Discussion
We investigated how dietary macronutrients affected host physiology and
gut microbiota and characterized how feeding behavior and macronutrient
selection were influenced by both immune activation and perceived
infection risk. We found that shifts in dietary macronutrients can
affect the abundance of some bacterial taxa and potentially alter
relationships between gut microbial communities and immune and stress
physiology. Additionally, a direct immune threat but not a perceived
risk of infection altered the feeding behavior of birds through reducing
the consumption of specific macronutrients, which could have
implications for responding to and recovering from infection. Taken
together these results suggest that both diet-induced shifts in the
microbiome and infection-induced shifts in macronutrient selection occur
in songbirds, and interactions between macronutrients, gut microbiota,
and feeding behavior likely have important consequences for host health.