RUI: Evolutionary Significance of Mitochondrial DNA Clade Boundaries

[0075607]系统地理学是研究动植物种群在地理背景下的进化关系（系统发生），即研究遗传变异的地理格局的学科。许多这样的研究使用线粒体DNA (mtDNA)，它是在细胞核外发现的，作为选择的遗传标记。这是因为人们发现这种遗传标记随着时间的推移具有很高的变化率，而且它是通过母系遗传的。通过这种类型的研究确定的遗传群体被称为mtDNA分支群。在许多系统地理学研究中，从整个物种范围的种群中取样的mtDNA分支群形成了非常独特的地理上受限的群体。一般来说，进化枝群之间的界限非常明显，似乎是线粒体基因流动的障碍。目前还没有有效地确定是什么因素影响了线粒体基因在种群之间跨越进化枝边界的流动速度和程度，或者这些边界是否也作为核基因流动的障碍。本研究将以西部栅栏蜥蜴（Sceloporus occidentalis）为模式生物，通过确定影响细胞核和线粒体基因跨界流动的因素，探讨线粒体DNA进化边界的进化意义。该物种是美国西部最常见的脊椎动物之一，具有非常复杂的mtDNA分支的地理分离模式，并且在大小，颜色和其他特征上具有高度的可变性，这些特征被认为是区分被认为是有效物种的种群的重要特征。进化枝的边界将通过在已识别的进化枝群之间的样条抽样进行详细检查。杂交带或杂交带的宽度和跨越边界的基因流动水平将根据以下因素进行比较：环境梯度、群体之间的遗传分化程度和群体之间的形态分化程度。此外，我将完成西部栅栏蜥蜴的系统地理学分析，以确定额外的分支边界，并测试关于该物种起源的一系列假设。这项研究将通过暑期研究项目和课堂教学为本科生的培训提供机会。它将：1)提供野外经验，学习基本的生态学、行为学和数据收集技术；2)提供分子实验室技术培训（包括DNA测序和基因分型）；3)促进批判性思维，提供数据分析技能以及良好的理论背景。具体子项目的离散性，即对特定分支边界的分析，以及在实验室中相对容易地收集遗传数据，将使本科生和研究生都能充分参与研究。

0075607ArchiePhylogeography is the study of the evolutionary relationships (phylogenies) of populations of animals and plants in a geographical context, that is, the study of geographical patterns of genetic variation. Many of these studies use mitochondrial DNA (mtDNA) which is found outside the nucleus of a cell as the genetic marker of choice. This is because this genetic marker has been found to have a high rate of change over time and because it is inherited through the maternal lineage. Genetic groups that are identified as a result of this type of study are called mtDNA clade groups. In numerous phylogeographic studies, mtDNA clade groups, sampled from populations throughout a species range, form very distinct and geographically circumscribed groups. In general, boundaries between the clade groups are very sharp and appear to act as barriers to gene flow of the mitochondrial genes. It has not been determined effectively what factors influence the rate and extent of mitochondrial gene flow across clade boundaries between the groups or if these boundaries also act as barriers to nuclear gene flow. This research will investigate the evolutionary significance of mitochondrial DNA clade boundaries by determining what factors affect nuclear and mitochondrial gene flow across the boundaries using the western fence lizard (Sceloporus occidentalis) as the model organism. This species is one of the most common vertebrates in the western U.S., has a very complex pattern of geographical separation of the mtDNA clades, and has a high degree of variability in size, coloration, and other features thought to be important in otherwise differentiating between populations that are considered valid species. Clade boundaries will be examined in detail using transect sampling between identified clade groups. The width of the intergrade or hybrid zone and the level of gene flow across the boundaries will be compared in relation to the following: environmental gradients, degree of genetic differentiation between the groups, and degree of morphological differentiation between the groups. In addition, I will complete a phylogeographic analysis of the western fence lizard to identify additional clade boundaries and to test a series of hypotheses regarding the origin of this species. This research will provide opportunities for the training of undergraduate students both through summer research programs and in classroom settings. It will: 1) provide field experience to learn basic ecology, behavior, and data collection techniques; 2) provide training in molecular laboratory techniques (including DNA sequencing and genotyping); and 3) promote critical thinking and provide data analysis skills as well as a sound theoretical background. The discrete nature of specific sub-projects, i.e., the analysis of particular clade boundaries, and the relative ease with which the genetic data can be collected in the laboratory will allow both undergraduate and graduate students to become fully involved in the research.