Fear generalization, cross-sensitization and behavioural responses to multiple dangers in a freshwater snail

Behavioural responses to multiple stressors play a major role in survival and fitness. In this context, an important issue that has rarely been tested is fear generalization, where responses to disparate threats are correlated at the individual level. Furthermore, while sensitization to stressors is well studied, cross-sensitization, where exposure to one threat increases behavioural responsiveness to unrelated threats, is under-studied. We exposed juvenile Physid snails (Physa acuta) to one of two disparate threats throughout their developmental period: predator cues and ash, a wildfire-derived environmental stressor. We then assayed snails' responses, relative to control snails that had no experience with either threat, to three acute exposures of each stressor. We documented consistent individual differences in snails' avoidance of predation cues and of ash. Exposure to either stressor led to sensitization at short- and long-term timescales. Importantly, snails exhibited fear generalization; individuals that avoided predation cues more strongly also avoided ash more strongly. We also documented cross-sensitization; snails reared with ash showed heightened responses to predator cues while snails reared with predator cues showed heightened responses to ash. To our knowledge, this is the first study documenting behavioural cross-sensitization for threats as disparate as predation risk and fire residue in a non-human animal.