Systematics and biology of the endemic water scavenger beetles of Hawaii (Coleoptera: Hydrophilidae, Hydrophilini)

Abstract.  Recent field surveys in the Hawaiian Islands have revealed an adaptive radiation of endemic water scavenger beetles (Coleoptera: Hydrophilidae). Phylogenetic analysis based on 55 adult morphological characters affirms that this endemic hydrophilid fauna is a monophyletic clade that incorporates the first well-supported transformation from an aquatic to terrestrial way of life within any lineage of the subfamily Hydrophilinae. The clade is prescribed to the genus Limnoxenus Motschulsky, where described members were previously placed. Five new species are described: L. waialeale sp.n. (Kauai), L. kauaiensis sp.n. (Kauai), L. oahuensis sp.n. (Oahu), L. punctatostriatus sp.n. (Kauai) and L. namolokama sp.n. (Kauai). Lectotypes are designated for the two previously described species L. semicylindricus (Eschscholtz) and L. nesiticus (Sharp). The Hawaiian lineage is a component of a larger clade that also includes the remaining four species of Limnoxenus from Europe, South Africa, and Australia, plus the monotypic genera Limnocyclus Balfour-Browne of New Caledonia and Hydramara Knisch of South America. The majority of the Hawaiian species exhibit vestigial wings, an extremely unusual condition in aquatic beetles. No other island-endemic members of the Hydrophilinae are known to be flightless, suggesting insularity per se is not responsible for this condition. L. nesiticus of Oahu has not been collected during the past 106 years, suggesting that it has been lost to anthropogenically mediated extinction.