ABSTRACT: Waterfowl, especially ducks of the genus Anas, are natural reservoir species for influenza A virus (IAV). Duck populations contain nearly all the known diversity of IAVs, and the birds are asymptomatic to infection. Previous work established that IAV infection status is correlated with changes in the cloacal microbiome in juvenile mallards. Here, we analyze five Anas species to determine whether these duck species have similar IAV+ and IAV- cloacal microbiomes, or if the relationships among a host, influenza virus, and the microbiome are species specific. We assessed taxonomic composition of the microbiome, alpha diversity, and beta diversity and found very few patterns related to microbiome and infection status across species, while detecting strong differences within species. A host species-specific signal was stronger in IAV- ducks than IAV+ ducks, and the effect size of host species on the microbiome was three times higher in IAV- birds than IAV+ birds. The mallards and the northern shovelers, the species with highest sample sizes but also with differing feeding ecology, showed especially contrasting patterns in microbiome composition, alpha diversity, and beta diversity. Our results indicate that the microbiome may have a unique relationship with influenza virus infection at the species level.IMPORTANCE Waterfowl are natural reservoir species for influenza A virus (IAV). Thus, they maintain high levels of pathogen diversity, are asymptomatic to the infection, and also contribute to the risk of a global influenza pandemic. An individual's microbiome is a critical part in how a vertebrate manages pathogens and illness. Here, we describe the cloacal microbiome of 300 wild ducks, from five species (four with previously undescribed microbiomes), including both IAV-negative and IAV-positive individuals. We demonstrate that there is not one consistent "flu-like" microbiome or response to flu across species. Individual duck species appear to have unique relationships between their microbiomes and IAV, and IAV-negative birds have a stronger tie to host species than the IAV-positive birds. In a broad context, understanding the role of the microbiome in IAV reservoir species may have future implications for avian disease management.
