Vertically transmitted rhabdoviruses are found across three insect families and have dynamic interactions with their hosts

Abstract

A small number of free-living viruses have been found to be obligately vertically transmitted, but it remains uncertain how widespread vertically transmitted viruses are and how quickly they can spread through host populations. Recent metagenomic studies have found several insects to be infected with sigma viruses (Rhabdoviridae). Here, we report that sigma viruses that infect Mediterranean fruit flies (Ceratitis capitata), Drosophila immigrans, and speckled wood butterflies (Pararge aegeria) are all vertically transmitted. We find patterns of vertical transmission that are consistent with those seen in Drosophila sigma viruses, with high rates of maternal transmission, and lower rates of paternal transmission. This mode of transmission allows them to spread rapidly in populations, and using viral sequence data we found the viruses in D. immigrans and C. capitata had both recently swept through host populations. The viruses were common in nature, with mean prevalences of 12% in C. capitata, 38% in D. immigrans and 74% in P. aegeria. We conclude that vertically transmitted rhabdoviruses may be widespread in a broad range of insect taxa, and that these viruses can have dynamic interactions with their hosts.

Host-pathogen coevolution increases genetic variation in susceptibility to infection

“…To test whether selection by parasites increases genetic variation in susceptibility to infection, we compared coevolved host-virus associations with novel associations that have no history of coevolution. We used four different species of Drosophila , each of which is naturally host to a different sigma virus [26-28, 30, 31]. We collected four species from the wild and created genetically diverse populations in the laboratory.…”

“…For example, in France and Germany in the 1980’s DMelSV evolved to largely overcome the effects of the resistant allele of p62 [51, 52]. Similarly, DImmSV has swept through European populations of D. immigrans in the last ~16 years and DObsSV through UK populations of D. obscura in the last ~11 years [28, 31]. If selection by pathogens continually changes and resistance evolves from new mutations, then this may cause a sustained increase in genetic variance in susceptibility to infection.…”

“…To examine how selection by pathogens affects levels of genetic variation we used a natural host-parasite system; Drosophila and sigma viruses [26, 27]. Sigma viruses are a clade of insect RNA viruses with negative-sense genomes in the family Rhabdoviridae [28-31]. They are vertically transmitted, and each sigma virus infects a single host species, simplifying studies of coevolution [28, 31].…”

“…Sigma viruses are a clade of insect RNA viruses with negative-sense genomes in the family Rhabdoviridae [28-31]. They are vertically transmitted, and each sigma virus infects a single host species, simplifying studies of coevolution [28, 31]. In Drosophila melanogaster infection reduces host fitness by approximately 25% and prevalence in wild populations is typically around 10% [32, 33].…”

Kanyawara Virus: A Novel Rhabdovirus Infecting Newly Discovered Nycteribiid Bat Flies Infesting Previously Unknown Pteropodid Bats in Uganda

“…These relationships are evident today in the strong ecological associations that many rhabdoviruses maintain with arthropods. Viruses of the genus Sigmavirus, for example, are transmitted only vertically among insects 20,26 , whereas viruses of the genera Ephemerovirus, Tibrovirus, and Vesiculovirus may infect mammals but typically are vectored by biting midges, mosquitoes, sandflies, or ticks 10,19 . Similarly, plant rhabdoviruses (genera Cytorhabdovirus and Nucleorhabdovirus) are vectored by aphids, leafhoppers, or plant hoppers, and even fish rhabdoviruses transmitted directly through water may have associations with arthropods 10,19,27 .…”