A new narrative for social immunity research in termites

Closely related workers of insect societies gain indirect fitness benefits by performing costly colony-defence tasks, resulting in the evolution of hygienic traits. In ants and in many bees and wasps, strict division of reproductive labour implies clear predictions for the expression of hygienic traits. Termites, however, differ from such canonical hymenopteran social patterns because they exhibit a high degree of developmental plasticity, with worker castes varying in reproductive potential. Termites therefore represent an ideal study system to explore the evolutionary origins of altruistic hygienic traits. In this review, we identify robust categories of social organisation and summarise our current understanding of hygienic trait expression in light of fitness prospects in termites. We also outline key gaps and hypotheses for future work, using a conceptual framework built around developmental flexibility and fitness to enable new insights into the evolution and expression of social immunity.