Collaborative Research: Analysis of a Forty Thousand Year Record of Genetic and Environmental Change in the Arctic

这是加州大学洛杉矶分校和圣克鲁斯分校、阿拉斯加大学费尔班克斯分校和史密森学会的首席研究人员共同提出的建议。该奖项将由生物学和北极自然科学项目部的种群生态学项目提供资金支持。未来气候变化对北极物种的影响是一个极不确定和令人关切的问题，自上一次冰川周期以来，北极经历了气候的巨大变化。因此，对之前扰动的生物反应的研究可能为未来全球气候变化如何改变北极物种的遗传多样性、饮食和地理范围提供重要证据。利用DNA分析，首席调查人员将基于来自贝林贾三个地区的样本，研究贫瘠的驯鹿和一种已灭绝的北极马的遗传多样性历史。从永久冻土中发现的骨骼是古代DNA的极好来源，可以确定14C的年代。最近的两项基因研究分析了埋藏在北极永久冻土中的棕熊骨骼的DNA序列，发现了过去4万年来三个不同的遗传时代的证据，每个时代都以种群更替事件为标志。这些以前未被识别的新纪元是由35000(Ka)BP以上的标本、21至10ka BP的标本的DNA序列以及现代种群的序列定义的。古气候研究提供的证据表明，这些时期之间的人口流动可以通过与威斯康星州中期、最后一次冰川高峰期和全新世有关的气候变化来解释。然而，古环境数据是稀疏和不确定的，这些遗传模式还没有在其他物种中得到验证。作为食草动物，驯鹿和马代表着不同于棕熊的营养水平，这两个物种都专门消耗不同类型的植被(分别是苔原和草原区)。首席调查人员预测，生态系统范围的气候变化对大型草食动物及其捕食者不利，将导致这两个物种在所有三个地区的种群周转同步循环。这些变化应该与之前在棕熊和灰狼身上观察到的变化相匹配。类似的区域或地方生态系统变化将在地方的子集中表现为同步循环。相反，这两个物种不同的遗传变化模式将意味着冻土带/森林优势的改变或新物种特有竞争对手和/或捕食者的存在。无论是哪种情况，这项研究都将为气候变化对北极哺乳动物遗传多样性的潜在作用提供重要证据。首席调查员将通过研究所有三个地点的三个独立类别的环境替代品，确定环境变化的具体原因，并重建过去的北极环境。首先，他们将为DNA研究中分析的遗骸开发稳定的同位素图谱。这些图谱将作为区域气候变化的替代指标，并允许推断动物饮食的变化。其次，他们将使用植入食草动物牙齿中的植物材料来重建这两种食草动物利用的当地植物群的变化。第三，他们将利用现有的花粉记录和其他古环境数据来重建观察到的基因更替期间的区域植被和一般气候。重要的是，他们将对贝林吉亚地区这两个食草动物物种的300块骨骼进行14C测年，这将把他们的结果放在一个时间背景下，从而与现有的气候数据相结合。边界影响：随着新技术和新问题的出现，所有数据将被置于公共领域，以供未来研究。此外，这项研究还将培训一批学生从事前沿、跨学科的研究，包括遗传学、花粉分析、高分辨率放射性碳测年和稳定的同位素生态学。

This is a collaborative proposal by Principal Investigators at the University of California-Los Angles and Santa Cruz, University of Alaska-Fairbanks, and the Smithsonian Institution. This award will be supported with funds from the Population Ecology Program in the Division of Biology and Arctic Natural Sciences Program. The effects of future climatic change on arctic species are a source of great uncertainty and concern and the Arctic has experienced large changes in climate since the last glacial cycle. Therefore, the study of biotic responses to the previous perturbations may provide important evidence of how the genetic diversity, diet, and geographic range of arctic species will be altered by future global climate change. Using DNA analysis, the Principal Investigators will examine the history of genetic diversity in the barren-ground caribou and an extinct arctic horse based on samples from three localities in Beringia. Bones recovered from the permafrost are an excellent source of ancient DNA and can be 14C dated. Two recent genetic studies analyzed DNA sequences from brown bear bones entombed in the arctic permafrost and found evidence of three distinct genetic epochs over the past 40,000 years, each marked by population turnover events. These previously unrecognized epochs are defined by DNA sequences from specimens older than 35 thousand (ka) BP, from specimens 21 to 10 ka BP, and by sequences from modern populations. Paleoclimate studies provide evidence that population turnover between these periods may be explained by changing climate relating to the mid-Wisconsin interstadial, the last glacial maximum, and the Holocene. However, paleoenvironmental data are sparse and inconclusive and these genetic patterns have not been verified in other species. As herbivores, caribou, and horses represent a different trophic level from brown bears and both species specialize on consuming different types of vegetation (tundra and grass-steppe, respectively). The Principal Investigators predict that ecosystem-wide climate change unfavorable to large herbivores and their predators would result in synchronous cycles of population turnover in both species across all three localities. These changes should match those previously observed in the brown bear and gray wolf. Similar regional or local ecosystem change would be manifest as synchronous cycles in a subset of localities. In contrast, differing patterns of genetic change in the two species would imply a change in the tundra/forest dominance or the presence of new species-specific competitors and/or predators. In either case, the study will provide important evidence of the potential role of climate change on genetic diversity in arctic mammals. The Principal Investigators will identify specific agents of environmental change and reconstruct past arctic environments through study of three independent classes of environmental surrogates in all three locations. First, they will develop stable isotope profiles for the remains analyzed in the DNA study. These profiles will serve as proxies for regional climate change and allow changing animal diets to be inferred. Second, they will use plant material imbedded in the teeth of herbivores to reconstruct the changes in local flora utilized by the two herbivores. Third, they will utilize existing pollen records and other paleoenvironmental data to reconstruct the regional vegetation and general climate during periods of observed genetic turnover. Importantly, they will 14C date 300 bones from the two herbivore species across Beringia which will place their results in a temporal context that will allow integration with existing climate data. Boarder Impact: All data will be placed in the public domain for future studies as new techniques and questions arise. Additionally, this research will train a group of students in cutting-edge, interdisciplinary research that incorporates genetics, pollen analysis, high-resolution radiocarbon dating, and stable isotope ecology.