Mushroom Body Volume Is Related to Social Aggression and Ovary Development in the Paperwasp Polistes instabilis

Abstract

The mushroom bodies (MB) are a complex neuropil in insect brains that have been implicated in higher-order information processing such as sensory integration and various types of learning and memory. Eusocial insects are excellent models to test functional neural plasticity in the MB because genetically related nest mates differ in task performance, environmental experience and social interactions. Previous research on eusocial insects shows that experience-dependent changes in brain anatomy (i.e., enlarged MB calyces) are positively correlated with task performance and social interactions. In this study, we quantified relationships of task performance and social and reproductive dominance with MB volume in Polistes instabilis, a primitively eusocial paper wasp. We used experimental removals of dominant workers to induce changes in aggressive behavior and foraging by workers. Ovary development and social dominance were positively associated with the volume of the MB calyces relative to the region containing the Kenyon cell bodies. In contrast to highly eusocial insect workers, foraging behavior was not positively correlated with MB calycal volume. We conclude that mushroom body volume is more strongly associated with dominance rank than with foraging behavior in Polistes instabilis.