Testing the Refugia Hypothesis in Southeast Alaska Using Paleogenetics and Glacial Chronology

在最后一个冰河时期，巨大的冰盖覆盖了北美北方。这些冰盖阻挡了亚洲和美洲之间动植物的移动数千年。许多物种灭绝，其他物种被迫进入冰盖北部和南部的孤立的无冰区域（避难所）。今天吗？南极洲的动植物携带着冰河时代和这种避难所隔离的遗传遗产，但人们并不完全知道它是如何影响和塑造许多物种过去的轨迹以及它们在冰盖退缩后的运动的。然而，这些知识对于了解植物和动物在未来如何应对环境变化非常重要。冰层覆盖的确切范围和时间也知之甚少，北美西北海岸沿着的岛屿被假设为躲过了冰河时代的冰川。这意味着它们可能是地质学过去动植物通行的独特瓶颈，甚至可能是美洲人类早期的门户。这项研究旨在提高对植物，动物甚至人类迁徙的关键地区的认识：阿拉斯加东南部。我们正在测试一个假设，即阿拉斯加东南部的沿海地区通过收集岩石样本来逃避冰盖，这些样本将告诉我们景观是否被冰覆盖，以及何时变得无冰。我们正在研究保存在数千年前死亡的哺乳动物化石骨骼中的DNA。这项研究项目提供了急需的见解标志性的哺乳动物的历史和他们的环境条件在阿拉斯加东南部。最西端的范围和时间的冰盖沿着北太平洋海岸在末次冰盛期知之甚少，留下悬而未决的基本问题，气候变化对生物多样性和冰后期殖民美洲的影响。各种证据表明，存在一个可行的，无冰的沿海走廊，可能在最后一个冰河时代的旧世界和新世界之间的生物交换中发挥了重要作用。该项目旨在对支持沿海避难所的假设进行最终检验。我们正在利用尖端技术在宇宙成因核素暴露测年和古遗传学分析的无与伦比的化石收集在阿拉斯加东南部的洞穴，以实现两个关键目标：（1）直接确定如果阿拉斯加东南部提供无冰避难所的陆生哺乳动物在末次冰期，（2）约束的范围和历史的西部科迪勒拉冰盖在末次冰期。无论该假设是否得到支持，这个高度跨学科的项目都将提供具有高度影响力的结果，并对跨越地质学，生物学，古生物学和考古学的许多不同学科产生重要影响。研究结果将回答一系列关于冰河时期阿拉斯加东南部动态冰川条件的关键问题，哺乳动物岛屿种群的地理历史，以及美洲冰后期人口的可用迁移走廊的配置和时间。这项研究将（a）为研究生和本科生提供培训机会，（B）通过网站广泛传播结果和相关主题的链接，如环境变化和人类移民，以及（c）在阿拉斯加东南部组织一个研讨会，由公众和K-12外展部分综合过去和当前的研究，并侧重于研究，自然资源管理，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Vast ice sheets covered northern North America during the last Ice Age. These ice sheets blocked movements of plants and animals between Asia and the Americas for many thousands of years. Many species died out and others were forced into isolated, ice-free areas (refugia) north and south of the ice sheets. Today?s plants and animals carry the genetic legacy of the Ice Age and this refugial isolation, but it is not completely known how it impacted and shaped the past trajectory of many species and their movements following the retreat of the ice sheets. Yet, such knowledge is important for understanding how plants and animals may respond in the future due to environmental changes. The exact extent and timing of ice coverage is also poorly known, and islands along the northwestern coast of North America are hypothesized to have escaped Ice Age glaciation. This means they could have acted as a unique bottleneck for the passage of plants and animals in the geologic past, and even perhaps that they were an early gateway for the peopling of the Americas. This research is aimed at improving knowledge of a critical region for plant, animal, and even human migration: Southeast Alaska. We are testing the hypothesis that coastal areas in Southeast Alaska escaped ice cover by collecting rock samples that will tell us whether or not landscapes were covered by ice and when they became ice-free. We are studying the DNA preserved in fossil bones from mammals that died thousands of years ago. This research project is providing much needed insights into the history of iconic mammals and their environmental conditions in Southeast Alaska.The westernmost extent and timing of ice cover along the North Pacific Coast during the Last Glacial Maximum is poorly known, leaving unanswered fundamental questions about the impact of climatic change on biotic diversification and postglacial colonization of the Americas. Various lines of evidence point to the existence of a viable, ice-free coastal corridor that may have played an important role for biotic exchange between the Old and New Worlds during the last Ice Age. This project is designed to be the definitive test of the hypothesis in support of coastal refugia. We are taking advantage of cutting-edge technologies in cosmogenic nuclide exposure dating and paleogenetic analyses of an unparalleled fossil collection from caves in SE Alaska to achieve two key objectives: (1) directly determine if SE Alaska provided ice-free refugia for terrestrial mammals during the LGM, and (2) constrain the extent and history of the western Cordilleran Ice Sheet during the LGM. Whether the hypothesis is supported or not, this highly interdisciplinary project will deliver results with high impact and have important implications for many different disciplines spanning the geological, biological, paleontological, and archeological sciences. The results will answer a broad range of key questions about the dynamic glacial conditions of SE Alaska during the Ice Age, biogeographic history of mammal island populations, and the configuration and timing of an available migration corridor for the postglacial peopling of the Americas. This research will (a) provide training opportunities for graduate and undergraduate students, (b) broadly disseminate results and links to associated relevant topics, such as environmental change and human migration, through a website, and (c) organize a workshop in SE Alaska with public and K-12 outreach components to synthesize past and current research and focus on the intersection between research, natural resource management, and the impact of future climate projections on biotic systems across the archipelago.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.