Evolution and biogeography of hydrothermal vent organisms in the eastern Pacific Ocean

This dissertation examines aspects of population genetics, biogeography, evolution, and species diversity of organisms found at hydrothermal vents in the eastern Pacific Ocean. The dissertation is composed of four chapters, each addressing a specific aspect of hydrothermal vent evolution or biogeography. Chapter I uses a multi-species phylogeographic approach to examine potential dispersal barriers for vent invertebrates along the East Pacific Rise and Galapagos Rift. Evidence for dispersal barriers was found in all the species analyzed, and in some cases, these barriers were common to several species. These results improve our understanding of dispersal dynamics and biogeography of vent-endemic animals in the East Pacific Rise and Galapagos Rift. Chapter II uses a molecular clock approach to estimate the age of vestimentiferan tubeworms. Results based on DNA sequence divergence data of a fragment of the mitochondria) Cytochrome Oxidase I gene (mtCOI) suggest a recent evolutionary origin (<140 My) for vestimentiferans. This estimation is inconsistent with the hypothesis of a Silurian origin (∼400 My) based on fossil findings. Chapter III uses population genetic and phylogenetic analyses to test the hypothesis of strict maternal transmission of endosymbionts in the vent clam Calyptogena magnifica. Genetic and evolutionary coupling was observed between genes of the endosymbiont and the maternally inherited clam mitochondria. These findings provide compelling evidence that vertical transmission is the only mode for endosymbiont transmission in this clam species. Chapter IV uses mtCOI sequences to assess genetic variability of Oasisia tubeworms throughout their known range. The results reveal that Oasisia is the vestimentiferan genus with the highest mtCOI genetic diversity. Additionally, sequence divergence observed among the most divergent Oasisia lineages suggests that some of them may correspond to undescribed species.