Connection, isolation and reconnection: Quaternary climatic oscillations and the Andes shaped the phylogeographical patterns of the Patagonian bee Centris cineraria (Apidae)

Abstract

The joint effect of the Andes as a geographical barrier and the Quaternary glaciations as promoters of genetic divergence remains virtually unexplored in southern South America. To help fill this knowledge gap, in this study we investigated the demographic history of Centris cineraria, a solitary bee mainly distributed in Patagonia. We used mitochondrial and nuclear markers and performed phylogeographical and dating analyses, adjusted spatio-temporal diffusion and species distribution models, and used Approximate Bayesian Computation to identify likely historical demographic scenarios. Our results revealed that during glacial periods the Andes represented a barrier due to the extent of the ice-sheets and the occurrence of unsuitable habitats, while interglacials allowed for gene flow across the Andes. Secondary contact between previously isolated lineages was evident across at least two low-altitude Andean areas, the northern one being a putative glacial refugium. Our findings also suggest that C. cineraria has persisted in situ in four periglacial refugia located along a north?south transect, congruent with the maximum extent of the ice sheet during the Greatest Patagonian Glaciation. As the first phylogeographical study of Patagonian insects, our work reveals that the interaction between Quaternary climatic oscillations and the Andes as a barrier was the main driver of the spatial and demographic history of C. cineraria.