Reproductive hierarchies and status discrimination in orphaned colonies of Pachycondyla apicalis ants

In group-living animals where dominance hierarchies occur, aggression can be reduced if individuals are able to recognize each other. To do this, and to adapt their behaviour suitably when faced with a rival, individuals may rely on two nonmutually exclusive recognition means: they could recognize group members individually and/or their social status. Within insect societies, although conflicts over reproduction resulting in hierarchy establishment are widespread, relatively little is known about the cognitive abilities involved in the regulation of agonistic interactions. We tested whether low-ranking workers of Pachycondyla apicalis ants are able to discriminate each other individually and/or if they can discriminate the status of their nestmates. We found no evidence of individual discrimination among subordinates whereas they were able to discriminate their nestmates on the basis of their social and reproductive status. Such a skill may allow them to regulate worker reproduction in queenright colonies efficiently. By considering the structure of the hierarchy and the nature of the dominance relationships in P. apicalis societies, we discuss the existence of a more accurate recognition system among the high-ranking workers.