Data from: Experience and motivation shape leader-follower interactions in fish shoals

Leadership is an important process shaping collective movement in some species. Recent work has demonstrated that experienced or motivated individuals can emerge as leaders, and provides insight into the mechanisms by which this occurs. Ultimately, leadership depends on the effectiveness with which would-be leaders can entrain followers, and although the properties of leaders have received much attention, less is known about the factors that affect the propensity of their groupmates to follow them. Here, the roles of experience and state (hunger) in shaping leader and follower behavior were investigated using shoals of sticklebacks (Gasterosteus aculeatus). A first experiment revealed that individuals trained to approach a target could entrain and lead their naive groupmates out of a refuge toward it, and that they did so more effectively when they (the trained fish) were food deprived. In the second experiment, the hunger level of the trained fish was held constant, whereas that of the naive fish was varied. Here, leadership by trained fish was only apparent when the hunger levels of the naive group members were intermediate. When naive fish were recently fed, they took a long time to visit the target and their arrival times were not affected by the presence of a trained individual. Very hungry groups recruited to the target most rapidly, but again with no evidence of influence by their trained groupmates. These experiments demonstrate that leadership in animal groups depends not only on the state and experience of the leader but also on that of the potential followers