Rank- and threat-dependent social modulation of innate defensive behaviors.

Fear and defense are among the most fundamental survival behaviors and are profoundly influenced by the social environment in group-living animals. However, it remains poorly understood how social context-and particularly dominance hierarchy, a defining feature of many social species-modulates defensive strategies under naturalistic conditions. To address this question, we investigated the social modulation of innate fear in mice exposed to two ethologically relevant threats: a transient visual looming stimulus and a sustained predatory threat posed by a live rat. We found that social presence alleviated threat-induced stress and modulated defensive behaviors in a rank- and threat-specific manner. During looming exposure, it reduced immediate defensive responses and alleviated post-looming anxiety, with dominants deriving greater benefit. During rat exposure, it promoted a shift from passive to active defense, again most prominently in dominants. These behavioral changes were accompanied by reorganization of transitions between defensive states, indicating that dominance hierarchy shapes both the expression and temporal organization of innate defensive behaviors. Conversely, threat exposure strengthened social engagement, with dominant mice exhibiting more proactive social behaviors and subordinate mice responding more readily to dominant social initiations. Together, these findings demonstrate how dominance hierarchy modulates defensive responses to distinct naturalistic threats and, in turn, how threat experience shapes social behavior, providing a behavioral framework for probing the neural basis of socially modulated innate fear.