Division of labor is associated with age-independent changes in ovarian activity in Pogonomyrmex californicus harvester ants

An age-independent division of labor can develop in both the reproductive (queen) and non-reproductive (worker) castes of Pogonomyrmex californicus harvester ants, and individuals develop biases for in-nest activities or external foraging. Additionally, ant ovaries normally atrophy in foragers compared to nest-biased workers (nurses). However, it is not clear whether these ovarian changes are due to changes in behavior or age, since foragers are typically older individuals. Here, we clarify this relationship in P. californicus queens and workers by comparing ovarian activity in same-aged ants that exhibit divergent behavioral biases. We found that foraging individuals had significantly reduced ovarian activity compared to their nest-biased counterparts, thereby linking changes in the ants' reproductive system to social task performance rather than to age. The general finding that ovarian physiology is associated with social insect behaviors is consistent with the hypothesis that reproductive physiology may have played an important role in the evolution of social insect behavior.