Significance of chemical recognition cues is context dependent in ants

Recognition of group members is of fundamental importance in social animals, allowing individuals to protect resources against intruders and parasites, as well as ensuring social cohesion within the group. In ants and other social insects, social recognition relies on multicomponent chemical signatures, composed primarily of long-chain cuticular hydrocarbons. These signatures are colony specific and allow discrimination between nestmates and non-nestmates. Nevertheless, the mechanisms underlying detection, perception and information processing of chemical signatures are poorly understood. It has been suggested that associative learning might play a role in nestmate recognition. We investigated whether Camponotus aethiops ants can associate a complete cuticular hydrocarbon profile, consisting of about 40 compounds, with a food reward and whether the new association, developed in an appetitive context, affects aggression against non-nestmates carrying the hydrocarbon profile associated with food. Individual ant workers were able to associate the non-nestmate chemical profile with food. However, conditioned ants were still aggressive when encountering a non-nestmate carrying the odour profile used as training odour in our experiments. This suggests that ants, like some, but not all other insects, show interactions between different modalities (i.e. olfactory and visual), and can treat complex chemical cues differently, according to the context in which they are perceived. This plasticity ensures that learning in an appetitive context does not interfere with the crucial task of colony defence.