastern Alaska, USA

Baichtal, James F.; Lesnek, Alia J.; Carlson, Risa J.; Schmuck, Nicholas; Smith, Jane; Landwehr, Dennis J.; Briner, Jason P.

doi:10.1130/ges02359.1

Cited by 11 publications

(8 citation statements)

References 83 publications

(121 reference statements)

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“…Hence, in the case of polar bears and brown bears, which have clearly demonstrated gene flow following their divergence (see below), the split time estimated using SMC++ is most likely underestimated, possibly associated instead with cessation of gene flow between the two lineages. Likewise, the ∼11.8-ka split time estimate for ABC-A and ABC-BC brown bears more likely reflects interpopulational gene flow termination accompanying fragmentation of Alexander Archipelago landmasses by sea-level rise at the end of the last Ice Age ( 32 ).…”

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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“…Recent studies based on cosmogenic exposure dating have demonstrated that areas in SE Alaska above sea level today were covered in ice during the local LGM (20–17 ka) and deglaciation began between ~16.3 to 15.1 ka along the coast (Lesnek et al, 2018, 2020; Walcott et al, 2022). Nevertheless, due to considerable sea‐level changes in the region (Baichtal et al, 2021; Bard et al, 1990; Shugar et al, 2014), areas that may now be submerged could have served as Pleistocene coastal refugia (Lesnek et al, 2020; Walcott et al, 2022), which could help explain the high level of endemism in the archipelago (MacDonald & Cook, 2007). For example, native bears in the region today appear to represent populations distinct from the mainland, suggesting long‐term isolation in the archipelago (Byun et al, 1997; Davison et al, 2011; MacDonald & Cook, 2007; Puckett et al, 2015; Talbot & Shields, 1996; Wooding & Ward, 1997).…”

Section: Discussionmentioning

confidence: 99%

“…After the LGM deglaciation, sea levels in the region varied and at time surpassed the modern sea level. During the early Holocene, sea levels on Prince of Wales Island were higher when compared to the northern islands (Baichtal et al, 2021). Furthermore, temperatures in the mid‐Holocene decreased resulting in an abrupt cooling event ~8.2 ka (Rohling & Pälike, 2005).…”

Section: Discussionmentioning

confidence: 99%

“…However, given the rapid sea-level rise following the glacial retreat in SE Alaska, it is possible that refugia were available in areas of the now-submerged continental shelf (Baichtal et al, 2021;Walcott et al, 2022) and that smaller species with small home ranges, such as Pacific marten (Colella et al, 2021)…”

Section: Con Clus Ionsmentioning

confidence: 99%

“…This regional difference in timing in deglaciation potentially created a migration route thousands of years earlier along the coast. Furthermore, sea levels during the last glaciation were considerably lower, exposing parts of the continental shelves, now submerged, that could have acted as ice age refugia (Baichtal et al, 2021; Walcott et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

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Ancient bears provide insights into Pleistocene ice age refugia in Southeast Alaska

et al. 2023

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During the Late Pleistocene, the Laurentide and Cordilleran Ice Sheets periodically covered much of North America, including portions of, or perhaps the entire, Alexander Archipelago located in Southeast (SE) Alaska. While the Laurentide Ice Sheet was at its maximum extent during the global last glacial maximum (LGM), a period that spanned ~26-19 thousand years ago (ka;Clark et al., 2009), the Pacific margin of the Cordilleran Ice Sheet only reached its greatest

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Phylogeography of mammals in Southeast Alaska and implications for management of the Tongass National Forest

Androski,

Wiens,

Cook

et al. 2024

J Wildl Manag

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Insular evolution on archipelagos generates a significant proportion of global biodiversity, yet islands are among the ecosystems most sensitive to accelerating anthropogenic disturbance, introductions of non‐native species, and emerging pathogens, among other conservation challenges. The Alexander and Haida Gwaii archipelagos along North America's North Pacific Coast support a disproportionate number of endemic taxa compared to other high‐latitude terrestrial ecosystems. In this region, endemics in Canada are explicitly protected, but in the United States, endemics have been operationally ignored. We reviewed regional research on terrestrial mammals and endemics from 2000–2022 to guide wildlife management. Elevated regional endemism is due to a combination of deep and shallow temporal processes (i.e., long‐term refugial isolation vs. recent colonization). With adequate sampling, genomic analyses are well‐suited to identifying nuanced patterns of divergence and endemism, thereby facilitating a deeper understanding of regional diversity. We identified 18 mammalian endemics in Southeast Alaska, USA, at varying taxonomic scales, but research effort has significant taxonomic biases and sampling infrastructure remains inadequate. Of the 66 terrestrial and aquatic mammal species in Southeast Alaska, only 55% are represented by ≥10 archived samples over the last 2 decades. Across taxa, major spatial and temporal sampling gaps limit interpretations of wildlife responses to changing environmental conditions. The Tongass National Forest is spread across an island archipelago, and climate change is projected to have disproportionate impacts on island endemics worldwide. In this case, the United States Forest Service is not closely monitoring endemic taxa, as was required by the Tongass Land Management Plan in 1997. Our review underscores a need for increased consideration of how endemism can be incorporated into land and wildlife management across the Alexander Archipelago. Moving forward, we encourage state and federal agencies, Indigenous communities, and international collaborators to continue to partner with natural history biorepositories to ensure strategic wildlife sampling infrastructure is built and made accessible to the broader scientific community as part of the land management process.

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Late Pleistocene and early Holocene sea-level history and glacial retreat interpreted from shell-bearing marine deposits of southeastern Alaska, USA

Cited by 11 publications

References 83 publications

Insights into bear evolution from a Pleistocene polar bear genome

Insights into bear evolution from a Pleistocene polar bear genome

Ancient bears provide insights into Pleistocene ice age refugia in Southeast Alaska

Phylogeography of mammals in Southeast Alaska and implications for management of the Tongass National Forest

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