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

During the Late Pleistocene, major parts of North America were periodically covered by ice sheets. However, there are still 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..., ,

更新世晚期（Late Pleistocene），北美大陆大部分区域曾周期性被冰盖覆盖。然而，针对阿拉斯加东南部沿岸的亚历山大群岛（Alexander Archipelago）在末次盛冰期（Last Glacial Maximum，简称LGM）期间是否存在无冰避难所，学界仍存在诸多疑问。科研人员已从阿拉斯加东南部的洞穴中发掘出大量亚化石标本，其中包括美洲黑熊（Ursus americanus）与棕熊（Ursus arctos，缩写U. arctos）；现今该群岛仍有这两种熊类分布，但它们与大陆熊种群在遗传层面存在显著差异。因此，这两种熊类为研究长期种群定居、潜在避难所存续以及谱系更替提供了理想的研究体系。本研究基于覆盖过去约4.5万年的99条全新完整线粒体基因组，对古代与现代棕熊、黑熊开展遗传分析。黑熊演化出两个阿拉斯加东南部的亚支系，二者分化时间早于10万年，其中一支形成于冰期前，另一支形成于冰期后。所有冰期后的古代棕熊均与……密切相关。