Résumé
Social organization and division of labour are fundamental to animal societies1,2,3, yet how these structures emerge from individual interactions and are shaped by neuromodulation remains unclear. Here, using behavioural tracking in a semi-natural environment, neural recordings and computational models that integrate reinforcement learning and social condition, we show that triads of isogenic mice develop specialized roles spontaneously while solving a foraging task under social constraints. Notably, despite minor intra-sex differences in behaviour when mice were tested alone, male triads formed stable worker–scrounger relationships driven by competition, whereas female triads adopted uniform, cooperative strategies. These sex-divergent roles were shaped by dopaminergic activity in the ventral tegmental area. Model analysis revealed how intra-sex and inter-sex parameter differences in resource exploitation, combined with contingent social interactions, drive behavioural specialization and division of labour. Most notably, it highlighted how contingency, amplified by competition, magnifies individual differences and shapes social profiles. The plastic, adaptive nature of social organization was apparent when sex mixing or reintroducing experienced individuals into naive groups reshaped role distribution. Furthermore, dopaminergic manipulations confirmed this plasticity, reshaping roles and altering group structure. Our findings support a multi-scale feedback loop whereby social context shapes neural states, which in turn reinforce behavioural specialization and stabilize social structures.