Meeting Abstract

38.1  Thursday, Jan. 5  Elaborate weapons: the costs of producing and carrying horns in a giant rhinoceros beetle MCCULLOUGH, E.*; WEINGARDEN, P.; EMLEN, D.; TOBALSKE, B.; University of Montana; University of Montana; University of Montana; University of Montana mccullough.e@gmail.com

The horns of giant rhinoceros beetles are among the largest sexually-selected traits observed in nature. Male ornaments and weapons are expected to be costly to produce and carry, yet empirical evidence for these costs remain equivocal. Remarkably, the costs of producing and carrying rhinoceros beetle horns are largely unexplored. Given the impressive size and elaborate shape of many beetle horns, we expected them to impose two primary costs: reduced locomotor performance and resource allocation tradeoffs. Surprisingly, the exaggerated horns of Trypoxylus dichotomus males do not appear to be particularly costly to carry. Even in the largest males, horns only increase body mass by 2%, and at the angles at which beetles typically fly, the horns represent a trivial increase in body drag. Furthermore, T. dichotomus horns do not appear to be particularly costly to produce. Males have larger wings and flight muscles than females, which suggests that they do not face resource allocation tradeoffs. We suspect that males may invest more in flight-related structures to compensate for the small reduction in flight performance imposed by horns. More importantly, our results suggest that even the exaggerated horns of giant rhinoceros beetles may not be as costly as they are expected to be.