Discrimination of conspecifics from heterospecifics in a hybrid zone: Behavioral and chemical cues in ants

Abstract

Species and nestmate recognition in social insects occurs mostly through cuticular hydrocarbons acting as chemical cues. These compounds generate a colony-specific odor profile depending on genetic and environmental factors. Species and nestmate recognition results in specific behavioral responses, regulating the level of aggression toward other individuals during an interaction. Although species discrimination and recognition cues have been poorly studied in the context of interspecific hybridization, such systems offer an opportunity to further investigate the influence of heritable and environmental factors on recognition. We explored the strength of discrimination in a hybrid zone between two ant species-Tetramorium immigrans and T. caespitum-by comparing cuticular hydrocarbon profiles and measuring intra-and interspecific worker aggression in both areas of sympatry and areas of allopatry among species. Species cuticular hydrocarbon profiles were well-differentiated and interspecific aggression was high, revealing highly discriminating species recognition cues. Hybrids' cuticular hydrocarbon profiles consisted of a mixture of the parental bouquets, but also exhibited hybrid-specific patterns. Behavioral assays showed that T. immigrans is as aggressive toward hybrids as toward heterospecifics. Finally, aggression between heterospecific workers was lower when interacting individuals came from areas of sympatry among species than from areas of allopatry. Taken as a whole, these findings paint a particularly complex picture of the recognition system in T. immigrans, T. caespitum, and their hybrids, and highlight that hybrid zones afford a still underexplored opportunity for investigating recognition mechanisms and discrimination between species.

Not dear neighbours: Antennation and jerking, but not aggression, correlate with genetic relatedness and spatial distance in the ant Lasius niger

“…The latter case could be partly explained by the homogeneous environmental conditions within the studied area. InCordonnier et al (2022), higher levels of aggression were observed between allopatric individuals compared with individuals sharing similar environmental characteristics. Here, the relative similarity between nests in terms of substrate or available food could also have induced a homogenisation of cuticular hydrocarbons, with a consequent reduction in recognition of non-nestmates and aggressiveness(van Zweden & d'Ettorre, 2010).…”