Host life history strategies can significantly influence disease dynamics. For example, cannibalism, which can be an alternative feeding strategy for animals, increases nutrients necessary for developmental processes, such as the immune response to parasites. Diet can also alter the host gut microbiome (community of bacteria) and a disruption in the host gut microbiome can affect subsequent disease risk. In our study, we tested the effect of a cannibalistic diet in Cuban Tree frog (Osteopilus septentrionalis) tadpoles on the frog gut microbiome and susceptibility to a parasitic gut nematode Aplectana. Juvenile Aplectana worms penetrate the frogs’ skin then travel to the colon where the worms develop and reproduce. Tadpoles were fed an herbivorous diet of Spirulina (control) or a cannibalistic diet of macerated conspecifics. After 7 weeks, a subset of tadpoles were necropsied and the gut bacterial DNA was sequenced to characterize the community. Post-metamorphic frogs were then exposed to Aplectana worms. We quantified the number of worms that penetrated the skin as well as the number of adult worms that established in the gut. We also quantified the frog antibody response to Aplectana.
Frogs fed an herbivorous diet as tadpoles were more susceptible to Aplectana worm penetration, but tadpole diet did not affect the number of worms that established in the gut. Additionally, juvenile frogs fed an herbivorous diet had a higher antibody response to Aplectana. This suggests that frogs fed a carnivorous diet as tadpoles have a more effective skin immunological response (e.g. inflammatory response) compared to frogs fed an herbivorous diet as tadpoles. In contrast, frogs fed an herbivorous diet were more immunologically competent during the establishment stage of the worm compared to frogs fed a carnivorous diet. We also found that a carnivorous diet significantly disrupted the gut bacterial community structure in tadpoles. After metamorphosis the bacterial community did not differ significantly between diet treatments. Our results suggest that tadpole diet can affect subsequent parasite susceptibility in frogs, but depends on the stage of infection. Our past research suggests that a disruption in the gut microbiome during the tadpole stage affects host parasite susceptibility during the establishment stage of the worm (when frogs are producing an antibody response). Therefore, we suggest that the gut microbiome, in part, may mediate the effect of cannibalism on parasite susceptibility during the establishment stage of the parasite in frog guts.