Development and evolution of brain allometry in wasps (Vespidae): size, ecology and sociality

We review research on brain development and brain evolution in the wasp family Vespidae. Basic vespid neuroanatomy and some aspects of functional neural circuitry are well-characterized, and genomic tools for exploring brain plasticity are being developed. Although relatively modest in terms of species richness, the Vespidae include species spanning much of the known range of animal social complexity, from solitary nesters to highly eusocial species with some of the largest known colonies and multiple reproductives. Eusocial species differ in behavior and ecology including variation in queen/worker caste differentiation and in diurnal/nocturnal activity. Species differences in overall brain size are strongly associated with brain allometry; relative sizes of visual processing tissues increase at faster rates than antennal processing tissues. The lower relative size of the central-processing mushroom bodies (MB) in eusocial species compared to solitary relatives suggests sociality may relax demands on individual cognitive abilities. However, queens have greater relative MB volumes than their workers, and MB development is positively associated with social dominance status in some species. Fruitful areas for future investigations of adaptive brain investment in the clade include sampling of key overlooked taxa with diverse social structures, and the analysis of neural correlations with ecological divergence in foraging resources and diel activity patterns.