Specialization of the cloacal microbiome relative to gut, oviduct, and feces of an oviparous lizard

Microbial diversity and community function are related, and both can be highly specialized in different regions of the gut. The cloacal microbiome of Sceloporus virgatus lizards has low diversity, suggesting a specialized function, and is known to transfer antifungal microbes to eggshells during oviposition. We hypothesize that the cloacal microbiome is distinct from other parts of the digestive and reproductive systems. Here, we compare the microbiome of tissue samples from the cloaca, lower intestine, upper intestine, and oviduct. We further assessed whether common methods of microbial sampling – cloacal swabs and feces – provide accurate representations of these tissues, and whether feces might “seed” the cloacal microbiome. We found that the upper intestine and oviduct had unique microbial communities, while the lower intestine and cloaca had similar communities with lower diversity indicative of regional specialization. The cloacal community, in particular, showed extreme specialization averaging 99% Proteobacteria (Phylum) and 83% Enterobacteriacaea (Family). Cloacal swabs recovered communities similar to that of lower intestine and cloacal tissues, but fecal samples had much higher diversity and a distinct composition (62% Firmicutes and 39% Lachnospiraceae) relative to all gut regions. This result serves as a caution against the frequent assumption that fecal samples provide an accurate representation of the gut. Finally, we found that defecation did not alter the cloacal microbiome, suggesting that community is robust to perturbations from transient microbiota.