Experimental effects of early-life diet quality and gut microbiota on host resistance to parasites

Background/Question/Methods

Nutritional resources can influence host-parasite dynamics because producing an immune response can be metabolically expensive. Specifically, supplemental macronutrients, such as lipids and protein, can each affect the development of the immune response, and thus resistance, to parasites. This relationship is complicated because the gut microbiota can also mediate the effect of nutrients on host immune responses. To disentangle the effect of early-life diet and gut microbiota on host resistance to parasites, we used a factorial design in which we supplemented nestling tree swallows (Tachycineta bicolor) with dietary macronutrients (lipids, protein, or control) crossed with a disruption in the gut microbiota (antibiotic or no antibiotic). We then characterized their resistance to parasitic nest flies (Protocalliphora sialia) whose larvae feed externally on the blood of nestlings. After one week of the treatments, blood and fecal samples were collected from nestlings to quantify blood loss and characterize the gut microbiota. Once nestlings fledged or died, we collected nests to quantify all larvae, pupae, and pupal cases to determine the total parasite abundance for each nest.

Results/Conclusions

Nestlings with more parasites had more blood loss than nestlings with fewer parasites but blood loss did not vary by diet treatment or gut microbiota treatment. Nestlings with a disrupted gut microbiota crossed with a lipid diet had more parasites than nestlings from the other treatments. Furthermore, these nestlings also had a higher ratio of larvae to pupae when they fledged, suggesting that parasites in these nests had slower developmental rates. This result suggests that dietary macronutrients can affect host-parasite interactions, but these effects may be dependent on gut microbiota composition. The specific role of the microbiome in shaping early-life host responses to parasitism will be discussed. This study aims to enhance our understanding of the role of diet in shaping host immunity and ultimately, host-parasite interactions.