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Ancient bears provide insights into Pleistocene ice age refugia in Southeast Alaska
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  • Flavio Augusto Da Silva Coelho ,
  • Stephanie Gill,
  • Crystal Tomlin,
  • Marilena Papavassiliou,
  • Sean Farley,
  • Joseph Cook,
  • Sarah Sonsthagen,
  • George Sage,
  • Timothy Heaton,
  • Sandra Talbot,
  • Charlotte Lindqvist
Flavio Augusto Da Silva Coelho
University at Buffalo
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Stephanie Gill
University at Buffalo
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Crystal Tomlin
University at Buffalo
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Marilena Papavassiliou
University at Buffalo
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Sean Farley
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Joseph Cook
University of New Mexico
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Sarah Sonsthagen
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George Sage
US Geological Survey Alaska Region
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Timothy Heaton
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Sandra Talbot
US Geological Survey Alaska Region
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Charlotte Lindqvist
University at Buffalo

Corresponding Author:cl243@buffalo.edu

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Abstract

During the Late Pleistocene, major parts of North America were periodically covered by ice sheets. However, there are still open questions about whether ice-free refugia were present in the Alexander Archipelago along the Southeast (SE) Alaska coast during the Last Glacial Maximum (LGM). Numerous subfossils have been recovered from caves in SE Alaska, including American black (Ursus americanus) and brown (U. arctos) bears, which today are found in the Alexander Archipelago but are genetically distinct from mainland bear populations. Hence, these bear species offer an ideal system to investigate long-term occupation, potential refugial survival, and lineage turnover. Here we present genetic analyses based on 99 new complete mitochondrial genomes from ancient and modern brown and black bears spanning the last ~45,000 years. Black bears form two SE Alaskan subclades that diverged >100,00 years ago, one preglacial and one postglacial. All postglacial ancient brown bears are closely related to modern bears in the archipelago, while a single preglacial brown bear is found in a distantly related clade. A hiatus in the bear subfossil record around the LGM and the deep split of their pre- and post-glacial subclades fail to support a hypothesis of continuous occupancy in SE Alaska throughout the LGM for either species. Our results are consistent with an absence of refugia along the SE Alaska coast, but indicate that vegetation quickly expanded after deglaciation, allowing bears to recolonize the area after a short-lived LGM peak.
09 Jan 2023Submitted to Molecular Ecology
10 Jan 2023Submission Checks Completed
10 Jan 2023Assigned to Editor
10 Jan 2023Review(s) Completed, Editorial Evaluation Pending
18 Jan 2023Reviewer(s) Assigned
27 Feb 2023Editorial Decision: Revise Minor
28 Mar 20231st Revision Received
29 Mar 2023Submission Checks Completed
29 Mar 2023Assigned to Editor
29 Mar 2023Review(s) Completed, Editorial Evaluation Pending
12 Apr 2023Editorial Decision: Accept