Shani found an interesting link between the level of aggression between workers from different monogyne Cataglyphis niger colonies and whether or not sexuals (gynes or drones) were present in the nest:
These are results from behavioral assays of dyadic encounters between a pair of workers from different colonies. There was a substantially elevated level of aggression (* indicates statistical significance in Kruskal-Wallis tests) in encounters between workers that came from two nests where we found sexuals (S-S) relative to encounters where one or both workers came from nests where we did not find sexuals (N-S or N-N). Note that all of the ants in this experiment were sampled at the same time during the reproductive season (just before the sexuals leave the nests for their mating flight). Interestingly, Shani also observed that nests that produce gynes are a little more aggressive than nests that produce drones.
Shani also analyzed the cuticular hydrocarbons (CHC) of the same colony samples, which are known to be the chemical cues used by ants to recognize their nestmates. She tested for an association between chemical dissimilarity of different colonies and the aggression in their interactions. Surprisingly, there wasn't much of an association between the two variables, except for a slight positive correlation for the nests that had sexuals (that were more aggressive in general):
One might expect that ants would be more aggressive towards non-nestmates that come from colonies with a more dissimilar colony odor, but this does not appear to have a substantial effect on their aggressiveness.
Shani also confirmed the "nasty neighbor" effect, which was previously reported in Cataglyphis. For more details please check out our paper on bioRxiv (now in review).