Social conformity in solitary crabs, Carcinus maenas, is driven by individual differences in behavioural plasticity

Abstract

Group living is widespread in the animal kingdom and recent studies into the mechanisms underlying group cohesion and behavioural synchrony have highlighted the importance of between-individual behavioural differences (‘animal personality’). In group-living animals, social conformity occurs when animals compromise their own behaviour to the level of a certain behaviour displayed by another individual or a group, and the degree to which individuals conform can depend upon interindividual differences in behavioural types. Social conformity can increase group cohesion and ultimately predator avoidance and/or resource acquisition for group-living individuals. However, it remains unclear whether similar conformity effects exist in solitary species, many of which form temporary aggregations and, if so, whether changes in behaviour in the presence of conspecifics are dependent on individuals' personalities in solitary contexts. We studied the effects of social context (i.e. the presence of a conspecific) on behaviour in solitary shore crabs, using automated video tracking. Individuals differed consistently in their activity levels within and across contexts and were significantly more active in solitary than dyadic contexts. No differences in activity between same- and opposite-sex dyads were found. Crabs' activity levels were more similar when tested together than when tested alone, indicating a social conformity effect. Furthermore, more active behavioural types decreased their activity to a greater extent when paired with a conspecific. The sex composition of the dyad had no effect on changes in activity. Overall, our findings suggest that social conformity is moderated by individual behavioural differences in a solitary organism. It is often presumed that, over evolutionary time, the social structure of animal populations has important consequences for the evolution of personalities and vice versa. We suggest that studying solitary or facultatively social organisms may allow researchers to tease out causality between personality differences and socioecological dynamics.