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Abstract:
Almost all animals and plants are inhabited by diverse communities of microorganisms, the
microbiota, thereby forming an integrated entity, the metaorganism. Natural selection should
favor hosts that shape the community composition of these microbes to promote a beneficial
host-microbe symbiosis. Indeed, animal hosts often pose selective environments, which
only a subset of the environmentally available microbes are able to colonize. How these
microbes assemble after colonization to form the complex microbiota is less clear. Neutral
models are based on the assumption that the alternatives in microbiota community composition
are selectively equivalent and thus entirely shaped by random population dynamics and
dispersal. Here, we use the neutral model as a null hypothesis to assess microbiata composition
in host organisms, which does not rely on invoking any adaptive processes underlying
microbial community assembly. We show that the overall microbiota community structure
from a wide range of host organisms, in particular including previously understudied invertebrates,
is in many cases consistent with neutral expectations. Our approach allows to identify
individual microbes that are deviating from the neutral expectation and are therefore
interesting candidates for further study. Moreover, using simulated communities, we demonstrate
that transient community states may play a role in the deviations from the neutral
expectation. Our findings highlight that the consideration of neutral processes and temporal
changes in community composition are critical for an in-depth understanding of microbiotahost
interactions.
