Dissertation Research: A 2400-Year Genetic Record of Thomomys talpoides During Holocene Climate Change

韦恩9801704由于气候温暖，自然选择可以有利于种群中对更温暖的温度有更好适应能力的个体；因此，种群的特征将随着时间的推移而改变。或者，来自较温暖地区的移民可能会提供更适合的个体，而原来的居民可能不太适合。是迁徙还是自然选择推动了种群的进化变化，这是进化生物学中的一个基本问题。这场辩论也与对全球变暖的担忧有关，因为栖息地的碎片化极大地限制了迁徙提供适当适应的个体的能力。有人提议进行一项研究，以评估迁徙或基因隔离是否影响了过去3000年来袖珍地鼠(Thomomys Talpoides)种群的进化变化，这些袋鼠种群保存在黄石国家公园拉马尔洞穴的袋鼠幼虫中。在此期间，种群的形态发生了变化，以响应温度的变化。为了评估这种变化是否是在基因隔离中发生的，研究人员将使用新的分子遗传学技术，这种技术允许在外来线粒体DNA序列出现时检测到迁移。初步结果显示，在拉马尔洞穴附近采集的古代和现代样本具有周围地区所没有的线粒体细胞色素b序列，这表明该种群持续存在，3000年来没有接收过来自其他地方的女性迁徙。调查人员将扩大对拉马尔洞穴化石的分析，以包括对沉积物中的地层水平进行更广泛的采样。这项分析应该明确地确定拉马尔洞穴的隔离程度，并可能是第一个直接评估在进化上重要的时间段内种群的时间隔离。结果将与关于人口对气候变化的反应有多快以及通过什么机制的辩论相关。

Wayne 9801704 As climates warm, natural selection can favor individuals within a population that have superior adaptations for the warmer temperatures; as a result the population will change in character over time. Alternatively, migration from warmer areas may supply more appropriately adapted individuals and the original inhabitants may be less fit. Whether migration or natural selection on pre-existing variation fuels evolutionary change in populations is a fundamental question in evolutionary biology. The debate also is relevant to concerns about global warming as habitat fragmentation greatly limits the ability of migration to supply appropriately adapted individuals. Research is proposed to assess if migration or genetic isolation has influenced evolutionary change over the last 3000 years in a population of pocket gophers (Thomomys talpoides) that were preserved in packrat middens in Lamar Cave in Yellowstone National Park. During this period, morphologic change has occurred in the population in response to changes in temperature. To assess if this change has occurred in genetic isolation, the investigators will use new molecular genetic techniques that allow for migration to be detected as the appearance of foreign mitochondrial DNA sequences. Initial results show that ancient and modern samples collected near Lamar Cave share mitochondrial cytochrome b sequences that are absent from surrounding localities suggesting that the population persisted and did not receive female migrants from elsewhere for 3000 years. The investigators will extend this analysis of Lamar Cave fossils to include a more extensive sampling of stratigraphic levels within the deposit. This analysis should definitively establish the degree of isolation of Lamar Cave and may be the first that directly assesses temporal isolation of a population over evolutionarily significant time periods. Results will be relevant to the debate about how rapidly and by which mechanisms populations respond to climate chang e.