Conflict over caste fate in insect societies.

Social inequality among individuals is a common cause of conflict in the animal kingdom. In eusocial insects, such as ants, bees, wasps, and termites, for example, the large differences in reproductive potential between castes result in conflicts over caste fate during development. Here, we present the first comprehensive review on caste fate conflict, drawing on data from diverse taxa and recent theoretical advances. In many eusocial species, caste fate is determined by differential feeding, which results in caste fate being socially controlled, thereby aligning larval development with the collective needs of the colony. However, in some taxa, mechanisms of individual self-determination disrupt this balance, leading to overproduction of reproductive individuals at the expense of workers, with significant costs to colony fitness. Such conflicts are particularly pronounced in some stingless bees and lower termites, where larvae can bypass social control to determine their own caste fate. Indications of caste conflict can also be found in other groups, such as in some parasitic ants and in ant hybrid zones. Overall, the observed dynamics illustrate how conflicts in biological systems can be resolved in favour of either individual or collective interests, and how this affects the functioning of higher levels of organisation.