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部。数千年来，这些冰盖阻碍了亚洲和美洲之间动植物的流动。许多物种灭绝，其他物种被迫进入孤立的无冰地区（避难所），位于冰盖的北部和南部。今天好吗?许多动植物携带着冰河时代和这种避难隔离的遗传遗产，但人们并不完全清楚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消退后的运动的。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是很重要的。冰川覆盖的确切范围和时间也鲜为人知，北美西北海岸的岛屿被假设躲过了冰河时期的冰川作用。这意味着在过去的地质时期，它们可能是动植物通过的一个独特的瓶颈，甚至可能是人类进入美洲的早期门户。这项研究的目的是提高对植物、动物甚至人类迁徙的关键地区的认识：阿拉斯加东南部。我们正在通过收集岩石样本来测试阿拉斯加东南部沿海地区没有被冰覆盖的假设，这些岩石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骨骼化石中的DNA。这项研究项目为了解阿拉斯加东南部标志性哺乳动物的历史及其环境条件提供了急需的见解。在末次盛冰期，北太平洋沿岸最西端的覆盖范围和时间知之甚少，留下了关于气候变化对生物多样性和冰川后美洲殖民的影响的基本问题。各种各样的证据表明，在最后一个冰河时期，存在一条可行的、无冰的沿海走廊，可能在新旧世界之间的生物交流中发挥了重要作用。该项目旨在成为支持沿海难民的假设的最终测试。我们利用宇宙核素暴露测年和古成因分析的尖端技术，对阿拉斯加东南部一组无与伦比的洞穴化石进行了分析，以实现两个关键目标：(1)直接确定阿拉斯加东南部在LGM期间是否为陆生哺乳动物提供了无冰的栖息地；(2)限制LGM期间西科迪勒兰冰盖的范围和历史。无论这个假设是否得到支持，这个高度跨学科的项目将产生具有高影响力的结果，并对跨越地质、生物、古生物学和考古科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键问题，包括冰河时期阿拉斯加东南部的动态冰川条件、哺乳动物岛屿种群的生物地理历史，以及冰河时代后美洲人类迁徙通道的结构和时间。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与相关主题的链接，如环境变化和人类迁移，以及(c)在阿拉斯加东南部组织一个研讨会，包括公共和K-12外展部分，以综合过去和当前的研究，并关注研究与自然资源管理之间的交集。以及未来气候预测对整个群岛生物系统的影响。该奖项反映了美国国家科学基金会的法定使命，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.