The differential response of workers and queens of the ant Lasius niger to an environment marked by workers: ants dislike the unknown.

It is well known that ants can use cuticular hydrocarbons (CHCs) as a specific recognition cue. Most previous studies addressed the perception of CHCs occurring on the cuticle. However, the presence of CHCs in the environment (e.g., on the substrate) and the role of these compounds as a signal cue are less clear. In this study of the ant L. niger, CHCs were extracted from corpses of workers, from the legs of workers and from filter paper marked by workers. Behavioural choice tests were then performed to study the reactions of workers and queens to CHC passively deposited on the substrate by walking workers. A GC-MS analysis of the CHCs revealed a complex mixture of 28 peaks composed of linear alkanes, alkenes and mono-, di- or trimethylalkane. This mixture was consistently present in the three sources tested (corpses of workers, the tarsus of workers and paper marked by walking workers). Nevertheless, discriminant analyses distinguished clearly among the three types of profiles. The results of our behavioural experiments showed that the workers were able to distinguish between marked and unmarked papers but that they exhibited no preferences for different types of marked papers (papers marked by workers from their own colony or papers marked by workers from a different colony). In queens, the perception of marked papers depended on age or physiological state. Just-mated queens did not discriminate between unmarked papers and papers marked by an alien colony. In contrast, the egg-laying queens 3 days after mating significantly favoured the marked papers. We discuss the ecological relevance of the differences in decision-making between castes.