Discrimination of non-nestmate early brood in ants: behavioural and chemical analyses.

Brood is critically important in social insect colonies. It carries the colony's fitness by delivering future reproductive adults as well as workers that will increase the colony's workforce. Adoption of non-nestmate brood can increase the colony workforce but entails the risk of rearing unrelated sexuals or social parasites. Thus, theory would predict that ant workers will evolve the ability to discriminate between nestmate and alien brood using the chemical cues displayed at the brood's surface. This appears especially true for eggs and first-instar (L1) larvae, which require more resources than older brood before becoming adult workers. However, the chemical signature of ant early brood stages and its recognition by workers remains understudied. To fill this gap, we investigated the chemical basis of early brood nestmate and cross-species recognition in six ant species. We also tested the discrimination behaviour of workers in brood retrieval trials. We observed species level cues and discrimination against heterospecific brood. We also found that eggs and most L1 larvae displayed a colony signature. However, only some species discriminated against non-nestmate early brood. Interestingly, these species belong to genera subject to brood parasitism. We hypothesize that non-nestmate brood discrimination could arise from species adaptations against brood parasitism. • Ant larvae appear to acquire their surface hydrocarbons after hatching. • Eggs and first-instar (L1) larvae display a species-specific hydrocarbon signature. • Ant workers discriminate against heterospecific eggs and L1 larvae. • Eggs and most L1 larvae display a colony signature in their surface hydrocarbons. • Brood parasitism might select for discrimination against non-nestmate early brood. [ABSTRACT FROM AUTHOR]