How tectonic, volcanic and climatic processes in Andean ‘sky islands’ shaped the diversification of endemic ground beetles

Aim: The Andean superpáramo ecosystem, above c. 4200 m a.s.l., currently forms an archipelago of isolated ‘sky islands’ which provides a unique setting to study biogeography. However, there is still a poor understanding of how past geological events, together with past climatic changes, have shaped the distribution of life in this ecosystem. Our aim was to investigate the importance of biogeographical barriers in local diversifications and to analyse how populations have become isolated on current ‘sky islands’. Location: Neotropics, Andes, Páramo, Ecuador. Taxon: Coleoptera, Carabidae, Platynini, Dyscolus. Methods: We first used distributional data of 45 superpáramo specialist species to define areas of endemism in northern Ecuador. We then selected 34 currently isolated populations of 12 species to perform a high-throughput genome skimming approach encompassing the complete mitogenome and the complete nuclear ribosomal cluster. We also generated a time-calibrated estimation for the diversification of the group, and compared it to geochronological data. Results: A high proportion (60%) of the sampled species are microendemic, being restricted to a single mountain summit. Three mutually exclusive areas of endemism are limited by deep transverse valleys across the Andes, and Pliocene speciation events are related to these orogenic barriers. The phylogeny obtained from the genome-skimming approach provides a robust base to analyse the diversification of superpáramo endemic species and populations throughout the Plio-Pleistocene. Main conclusions: The opening of the Interandean Valley did not play a significant role in the diversification of the group prior to the Pleistocene. More recently, multiple populations have become isolated on the superpáramo of various volcanoes by independently colonizing this habitat during repeated cycles of glacial–interglacial periods. Our results highlight the joint contribution of orogeny and climatic fluctuations for explaining the current patterns of distribution. Each species had a different colonization history, with its populations reaching the different volcanoes at different glacial–interglacial cycles. Our approach also can provide a powerful tool to constrain the geological processes responsible for the topographic changes along and across the Cordillera.