Conserved worker policing in African carpenter ants with drastically different egg chemotypes

Abstract

Distinctive chemical signatures have the potential to serve as discriminatory cues for olfactory recognition mechanisms. Cuticular hydrocarbon (CHC) profiles are among the most prominent chemical signatures in insects that can be highly diverse even among closely related species and between populations with similar ecology. Particularly within the major insect order Hymenoptera, CHC profiles are characterized by high complexity and variation with the potential to evolve rapidly. In this study, we found two very distinct CHC chemotypes distinguishing sympatric colonies of the African carpenter ant Camponotus maculatus (Hymenoptera: Formicinae). These chemotypic differences were mainly detected on the surface profiles of eggs produced by either queens or isolated worker groups. In one chemotype, queen- and worker-laid eggs are very similar. This is largely contrasted by the other chemotype, where queen-laid eggs clearly differ from worker-laid eggs with several prominent queen-exclusive compounds. However, workers display a stable behavior of discriminating against and selectively disposing of worker-laid eggs i.e., worker policing, independent of egg chemotype. Furthermore, genetic barcoding of workers revealed a clear separation between colonies characterized by producing these two distinct egg chemotypes, which may indicate that these colonies belong to a cryptic species complex. Interestingly, worker policing behaviour appears to be evolutionarily conserved, despite the strikingly different egg surface profiles.

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