Meeting Abstract

115.2  Tuesday, Jan. 7 10:30  Beetle horn diversity: does shape affect performance during fights? MCCULLOUGH, E.L.; University of Montana, Missoula mccullough.e@gmail.com

Rhinoceros beetles exemplify the elaborate morphologies that can result from sexual selection. Males have long horns on their head and prothorax that they use in fights over reproductive access to females. Species vary dramatically in the shape and size of their horns, yet this variation is poorly understood. Species also fight in different ways, and males sometimes fight vigorously enough to break their horns. Here, I used finite element analysis to assess whether variation in horn shape affects performance during combat. Specifically, I constructed finite element models of the head horns of three rhinoceros beetle species (Trypoxylus dichotomus, Golofa porteri, and Dynastes hercules), and compared the patterns of stress distribution and total strain energy under loading conditions that mimicked typical and atypical fights. In all three species, typical loading conditions produced the lowest stress distributions and the lowest total strain energies. These results indicate that horns are the least likely to fail, and the most efficient at transmitting fighting forces under conditions that mimic typical fights. More importantly, these results suggest that the variation in horn morphology among species reflects differences in fighting style, and that horns have been selected to maximize fighting performance.