Université Pierre-et-Marie Curie, Laboratoire d'Ecologie, CNRS-UMR 7625, 7 quai Saint Bernard, 75005 Paris, France.
Long-chain cuticular hydrocarbons protect insects against dessication, and may act as pheromones. In ants they are often components of the colonial odour, and may also encode information that helps to regulate the reproductive conflicts which underlie sociality. Colonies of Diacamma ceylonense consist exclusively of workers, all of whom have similar reproductive potentials at emergence. However, only one worker (the 'gamergate') mates and monopolizes reproduction. She prevents other workers from mating by mutilating their innervated vestigial wings. These permanently virgin workers have undeveloped ovaries when the gamergate is present, but she does not interact physically with them. Once she is removed, several workers begin to compete aggressively for the production of males (unfertilized eggs). This suggests that the gamergate produces a pheromone that results in suppressed egg production by workers. Cuticular hydrocarbons from gamergates and infertile workers of different ages show the same compounds (mostly alkanes and mono-methyls, and a few di-methyls and alkenes; C. Malosse pers. comm.), but in varying proportions. Discriminant analysis of data from different functional groups of workers, together with temporal evolution of individual profiles (measured by SPME) revealed a strong correlation between the proportions of 17 major peaks (C25 to C35) and egg-laying ability, suggesting that cuticular hydrocarbons can function as a signal of fertility. Such chemical modifications, which are also found in solitary insects, may have been a prerequisite for the evolution of sterile colony members as they provide the information necessary for the surrender of direct reproduction in the presence of an effective egg-layer.