Stable social groups foster conformity and among-group differences

Abstract

The social niche hypothesis theorizes that repeated social interactions between group members is an important mechanism for generating consistent individual differences in behaviour. However, such frequent interactions also have the potential to mask or suppress behavioural differences if individuals conform towards a group behavioural norm (i.e. the social conformity hypothesis) by either synchronizing their behaviour or shifting their behaviour towards that of influential group members. Both of these predictions hinge on the notion that social feedback among group members plays a key role in modulating consistent behavioural variation; thus, in the absence of such feedback, it could be expected that such consistent variation will be reduced. Here, we investigated how a 1-month housing with a stable social group, as opposed to being socially isolated, affected consistent individual differences in the shoaling tendencies of threespine stickleback, Gasterosteus aceluteus . Specifically, we repeatedly tested the tendency of individual sticklebacks to shoal with conspecifics before and after their social experience. In support of the social conformity hypothesis, we observed a four-fold increase in among-group differences, but no change in among-individual differences, in the shoaling tendencies of sticklebacks housed in groups. A post hoc analysis revealed that the increase in among-group differences may have been driven by the most ‘social’ pretreatment group member. Conversely, fish that were housed in isolation, expressed a notable, albeit nonsignificant, decrease in individual shoaling variation and repeatability. This decrease in shoaling variation corresponded with an increase in the average shoaling tendencies of solitary fish post-treatment, suggesting that solitary fish converged towards a similarly high level of shoaling tendencies post-treatment. For both treatment groups, however, we found among-individual positive correlations in pre- and post-treatment shoaling tendencies, suggesting that individuals may inherently differ in their shoaling tendencies, but that the social environment plays an important role in mediating the expression of these differences. • Social groups can either suppress or generate consistent variation in behaviour. • Group differences in shoaling tendencies emerged in fish social groups after 1 month. • Fish altered their shoaling behaviour according to their most social group member. • Fish housed in isolation became more social and lost variation in shoaling behaviour. • Our results provide support for the social conformity hypothesis.