Applying the Anna Karenina principle for wild animal gut microbiota: Temporal stability of the bank vole gut microbiota in a disturbed environment.

Gut microbiota play an important role in host health. Yet, the drivers and patterns of microbiota imbalance (dysbiosis) in wild animals remain largely unexplored. One hypothesised outcome of stress on animal microbiomes is a destabilised microbial community that is characterised by an increase in inter-individual differences compared with microbiomes of healthy animals, which are expected to be (a) temporally stable and (b) relatively similar among individuals. This set of predictions for response of microbiomes to stressors is known as the Anna Karenina principle (AKP) for animal microbiomes. We examine the AKP in a wild mammal inhabiting disturbed environments by conducting a capture-mark-recapture survey of bank voles Myodes glareolus in areas that contrast in levels of radionuclide contamination (Chernobyl, Ukraine). Counter to key predictions of the AKP, bank voles that are not exposed to radionuclides harbour variable (increased inter-individual differences) and temporally dynamic gut microbiota communities, presumably tracking the natural spatio-temporal variation in resources. Conversely, bank voles exposed to radionuclides host more similar gut microbiota communities that are temporally stable, potentially due to a dysbiosis or selection (on host or bacteria) imposed by chronic radiation exposure. The implication of these data is that environmental stress (radiation exposure) can constrain the natural spatial and temporal variation of wild animal gut microbiota.