Ontogenesis and dynamics of aggregation in a solitary spider

Aggregation is a prerequisite for transitions from a solitary to a social life. One evolutionary route to sociality implies the maintenance of cohesion among juveniles. The study of the influence of ontogenesis on mutual tolerance appears of fundamental importance for understanding social transitions. Spiders are particularly relevant models to address these questions. All solitary spiders have a transient gregarious phase prior to their dispersal and solitary and social species are included within the same genus. We characterized the patterns of aggregation during ontogenesis in the solitary spider Agelena labyrinthica. Our results showed that the intensity of aggregation in solitary spiderlings declined from the day of emergence to the sixth week. We developed an agent-based model implementing behavioural rules measured experimentally to explore their relative contribution in the ontogenetic shift in social behaviours observed in solitary spiders. Combining experimental and theoretical approaches, we demonstrated that aggregation relied on a modulation of individual behaviours depending on the number of conspecifics perceived locally and that the decline in aggregation with age relied on variations in the strength of interattraction occurring during ontogenesis.