Trapped by climate: Interglacial refuge and recent population expansion in the endemic Iberian adder Vipera seoanei

Abstract

Aim: Climate variability is a major force affecting diversification processes and restricting species to specific areas, and thus, it has important impacts on species biogeographic patterns. This study aims to infer the role of climate in the evolutionary history of the endemic Iberian adder Vipera seoanei. Location: Northern Iberian Peninsula and south-western France. Methods: We combined genetic analyses with ecological niche-based modelling. Genetic analyses, based on sequencing of mitochondrial markers (cyt b, ND4), include phylogenetic and phylogeographic analyses, spatial interpolations of genetic variability and diversity, and identification of putative geographical origin of the most recent common ancestor of the species. Ecological modelling involved the combination of six modelling algorithms and projections to past conditions (Last Interglacial - LIG, Last Glacial Maximum - LGM) and the identification of climatic stable areas. Results: The species shows a shallow phylogeographic structure, dated at middle-upper Pleistocene, and low haplotype diversity, with the highest genetic diversity located in north-western Iberia. This region is identified as the putative origin of the ancestral populations. Projections to past periods spatially fit genetic results, indicating range contractions to north-western Iberia during the LIG and expansions during the LGM. Main conclusions: This study exemplifies how the combination of phylogeographic and ecological niche-based models is a powerful tool for inferring evolutionary scenarios and responses of species to Pleistocene climatic oscillations. Vipera seoanei responded accordingly to a cold temperate model and fits a simplified example of 'R' type species where interglacial warming periods during the Pleistocene probably caused major range reductions with persistence in a single refuge in north-western Iberia. The single mtDNA lineage observed in this study does not support the differentiation at subspecific level in V. seoanei. Our work highlights the importance of climate in explaining evolutionary processes and current biogeographical patterns of species with restrictive ranges.