The effects of Quaternary sea-level fluctuations on the evolutionary history of an endemic ground lizard (Tropidurus hygomi)

The Quaternary period is marked by many extensive glaciations and sea level oscillations, mainly during the Pleistocene. Sea level oscillations possibly shaped landscapes in coastal regions, which may have played an important role in the diversification of organisms that live in these areas. In this study, we investigated the population history of the lizard Tropidurus hygomi, which is endemic to a narrow region of the northeastern coast of Brazil, inhabiting areas of white sandy coastal dunes in the Restinga formation. We specifically asked: how did sea level changes in the Quaternary shape population structure and historical demography of T. hygomi? We collected 72 tissue samples throughout the distribution of the species and obtained sequences from the mitochondrial gene cytochrome b. Different tests for population structure identified five distinct mitochondrial DNA clusters (mtDNA clusters) in T. hygomi. Divergence time estimate showed that splits among these mtDNA clusters took place in the Pleistocene, and exhibited temporal agreement with marine transgressive events during these periods. As T. hygomi is a threatened species and our data suggest the presence of five mtDNA clusters, further conservation actions for this species should consider these independent mtDNA clusters in order to preserve the evolutionary history and the diversity within the species.