Gut Microbiota Composition is Correlated to Host Hummingbird Protein Requirements

The gut microbiome shapes and is shaped by a host animal’s physiology. Avian taxa hold physiological characteristics unique from mammals and might inform novel pressures experienced by microbial communities. Further, the symbionts’ relative abundance and their abilities to adapt to available resources are of critical importance to a holobiont’s fitness in rapidly changing climates. Therefore, wild populations of hummingbirds Selasphorus rufus and Calypte anna were studied. The two systems differ in S. rufus’s annual migrations from wintering grounds to their breeding grounds in the Pacific Northwest, whereas C. anna are resident in the latter region. Previous findings have indicated host microbiome composition varied with hummingbird fat score and the month during which fecal sampling occurred. Although fat is an important resource, especially for S. rufus in their migrations, protein requirements are critical because other annual activities, pressuring the organism to access nitrogen. Three of these activities are producing an egg, replacing molted feathers, and carrying parasites. The hypothesis for this study was that birds performing these activities will have microbiota that will make nitrogen available to them. Analysis of OTUs from 16S rDNA V3-V5 amplicon sequencing showed Actinobacteria are more abundant in these hummingbird species than in mammals, replicating our lab’s previous findings. Notably, S. rufus adult females with evidence of recent or current egg production had significantly lower relative levels of Actinobacteria and significantly higher abundances of five of the other ten most abundant bacterial phyla than S. rufus males. The composition of major bacterial phyla in C. anna adults undergoing body, wing, and tail molt did not differ significantly from that of C. anna adults not undergoing molt. Tenericutes were significantly more abundant in S. rufus individuals with high numbers of Mallophaga eggs when compared with birds with few eggs. We described differences in nitrogen-limiting physiological processes and nutritional deficits in wild avian models to provide ways of understanding holobiont success in changing environments