Picky eaters: Selective microbial diet of avian ectosymbionts

Individual organisms can function as ecosystems inhabited by symbionts. Symbionts may interact with each other in ways that subsequently influence their hosts positively or negatively, although the details of how these interactions operate collectively are usually not well understood. Vane-dwelling feather mites are common ectosymbionts of birds and are proposed to confer benefits to hosts by consuming feather-degrading microbes. However, it is unknown whether these mites exhibit generalist or selective diets, or how their dietary selection could potentially impact their symbiotic functional nature. In this study, we conducted 16S rDNA and ITS1 amplicon sequencing to examine the microbial diet of feather mites. We characterized and compared the diversity and composition of bacteria and fungi in the bodies of mites living on feathers of the Prothonotary Warbler, Protonotaria citrea, to microbial assemblages present on the same feathers. We found less diverse, more compositionally similar microbial assemblages within mites than on feathers. We also found that mites were resource-selective. Based on the identity and known functions of microbes found within and presumably preferred by mites, our results suggest that these mites selectively consume feather-degrading microbes. Therefore, our results support the proposition that mites confer benefits to their hosts. This study provides insight into symbioses operating at multiple biological levels, highlights the ecological and evolutionary importance of the synergistic interactions between species, and greatly expands our understanding of feather mite biology.