From Gondwana to the Yellow Sea, evolutionary diversifications of true toads <i>Bufo</i> sp. in the Eastern Palearctic and a revisit of species boundaries for Asian lineages.

Abstract

Taxa with vast distribution ranges often display unresolved phylogeographic structures and unclear taxonomic boundaries resulting in hidden diversity. This hypothesis-driven study reveals the evolutionary history of Bufonidae, covering the phylogeographic patterns found in Holarctic bufonids from the West Gondwana to the phylogenetic taxonomy of Asiatic true toads in the Eastern Palearctic. We used an integrative approach relying on fossilized birth-death calibrations, population dynamics, gene-flow, species distribution, and species delimitation modeling to resolve the biogeography of the clade and highlight cryptic lineages. We verified the near-simultaneous Miocene radiations within Western and Eastern Palearctic <i>Bufo</i>, c. 14.49-10.00 Mya, temporally matching with the maximum dust outflows in Central Asian deserts. Contrary to earlier studies, we demonstrated that the combined impacts of long dispersal and ice-age refugia equally contributed to the current genetic structure of <i>Bufo</i> in East Asia. Our findings reveal a climate-driven adaptation in septentrional Eastern Asian <i>Bufo</i>, explaining its range shifts toward northern latitudes. We resolve species boundaries within the Eastern Palearctic <i>Bufo</i>, and redefine the taxonomic and conservation units of the northeastern species: <i>B. sachalinensis</i> and its subspecies.