A propolis-rich hive environment affects redox gene expression and gut microbiota at the individual and social level in honey bees.

The microbiome of the honey bee is associated with immunity, oxidative state, and disease susceptibility. Here we investigated the effects of increased colony-level propolis exposure on gut microbiota and host worker immune and redox gene expression. Sampling pre-marked adult worker bees at 9-days post emergence revealed significantly larger populations of core microbiota in worker guts from propolis-rich colonies, but little change in taxonomic composition or relative structure. We found an overall trend towards decreased expression of immune genes in propolis-rich colonies. The expressions of both pro-phenol oxidase and catalase were significantly reduced in the worker fat body suggesting that propolis-rich colonies better support host redox balance in individual workers. Increased propolis levels resulted in greater expression of superoxide dismutase from the worker fat body and social head glands, consistent with tissue-specific expression considered beneficial in model organisms and humans. Our results suggest that propolis-rich conditions and social head gland secretions contribute to total redox activity throughout the niche space of social immunity. Moreover, our results are consistent with a companion paper that sampled the same colonies and age cohorts, reporting drastic increases in beneficial native bacteria and reduced pathogen prevalence on the mouthparts, a primary marker of social immunity.