DISSERTATION RESEARCH: Investigating the Joint Effects of Phylogeny and Adaptation on Phenotypic Variation at a Continental Scale (Serpentes:Thamnophis)

地方适应是地理上可变的物种的一个标志，它们分布广泛，跨越了基因流动的地理障碍。确定这些局部适应所依赖的潜在种群结构是进化生物学的核心目标。然而，进化历史对当代种群结构推断的影响在很大程度上尚未被探索。本研究的目的是研究进化历史对区域和大陆尺度种群间遗传和形态变异的影响。本研究的经验数据和结果将作为在学术和公共环境中教授进化，特别是遗传漂变的模型。广泛分布的生物之间广泛的表型变异往往使分类关系的确定复杂化。普通束带蛇Thamnophis sirtalis的分布范围横跨整个北美，不包括墨西哥和西南沙漠。十二T sirtalis亚种目前通过颜色图案识别和定义。其中一个亚种，T. S。pickeringii，共同出现的两个分布不太广泛的同源物（T。elegans和T.在太平洋西北部横跨圣胡安群岛。直到约20，000年前，该地区经历了多次更新世冰川事件，之后植物群和动物群将岛屿从邻近的大陆避难所中分离出来。本项目旨在通过比较已知人口统计学历史的模拟数据和来自两个实证研究系统的基因组数据来研究进化历史和当代种群变化之间的关系：1）年轻的圣胡安群岛Thamnophis物种组合，2）所有Thamnophis sirtalis亚种的大陆尺度采样。这两个系统发生在多个已知的更新世避难所附近，并跨越地理障碍，为其他北美植物群和巨型动物的基因流，但目前还不清楚是否一个多面手外温动物将显示在以前的地理研究中观察到的模式。利用基因组数据，该项目将测试1）T。Sirtalis亚种的命名（以及表型）代表了独特的进化谱系; Sirtalis发生在沿着已知的或新的基因流动的障碍，或3）不同亚种间的历史性隔离和非均匀选择力的组合效应产生与表型变异不一致的信号。

Local adaptation is a hallmark of geographically variable species with wide distributions that span geographic barriers to gene flow. Determining the underlying population structure upon which to place these local adaptations is a central objective in evolutionary biology. However, the impact of evolutionary history on inference of contemporary population structure has been largely unexplored. This research aims to examine the effects of evolutionary history on genetic and morphological variation among populations at regional and continental scales. Empirical data and the results from this study will serve as a model for teaching evolution, specifically genetic drift, in both academic and public settings. Extensive phenotypic variation between widespread organisms often complicates determination of taxonomic relationships. The range of the common garter snake Thamnophis sirtalis spans all of North America, excluding Mexico and the desert southwest. Twelve T. sirtalis subspecies are currently recognized and defined by color patterning. One of these subspecies, T.s. pickeringii, co-occurs with two less widely distributed congeners (T. elegans and T. ordinoides) in the Pacific Northwest across the San Juan Archipelago. This region was subject to multiple Pleistocene glaciation events up until ~20,000 years ago, after which flora and fauna recolonized the islands from neighboring mainland refugia. This project aims to investigate the relationship between evolutionary history and contemporary population variation by comparing simulated data of known demographic histories to genomic data from two empirical study systems: 1) the young San Juan Archipelago Thamnophis species assemblage, 2) a continental-scale sampling of all Thamnophis sirtalis subspecies. These two systems occur in proximity to multiple known Pleistocene refugia and across geographic barriers to gene flow for other North American flora and megafauna, but it is unclear whether a generalist ectotherm will show the patterns observed in previous phylogeographic studies. Using genomic data, this project will test whether 1) T. sirtalis subspecies designations (and therefore phenotypes) represent unique evolutionary lineages, 2) distinct evolutionary lineages within T. sirtalis occur along known or novel barriers to gene flow, or 3) the combined effects of historical vicariance and non-uniform selective forces across different subspecies produce a signal discordant with phenotypic variation.