The composition of animal gut microbiomes typically differs from that of external environmental microbiota, in part due to biogeochemical differences between the gut and the environment. However, through defecation, animals transfer a portion of their gut microbiome to the environment together with organic matter, nutrients, and metabolic byproducts. These inputs can directly shape the external environment in a way that may support the persistence of gut microbiota outside the host gut. This coupled gut-environment meta-ecosystem – which we term the meta-gut – may allow ex situ gut microbes to persist in the environment and, at sufficiently high densities, influence ecosystem processes. We surveyed hippopotamus pools spanning a gradient of hippo loading in the Mara River, Kenya, for their biogeochemistry, ecosystem function and microbial community composition. We found that hippos alter the biogeochemistry of pools variably depending on hippo number and water residence time, with large inputs of hippo feces under low flow conditions causing pools to switch from an oxic to an anoxic state. These anoxic conditions facilitate the external persistence of hippo gut microbes. 16S rRNA sequencing of the total RNA has shown that the microbial community in the river begins to functionally resemble that of the hippo gut. The presence and activity of hippo gut microbes in the bottom waters of hippo pools could accelerate the decomposition of organic matter, despite the anoxic conditions, and potentially contribute to the higher rates of ecosystem respiration and concentrations of carbon dioxide and methane we have measured in the pools. Understanding the potential influence of animal microbiomes on the environment may be particularly important in systems in which native biodiversity is declining, being replaced by livestock, or being restored.

Primary Presenter: Christopher Dutton, University of Florida (cldutton@gmail.com)

Authors:

Christopher Dutton, University of Florida  (cldutton@gmail.com)

Amanda Subalusky, University of Florida  (asubalusky@ufl.edu)

Alvaro Sanchez, Yale University / CNB-CSIC  (alvaro.sanchez@cnb.csic.es)

Sylvie Estrela, Yale University  (sylvie.estrela@yale.edu)

Nanxi Lu, Yale University  ()

Stephen Hamilton, Cary Institute of Ecosystem Studies  ()

Laban Njoroge, National Museums of Kenya  ()

Emma Rosi, Cary Institute of Ecosystem Studies  ()

David Post, Yale University  (david.post@yale.edu)