Layered social competition coordinates reproductive hierarchy formation in ants

Social interactions establish reproductive hierarchies and regulate division of labor in eusocial insect colonies. In the ant Harpegnathos saltator , queen loss induces a subset of workers to transition into reproductive pseudo-queens, known as gamergates, through a ritualized antennal-dueling tournament that can last for more than a month. Gamergate transition is associated with sustained dueling engagement, yet the interaction networks and social dynamics that shape reproductive hierarchy formation remain unclear. Here, we combine long-term automated tracking with behavioral classifiers to systematically quantify social interactions, including antennal dueling and two distinct biting behaviors: aggressive grooming and mandible locking. We find that antennal dueling is organized into two activity states, an engaged state and a disengaged state, and that persistent maintenance of the engaged state, rather than transient entry into it, predicts successful transition to gamergate fate. Early access to abundant food shapes dueling activity and biases ants toward entry into the engaged state. Moreover, engaged-state individuals exhibit a strong assortative preference for dueling with one another and cluster spatially within the colony. We further show that mandible locking precedes transitions out of the engaged state, whereas aggressive grooming reinforces the disengaged state, together contributing to stabilization of worker fate. Our findings reveal how structured social interactions organize reproductive hierarchy formation by regulating stable behavioral states associated with caste fate.