Gut microbiomes of captive primates show phylosymbiosis, respond to dietary sugar reduction, and select for host-specific dietary microbes.

Host-associated microbiomes are influenced by evolutionary history and proximate factors such as diet and environment. Zoos house animals in relatively standardized and manipulatable environments, making zoo populations valuable for studying microbiomes. Using a small population of five closely related primate species housed under nearly identical environments, we investigated gut microbiome variation regarding (a) congruence between host evolutionary history and gut bacterial composition (i.e. phylosymbiosis), (b) a longitudinal reduction in dietary sugar intake, and (c) ingestion of bacteria from dietary sources. We found that the primate gut microbiomes varied across individuals and showed phylosymbiosis. When animals were fed diets with reduced sugar and increased fiber, we found host-specific changes in taxonomically distinct microbes (Phascolarctobacterium, Megasphaera, and Sharpea). Yet, these bacterial genera share similar functional potential (fiber degradation), indicating that the distinct bacterial communities may fulfill similar functions. Although all individuals received the same diet, the diet-associated bacteria in primate gut microbiomes were distinct across individuals of different species, suggesting a mechanism that selects for unique dietary microbes to persist in animal guts. Our findings show that the microbiomes of a small, captive primate population housed under uniform environmental conditions still show patterns congruent with combined influences of evolutionary history and diet.