The behavioural composition of a group and the dynamics of social interactions can both influence how social animals work collectively. For example, individuals exhibiting certain behavioural tendencies may have a disproportionately large impact on the group, and so are referred to as keystone individuals, while interactions between individuals can facilitate information transmission about resources. Despite the potential impact of both behavioural composition and interactions on collective behaviour, the relationship between consistent behaviours (also known as personalities) and social interactions remains poorly understood. Here, we use stochastic actor-oriented models to uncover the interdependencies between boldness and social interactions in the social spider We find that boldness has no effect on the likelihood of forming social interactions, but interactions do affect boldness, and lead to an increase in the boldness of the shyer individual. Furthermore, spiders tend to interact with the same individuals as their neighbours. In general, boldness decreases over time, but once an individual's boldness begins to increase, this increase accelerates, suggesting a positive feedback mechanism. These dynamics of interactions and boldness result in skewed boldness distributions of a few bold individuals and many shy individuals, as observed in nature. This group behavioural composition facilitates efficient collective behaviours, such as rapid collective prey attack. Thus, by examining the relationship between behaviour and interactions, we reveal the mechanisms that underlie the emergence of adaptive group composition and collective behaviour.

Groups of social predators capture large prey items collectively, and their social interaction patterns may impact how quickly they can respond to time-sensitive predation opportunities. We investigated whether various organizational levels of resting interactions (individual, subgroup , group), observed at different intervals leading up to a collective prey attack, impacted the predation speed of colonies of the social spider Stegodyphus dumicola. We found that in adult spiders, overall group connectivity (average degree) increased group attack speed. However, this effect was detected only immediately before the predation event; connectivity between 2 and 4 days before prey capture had little impact on the collective dynamics. Significantly, lower social proximity of the group's boldest individual to other group members (closeness centrality) immediately prior and 2 days before prey capture was associated with faster attack speeds. These results suggest that for adult spiders, the long-lasting effects of the boldest individual on the group's attack dynamics are mediated by its role in the social network, and not only by its boldness. This suggests that behavioural traits and social network relationships should be considered together when defining keystone individuals in some contexts. By contrast, for subadult spiders, while the group maximum boldness was negatively correlated with latency to attack, no significant resting network predictors of latency to attack were found. Thus, separate behavioural mechanisms might play distinctive roles in determining collective outcomes at different developmental stages, timescales, and levels of social organization.

No abstract

Significance statement 14Certain animals in a group, such as leaders, may have a more important role than other 15 group members in determining their collective behavior. Often these individuals are defined 16 by their behavioral attributes, for example, being bolder than others. We show that in social 17 spiders both the behavioral traits of the influential individual, and its interactions with other 18 group members, shape its role in affecting how quickly the group collectively attacks prey. 19 20 Abstract 21Groups of social predators capture large prey items collectively, and their social interaction 22 patterns may impact how quickly they can respond to time-sensitive predation 23 opportunities. We investigated whether various organizational levels of resting interactions 24 (individual, sub-group, group), observed at different intervals leading up to a collective prey 25 attack, impacted the predation speed of colonies of the social spider Stegodyphus dumicola. 26We found that in adult spiders overall group connectivity (average degree) increased group 27 attack speed. However, this effect was detected only immediately before the predation 28 event; connectivity two and four days before prey capture had little impact on the collective 29 dynamics. Significantly, lower social proximity of the group's boldest individual to other 30 group members (closeness centrality) immediately prior and two days before prey capture 31 was associated with faster attack speeds. These results suggest that for adult spiders, the 32 long-lasting effects of the boldest individual on the group's attack dynamics are mediated by 33 its role in the social network, and not only by its boldness. This suggests that behavioural 34 traits and social network relationships should be considered together when defining 35 keystone individuals in some contexts. By contrast, for subadult spiders, while the group 36 maximum boldness was negatively correlated with latency to attack, no significant resting 37 network predictors of latency to attack were found. Thus, separate behavioural mechanisms 38 might play distinctive roles in determining collective outcomes at different developmental 39 stages, timescales, and levels of social organization. 40 41 reduce the time and effort needed to capture prey, and increases the probability of success, 52 thus conferring important fitness benefits to all group members (Pasquet and Krafft, 1992). 53 At the same time, social groups often rely on particular individuals to expedite group 54 dynamics; such individuals have been termed 'keystone' individuals (Modlmeier et al., 55 2014b). 56It is still unknown how keystone individuals influence the performance of a group. 57Generally speaking, keystone individuals can either perform the work itself or catalyse the 58 work of other group members (Robson and Traniello, 1999), for example through social 59interactions. A recent model predicts that when the behaviour of group members is 60 persistent, social interactions play a larger role than behaviour in shapin...

No abstract