Limits to behavioural plasticity in tropical paper wasps

Cooperative breeders are defined by a division of reproductive labour among group members who can respond flexibly to changing conditions via phenotypic plasticity. But such plasticity can be costly and is likely influenced by previous experience. Polistes paper wasps live in small societies where non-reproductive (worker) and reproductive (queen) individuals can switch roles throughout adulthood. Such plasticity in reproductive roles positions them as important models for social evolution. However, the limits of their individual-level plasticity have not been fully tested. We experimentally forced queens and workers of Polistes canadensis to nest alone, requiring them to express reproductive and non-reproductive characteristics simultaneously. At the behavioural level, although all isolated wasps laid eggs and foraged, ex-queens were less good than ex-workers at brood rearing. We attribute this to subtle differences in neuroplasticity. Whilst brain transcription of both ex-queens and ex-workers changed in response to the manipulation, converging on a state intermediate to that of control queens and workers, ex-queens did not up-regulate some key molecular processes required for expression of an effective worker phenotype. Our findings demonstrate that both Polistes queens and workers can exhibit behavioural, physiological and molecular plasticity, but reveal how previous life-history can impose limits to that plasticity.