Gradual adaptation toward a range-expansion phenotype initiated the global radiation of toads

Recent studies have identified range expansion as a potential driver of speciation. Yet it remainspoorly understood how, under identical extrinsic settings, differential tendencies for geographicmovement of taxa originate and subsequently affect diversification. We identified multiple traitsthat predict large distributional ranges in extant species of toads (Bufonidae) and used statisticalmethods to define and phylogenetically reconstruct an optimal range-expansion phenotype. Ourresults indicate that lineage-specific range-shifting abilities increased through an accumulation ofadaptive traits that culminated in such a phenotype. This initiated the episode of global colonizationand triggered the major radiation of toads. Evolution toward a range-expansion phenotype might becrucial to understanding both ancient widespread radiations and the evolutionary background ofcontemporary invasive species such as the cane toad.