The RNA virome of early metazoans sheds light on long-term virus-host relationships

Ctenophores and placozoans, two ancient lineages of metazoans, harbor RNA viromes that remain largely unexplored. Despite their evolutionary importance, the diversity and evolution of these viral communities have yet to be thoroughly investigated. To address this knowledge gap, researchers analyzed publicly available transcriptome data from the Sequence Read Archive (SRA) to uncover the viral landscape of these early metazoans.

The study identified 26 putative novel viruses, classified into 11 distinct virus groups, including members of the Flaviviridae and Chuviridae families. Notably, some of these novel viruses displayed high levels of divergence, branching deeply within their phylogenetic trees or forming unique lineages, suggesting a possible early divergence in metazoan evolution.

In contrast, other viruses showed patterns consistent with more recent diversification and host jumping events. The researchers also detected RNA viruses across multiple species and tissues within both ctenophores and placozoans, indicating a broader host range than previously known. These findings not only expand our understanding of the viral diversity and host associations in early metazoans but also shed light on the evolutionary dynamics of virus-host relationships in aquatic environments, hinting at a complex interplay between viruses and their hosts throughout the history of animal evolution.