Morphology and Evolution of the Water Scavenger Beetle subfamily Acidocerinae (Coleoptera: Hydrophilidae)

Abstract

Water scavenger beetles in the subfamily Acidocerinae (Insecta: Coleoptera: Hydrophilidae) are a cosmopolitan group that can be found in a wide range of habitats, including fully aquatic environments, hygropetric habitats, and terrestrial niches. This broad habitat range has resulted in apparently convergent morphologies associated with particular ecologies and caused significant taxonomic confusion across the group. Understanding habitat shifts and their correlation with morphological variation in acidocerine water scavenger beetles was the main objective of this dissertation. To understand morphological variation in the subfamily Acidocerinae, we revised Quadriops Hansen, the only known terrestrial genus in the subfamily and described three new genera: the aquatic Aulonochares, the hygropetric Ephydrolithus, and the ecologically variable Primocerus. Then, based on a molecular phylogeny, the taxonomy and classification of the entire subfamily was revised, including morphological diagnoses, illustrative images, an identification key for each of the 23 recognized genera, and a catalog (complete to October 2019) containing 469 species of acidocerines with their distributions. The phylogeny was also used for analyzing habitat shifts in the Acidocerinae using phylogenetic comparative methods. We investigated the effect of habitat shifting on the diversification rate of the subfamily, as well as its association with variation in a suite of five morphological traits. This dissertation constitutes the most comprehensive treatment of a hydrophilid subfamily to date and is the first step towards understanding habitat shifting across the water scavenger beetle family Hydrophilidae.