A phylogenomic data-driven exploration of viral origins and evolution

Nasir, Arshan; Caetano-Anollés, Gustavo

ToP also provide interesting information regarding the evolution of virion morphotypes. Most basal branches were populated by spherical or filamentous virions (two of the simplest designs from the point of view of tensegrity). They gradually become more decorated, with additional features such as spikes and glycoproteins (retroviruses) in spherical virions, and rod-like designs (inoviruses) likely evolving from filamentous versions. Perhaps the rods and spheres combine to form the head-tail morphotype so abundant in prokaryotic viruses. Thus, mapping of virion morphotypes onto ToP likely hints toward the origin of viruses from a limited number of structural designs (43) . However, we caution that morphological similarities may also stem from convergent evolution. At this point, we lack evidence to confirm homologies between different virion morphotypes. Nevertheless, the early appearance of spherical and filamentous virions harboring segmented RNA genomes is remarkable and worthy of further attention.