Parasite infection disrupts escape behaviour in fish shoals

Many prey species have evolved collective responses to avoid predation. They rapidly transfer information about potential predators to trigger and coordinate escape waves. Predation avoidance behaviour is often manipulated by trophically transmitted parasites, to facilitate their transmission to the next host. We hypothesised that the presence of infected, behaviourally altered individuals might disturb the spread of escape waves. We used the tapeworm Schistocephalus solidus, which increases risk-taking behaviour and decrease social responsiveness of its host, the three spined stickleback, to test this hypothesis. Three subgroups of sticklebacks were placed next to one another in separate compartments with shelter. The middle subgroup contained either uninfected or infected sticklebacks. We confronted an outer subgroup with an artificial bird strike, and studied how the escape response spread through the subgroups. With uninfected sticklebacks in the middle, escape waves spread rapidly ...