Social transmission of fear is disrupted by pharmaceutical pollution

Jack Lewis Manera , Eleanor R Moore, Mirjam Amcoff, Bob B M Wong, Jake Mitchell Martin , Niclas Kolm, Michael Grant Bertram

Social information transfer enables rapid responses to threats and underpins collective predator avoidance across taxa. Yet whether the growing threat of environmental pollutants, such as pharmaceuticals, disrupt this process remains unknown. Here, we show that the widespread antidepressant pollutant amitriptyline disrupts fear contagion—the automatic matching of an individual’s behavioural state to that of a frightened conspecific—in the guppy (Poecilia reticulata). Amitriptyline exposure impaired the translation of socially acquired threat information into behavioural responses and weakened behavioural coupling with distressed conspecifics, while responses to directly detected threats remained unaffected. These findings provide empirical evidence that pollution can degrade the dynamics of fear contagion—a fundamental mechanism underpinning rapid, socially mediated responses to predation risk. By eroding the integrity of social information networks, psychoactive contaminants may compromise coordinated antipredator behaviour and reshape predator–prey dynamics in polluted ecosystems, revealing a previously unrecognised dimension of ecotoxicological risk.