Amazonian social spiders share similar within-colony behavioural variation and behavioural syndromes

Although discrete morphological castes are a rarity in animal societies, trait differences among group constituents are pervasive and can have similar effects on group function. Spider societies lack discrete morphological castes, but colony constituents can differ along any number of trait axes (e.g. body size). Here we tested for consistent individual differences in social tendency in five tropical spider species (genus Anelosimus). We further determined the extent to which social tendency is correlated with other aspects of an individual’s behaviour that might reflect division of labour within colonies. We found that all five species showed repeatable within-species variation in social tendency, and increased social tendency was correlated with reduced aggressiveness towards prey and diminished boldness towards an aversive stimulus (i.e. test species shared a similar ‘behavioural syndrome’ of aggressiveness/sociality). Furthermore, colonies of some species (e.g. Anelosimus eximius, Anelosimus oritoyacu) appeared to be composed of varying proportions of two ‘behavioural types’, whereas other species (Anelosimus domingo, Anelosimus guacamayos) showed a more continuous distribution of trait values. Interestingly, irrespective of species, we detected a negative relationship between the frequency of aggressive colony constituents and group size, where larger colonies tended to have fewer aggressive females. Our results indicate that (1) the majority of social Anelosimus show similar within-species behavioural variation and syndromes, and (2) colony size either mediates the expression/development of individuals’ behavioural types, or is regulated by the frequency of behavioural types.

► We tested for consistent individual differences in social tendency in five tropical spider species (genus Anelosimus). ► All five species showed repeatable within-species variation in social tendency. ► Test species shared similar ‘behavioural syndromes’ of aggressiveness/sociality. ► Frequency of aggressive colony constituents was negatively correlated with group size. ► Group living in Anelosimus appears to be associated with depressed aggressiveness and diminished boldness.