The effect of chemical distances, physical distances, and the presence of sexuals on aggression in Cataglyphis desert ants

In social insects, non-nestmates interactions are typically agonistic and many factors may influence the degree of exhibited aggression. Two of these factors are the physical proximity between nests and the chemical dissimilarity between colonies chemical signatures. We studied a population sample of 43 colonies of Cataglyphis niger ants distributed along a transect of [~]4KM. This geographic distribution allowed us to examine correlations of aggression levels with physical and chemical distances. Ants were collected before mating season, when sexuals (unmated gynes and drones) could be found in nests. In our sample, colonies had either gynes or drones but never both. The presence of sexuals, therefore, was another factor we took into account in our behavioral analyses. Workers from nests with sexuals were more aggressive towards conspecifics than workers from nests where sexuals were absent. We also found those workers to be more vigorously active towards colonies with greater chemical distances, while workers from nests without sexuals were indifferent to chemical distances. We therefore concluded that ants are able to detect differences in chemical dissimilarity, but their aggression levels are mainly determined by other mechanisms. A possible additional mechanism is associative learning and long term memory of the chemical signatures of neighboring colonies. Such learning is supported by our finding that aggression is higher towards neighboring nests, which is in line with the previously reported nasty neighbour effect in Cataglyphis ants. These results suggest that previous experience and learning of neural templates representing neighbors chemical cues is a stronger component than chemical dissimilarity in the mechanisms which determine aggression towards conspecifics in this species. We discuss possible explanations for the observed effect of the presence of sexuals on agonistic behavior and responsiveness to chemical distances.