Strain differences in zebrafish (Danio rerio) social roles and their impact on group task performance

"Key" individuals in a social group are those that are centrally connected and thus serve as a hub for information flow across the group. From this position, they have the potential to have a powerful influence on group dynamics and performance. Here, we use metrics from social network theory to identify Key individuals in groups of 3-4 zebrafish (Danio rerio), and to measure the impact of removing those individuals from the group. We compared the results for two genetically distinct strains of zebrafish and found that although their social dynamics were superficially similar, one strain (Scientific Hatcheries, SH) responded to social perturbation, whereas the other (Parganas North, PN) did not. For both strains, groups that retained their Key fish performed better on a simple group foraging-learning task than did those from which the Key fish had been removed. However, the SH strain learned the task more quickly than did the PN strain, perhaps in part because of sex differences in task performance or because of strain differences in the reaction to experimental disturbance. We also confirm the utility of measures of social dynamics and social role that can be estimated reliably from very short observation sessions and by relatively untrained observers. These results set the stage for future research into the genetic mechanisms underlying social roles and group learning in vertebrates.