A comprehensive biogeographical overview of the evolutionary history of the higher attine ants

We investigated the biogeographical history of the higher attines, a group of fungus-farming ants that are widespread across American landscapes. We aimed to determine the tempo and direction of dispersal of their ancestors among the major biomes of the Americas and the importance of range expansion in lineage diversification. We tested the hypothesis that Amazonia and the ‘Dry Diagonal’ played pivotal roles in the evolutionary history of fungus-farming ants using previously reported, freely available molecular data, including comprehensive data from the three leafcutter ant genera (Amoimyrmex, Atta, and Acromyrmex). Amazonia was identified as the primary source of new higher attine lineages, although most Mycetomoellerius and leafcutter ants have diversified within the ‘Dry Diagonal’ and dispersed throughout the Atlantic Forest. The initial diversifications would have taken place in the Miocene Amazonia, where the Pebas system was being formed. The Pebas system might have contributed as a dispersal barrier for populations on the east and west sides. Our data indicate that from the Middle Miocene onwards there were pulses of diversification combined with large scatterings. Dispersal events included long distances to Middle America from Amazonia and subsequent back and forth between the Atlantic and Amazonian forests. The role of the ‘Dry Diagonal’ in the diversification of higher attines is clear, because many groups had such an ancestral range and colonized most of the tropical and subtropical savannas/grasslands of South America.