Status discrimination through fertility signalling allows ants to regulate reproductive conflicts

Dominance hierarchies allow group-living animals to regulate the partitioning of reproduction, but the recognition systems underlying dominance interactions remain equivocal. Individual recognition, a cognitively complex recognition system, is often posited as an important mechanism for the regulation of linear dominance hierarchies because of its high level of precision. However, providing it actually allows a fine-scale discrimination of the individuals' statuses, status discrimination may offer an alternative, simpler, recognition system allowing the same level of precision while saving the memory-related costs associated with individual recognition. With the aim of disentangling the cognitive mechanisms underlying the formation and maintenance of hierarchies, we here studied the within-group recognition systems in the ant Neoponera apicalis, where orphaned workers compete over male parentage in a linear hierarchical structure. Overall, we found that status discrimination abilities were in fact sufficient for the establishment and stabilization of linear hierarchies. The observed level of accuracy allowed fine-scale discrimination of all top rankers' hierarchical status, and thus translated into a functional individual discrimination of all competing workers at the top of the hierarchy. Low-ranking workers did not exhibit such fine-scale status discrimination. We moreover showed that a putative signal of fertility, 13-methylpentacosane, precisely labelled the workers' position in the hierarchy, thereby providing the recognition cue likely to explain the individuals' discrimination abilities. This signal could therefore play a key role in the regulation of the reproductive conflict in this species. In contrast with the traditional view, our study shows the implication of a cognitively simple but equivalently efficient recognition system during the emergence and stabilization of a linear dominance hierarchy.