Horns positive allometry in a Mexican population of Strategus aloeus (L.) (Coleoptera: Scarabaeoidea: Dynastinae)

Abstract

The scaling relationships between horns and body size in a Mexican population of males of the rhinoceros beetle Strategus aloeus are analysed. We performed an allometric analysis using a sample of 94 specimens from many localities in Mexico. Our results suggest that median horn frequency in Strategus aloeus has a non-linear bimodal distribution and adjacent horns frequency has a non-linear distribution, however, residual and logarithmic transformation suggest linearity. Therefore we analysed data of horns using MA (model II) regression between log horns length and log body length; results of MA regression show strong positive allometry. These results suggest that bigger males possess larger disproportioned horns than small males, and that males could be investing more in developing the principal horn than in adjacent horns, possibly reflecting strong sexual pressures. This supports the idea that positive static allometry in horn and adjacent horns in S. aloeus could be explained by an extreme reaction norm, suggested by the “positive allometry reaction norm model”.