Behavioural individuality of female mice and social organization

The mechanisms underlying social organization in mice have predominantly been studied in male colonies, where sociability predicts higher rank and high-ranked individuals show greater anxiety. Here, we demonstrate that groups of isogenic female mice also form stable social hierarchies. Our data indicate that females destined for high rank already exhibit greater sociability and possibly higher anxiety before group formation, and these traits remain consistent afterwards. We further investigated the influence of sex by creating mixed-sex colonies, which revealed a similar hierarchical structure, with both males and females having equal chances of becoming high- or low-ranked. We previously found reduced dopamine neuron activity in high-ranked males; in contrast, high-ranked females show the opposite pattern. Furthermore, while glucocorticoid receptor signaling in dopaminoceptive neurons restricts high rank in males, this effect is absent in females. Overall, these results highlight sex-specific mechanisms that contribute to social ranking and related behavioral traits in mice.