Meeting Abstract
Animal weapons include such intriguing structures as horns on bighorn sheep, antlers on deer, and tusks on elephants. In spite of the interest these structures have attracted, we still do not know why there is such amazing weapon diversity. Through this project we aimed to understand how weapon differences arise even within a species, to provide insight on early divergence of weapon shape and size. Patchy but widely distributed species, such as the leaf-footed bug Narnia femorata (Hemiptera: Coreidae), are good candidates to study the processes that can lead to the diversification of animal weapons. This cactus-feeding species is found in the US Southwest and Florida, and has known association with at least four genera and 13 species of cacti through its extensive range. Adults are sexually dimorphic, females have on average larger bodies but males have enlarged hind femurs used in male-male combat. Males establish territories on their host plants and defend them against other conspecifics using their hind legs [=weapons]. Larger males are more likely to be dominant over smaller ones when defending their territories. Combining fieldwork with common garden/reciprocal transplant experiments, we examined the variation of male weapon morphology across a broad landscape. We found both phenotypic plasticity and evolved differences in weapon shape and size. Interestingly, the divergence in weaponry is mainly due to changes in allometric intercepts of hind femur traits (length and width) and body size, with no changes in allometric slopes. We discuss possible implications for population divergence in the context of the combat behavior of this species.
