Climatic refugia boosted allopatric diversification in Western Mediterranean vipers

Aim The ecological dimension of evolutionary processes has been scarcely addressed in phylogeographic studies. We reconstruct the historical biogeography of Western Mediterranean vipers to discover the role of climate in fostering diversification. Location Western Mediterranean Basin. Taxon Vipera aspis and Vipera latastei-monticola complex. Methods We used nearly range-wide phylogeographic analyses of three mitochondrial genes followed by geographic assignment of 4,056 records to genetic units to test phylogenetic niche conservatism, under a 3D hypervolume approach, and reconstruct paleoclimatic scenarios for the diversification of main lineages during Pleistocene. Results Bayesian inferences from mtDNA recovered three Miocene clades and nine Pliocene lineages that diversified during the Pleistocene. Diversification was mostly restricted to southern regions of Iberian and Italian peninsulas and to the north-western African mountains until the late Pliocene. Some lineages expanded northwards during the Pleistocene. Accordingly, genetic diversity was higher in southern regions. Ecological niche tests mostly supported allopatric diversification with niche conservatism, although niche shifts occurred with two divergence events. Palaeoclimatic models identified particular requirements for the current distribution of main lineages and distinct responses to the cooling and warming events of the Pleistocene. Areas of climatic stability during the Pleistocene were identified for main lineages; however, climatic stability was weakly correlated with haplotype diversity. Main conclusions In the Western Mediterranean biodiversity hotspot, palaeo-tectonic and palaeo-climatic factors drove diversification since the Miocene. Comparisons among patterns of diversification, haplotype diversity, and climatic stability suggest that southern Iberian and Italian peninsulas, and north-western African mountains acted as refugia since the Pliocene, while some northern areas favoured population persistence during the Pleistocene. Climate adaptation likely played a secondary role in the diversification of some lineages.