Larval Density, Sex, and Allocation Hierarchy Affect Life History Trait Covariances in a Bean Beetle

Life history theory aims to understand how different environments result in differential investment in fitness-related traits. While trade-offs between traits are expected, many studies show positive or no correlation between pairs of costly traits. One hypothesis that may explain the inconsistency of trade-offs in the literature is that trait investment may occur in a dichotomous hierarchy (the tree model), which allows for differential trait investment weighted by the traits' respective positions within the hierarchy. Previous mathematical models predict different covariances between traits depending on their position on the allocation tree. While hierarchical differential investment is often used to discuss findings in life history theory, the role of an allocation hierarchy in trait covariances has not been directly tested. In turn, this study aims to identify trait covariances between behavioral and morphological phenotypes on different branches of an allocation tree for the bean beetle, Callosobruchus maculatus. While trade-offs between copulatory behaviors and morphology were found for both males and females, only traits at the base and far from each other in the hierarchy negatively covaried. This study empirically shows that trade-offs may be the result of hierarchical investment.