Horn scaling relationships in three species of Bledius Leach 1819 (Insecta: Coleoptera: Staphylinidae) show no indication of fitting non-linear allometric models

The males of some species of the rove beetle genus Bledius Leach (1819) have a pronounced horn protruding from the anterior margin of the pronotum. The horn function is not known, however in many other horn-bearing beetles, these structures are implicated in male-male combat over females. In this study, scaling relationships are investigated for three species; B. spectabilis Kraatz, 1857, B. frisius Lohse, 1978 and B. tricornis (Herbst, 1784). Based on data collected from museum specimens, we fitted and compared different allometric models on pronotal width versus horn length in each species. A simple linear allometric model best describes the scaling relationship of horns in all three species. The horn allometry in the three Bledius species do not accordingly follow a ‘switch point’ model or a curved allometric relationship, models that are commonly reported to explain the scaling relationship of horns in many other beetle species. We therefore found no evidence of male dimorphism (minor/major phenotypes) in the species examined. The potential function of the horn in Bledius is discussed in light of similar studies