Dissertation Research: Historical Biogeography of the North American Deserts: A Comparative Phylogeographic Approach

犹他州立大学的约瑟夫·门德尔松博士和丹尼尔·马尔卡希先生获得了一笔拨款，用于对北美西部的三种爬行动物进行比较系统地理学研究。系统地理学研究估计种内关系，通常基于线粒体DNA （mtDNA）序列。这些种群水平的系统发育——亲缘关系的分支图——然后被覆盖在物种的地理分布上。然后可以对物种的起源、扩散和随后的分裂进行推断，同时还可以对基因流动、种群水平的相互作用和遗传多样性进行估计。系统地理学是生物地理学中一种新兴的研究方法，其研究往往集中在一个物种上。在这项研究中，作者比较了三种分布广泛、亲缘关系较远的爬行动物（夜蛇、侧斑蜥蜴和沙漠刺蜥蜴）的个体系统地理学。这些爬行动物遍布北美西部所有的沙漠和其他主要的生物地理区域。对每个物种的系统地理学假设进行比较和测试，以确定这些生物地理区域的一致性，假设这些区域的形成本身影响了每个独立群体内的基因流动、遗传多样性和进化。系统地理学研究为研究生活史特征提供了一个进化框架。关于本研究中蜥蜴物种的体型和产卵量的比较，有大量的文献存在。在这些物种中提供一个系统发育假说，可以从进化的角度来看待这些特征。对广泛分布的常见物种的比较系统地理学研究也为评估这些物种的遗传多样性模式提供了一个框架。本研究中物种的地理分布范围包括整个美国西部和墨西哥北部，包括科罗拉多州西部和华盛顿州南部的几乎所有国家公园。这项研究将为指导该地区的保护工作提供必要的数据。

A grant has been awarded to Dr. Joseph Mendelson and Mr. Daniel Mulcahy at Utah State University to conduct a comparative phylogeographic study among three reptile species in western North America. Phylogeographic studies estimate within-species relationships, generally based on mitochondrial DNA (mtDNA) sequences. These population-level phylogenies-branching diagrams of relatedness-are then overlain on the geographic distribution of the species. Inferences can then be made on the origin, dispersal, and subsequent fragmentation of the species, along with estimates of gene flow, population level interactions, and genetic diversity. As a recently developed technique in biogeography, phylogeographic studies tend to focus on one species at a time. In this study, the authors compare individual phylogeographies among three widespread, distantly related reptile species (Night snake, Side-blotched lizard, and Desert Spiny Lizard). These reptiles occur throughout all the deserts and other major biogeographic regions of western North America. Phylogeographic hypotheses for each species are compared and tested for congruence across these biogeographic regions, with the hypothesis that the formation of these regions themselves influenced gene flow, genetic diversity and evolution within each independent group. Phylogeographic studies provide an evolutionary framework for studying life-history traits. A wealth of literature exists on the comparisons of body size, and clutch sizes in the lizard species of this study. Providing a phylogenetic hypothesis within these species allows for an evolutionary perspective of such traits. Comparative phylogeographic studies on widespread-common species also provide a framework for assessing patterns of genetic diversity within these species. The geographic range of the species in this study encompasses the entire western United States and northern Mexico, including virtually every National Park west of Colorado and south of the state of Washington. This study will provide data essential for directing conservation efforts across this region.