Social parasite pressure affects brood discrimination of host species in Temnothorax ants

Social parasites exploit complete societies, on which they are dependent. In ants, slave-making species invade, exploit and raid host colonies, impacting their survival and exerting powerful selection pressure on their host species. Recent studies suggest that host ant species may develop a parasite brood intolerance, which could be the first step of a slave rebellion in parasitized colonies. However, enslaved workers of slave-making ants not only raise and feed their parasites, but also accept alien conspecific brood brought during seasonal raids. We compared the agonistic and grooming behaviour (a sign of brood integration) of two sympatric nonhost species (one showing intraspecific parasitism) and of enslaved and free-living host species confronted with alien conspecific worker pupae to assess whether parasite pressure could have decreased brood tolerance in host species. Free-living colonies of species suffering from interspecific or intraspecific parasitism were more aggressive and performed less grooming towards alien conspecific brood than colonies of nonhost species. Moreover, slave workers were not more aggressive towards alien parasites than towards alien conspecific brood but groomed alien parasites more than alien conspecific brood. We discuss how host–parasite coevolution could impact the social recognition mechanisms in host species.