The link between social rank and behaviors in female mice groups

The mechanisms underlying the emergence of a social organization in mice are mainly studied in unisex male colonies. In isogenic male mice groups, we previously showed that sociability trait predicts rank attainment in social hierarchy whereas differences in anxiety between highest and lowest ranked individuals appears after rank establishment (Battivelli et al. 2024).Here we show that isogenic female mice grouped by four rapidly form enduring social hierarchy, that can be analysed using a precedence test based on encounters within a plastic tube from which lower-ranked individuals come out backward. Assessing individual behavior before and after colony formation, we showed that for females higher sociability and anxiety are pre-existing traits in future highest ranked individuals. This differs from male colonies for which only a difference in sociability preexisted. We further assessed whether ranking was sex dependent. We grouped a vasectomized male with three females. They formed a hierarchical organization similar to that of unisex colonies with an equal probability for both sexes to reach highest and lowest ranks.