Discrimination against non-nestmates functions to exclude socially parasitic conspecifics in an ant

Abstract

Social animals utilise various communication methods to organise their societies. In social insects, nestmate discrimination plays a crucial role in regulating colony membership. Counter to this system, socially parasitic species employ diverse behavioural and chemical strategies to bypass their hosts detection. In this study, we tested whether such parasitic adaptations could be detected in the incipient stage of social parasitism that is observed as intraspecific phenomena in some social insects. The Japanese parthenogenetic ant Pristomyrmex punctatus harbours a genetically distinct cheater lineage which infiltrates and exploits host colonies. We found that intrusion of this intraspecific social parasite was defended by nestmate discrimination of host colonies without any behavioural strategies specialised in social parasitism. Most of the cheaters were eliminated through aggressions by host workers that are typically observed against non-nestmates, resulting in a low intrusion success rate for the cheaters (6.7%). This result contrasts with the expectation from interspecific social parasitism but rather resembles the intraspecific counterpart reported in Cape honeybees (Apis mellifera capensis), illustrating the role of nestmate discrimination against the intrusion of intraspecific social parasites.