Complex phylogeography in the Southern Smooth Snake (Coronella girondica) supported by mtDNA sequences

Abstract

Palearctic reptiles with wide distribution through the Western Mediterranean are expected to display genetic substructuring because of the combining effects of current or past geographic barriers and climate fluctuations. We have examined this issue by sequencing cytochrome b and 16S rRNA mitochondrial fragments of 80 individuals of the snake Coronella girondica from 71 localities, covering the range of the species across Tunisia, Algeria, Morocco, Spain, Portugal, southern France and north-western Italy. According to the obtained genealogy, C. girondica is structured into three divergent and well-supported clades (north-western Africa, Betic range and Iberia–France–Italy), which greatly match other phylogeographies already published for this region. Our estimations suggest that the divergence among the three clades took place approximately 1.4-2.0 Ma, which roughly coincides with the Plio-Pleistocene transition, characterized by an increase in climate variability. The existence of a clade in a narrow belt of south-eastern Iberia represents another example of the high endemism rate of the region, with a key geographical situation and an important role in vicariant processes. Since the split among the three major lineages would be take place after the opening of the Strait of Gibraltar, overwater dispersal is here suggested. The subsequent genetic substructuring of these clades during the Pleistocene fits within the refugia-within-refugia model, highlighting the importance of the region as a scenario for multiple vicariant events.