Ancient bears provide insights into Pleistocene ice age refugia in Southeast Alaska
Ancient bears provide insights into Pleistocene ice age refugia in Southeast Alaska
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DOI：
10.1111/mec.16960
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发表时间：
2023-04-25
影响因子：
4.9
通讯作者：
Lindqvist, Charlotte
中科院分区：
文献类型：
--
作者：
da Silva Coelho, Flavio Augusto;Gill, Stephanie;Lindqvist, Charlotte
在晚更新世，北美的大部分地区周期性地被冰原覆盖。然而，在末次盛冰期（LGM）期间，沿着阿拉斯加东南海岸的亚历山大群岛是否存在无冰避难所仍然存在疑问。从阿拉斯加东南部的洞穴中发现了许多亚化石，包括美洲黑熊（Ursus americanus）和棕熊（U. arctos），它们今天在亚历山大群岛被发现，但在基因上与大陆的熊种群不同。因此，这些熊种提供了一个理想的系统来研究长期占领，潜在的避难生存和血统更替。在这里，我们提出了基于古代和现代棕熊和黑熊的99个新的完整线粒体基因组的遗传分析，这些基因组跨越了近45,000年。黑熊形成了两个东南阿拉斯加分支，一个是冰期前分支，另一个是冰期后分支，它们在大约10万年前分化。所有冰期后的古棕熊都与群岛上的现代棕熊密切相关，而在一个远亲分支中发现了一只冰期前棕熊。北极熊亚化石记录的中断以及它们在冰期前和冰期后亚枝的深度分裂，无法支持两个物种在整个冰期期间连续占据阿拉斯加东南部的假设。我们的结果与阿拉斯加东南海岸缺乏避难所的情况一致，但表明冰川消退后植被迅速扩大，使熊在短暂的LGM高峰后重新定居该地区。
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 similar to 45,000 years. Black bears form two SE Alaskan subclades, one preglacial and another postglacial, that diverged >100,000 years ago. All postglacial ancient brown bears are closely related to modern brown 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 postglacial 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.