Research published today in Virology Journal shows the remarkable evolutionary history of an important group of viruses. The Nucleo-Cytoplasmic Large DNA Viruses (NCLDV) comprise at least six families of viruses that infect a broad variety of eukaryotic hosts. Poxviridae, Asfarviridae, Iridoviridae, Ascoviridae, Phycodnaviridae, and Mimiviridae are all thought to have evolved from one ancestral virus many millions of years ago, before diverging into distinct families. This group of viruses ranges from the causative agent of smallpox (Poxviridae) to the largest viruses ever observed and that infect amoeba (Mimiviridae)!

Natalya Yutin and Eugene Koonin undertook a comprehensive genome comparison that revealed a set of approximately fifty conserved, core genes that could be mapped to the genome of the putative common ancestor. Core genes are those required for the basic biological processes of the virus, and are therefore found in all of the virus families. Many of the core genes from each family showed a high level of genetic similarity, confirming the authors’ previous findings that they evolved from a single ancestor.

However, the authors were surprised to find that a number of core genes, carrying out the same function in these diverse viruses, were unrelated to each other. Instead, these core genes were independently acquired from their eukaryotic hosts. This remarkable example of convergent evolution reveals the complex genetic history of a fascinating group of viruses.

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