Meeting Abstract
The elaboration of exaggerated, sexually selected weapons and ornaments often comes at a cost to other traits. For example, by sustaining the growth of an exaggerated weapon, resources may become depleted and limit the size to which other structures can grow. Such interactions are known as resource allocation trade-offs, and have the potential to constrain the production of phenotypic variation and bias evolutionary trajectories. Across many species of Onthophagus beetles, males produce extravagant horns of various sizes and shapes which are used as weapons in male competition over mates. Previous studies have reported resource allocation trade-offs between these horns and both proximally- (i.e. antennae, eyes, wings) and distally-located (i.e. genitalia) structures. However, more recent studies have largely failed to recover these patterns, leading to the hypothesis that trade-offs may manifest only in certain species, populations, or under particular (e.g. stressful) environmental conditions. In order to test this hypothesis, we investigate (a) patterns of resource allocation into horns, eyes, and genitalia in O. gazella and O. taurus, two species that differ markedly in the average degree of investment into horns. We then assess (b) how these patterns of resource allocation are influenced by nutrient limitation during larval development. Specifically, we test the hypotheses that stressful conditions facilitate the emergence of resource allocation trade-offs, and that this should be most pronounced in species that invest disproportionately into secondary sexual traits. We present our most recent results and discuss their implications for morphological evolution and diversification.
