SRA

Social insects in general and leaf-cutting ants in particular have increased selection pressures on their innate immune system due to their social lifestyle and monoclonality of the symbiotic fungus cultivar. As this symbiosis is obligate for both parties, prophylactic behavioral defenses against infections are expected to increase either ant survival or fungus garden survival, but also to possibly trade-off when infections are specific depending on what types of infection are most dangerous. We examined the effectiveness of prophylactic behaviors and modulations of innate immune defense reactions by a combination of infection bioassays and genome-wide transcriptomic studies (RNA-Seq), using an ant pathogen (Metarhizium brunneum) and a garden pathogen (Escovopsis weberi) and administering infections both directly and indirectly (via the symbiotic partner). Upon detection of pathogen conidia, ant workers responded by increasing both general activity and the frequency of specific defense behaviors (self-grooming, allo-grooming, garden-grooming), independent of the pathogen encountered. This trend was also evident in the patterns of gene expression changes. Both direct and indirect infection with M. brunneum induced a general up-regulation of gene expression, including a number of well-known immune-related genes. In contrast, direct infection of the fungus garden by E. weberi induced an overall down-regulation of ant gene expression whereas indirect infection did not, suggesting that increased activity of ants to remove fungus garden infections is costly and involves trade-offs with the activation of other physiological pathways.