Present and past climatic effects on the current distribution and genetic diversity of the Iberian spadefoot toad (Pelobates cultripes): an integrative approach

Aim: Predicting species responses to global change is one of the most pressing issues in Conservation Biogeography. A key part of the problem is understanding how organisms have reacted to climatic changes in the past. Here we use species distribution modelling to infer the effects of climate changes since the Last Interglacial (LIG, about 130,000 ybp) on patterns of genetic structure and diversity in the Western Spadefoot toad (Pelobates cultripes) in combination with spatially-explicit phylogeographic analyses. Location: Iberian Peninsula and mainland France. Methods: 524 individuals from 54 populations across the species range were sampled to document patterns of genetic diversity and infer their evolutionary history based on data from mtDNA and fourteen polymorphic microsatellites. Generalized linear models based on distribution data were used to infer climatic favourability for the species in the present and in projected scenarios for the LIG, the Mid Holocene and the last glacial maximum (LGM). Results: Estimates of genetic diversity show a decreasing trend from south to north, suggesting persistence of higher historical population sizes in the southern Iberian Peninsula. Species distribution models show differences in climatic favourability through time, with significant correlations between historically stable favourable areas and current patterns of genetic diversity. These results are corroborated by Bayesian Skyline Plots and continuous diffusion phylogeographic analyses. Main conclusions: The results indicate the presence of southern refugia, with moderate recent expansions at the northern end of the species’ range. Populations at the northern range margin exhibit the lowest genetic diversity and occupy historically unstable areas, classified as marginal in terms of favourability, rendering them most vulnerable to climate-mediated changes in the medium to long term