Diet has no effect on susceptibility to an RNA virus across host species

The likelihood of a successful host shift of a parasite to a novel host species can be influenced by environmental factors that can act on both the host and parasite. Factors such as resource availability or temperature can drive changes in species distributions and abundances making encounters between infected and susceptible individuals more likely. They can also act as stressors that can change the physiology of the interacting parties, including altering the host immune response or varying parasite virulence. Changes in nutritional resource availability have been shown to alter pathogen susceptibility and the outcome of infection in a range of systems. Here we infected 27 species of Drosophilidae with an RNA virus on three different food types of differing protein to carbohydrate ratios. We then measured how viral load and mortality across the species was affected by changes in diet. We found that changes in the ratio of protein to carbohydrate in the diet did not alter the outcomes of infection, with strong positive inter-species correlations in both viral load and mortality across diets, and a strong positive correlation between mortality and viral load.