Collective behaviours in wildlife, such as schooling in fish, are key traits shaping ecological communities and demographic processes. The performance and outcomes of such collective actions rely heavily on the interactions among group members. Yet, whilst exposure to pharmaceutical pollutants have been shown to elicit a range of behavioural effects on individual organisms, research on how these individual effects manifest at the group-level is severely lacking. This is a critical knowledge gap because many animal species rely on the ability to form cohesive groups that are essential to their feeding and mating biology, as well as for their capacity to avoid predators.
In this study, we examined how a multi-generational exposure to a pervasive antidepressant pollutant, fluoxetine, affects the structure, movement and foraging behaviour of guppy (Poecilia reticulata) schools. We tested mixed-sex schools of fish across two ecological contexts (in an open arena and in the presence of food) five times, both before and after exposure to one of three ecologically relevant exposure treatments (0 ng/L, 30ng/L, and 300 ng/L). We quantified repeatable group-level behaviours and outcomes, including group cohesion, alignment, leadership, and foraging efficiency using high-throughput animal tracking software. Since fluoxetine has previously been shown to increase activity and decrease sociality in fish, we predicted that fluoxetine exposed fish would exhibit weaker collective movement (e.g. reduced cohesion and alignment), resulting in a breakdown in group performance and consistency across contexts. I will present preliminary findings from this work, and show how behavioural tests in social isolation are insufficient for predicting the environmental risk of chemical pollutants in social species. I will also discuss robust methodological approaches for testing ecologically relevant behaviours across multiple levels of biological organization – from individuals to animal social groups.