There has been a four-fold increase in the number of rhabdoviruses over the past five years, with rhabdoviruses being found in a diverse array of arthropods. In most cases we know nothing about the biology of these new viruses beyond the host they were isolated from. After using RNA-seq to indentify novel rhabdoviruses in Drosophilidae, we produced a comprehensive phylogeny of the rhabdoviruses. We reconstructed the ancestral and present host associations of viruses to predict which are vector-borne pathogens and which are specific to vertebrates or arthropods. We have found the majority of rhabdoviruses are arthropod vectored vertebrate viruses, but the sigma virus clade and another (as yet unnamed) clade appear to be insect-specific.
A striking pattern that emerged from our reconstructions of host use, is that switches between major groups of hosts have occurred rarely during the evolution of the rhabdoviruses. This is perhaps unsurprising, as both rhabdoviruses of vertebrates (rabies virus in bats) and invertebrates (sigma viruses in Drosophilidae) show a declining ability to infect hosts more distantly related to their natural host. Within the major clades, closely related viruses often infect closely related hosts, suggesting that following major transitions between distantly related host taxa, viruses preferentially shift between more closely related species.
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The figure below shows the reconstructed host associations across the rhabdovirus phylogeny. The first part shows the basal rhabdovirus clades, including the fish infecting novirhabdoviruses, a clade of insect viruses, the plant infecting cyto- and nucleo- rhabdoviruses and the vertebrate infecting lyssaviruses, which include rabies virus.
The second part of the figure shows the dimarhabdovirus supergroup, that from our analysis we estimate are arboviruses. Derived from these are the sigma viruses, which are a clade of insect specific viruses.