Recognizing reproductives and hydrocarbon signal variation in the trap-jaw ant Odontomachus brunneus

Cuticular hydrocarbons are thought to present an assortment of information necessary for maintaining a eusocial society. Nestmate status and reproductive status of individuals are both prime examples of such information conveyed through hydrocarbons. While, in ants, the role cuticular hydrocarbons as nestmate signals has been well demonstrated, fertility status has only been experimentally linked to hydrocarbons in a few species. In this study we provide experimental evidence that reproductives of the ant Odontomachus brunneus are recognized through hydrocarbons. First we compare the cuticular hydrocarbon profiles of dominant and reproductive workers and queens to non-reproductive workers. Through split/reunification tests we document the existence of worker policing in both queenless and queenright colonies, as supernumerary reproductives are treated aggressively by nestmates. Next, we induce aggression and replicate queen-like submissive nestmate responses by supplementing the hydrocarbon profile of workers with (Z)-9-nonacosene, a compound significantly more abundant on reproductives. Finally, we compare the hydrocarbon profiles of reproductive and non-reproductive O. brunneus individuals across several Florida populations. While the nestmate signatures are vastly different across populations, variation within the hydrocarbon profile that correlates with reproduction is conserved across populations. This suggests that selection works on cuticular hydrocarbon profiles to conserve some components while diversifying others.