Explosive Cenozoic origin and diversity-dependent diversification dynamics shaped the evolution of Australian skipper butterflies

Abstract

Australia was predominantly tropical for most of the early Cenozoic, then transitioned to a cooler and drier climate in the Oligocene. In response to this increasing aridity, some lineages adapted to more xeric ecosystems, contracted, or became restricted to increasingly fragmented mesic refugia, or went extinct. Yet, the lack of macroevolutionary studies at a continental scale precludes a better understanding of Australian biodiversity patterns and processes during the Cenozoic. Here, we infer a robust dated phylogenomic tree for a radiation of Australian endemic butterflies, the Trapezitinae skippers, to test the impact of biotic and abiotic drivers on Cenozoic diversification dynamics in Australia. These butterflies originated during the Eocene (ca. 42 Ma) in the mesic biome of Australia. Trapezitinae exploded in diversity during a cool, dry period in the late Oligocene and early Miocene, then experienced a sharp deceleration in speciation. Xeric ecosystems appear to have been colonized more recently, supporting the hypothesis of arid and semi-arid biomes as evolutionary sinks. Temperature-dependent and phytophagy-dependent diversification models received little support. Instead, we find evidence for diversity-dependent processes with a declining diversification in Trapezitinae likely linked to limited ecological opportunities following a rapid initial burst of diversification.