Riverscape Genetics of Rainbow (Etheostoma caeruleum) and Orangethroat (E. spectabile) Darters

Freshwater darters are widely distributed in the Central and Southern United States. This dissertation examines two groups of darters, the species Rainbow Darter (Etheostoma caeruleum) and select members of the Orangethroat Darter complex (Ceasia). In Chapters 1 and 2, I conducted a riverscape analysis of Rainbow Darters and Ceasia members to evaluate population genetic structure and diversity, and to identify the possible drivers, contemporary or historical, that underlie the genetic patterns. Chapter 1 analysis of Rainbow Darters identified two genetic clusters, one comprised of fish collected from more southerly sites and one comprised of fish from more northernly sites that corresponded to sites that were either unglaciated or glaciated during the last glacial maximum (LGM). Chapter 2 analysis of Ceasia revealed two well-differentiated genetic clusters of in samples from glaciated regions and a single cluster in the unglaciated region. This suggests that there was expansion from two isolated glacial refugia, with little subsequent post-glacial gene flow. In both analysis, fish collected from throughout the unglaciated region were less genetically differentiated. In Chapter 2 in particular fish assigned to E. burri and E. uniporum based on collection sites and morphological characters were not genetically differentiated from E. spectabile samples from the region. Hybridization and introgression occurring in the Central Highlands may confound genetic delineation of species in this region of high endemism and diversity. Overall, the findings demonstrate the lasting legacy of glacial history on contemporary genetic structure and diversity of a North American riverine species. Chapter 3 utilized genetic and meristic analysis to determine possible genetic interactions between all study species. Distinct genetic clusters were determined that corresponded with Rainbow Darters and Ceasia members. Morphological hybrids were identified but no genetic evidence of apparent hybridization was present to support their hybrid status. Results show that genetically determined groups better corresponded to current species delimitations than groups determined through morphological characters.