Reproductive potentials of task-shifting workers in a queenless ant

Eusocial insects, such as ants and honeybees, are characterized by the sophisticated division of labor among workers. In addition to age polyethism, the division of labor is maintained by task shifting of workers in fluctuating environments. While task experience is considered a key factor in realizing the task shifting, our previous study suggests that the experience promotes the task shifting of not nurses but foragers in a queenless ant, Diacamma cf. indicum from Japan. Therefore, we hypothesize that different mechanisms, e.g., reproductive potential, underlie task shifting between the nurse and the forager. In this study, we examined the relationship between the ovarian development of workers and their task shifting, using D. cf. indicum. We also examined the relationships between the expression levels of Vitellogenin (Vg), VgR, Vg-like A, Vg-like B, Vg-like C, and foraging gene and the task shifting of the nurses. Our results showed that more than half of the nurses maintained their reproductive potential—as evidenced by their well-developed ovaries—even when they had shifted to the foraging task. In contrast, the foragers—whether they had shifted to the nursing task or not—remained with regressed ovaries. Finally, we found that the nurses who shifted to the foraging task exhibited low expression levels of Vg, VgR, and Vg-like A. In conjunction with previous studies, our results suggest that this physiological contradiction may underlie the different mechanisms that lead to the task shifting between the nurse and the forager in this species.