Body size is linked to female dominance and reproduction in a Neotropical eusocial paper wasp

Reproductive division of labor amongst nestmates is a defining feature of eusocial insects, where reproduction is limited to one or a few individuals, while the remaining forage and care for brood. When caste determination occurs, and the flexibility of castes, are important in shaping individual opportunities for cooperation, conflict, and reproduction amongst female nestmates. Because body size (including wing length) is fixed for insects upon adult emergence, morphology can be used to assess pre-adult effects on caste determination. Differences in body size may lead to advantages and disadvantages amongst nestmates when competing for resources and reproductive opportunities. Our goal was to measure the relationships of body size differences in female Mischocyttarus pallidipectus paper wasps with reproductive development and dominance behavior. Using in-field dissections and morphology measurements, we found that larger females were more likely to have developed ovaries. Additionally, female aggression towards nestmates increased with increasing body size. However, we found variation in these body size effects, and smaller reproductive and dominant females were present on some observed nests. These data suggest that factors during pre-adult development can lead to size differences between females, and that body size can bias the outcome of adult dominance interactions, with impacts on reproductive development. Though these wasps are monomorphic, body size differences may be advantageous in adult reproductive competition in this species, where caste is influenced by aggression and nutrient acquisition in adulthood.