Status discrimination through fertility signalling allows ants to regulate reproductive conflicts Boris Yagound a, * , Pierre Blacher a , Dominique Fresneau a , Chantal Poteaux a , Nicolas Châline a, b a Laboratoire d’Ethologie Expérimentale et Comparée, E.A. 4443, Université Paris 13, Sorbonne Paris Cité, Villetaneuse, France b Department of Experimental Psychology, Institute of Psychology, University of São Paulo, São Paulo, Brazil article info Article history: Received 6 January 2014 Initial acceptance 10 February 2014 Final acceptance 25 March 2014 Published online MS. number: 14-00012R Keywords: cuticular hydrocarbons dominance hierarchy individual recognition Neoponera (formerly Pachycondyla) apicalis recognition system status discrimination 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 alter- native, 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 equiv- alently efficient recognition system during the emergence and stabilization of a linear dominance hierarchy. Ó 2014 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. The existence of recognition systems is a central feature of group living. Recognition is used in a wide range of social interactions, thereby allowing group members to adapt their behaviour ac- cording to the age, sex, kinship, group membership, hierarchical status, reproductive status, species and neighbourhood of the in- dividuals with which they interact (Sherman, Reeve, & Pfennig, 1997; Thom & Hurst, 2004; Tibbetts & Dale, 2007). Understanding the exact nature of the recognition mechanisms across taxa, their contexts and associated costs and benefits is therefore a major challenge in the biological sciences (Wiley, 2013). Dominance hierarchies are widespread throughout the animal kingdom. These hierarchies are characterized by asymmetries among group members in the partitioning of resources (Zanette & Field, 2009), and can induce important fitness consequences by mediating access to reproduction, food resources or susceptibility to diseases (Ellis, 1995). Nevertheless, the overt aggression often associated with these hierarchies can also bear important costs in terms of time, energy, physical injuries or vulnerability to predators (Hsu, Earley, & Wolf, 2006; Rutte, Taborsky, & Brinkhof, 2006). Reducing these costs may imply the use of ritualization mecha- nisms, as is frequently observed in hierarchical contests (Hemelrijk, 2000; Hsu et al., 2006; Tibbetts & Dale, 2007). These mechanisms allow the individuals to adapt their behaviour towards encountered nestmates without the need for overt aggressive interactions, and therefore play a key role in the stabilization of dominance hierarchies. * Correspondence: B. Yagound, Laboratoire d’Ethologie Expérimentale et Com- parée, E.A. 4443, Université Paris 13, Sorbonne Paris Cité, 99 avenue J.-B. Clément, 93430 Villetaneuse, France. E-mail address: boris.yagound@leec.univ-paris13.fr (B. Yagound). Contents lists available at ScienceDirect Animal Behaviour journal homepage: www.elsevier.com/locate/anbehav http://dx.doi.org/10.1016/j.anbehav.2014.04.014 0003-3472/Ó 2014 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. Animal Behaviour 93 (2014) 25e35