Nestmate discrimination expels intrusion of intraspecific cheaters in an ant

Abstract

AbstractSocial 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 adaptive strategies to bypass their host’s detection. Such relationships between hosts and social parasites could be applied to intraspecific social parasitism known in some social insects. Here we show that nestmate discrimination functions as an effective border defence against intrusion of intraspecific social parasites in the Japanese parthenogenetic antPristomyrmex punctatus. This species harbours a genetically distinct cheater lineage which infiltrates and exploits host colonies. Our behavioural observations revealed that the cheaters did not show any behavioural strategies to circumvent nestmate discrimination; most of them were eliminated through aggressions by host workers that are typically observed against non-nestmates, resulting in a very 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). Our study thus illustrates the role of nestmate discrimination as “social immunity” against the intrusion of cheaters, highlighting the evolutionary analogy to immune systems in multicellular organisms.