Parasite infection impairs the shoaling behaviour of uninfected shoal members under predator attack

Abstract A key benefit of sociality is a reduction in predation risk. Cohesive group behaviour and rapid collective decision making are essential for reducing risk groups. Parasite infection might reduce an individuals’ grouping behaviours thereby change the as whole. To investigate relationship between parasite behaviours, we studied groups three-spined sticklebacks, Gasterosteus aculeatus , varying number individuals experimentally infected with cestode Schistocephalus solidus . We six sticklebacks containing 0, 2, 3, 4 or 6 before after simulated bird attack. predicted that would have reduced shoaling swimming speed presence within cohesion speed. Uninfected fish increased more than In both uninfected fish, were dominated by frequent character (uninfected versus infected). Interestingly, equal numbers showed least had lowest speeds, suggesting these failed to generate majority therefore displayed signs indecisiveness their most. Our results provide evidence negative effect on group’s behaviour, potentially deteriorating making. The thus far-reaching consequences natural populations under Significance statement Parasite-infected often show deviating behaviours. This anti-predator benefits living. However, it unknown whether such deviations influence members By infecting investigating rates, differ from sticklebacks. Additionally, affected shoal members. shoals less cohesive move slower compared fish. Furthermore, rate crucial how behaves.