Behavioural syndromes at multiple scales in Myrmica ants

Behavioural syndromes (correlations between suites of behavioural traits) have been documented in a wide range of animals and are important for the understanding of evolution and ecology. Previous research has focused primarily on behavioural syndromes composed of individual animals: we investigated behavioural syndromes at the individual, caste and colony levels in Myrmica ants. We first related an individual’s position on a behavioural syndrome (i.e. its behavioural phenotype) to the role it took within the colony (i.e. its caste). At an individual level, behavioural phenotype was strongly related to task allocation: individuals from the patroller caste were bolder, more aggressive and more active than individuals from both the foraging-recruit and brood-carer castes, which did not differ from each other. Second, the patroller caste exhibited a boldness–aggression syndrome that was not present in brood carers. Finally, at a colony level, sociability was correlated with boldness. Colonies containing individuals that spent more time interacting with one another were also composed of individuals that responded boldly to an introduced alarm stimulus. Furthermore, the mean behavioural scores of the patroller and brood-carer castes were positively correlated in many key behaviours, including activity level, aggression, sociability and response to an alarm, which suggests that colonies were internally concordant (behaviourally consistent across castes). Our results show conclusively that ants exhibit behavioural syndromes not only at the individual level but also at the caste and colony levels. This raises the intriguing possibility that other highly social animal groups may similarly exhibit group-level behavioural syndromes.