Morphology of mandibles of clown beetles (Coleoptera: Histeridae): hidden diversity, sexual dimorphism, and implications for prey range

Clown beetles (Histeridae) are stable components of carrion communities, but their prey range is poorly recognised. An indirect way to deduce species’ diet is to study the functional morphology of their mandibles. The use of a multimodal approach in the study of Margarinotus brunneus, Margarinotus striola succicola, Saprinus semistriatus, and Saprinus planiusculus revealed a hidden morphological diversity in their mandibles. Geometric morphometric analysis showed inter- and sex-specific differences in their shape. Synchrotron X-ray microtomography revealed variability in musculature between genera and the presence of a joint-like structure at the basal margins in the Saprinus species. Scanning electron microscopy showed variation in the surface of inner margins. Traditional morphometrics revealed differences in mandibular arc according to beetle species, sex, and left and right body sides. All species retained a roughly 17° asymmetry, with the right mandible always having the higher arc. We conclude that Saprinus species are adapted for cutting and puncturing soft-bodied prey, whereas Margarinotus beetles also feed on hard-bodied prey. Future studies should consider our findings for better planning of prey-choice experiments. Emphasis should be placed on recognising whether subtle differences in mandible shape involve differences in diets. This will be critical to determine the role of species in carrion ecosystems.