The evolution of hydrocarbon pheromone parsimony in ants (Hymenoptera: Formicidae) – interplay of colony odor uniformity and odor idiosyncrasy. A review

Hefetz, A.

Abstract: Hydrocarbons are the main lipid constituents on the insect cuticle, and generally provide the insect with a waterproof layer to prevent desiccation. In many insects this class of chemicals has been coopted to serve as pheromones. In social insects, in particular in ants cuticular hydrocarbons (CHCs) have at least two pheromonal functions. They act as recognition cues that facilitate colony insularity, protecting it from parasites or conspecific invasions. Supporting evidence for this function are their extreme complexity, their colony specific composition, and in a few cases also demonstrating elevated or reduced aggression between encountering ants as a function of the label (alien or nestmate) they were painted with. The second function of CHCs is in signaling fertility. In many ant species it was demonstrated that fertile individuals (queens, gamergates, or egg laying workers) have Chc profiles that are distinct from that of their sterile nestmates. This can be expressed as the augmentation of a single or a small subset of the blend components, or differences in the entire blend. The fact that these signals have an abundance of branched alkanes, which lower the break point of cuticular impermeability thus imposing cost on the individual, indicates that these may constitute honest signals. This dual function seems contradictory since nestmate recognition necessitates a uniform colony odor, i.e., uniform Chc composition, whereas fertility signal requires idiosyncrasy since the fertile individual needs to be singled out among the colony members rather than conform to colony odor. A possible resolution is that species that use CHCs for nestmate recognition do not use them as fertility signals and vice versa. I propose an alternative solution whereby workers have variable discrimination thresholds and response to differences in the pheromone blend, large or small, in a contextdependent manner.

Myrmecol. News 10: 59-68; printable