Costs and the diversification of exaggerated animal structures

Sexual selection can favor production of extravagant ornaments and weapons in the contest for access to the opposite sex. Existing explanations for th e diversity of sexually selected structures focus on reproductive benefits conferred by particular ornament or weapon morphologies. Here, I show that costs of weapon production also may drive patterns of weapon evolution. In beetles, production of horns reduces the size of neighboring morphological structures (antennae, eyes, pr wings, depending on the location of the horn s), and these tradeoffs reveal unexpected functional associations between e cology and horn morphology. This study illustrates a critical but overlooke d role of costs in sexual selection and has implications for understanding the evolution of animal morphology.