Loss of the sticky harpoon – COI sequences indicate paraphyly of Stenus with respect to Dianous (Staphylinidae, Steninae)

The speciose staphylinid subfamily Steninae comprises more than 2700 species of the two genera Stenus and Dianous. Whereas the labium of Dianous beetles is short and unspecialized, the members of Stenus are characterized by a protruding elongated labium that functions as a prey-capture apparatus. This is considered the derived state and the most prominent apomorphic character for Stenus. To elucidate the phylogenetic relationship of Stenus and Dianous, we analyzed 807 bp of the mitochondrial cytochrome c oxidase I (COI) gene in 30 Stenus and 12 Dianous species. Our analysis indicates the evolutionary origin of Dianous within Stenus, suggesting a secondary loss of the specialized prey-capture apparatus. Whereas the derived phylogenetic position of Dianous within Stenus is supported by maximum parsimony, neighbor joining, maximum likelihood, and Bayesian analyses, the resolution of COI seems to be insufficient to consistently resolve basal relationships of Stenus species.