Cloacal virome of an ancient host lineage - The tuatara (Sphenodon punctatus) - Reveals abundant and diverse diet-related viruses.

Tuatara (Sphenodon punctatus) are one of the most phylogenetically isolated vertebrate species and provide a unique host system to study virus evolution. While the tuatara genome, sequenced in 2020, revealed many endogenous viral elements, we know little of the exogenous viruses that infect tuatara. We performed a metatranscriptomics study of tuatara cloaca samples from a wild population on Takapourewa (Stephens Island), Aotearoa New Zealand. From these data we identified 49 potentially novel viral species that spanned 19 RNA viral families and/or orders, the vast majority (48) of which were likely dietary-related. Notably, using a protein structure homology search, we identified a highly divergent novel virus within the Picornaviridae which may directly infect tuatara. Additionally, two endogenous tuatara adintoviruses were characterised that exhibited long-term viral-host co-divergence. Overall, our results indicate that the tuatara cloacal virome is highly diverse, likely due to a large number of dietary-related viruses.