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 be-tween 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 hetero-specific 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.(c) 2023 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Automated summary

Brood plays a critical role in social insect colonies as it contributes to the colony's fitness by producing future reproductive adults and increasing the workforce. Ant workers have evolved the ability to distinguish between nestmate and non-nestmate brood, especially in the early stages that require more resources. However, the chemical basis of this recognition and discrimination behavior remains understudied. In this study, we investigated the chemical cues and discrimination behavior of six ant species towards early brood, finding species-specific cues and discrimination against hetero-specific brood. We propose that the discrimination against non-nestmate brood may be an adaptation against brood parasitism.