Influence of resource level on maternal investment in a leaf-cutter bee (Hymenoptera: Megachilidae)

Abstract

Fisher's (1930) prediction of equal investment for each sex in a panmictic population is influenced by a number of ecological factors, among which resource availability plays a major role, particularly when the population exists under changing resource availability. Rosenheim et al. proposed a multifaceted parental investment model based on the underlying assumption that individual females determine their sex investment according to resource availability and oocyte availability to maximize reproductive success. The model predicts that greater availability of resources used for provisions will lead to (1) an increase in the proportion of females produced (when the female is the larger sex) and (2) an increase in the amount of provisions per offspring and thus an increase in offspring size. I tested these predictions by a controlled experiment using a leaf-cutter bee, Megachile apicalis. I presented two levels of food resources to the nesting females, which were allowed to forage and nest in cages. The experimental results supported these parental investment model's predictions.