Global climate cooling spurred skipper butterfly diversification

Characterizing drivers governing the diversification of species-rich lineages is challenging. Although butterflies are one of the most well-studied groups of insects, there are few comprehensive studies investigating their diversification dynamics. Here, we reconstruct a phylogenomic tree for ca. 1,500 species in the family Hesperiidae, the skippers, to test whether historical global climate change, geographical range evolution, and host-plant association are drivers of diversification. Our findings suggest skippers originated in Laurasia before the Cretaceous-Paleogene mass extinction, in a northern region centered on Beringia before colonizing southern regions coinciding with global climate cooling. Climate cooling also fostered the diversification of skippers throughout the Cenozoic possibly by fueling biome transitions from closed to open ecosystems such as grasslands. An early shift from dicot-feeding to monocot-feeding reduced extinction rates and increased speciation rates, explaining the large diversity of grass-feeding adapted skippers. A dynamic geographic range evolution and host-plant shifts linked with long-term climate change explain skipper butterfly diversification.