Disruption of collective behaviour correlates with reduced interaction efficiency.

Group-living organisms commonly engage in collective behaviour to respond to an ever-changing environment. As animals face environmental change, establishing the mechanisms of information used to collectively behave is critical. Western honeybees (Apis mellifera) are highly social insects that tightly coordinate many individuals to ensure optimum colony function. We used fanning, a collective thermoregulatory behaviour that depends on both social and thermal contexts, as a case study for collective behaviour. To identify potential mechanisms behind the coordination of fanning, we used oxytetracycline, an antibiotic used in apiculture and known environmental pollutant that impairs bee physiology and behaviour. Specifically, we hypothesized that interactions drive the fanning response in honeybees and predicted that oxytetracycline would disrupt social interactions which will lead to a reduced fanning response. We found that longer exposure to antibiotics decreases fanning. Using automated tracking, we show that antibiotic treatment reduces the number of interactions, impeding the social dynamics within these small groups. Our results contribute strong evidence that interactions between individuals may drive the collective fanning response in honeybees. This work emphasizes the importance of understanding the social mechanisms that underlie collective animal coordination and how the effects of pollutants on an individual can scale to affect populations.