Allometry of appendages and antenna structures differs between sexes and male morphotypes of a polyphenic neotropical...

In insects, static allometry provides a means to assess size relationships among morphological appendages and their adaptive implications. As polyphenic dung beetles exhibit behavioural differences between sexes and male morphotypes, we hypothesized that these differences, alongside the presence of horns, would influence the allometric patterns of their appendages either adaptively and/or via resource allocation trade-offs. Accordingly, we investigated the allometry of morphological appendages (i.e. antennae, eyes, forelegs and wings) between sexes and male morphotypes in a key dung beetle species of the Neotropical savannahs, Oxysternon palemo (Scarabaeinae: Phanaeini). We also assessed potential resource allocation trade-offs between horns (i.e. head and pronotum) and appendages across the three male morphotypes. Our findings reveal that females possess larger appendages, except for antennae, while gamma and beta males exhibit reduced allometric scaling for forelegs. Additionally, alpha males displayed larger antennae, which were equipped with more prominent and denser sensilla. Contrary to our expectations, we detected no trade-offs involving male horns, and the relative size of their appendages appeared to positively covary with the relative size of horns. We propose that selective pressures arising from behavioural differences coevolve with patterns of appendage investment between sexes and morphotypes in dung beetles.