The dual strategy: resisting and tolerating pathogens in ant colonies

Abstract

Ant colonies are vulnerable to disease outbreaks due to their dense, genetically related populations and confined living conditions. To mitigate the impact of entomopathogens such as Beauveria bassiana, ants employ resistance strategies to reduce pathogen load and tolerance strategies to endure infections without reducing pathogen presence. Investment in these strategies probably depends on the intensity and duration of pathogen exposure, may be colony-specific and shaped by trade-offs. To investigate colony-specificity of sanitary responses, we divided Myrmica rubra ant nests into two sister colonies exposed to either a fixed or removable pathogen load, where workers were forced to respectively coexist with nestmate cadavers or could discard them. While sister colonies exhibited similar performance in tolerance-related behaviours, they differed in resistance responses. Under severe pathogenic risk (sporulating cadavers), workers engaged in more frequent social and extensive grooming, and colonies compensated for worker mortality by increasing brood production. A trade-off between tolerance and resistance strategies emerged during control but disappeared when colonies faced sporulating cadavers. These findings highlight the flexibility of ant colonies in adjusting their defence strategies and suggest that severe pathogenic threats may override constraints on resource allocation between tolerance and resistance strategies.