How an ant manages to display individual and colonial signals by using the same channel

Cuticular hydrocarbons are used by some ants to discriminate nestmates from nonnestmates. Every member of the colony bears the same pattern because they are continuously exchanged among nestmates. The postpharyngeal gland (PPG) stores the blend of hydrocarbons and is involved in the distribution of this common mixture. However, some individuals might display individual information on the cuticle (such as a chemical signal of fertility) that must not be mixed within the common pool. We investigated how this paradox is solved in the ant Pachycondyla goeldii by analyzing the nature and localization of colonial and fertility signals. Workers in a queenless condition showed a dominance hierarchy that was correlated with ovarian development. Hydrocarbons from the cuticle and the PPG analyzed by gas chromatography (GC) and identified by GC-mass spectrometry showed a clear discrimination among colonies, supporting the involvement of the PPG in the colonial identity signal. We identified and selected 11 cuticular hydrocarbons that permitted us to discriminate ovarian development classes and that might function as a fertility signal. They allowed clear colony discrimination as well, which suggests that the two signals (the individual signal of fertility and the common signal of colony identity) can be conveyed by the same compounds. However, the hydrocarbons in the PPG did not discriminate among ovarian developmental classes, suggesting that the portion of variation in the cuticular hydrocarbons constituting the fertility signal is superimposed on the signal of colony identity.