Evolution and biogeography of acidocerine water scavenger beetles (Coleoptera: Hydrophilidae) shaped by Gondwanan vicariance and Cenozoic isolation of South America

The water scavenger beetle subfamily Acidocerinae is a cosmopolitan, ecologically diverse lineage with more than 500 described species whose morphology and classification are poorly understood. We present the first phylogenetic analyses of the subfamily inferred from five loci (18S, 28S, H3, CAD, COI). We used secondary calibrations to estimate divergence times and employ this phylogeny to revise the classification and examine the historical biogeography of this lineage. Most genera are resolved as reciprocally monophyletic, with several exceptions: Horelophopsis syn. n. is recovered as a derived lineage of and placed in synonymy with Agraphydrus. The large genus Helochares, as well as its primary constituent subgenera Helochares (s. str.) and Hydrobaticus are found to be polyphyletic. Batochares stat. n. and Sindolus stat. rev. are elevated from subgenera of Helochares to generic rank. Crephelochares stat. rev. is removed from synonymy with Chasmogenus. We found that the crown Acidocerinae date to the mid-Jurassic in South America + Africa (West Gondwana). South America and Africa remain important areas of endemism throughout the evolution of the lineage and are resolved either individually or in combination as the ancestral area for all but one clade that is older than 90 million years ago. Six of the seven lineages occurring in South America diverged more than 100 million years ago and are endemic to the region, suggesting the Neotropical acidocerine fauna became isolated following the breakup of West Gondwana. Conversely, lineages found on other Gondwanan fragments (India, Madagascar, Australia) are comparatively young and derived, with all being Cenozoic in age. The few taxa that occur in North America today are all the result of recent Cenozoic dispersal from South America, although North America may have played an important role as an ancestral area in the Mesozoic.

Automated summary

The water scavenger beetle subfamily Acidocerinae, with over 500 described species, is cosmopolitan and ecologically diverse. Phylogenetic analyses revealed most genera to be reciprocally monophyletic, with some exceptions. The lineage is estimated to have originated in South America + Africa during the mid-Jurassic, with South America and Africa remaining important areas of endemism throughout its evolution.