Linking levels of personality: personalities of the ‘average’ and ‘most extreme’ group members predict colony-level personality

• We examined the effects of colony morphology and composition on colony-level personality in Stegodyphus sarasinorum.
• Individual differences in behaviour were stable and correlated across contexts in a behavioural syndrome.
• Natural and artificially reconstituted colonies showed stable differences in collective foraging behaviour.
• Colonies with smaller and bolder spiders showed more aggressive foraging behaviour.
• The best predictor of colony-level behaviour was boldness of the boldest individual (explaining 67–69% of the variation).

Understanding how colony-level behaviour is determined is of evolutionary significance because colony-level traits can influence individual fitness and group success. Here we explore how the composition of individual behavioural types within colonies influences colony-level behaviour in the social spider Stegodyphus sarasinorum. First, we tested whether S. sarasinorum show stable individual differences in behaviour (i.e. individual personalities) and whether aspects of individuals' behaviour are correlated across contexts, in the form of a behavioural syndrome. As documented in many other animals, S. sarasinorum showed stable individual differences in behaviour that were repeatable across time, and correlated across contexts (i.e. aggressiveness, boldness). Second, we tested for and confirmed the presence of consistent intercolony variation (i.e. colony-level personalities) in collective foraging behaviour. Third, we generated artificially reconstituted colonies of known group size and personality composition to test for associations between colonies' personality composition and their collective foraging behaviour. In experimental colonies, we found that the average phenotypes of colony constituents were associated with colony-level behaviour, where colonies composed of smaller and bolder spiders were more responsive during foraging. However, the single best predictor of colony-level behaviour was the behavioural type of the single most extreme individual, where the boldness score of boldest individuals explained 66–69% of the variation in colony-level behaviour. Together, our results suggest that variation in the personality composition of social groups may be an important driver of variation in colony-level personality.