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

这是由加州大学洛杉矶分校和圣克鲁斯分校、阿拉斯加费尔班克斯大学和史密森学会的主要研究人员合作提出的一项建议。该奖项将由生物学部人口生态项目和北极自然科学项目资助。未来气候变化对北极物种的影响是一个很大的不确定性和令人担忧的来源，自上一个冰期以来，北极经历了巨大的气候变化。因此，研究生物对先前扰动的反应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，主要研究人员将根据白令陆桥三个地方的样本，研究贫瘠的北美驯鹿和一种已灭绝的北极马的遗传多样性历史。从永久冻土层中发现的骨头是古代DNA的极好来源，可以追溯到14摄氏度。最近的两项基因研究分析了埋在北极永久冻土中的棕熊骨骼的DNA序列，发现了过去4万年中三个不同的基因时代的证据，每个时代都以种群更替事件为标志。这些以前未被认识到的时代是通过来自3.5万ka BP以上标本的DNA序列、21至10 ka BP标本的DNA序列以及来自现代人群的序列来确定的。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用与威斯康星中部间冰期、末次极大期和全新世有关的气候变化来解释。然而，古环境数据稀少且不确定，这些遗传模式尚未在其他物种中得到验证。作为食草动物，驯鹿和马代表着与棕熊不同的营养水平，这两个物种专门消耗不同类型的植被（分别是苔原和草草原）。研究人员预测，整个生态系统的气候变化对大型食草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更替同步循环。这些变化应该与之前在棕熊和灰狼身上观察到的变化一致。类似的区域或地方生态系统变化将表现为局部地区的同步循环。相反，两个物种基因变化的不同模式意味着苔原/森林优势的变化或新的物种特异性竞争对手和/或捕食者的存在。无论哪种情况，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。首席研究员将通过对三个地点的三种独立的环境替代物的研究，确定环境变化的具体因素，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剖面。这些概况将作为区域气候变化的代理，并允许推断动物饮食的变化。其次，他们将利用植食动物牙齿内嵌的植物材料来重建两种植食动物利用的当地植物区系变化。第三，利用现有的花粉记录和其他古环境数据，重建遗传转换期间的区域植被和一般气候。重要的是，他们将对白令陆桥上两种食草动物的300块骨头进行14C测年，这将把他们的结果放在一个时间背景下，以便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，这项研究将培养一批学生进行尖端的跨学科研究，包括遗传学、花粉分析、高分辨率放射性碳定年和稳定同位素生态学。

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.