Associations and interactions between prokaryotes and other gut biota in non-human primates

The influence of gut microbiota on vertebrate health, development, growth, and physiology is increasingly evident. Considerable research has concentrated on Primates, not only because many non-human species have long acted as laboratory models to better understand human health, but also to improve our knowledge of the ecology of this mammalian Order with the highest proportion of endangered wild taxa. While bacteria have been the primary focus, other gut components (archaea, protozoa, fungi, viruses, and helminths) also play critical roles in host survival. Only recently have there been microbiota studies examining interactions among gut components and their influence in both captive and wild non-human primates. Here we systematically reviewed all research articles on non-human primates where gut bacteria were studied together with at least one other gut taxon. Studies on humans were included in each comparison where these suggested (i) potential health outcomes of patterns observed in non-human primates, or (ii) how approaches used in human microbiota studies could more effectively advance non-human primate research and conservation. Specifically, we focused on associations (such as covariations in diversity indices or abundance between taxa), direct interactions (one taxon affecting another with experimental evidence), and external influences (e.g., disease, diet, environment) impacting multiple taxa. We found that for non-human primates, direct interactions among bacteria and other gut taxa have rarely been confirmed except under experimental captive conditions, especially for wild species. However, the associated changes in richness, abundance, and/or metabolic pathways indicate interdependence among gut taxa, confirming their links with host nutrition and immunity and, consequently, their potential impact on host health and species conservation.