Assessment between species: information gathering in usurpation contests between a paper wasp and its social parasite

Costs associated with escalated fighting may be minimized where individuals are able to gather information regarding the likely outcome of conflicts. In particular, the ability to assess resource-holding potential (RHP) has been shown to be important in determining the dynamics of animal contests. While assessment rules have been investigated in contests in a range of species, little is known about the potential for assessment in contests between species. We examined the role of assessment in usurpation contests between the paper wasp Polistes dominulus and the social parasite Polistes semenowi. First, we investigated whether parasite clypeal patterns function as signals of RHP by staging contests with parasites in which the clypeal pattern was concealed with paint. Second, we examined the importance of body size as a determinant of RHP. Finally, we explored whether individuals use information about their own RHP, and that of their rivals, in deciding when to withdraw. We found no evidence that parasite clypeal patterns act to signal RHP to hosts: initial fights were neither longer nor more intense when the patterns were concealed. We also found no evidence for RHP assessment during contests: although body size predicted contest outcome, fight duration and intensity were not significantly related to either winner or loser size. We suggest that the high value of the nest to both parties, combined with the potential for ‘divisive’ asymmetries in RHP between hosts and parasites, may result in selection for escalated conflict over rival assessment during usurpation fights.