Presence of conspecifics reduces between-individual variation and increases avoidance of multiple stressors in bluegill

Individual animals differ in their responses to external stressors, and sociability has been shown to impact whether or not an individual will avoid a stressor. However, the effect of collective group behaviour on individual avoidance in response to a stressor has not been elucidated. In this study, we sought to determine whether stressor avoidance behaviour in individuals is affected by the behaviour of a familiar shoal, and if social personality is a driver of avoidance behaviour. Bluegill, Lepomis macrochirus, were exposed to either carbon dioxide or rising temperatures in a shuttle box choice tank. All bluegill were exposed to a stressor in isolation, then their social personalities were quantified using a social network assay. Bluegill were then exposed to the same stressor in the presence of a familiar shoal, with the entire shoal being able to respond to the stressor. We found that being in a shoal significantly decreased individual avoidance thresholds to both carbon dioxide and temperature, but neither avoidance behaviour in isolation nor individual social personality type was predictive of this response. The presence of the shoal was the primary driver of the difference in avoidance behaviour when bluegill were in isolation versus when they were in groups. Potential mechanisms, both behavioural and physiological, for the relationship between group behaviour and stressor avoidance are discussed. Our results provide evidence that group movements impact individual avoidance of stressors, which may have implications for the behaviour of animals in response to decreasing habitat quality.