The Neutral Metaorganism
Almost all animals and plants are inhabited by diverse communities of microorganisms, the microbiota. The hosts often pose highly selective environments, which only a subset of the environmentally available microbes are able to colonize. From the hosts perspective it seems useful to shape the community composition of these allowed microbes to promote a beneficial host-microbe symbiosis. In contrast to this, neutral models assume that the structure of the microbiota is entirely shaped by random population dynamics and dispersal. We here show that microbiota community structure from a wide range of host organisms, in particular including previously understudied invertebrates, is in almost all cases consistent with neutral expectations. Moreover, we demonstrate that apparent discrepancies with the neutral model can be due to transient community states rather than host selection. In conclusion, even though hosts are often assumed to control microbiota composition to ensure beneficial interactions, our broad-scale analysis highlights that following colonization, it could rather be neutral processes that determine microbial community structure.