Familiarity, personality, and foraging performance in three-spined sticklebacks.

Animals can gain large benefits from living in groups but must coordinate with their groupmates in order to do so. Social interactions between groupmates drive overall group coordination and are influenced by the characteristics of individual group members. In particular, consistent inter-individual differences in behaviour (e.g. boldness) and familiarity between individuals in groups profoundly affect the individual interactions that mediate group coordination. However, the effects of boldness and familiarity have mostly been studied in isolation. Here we describe how familiarity and boldness interact to affect individual performance, leadership, and group coordination in small shoals of three-spined sticklebacks (Gasterosteus aculeatus) solving a novel foraging task. Groups of higher average boldness were less cohesive, but only when group members were familiar with one another. Familiarity affected shy and bold individuals' foraging performance and leadership tendencies differently depending on group characteristics: the shyest group member experienced declining foraging success and leadership with increased group boldness in familiar groups, but experienced the opposite effect on foraging and no effect on leadership in unfamiliar groups. The boldest group member, in contrast, exhibited the opposite pattern: leading and eating more with increasing group boldness in familiar groups, but eating less with increasing group boldness in unfamiliar groups. These results suggest that both boldness and familiarity are important for establishing group behaviour and coordination, and that consistent inter-individual differences in behaviour may primarily impact group coordination once familiarity has been established.