Unprecedented Symbiont Eukaryote Diversity Is Governed by Internal Trophic Webs in a Wild Non-Human Primate

Research on host-associated microbiomes has highlighted major divisions between the role of eukaryotes in free-living and symbiont systems. These trends call into question the relevance of macroecological processes to host-associated systems and the relative importance of parasitism, commensalism, and mutualism as evolutionary patterns across the domains of life. However, it is unclear as to whether these apparent differences reflect biological realities or methodologies in community characterization: free-living eukaryotes tend to be characterized using metabarcoding whereas symbiont eukaryotes are typically characterized with microscopy. Here, we utilize an Illumina high-throughput metabarcoding approach to characterize the diversity and dynamics of eukaryotic symbiont communities in the feces of a wild non-human primate, Macaca fascicularis, revealing functionally and taxonomically diverse communities of eukaryotes hitherto unreported from any vertebrate. Importantly, community assembly was consistent with top-down and bottom-up trophic food web dynamics, highlighting the applicability of macroecological principles to these communities. Ultimately, our findings highlight vertebrate-associated symbiont communities of the gut that are much more similar to free-living systems than previously realized. Additionally, our results support a role for symbiosis as a major recurrent life strategy among eukaryotes and highlight the potential for vertebrates to host vast reservoirs of unexplored eukaryotic diversity.