Biogeographic mirages? Molecular evidence for dispersal-driven evolution in Hydrobiusini water scavenger beetles

Water beetles of the tribe Hydrobiusini are globally distributed in the northern hemisphere and all austral continents except Antarctica. A remarkable clade also occurs in the Hawaiian Islands. The phylogenetic relationships among genera were recently investigated using a combination of molecules and morphology. Here, we use this phylogenetic framework to address the biogeographic evolution of this group using Bayesian fossil-based divergence times, and model-based maximum likelihood ancestral range estimations. We recover an origin of the tribe in the Cretaceous ca. 100 Ma. Our biogeographic analyses support an origin of the tribe in Laurasia followed by the colonization ofAustralia. However, a Gondwanan origin of the group cannot be ruled out when considering the fossil record. The timeframe of the tribe's evolution as well as the model-based approach of ancestral range estimation favour a scenario invoking multiple transoceanic dispersal events over a Gondwana vicariance hypothesis. The Hawaiian radiation originated from long-distance dispersal to now-submerged islands, paired with dispersal to new islands as they formed.