Food resources, chemical signaling, and nest mate recognition in the ant Formica aquilonia

Animals such as social insects that live in colonies can recognize intruders from other colonies of the same or different species using colony-specific odors. Such colony odors usually have both a genetic and an environmental origin. When within-colony relatedness is high (i.e., one or very few reproductive queens), colonies comprise genetically distinct entities, and recognition based on genetic cues is reliable. However, when nests contain multiple queens and colonies comprise multiple nests (polydomy), the use of purely genetically determined recognition labels may become impractical. This is due to high within-colony genetic heterogeneity and low between-colony genetic heterogeneity. This may favor the use of environmentally determined recognition labels. However, because nests within polydomous colonies may differ in their microenvironment, the use of environmental labels may also be impractical unless they are actively mixed among the nests. Using a laboratory experiment, we found that both isolation per se and diet composition influenced the cuticular chemical profiles in workers of Formica aquilonia. In addition, the level of aggression increased when both the proportions of dietary ingredients and the availability of food were altered. This suggests that increased aggression was mediated by changes in the chemical profile and that environmental cues can mediate recognition between colonies. These results also suggest that the underlying recognition cues are mutable in response to extrinsic factors such as the amount and the composition of food.