Patterns of fluctuating asymmetry in beetle horns: no evidence for reliable signaling

Negative relations between trait size and levels of fluctuating asymmetry i n secondary sexual traits have been claimed to be indicative of honest sign aling of male quality. Comparative studies of beetle horns have been used t o illustrate the required negative relation between trait size and asymmetr y. However, such studies may be confounded by measurement error or sampling bias due to population differences or differences within species in the ph enotypic expression of hornedness. We examined the patterns of fluctuating asymmetry within two species of horned beetle. We found that, in agreement with theory, horns exhibit greater asymmetry than naturally selected traits . However, we found a strong positive relation between horn size and asymme try in Onthophagus taurus, a species with male dimorphisms, and a flat rela tion in Bubas bison, a species with continuous variation in horn size. We s uggest that these differences may reflect functional differences in horns. We conclude that patterns of asymmetry in horned beetles do not support the notion of honest signaling.