Meeting Abstract
Sexual selection results in the evolution of exaggerated weapons in some species, but not in others. Trypoxylus dichotomous, a species of Rhinoceros Beetle, possesses enormous horns that are used by males in intrasexual combat for reproductive access to females. However, this widespread species shows different horn allometry across populations. We aim to use this natural variation to measure the functional ramifications of horn length variation and to understand the evolution of these exaggerated weapons. We collected force production data in the field for several populations and analyzed the horns as a simple lever system to understand how morphology leads to performance variation. We confirm that horn length allometry varies across populations with upper end differences in horn size varying by 1.4 times from the same sized beetles in other populations. In addition, mechanical advantage and muscle cross-sectional area seem to vary independently. Therefore, the force that horns can produce, an estimate of weapon performance, varies significantly across populations with similarly sized beetles being able to produce 2.1 times the force in different populations. We suggest that both horn length and horn force production may be under differential sexual selection in different populations due to variation in the details of ecology and mating systems.
