Worker propensity affects flexible task reversion in an ant

Abstract

Social animals exhibit well-organized task allocation among group members. In ants, a large group of eusocial Hymenoptera, the division of labor among workers is maintained by behavioral flexibility, providing robustness against fluctuating environmental conditions. Under stable conditions, worker tasks shift from the inside (e.g., nurses) to the outside (e.g., foragers) of the nest as age increases along this gradient. If the colony’s age structure is unbalanced, some workers compensate for vacant tasks, regardless of their age. However, such behavioral flexibility mechanisms are not clearly described in most ant species. In this study, using the ant Diacamma sp. from Japan, we focused on task reversion (i.e., foragers shifting to nursing roles, reverted nurses). By intermittent observation, we examined how the proportion of trials detected outside the nest of foragers, as foragers’ behavioral propensity, impacts task reversion when caste composition is significantly altered. We revealed that foragers with low proportion were the most likely to become reverted nurses, suggesting that the worker propensity is strongly correlated to task reversion. Moreover, task allocation among workers emerged on day 2 after colony disturbance, suggesting that the division of labor can promptly reconstruct when the age structure of the colony is accidentally altered by external factors. It also illustrates the importance of behavioral propensity in maintaining social systems. We also discussed the mechanisms of flexible task allocation among the workers in terms of self-organized process. In eusocial Hymenoptera (e.g., wasps, honeybees, and ants), the division of labor is maintained by workers’ behavioral flexibility, which is itself driven by the needs of the colony. However, the detailed mechanisms underlying ant behavioral flexibility remain unclear. Focusing on task reversion in foragers shifting to nursing roles regardless of their age-dependent assigned task, we revealed that behavioral propensity strongly affects task reversion in the Diacamma sp. As ant colonies generally have an unbalanced age structure and inhabit unstable environments, behavioral flexibility is thought to be important to maintain the division of labor. Moreover, our study could be applied to examining molecular and physiological basis of task reversion in ant species.