RUI: Evolutionary Significance of Mitochondrial DNA Clade Boundaries

California State University-Long Beach, Long Beach CA

Investigators

Abstract

0075607 Archie Phylogeography 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.