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. While previous research has largely focused on learned fear paradigms, these approaches fail to capture the complexity of naturalistic threats. It remains poorly understood how social context--and particularly dominance hierarchy, a defining feature of many social species--modulates defensive strategies under ethologically relevant 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 live rat. Pair-housed mice with established dominance ranks were tested alone or with their social partner, and their behaviors were quantitatively analyzed. We found that social presence alleviates threat-induced stress and modulates defensive behaviors in a rank- and threat-specific manner: during looming exposure, it reduces immediate defensive responses and alleviates post-looming anxiety, with dominants showing greater benefit; during rat exposure, it promotes a shift from passive to active defense, again most prominently in dominants. Furthermore, threat exposure reinforces social roles and enhances group cohesion. 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 framework for probing the neural basis of socially modulated innate fear.