Fig. 3.

Models of viral origin. (A) Map showing geographic location of Madagascar relative to Africa. (B) Evolutionary timeline. Mammalian invasions of Madagascar are believed to have involved only five orders of terrestrial mammals—primates, rodents, carnivores, afrosoricida, and artiodactyls. Molecular and fossil data suggest the most recent colonization occurred 14 million years ago (23). The oldest known lentiviral sequences have been dated to between 7 and 11 million years old (14). (C) Proposed models of primate lentivirus evolution. Three evolutionary scenarios can be proposed to account for the presence of lentiviruses in both streprsirrhine (S) and haplorrhine (H) primates; (1) ancestral codivergence of primate lentiviruses into haplorrhine and strepsirrhine lineages in broad concert with their hosts; (2) transfer of lentiviruses between Malagasy strepsirrhines and African haplorrhines subsequent to their divergence, mediated either by a nonprimate vector or via temporary contact between Malagasy and African primate populations during intermittent periods of land-bridge or dry way-point access between the two regions (23); (3) transfer mediated by an aerial vector species.