Tolerance toward foreigners in ants requires chronic exposure for establishment but only sporadic exposure for maintenance

Social insects discriminate between foreigners and members of their own colony via complex olfactory cues. How plastic this discriminatory behavior is, and whether and under what circumstances ants can learn to accept genetically distinct individuals as nestmates, is poorly understood. Here, we study this question in the clonal raider ant, Ooceraea biroi, which provides unparalleled experimental control over the genotype of individuals and the genotypic composition of colonies. Using a cross-fostering design with mixed-genotype colonies of wild-type and transgenically labelled individuals, we show that ants become non-aggressive specifically toward their foster genotype. This tolerance is transient, and aggression resumes after two weeks of being isolated from the foster colony. However, even sporadic re-exposure to individuals from the foster colony is sufficient to maintain tolerance for over a month, while the same paradigm fails to establish tolerance in the first place. This shows that non-nestmate discrimination is remarkably plastic and that, once established, tolerance toward foreigners can be maintained by only intermittent contact. These dynamics echo general principles of social learning and contact-dependent tolerance described in other social species, including humans.