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

在上一个冰河时代，北美北部覆盖着巨大的冰盖。数千年来，这些冰盖阻碍了动植物在亚洲和美洲之间的流动。许多物种灭绝，其他物种被迫进入冰盖北部和南部与世隔绝的无冰地区(避难所)。今天？S的动植物携带着冰河时代和这种避难所与世隔绝的遗传遗产，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消退后的运动。然而，这些知识对于理解植物和动物未来可能因环境变化而做出的反应是重要的。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认为已经逃过了冰河时代的冰川。这意味着，在过去的地质历史中，它们可能是动植物通过的独特瓶颈，甚至可能是美洲人民早期的门户。这项研究旨在提高对动植物甚至人类迁徙的关键地区--阿拉斯加东南部的认识。我们正在通过收集岩石样本来检验阿拉斯加东南部沿海地区没有被冰覆盖的假设，这些样本将告诉我们风景是否被冰覆盖，以及它们何时变得不再结冰。我们正在研究保存在几千年前死亡的哺乳动物骨骼化石中的DNA。这一研究项目为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亟需的见解。上一次冰盛期北太平洋海岸最西端的冰盖范围和时间鲜为人知，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根本问题。各种证据表明，存在一条可行的、无冰的沿海走廊，这条走廊可能在上一次冰河时代新旧大陆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。我们正在利用来自阿拉斯加东南部洞穴的无与伦比的化石收集的宇宙成因核素暴露测年和古成因分析方面的尖端技术来实现两个关键目标：(1)直接确定阿拉斯加东南部是否在末次冰盖期间为陆地哺乳动物提供了无冰避难所，(2)限制了末次冰盖期间科迪勒西部冰盖的范围和历史。无论这一假设是否得到支持，这个高度跨学科的项目都将产生影响巨大的成果，并对横跨地质、生物、古生物和考古科学的许多不同学科产生重要影响。这些结果将回答一系列关键问题，包括冰河时代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，以及为美洲冰后期人口提供的可用迁徙走廊的配置和时机。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，如环境变化和人类迁徙，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外联部分，以综合过去和当前的研究，并重点关注研究、自然资源管理和未来气候预测对整个群岛生物系统的影响之间的交集。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.