Title: Phylogeography and Population Genetic Structure of Least Terns (Sterna antillarum). Abstract approved________________________________________________________

Historically, least terns (Sterna antillarum) were one of the most common tern species in North America. However, population declines have resulted from direct and indirect anthropogenic pressures on their breeding and foraging habitat. Three subspecies of least terns have been described within the United States: California least tern (S. a. browni), Interior least tern (S. a. athalassos), and East Coast least tern (S. a. antillarum). California and Interior subspecies are listed as endangered under the U.S. Endangered Species Act. However, the taxonomic status of least terns is a highly contentious issue which has implications for setting conservation priorities at erroneous levels of taxonomic distinctness. Thus, understanding population structure and taxonomy is critical for successful conservation of least terns. To clarify the phylogeographic patterns and population structure and evaluate the traditional subspecific designations, we examined variation in two mitochondrial DNA (mtDNA) genes and 10 microsatellite loci among least terns in North America. MtDNA control region sequences and 10 polymorphic microsatellite loci were used to evaluate traditional subspecific designations and genetic structure in least terns