Sexual horn dimorphism predicts the expression of active personality trait: males perform better only in the sexually horn dimorphic Onthophagus dung beetle

The potential sex-specific differences in animal personality traits (i.e., consistent inter-individual variation in observed behavior) is an active field of inquiry in behavioral ecology. Sexual horn dimorphism, a special type of trait divergence where males develop large and elaborate horns, presents an opportunity to test whether sex-specific morphologies covary with changes in personality expression. We compared the activity personality trait between sexes in two dung beetle species: hornless Onthophagus ruficapillus and sexually horn dimorphic Onthophagus furcatus. We measured speed and distance moved in artificially constructed circular tracks to simulate physical activity in brood tunnels. Both measures were positively correlated and showed moderate levels of repeatability in either species, hence representing a personality axis. Sex-specific differences in locomotory performance emerged only in the horn dimorphic O. furcatus: males exhibited a more active personality than females. Season, body size and its interaction with sex did not alter the observed activity levels. Finally, O. furcatus not only showed stronger relationship between the activity measures, but it also presented lower within-individual variation for both metrics. Our results contribute to the growing body of literature on how consistent individual differences can either interact with and be a result of sex-based biological processes.