Different roles of environmental selection, dispersal, and drift in the assembly of intestinal microbial communities of freshwater fish with and without a stomach

The composition of intestinal microbiota commonly varies among individual animal, and may affect host health. However, we have limited knowledge about the different relative roles of assembly processes, such as dispersal and environmental selection, for the composition of gut microbiota. Here, we conducted a field study analyzing intestinal microbial communities of two fish species that either have (perch) or lack (roach) a stomach. We found that environmental selection (i.e. diet, host habitats), dispersal (i.e. microbes associated with food sources) and drift appeared to be of equal importance for the assembly of intestinal microbial communities in roach, while ecological drift appeared most important in perch, followed by dispersal and environmental selection. Furthermore, we found that fish condition was positively related to microbes associated with invertebrates as diet, but negatively related to those associated with zooplankton as diet. These results emphasize the important combined roles of environmental selection, dispersal and drift in shaping the host-associated microbial communities, but also that several species need to be studied to reach general conclusions.