Fertility Signaling and Partitioning of Reproduction in the Ant Neoponera apicalis.

All individuals in social insect colonies benefit from being informed about the presence and fertility state of reproducers. This allows the established reproductive individuals to maintain their reproductive monopoly without the need for physical control, and the non-reproductive individuals to make appropriate reproductive choices. Here, we studied whether fertility signaling is responsible for the partitioning of reproduction in the ant Neoponera apicalis. This species forms small colonies from one single-mated queen, with workers establishing reproductive hierarchies when hopelessly queenless. Previous studies identified putative fertility signals, particularly the hydrocarbon 13-methylpentacosane (13-MeC25), and have shown that precise status discrimination based on these signals could be involved in the regulation of reproductive activities. Here, we extend these findings and reveal that all individuals, be they queens or workers, differ in their cuticular hydrocarbon profile according to fertility state. Proportions of 13-MeC25 were a strong predictor of an individual's ovarian activity, and could, thus, advertise the established reproducer(s) in both queenright and queenless conditions. Furthermore, this compound might play a key role in the establishment of the reproductive hierarchy, since workers with low fertility at the onset of hierarchy formation already have relatively high amounts of 13-MeC25. Dyadic encounters showed that individuals with experimentally increased amounts of 13-MeC25 triggered less agonistic interactions from top rankers, in accord with them "advertising" higher status. Thus, these bioassays supported the use of 13-MeC25 by competing ants. This simple recognition system potentially allows permanent regulation of partitioning of reproduction in this species.