Host gene evolution traces the evolutionary history of ancient primate lentiviruses

Simian immunodeficiency viruses (SIVs) have infected primate species long before  human immunodeficiency virus has infected humans. Dozens of species-specific lentiviruses are found in African primate species, including two strains that have repeatedly jumped into human populations within the past century. Traditional phylogenetic approaches have grossly underestimated the age of these primate lentiviruses. Instead, here we review how selective pressures imposed by these viruses have fundamentally altered the evolutionary trajectory of hosts genes and, even in cases where there now remains no trace of the viruses themselves, these evolutionary signatures can reveal the types of viruses that were once present. Examination of selection by ancient viruses on the adaptive evolution of host genes has been used to derive minimum age estimates for modern primate lentiviruses. This type of data suggests that ancestors of modern SIV existed in simian primates more than 10 Ma. Moreover, examples of host resistance and viral adaptation have implications not only for estimating the age and host range of ancient primate lentiviruses, but also the pathogenic potential of their modern counterparts.