Nestmate recognition of early brood in ants

Abstract Brood is critically important in social insect colonies. It carries the colony fitness through delivering future reproductive adults as well as workers that will increase the colony’s workforce. Adoption of non-nestmate brood can be a mean to increase colony’s workforce but entails the risk of rearing unrelated sexuals or social parasites. For early brood (eggs and L1 larvae), this balance is less positive as young brood need a substantial amount of resource before becoming workers. Thus, it appears beneficial for ant workers to discriminate between nestmate and alien brood using the chemical cues displayed at the brood’s surface. However, the chemical signature of ant early brood stages and its use by workers remains understudied. To fill this gap, we investigated the chemical basis of early brood nestmate and cross-species recognition in six Formicoid ants. We also tested the discrimination behaviour of workers in brood retrieval trials. We observed clear species-level cues and discrimination against heterospecific brood. We also found that eggs and most young larvae display a colony signature but that only some species discriminate against non-nestmate eggs and L1 larvae. Interestingly, these species appear to also be those belonging to genera subject to brood parasitism