Novel fecal microbiome identification of mature female leopard tortoises (Stigmochelys pardalis, n = 16) fed exclusively one of three, nutritionally complete, pelleted diets was evaluated in a blind, complete randomized design study. Two diets included insoluble fiber (powdered cellulose) consisting of either 2.0 mm or 0.2 mm length. There were no differences in diversity indices (J’ and H’) of total OTUs by diet, with and without unidentified sequences. Analysis of phyla similarity by diet revealed three distinct groups with \u3e 92% similarity. Analysis of genera similarity revealed two distinct groups with \u3e 80% similarity. At both phyla and genera levels, fecal microbiomes were more similar between tortoises fed the cellulose-added diets versus the control diet, suggesting that the hindgut microbial communities adjusted in the hindgut of tortoises fed the cellulose-added diets by shifting proportions of microbes, based on their role in the hindgut (i.e., cellulose digestion), to accommodate for the addition of cellulose in the two treatment diets. This suggests that adaptability of the hindgut microbial communities should be considered when choosing dietary fiber lengths for hindgut-fermenting vertebrates
