Worker propensity affects flexible task reversion in an ant

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.