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 Stegodyphus dumicola. 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.
Spider resting interaction networks
Edge list of spider resting interactions. 24 groups of 10 adult female spiders, from 3 source colonies. Groups had one of three boldness compositions: all bold spiders, all shy spiders, and 9 shy individuals with one bold individual. Overall, these groups contained more initially shy individuals than bold individuals because this represents the spiders’ natural boldness distribution. We manually recorded the physical contacts among spiders three times a week, during the day, while spiders are inactive for long periods of time. Therefore, we refer to these interactions as ‘resting interactions’ and define an interaction as a physical contact between any body parts of two spiders, when the colony is not active. Colony activity is minimal in the lab (initial web construction and collective predation when fed) and most of the time spiders are resting. Therefore, observing their interactions every 2-3 days samples most social interactions. We used the interactions to construct unweighted (binary), undirected (symmetrical), networks for each spider group during each observation. Spiders were collected from roadside Acacia trees in the Northern Cape of South Africa in March 2016. Groups were housed in large round containers (11cm diameter, 10cm depth) with a vertical wire mesh (a 5x5cm sheet) to allow the spiders to build both a retreat and a capture web. Experimental observations were made during June-August, 2016.
spider_networks.csv
Spider boldness measurements
Each spider’s boldness was measured once a week a total of 7 times, using an assay that recorded the recovery of a spider from exposure to air puffs, which mimic the approach of an avian predator. After placing spiders individually in a plastic container (15x15cm) we waited for 30sec until the spiders were acclimated and stopped moving around the arena. We then administered two puffs of air to the anterior prosoma using an infant nose-cleaning bulb. Spiders react to the air puffs by huddling, i.e. pulling their legs under their body, and remaining motionless. Boldness was measured as the latency to resume movement and move one body length. Because bolder individuals resume movement faster, the latency to resume movement was subtracted from the maximum duration of the procedure (600s) to create a metric that increases with boldness. We designated as ‘shy’ those individuals with a latency to resume movement of 400-600s (boldness of 0-200), while ‘bold’ individuals were those with a latency to resume movement of 0-200s (boldness of 400-600).
spider_boldness.csv
