An integrated approach of the interactions between nutrition and resistance to infection in fruit flies

While it is well established that nutrition affects a large range of life history traits, our understanding of the effects of diet on immunity and resistance to infections remains limited. This thesis focused on better understanding the effects of macronutrients, protein and carbohydrate, on resistance to infection using the fruit fly, Bactrocera tryoni. The results revealed that infected female flies shifted their diet choice to a carbohydrate-biased diet after septic infection with a pathogenic bacterium, which promoted their survival after infection and contained the growth of pathogen population. Moreover, the dietary macronutrient balance had long-term effects which can be observed across developmental stages and generations. Dietary manipulations at larval stage greatly affected a number of adult traits including the fly's ability to resist infection. Interestingly, these effects were sex-specific with infected females- but not males- surviving better the infection at adult stage when fed a sugar-biased larval diet compared to those fed a protein-biased larval diet. This sex-specific effect of the diet composition was also observed in offspring that parents had been fed different macronutrient ratios. Surprisingly, when both parents were fed unbalanced diets, their sons, and not their daughters, had a greater survival after infection. In contrast, when only mothers experienced unbalanced diets, their sons resisted less well the infection. Oral immune priming was also investigated but no evidence for positive effects of priming on the survival of B. tryoni after infection was observed. This work highlights the complexity of the interactions between nutrition and resistance to infection, not only at the individual level but also at developmental and generational levels. Better understanding the nutritional components that influence resistance to infection is an important challenge with broad implications spanning from health to organismal science.