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

Abstract

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

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

“…Still, not all island populations have been characterized genetically. Two paleoendemics have mixed support: the Dall Island black bear ( Ursus americanus pugnax ) and Sitka brown bear ( Ursus arctos sitkensis ; da Silva Coelho et al 2023). These subspecies are listed in both the paleoendemic and neoendemic categories but were only counted towards paleoendemic totals to avoid inflation of the total number of endemics.…”

“…Notably, 2 bear taxa originally described as paleoendemics in numerous early molecular studies were recently flagged as neoendemics. Mitogenomes from pre‐ and post‐LGM fossil black bears and brown bears from Dall and Coronation islands suggest replacement of Southeast Alaska bears by new arrivals occurred during the LGM but does not rule out post‐LGM genetic swamping of a refugial population or population contraction and genetic drift in endemic Southeast Alaska bears (da Silva Coelho et al 2023). Paleogenomics using ancient DNA, environmental DNA, or sedimentary DNA is an exciting new avenue for interpreting complex phylogeographic patterns in Southeast Alaska mammals (Bohmann et al 2014).…”

“…Combined with evidence of substantial species turnover before and after the LGM, their results suggest that the Shu'ká Káa cave site was covered by ice or snow during this period (Heaton and Grady 2003, Lesnek et al 2018). Until recently, no pre‐LGM fossils had been documented on the other outer islands of the Alexander Archipelago (da Silva Coelho et al 2023), although the presence of karst (landscapes where dissolving limestone bedrock forms an intricate network of caves, springs, and sinkholes) along the western edge suggests there may be other, unexplored caves in the area (Baichtal and Swanston 1996, Heaton 2002).…”

Ice age land bridges to continental islands: Repeated migration of the forest‐dwelling sable in northeastern Asia

“…Previous studies on the faunal assembly in northern island systems in response to climate changes and the formation of land bridges during glacial periods have been actively investigated primarily in the British Isles and Ireland, as well as the islands of the northwest coast of North America (e.g. Colella et al., 2021; da Silva Coelho et al., 2023; Kotlík et al., 2018; Montgomery et al., 2014; Shafer et al., 2010). Those studies often focused on the dynamics of glacier development during the Last Glacial, the presence of ice‐free refugia that allowed species to survive and the colonization process after the glacial period in the Holocene.…”

“…The SHSK may represent a good system for comparison with other continental island systems at high latitudes, including those in Europe and North America (e.g. Colella et al., 2021; da Silva Coelho et al., 2023; Kotlík et al., 2018; Montgomery et al., 2014; Shafer et al., 2010). The system offers more robust and variable insights into how cold‐adapted organisms have responded to climate changes in the Quaternary, and how this may continue into the future.…”