Effects of early-life diet & gut microbiome on host resistance to nest parasites in Tree Swallows

Effects of early-life diet and the gut microbiome on host resistance to nest parasites in Tree Swallows
Dr. Ashley Love, University of Connecticut
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Many factors can shape the diet of wild birds, whether this occurs through direct manipulations such as supplemental feeding, or through shifts in nutritional resources due to factors like urbanization, habitat alteration, and invasive species. Dietary 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 microbiome 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 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 quantified nestling resistance to naturally occurring 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 microbiome. Once nestlings fledged, we collected nests to quantify all larvae, pupae, and pupal cases to determine the total parasite abundance for each nest. 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 that were fed a lipid diet had more parasites in the nest than nestlings from the other treatments. Furthermore, these nestlings also had a higher ratio of larvae to pupae in the nest 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. This study aims to enhance our understanding of the role of diet in shaping avian responses to nest parasites.