Seasonal shifts in the gut microbiome indicate plastic responses to diet in wild geladas

Animals have evolved numerous strategies to cope with energetic challenges, with dynamic changes to the gut microbiome potentially constituting one such strategy. We tested how proxies of food availability (rainfall) and thermoregulatory stress (temperature) predicted gut microbiome composition of geladas (Theropithecus geladas), a grazing, high-altitude primate inhabiting a seasonal environment. The gelada gut microbiome varied across seasons, reflecting more efficient digestion of the primary foods eaten at certain times of year. In rainier periods, the gut was dominated by cellulolytic/fermentative bacteria that specialized in digesting grass, while during dry periods the gut was dominated by bacteria that break down starches found in underground plant parts. Temperature had a smaller, but detectable, effect on the gut microbiome. We found an increase in microbes involved in metabolism and energy production during cold and dry periods, suggesting buffering when thermoregulatory and nutritional stress co-occurred. Our results suggest that the gelada gut microbiome may shift to compensate for host diet and energetic demands.