Robert J. Gifford; PNAS June 29, 2021

Figure: Timeline of vertebrate virus evolution based on direct evidence from the genomic fossil record. Minimum age estimates for various vertebrate virus lineages, as derived from identification of orthologous EVEs in related host taxa. Bornavirus-specific calibrations are taken from Kawasaki et al. (5) and are shown in relation to those obtained for circoviruses (1) (family Circoviridae), filoviruses (family Filoviridae) (1), hepadnaviruses (family Hepadnaviridae) (3), parvoviruses (family Parvoviridae) (19), and retroviruses (family Retroviridae).

It has always seemed likely that viruses originated early in the history of life. However, until the identification of endogenous viral elements (EVEs), there was little if any direct evidence for most virus groups ever having existed in the distant past (1). EVEs are virus-derived DNA sequences found in the germline genomes of metazoan species. Uniquely, they preserve information about the genomes of viruses that circulated tens to hundreds of millions of years ago. Comparative analysis of EVE sequences has now provided robust age calibrations for a diverse range of virus groups, completely transforming perspectives on the longer-term evolutionary interactions between viruses and hosts (2). As progress in mapping the complete genome sequences of species has accelerated, the abundance of “fossilized” viral sequences in eukaryotic genomes has become apparent. Increasingly, the challenge is not finding EVEs, but scaling analytical approaches to tackle the exponentially increasing volume of EVE sequence data (3, 4). In PNAS, Kawasaki et al. (5) utilize sophisticated computational approaches to implement a broad-scale analysis of the viral “fossil record,” focusing on a group of viruses called “bornaviruses.”

Bornaviruses (family Bornaviridae) are a poorly understood group of single-stranded negative sense RNA viruses (order Mononegavirales) that infect vertebrates.

See more: https://www.pnas.org/content/118/26/e2108123118