Fig. 4.

Exogenous versus endogenous distribution of virus families that have been incorporated into the vertebrate germline. Circles indicate the known presence of exogenous viruses in vertebrate groups, determined through reference to the NCBI virus genomes resource [56], supplemented with information obtained from recently published papers [64–70]. Shaded boxes indicate the presence of endogenous viral elements, as determined in the present study. RT retroviruses, DNArt reverse transcribing DNA viruses, DNAss single-stranded DNA viruses, DNAds double-stranded DNA viruses, RNAds double-stranded RNA viruses, RNAss-ve single-stranded negative sense RNA viruses, RNAss + ve single-stranded positive sense RNA viruses