Aggression is task dependent in the red harvester ant (Pogonomyrmex barbatus)

In many animal species, the propensity for aggression is linked to social context. In social insects, aggressive interactions between colonies are related to the assessment of cuticular hydrocarbon profiles. We investigated how, in the red harvester ant, Pogonomyrmex barbatus, an individual ant’s task environment contributes to its hydrocarbon profile, and how task-specific differences in profiles are linked to aggression. We compared the hydrocarbon profiles of 200 individuals from 4 task groups and 10 colonies, and measured aggression of ants of specific task groups toward non–nest mates of neighboring and distant colonies. We found that task groups can be distinguished by their hydrocarbon profiles. Hydrocarbon profiles are more closely associated with task group membership than with colony identity. Ants of the patroller task group were more likely to be aggressive to non–nest mates than ants of any other task group. There was no correlation between the extent of aggression between task groups and the magnitude of difference in their hydrocarbon profiles. Nearby nests did not differ more in hydrocarbon profile than distant nests. Our results suggest that aggression in P. barbatus is task dependent and is not directly correlated with the magnitude of difference in hydrocarbon profiles.