Testing the signal value of clypeal black patterning in an Italian population of the paper wasp Polistes dominula

In recent years, a number of studies have suggested that visual status signaling operates in social wasps. In the paper wasp Polistes dominula, status is thought to be signaled by a region of black pigmentation on the yellow clypeus. Specifically, studies of the invasive North American population have indicated that the clypeal patterning of P. dominula females conveys information on their agonistic abilities in various natural contexts such as dominance within the nest and competitive interactions. However, studies of native European populations have, so far, failed in demonstrating such a function of the clypeal patterning. The present work investigated the status signaling in an Italian population of this species, eliminating any chemical and behavioral factors of the signaler and controlling for signaler size, therefore, focusing on visual stimulus alone. Using tightly controlled laboratory settings, we performed two bioassays representing two distinct natural contexts: a competitive interaction over food resources and a nest defense scenario. To this end: (1) we offered to future foundresses food patches guarded by two odorless conspecific lures differing only in visual facial cues and (2) we presented odorless wasp lures with a different clypeal patterning to solitary foundresses defending their own nest. We found no evidence for any role of the clypeal patterning in the rival assessment in both contexts. Hence, we conclude that P. dominula foundresses belonging to the Italian population lack visual status signaling on their clypeus. Further studies will elucidate factors and mechanisms underlying the geographical variation and evolution of visual signals in paper wasps.