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

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Longdon, Ben ; Day, Jonathan P. ; Schulz, Nora ; Leftwich, Philip T. ; de Jong, Maaike A. ; Breuker, Casper J. ; Gibbs, Melanie ; Obbard, Darren J. ; Wilfert, Lena ; Smith, Sophia C. L. ; McGonigle, John E. ; Houslay, Thomas M. ; Wright, Lucy I. ; Livraghi, Luca ; Evans, Luke C. ; Friend, Lucy A. ; Chapman, Tracey ; Vontas, John ; Kambouraki, Natasa ; Jiggins, Francis M. (2017)

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 ($\textit{Rhabdoviridae}$). Here, we report that sigma viruses that infect Mediterranean fruit flies ($\textit{Ceratitis capitata}$), $\textit{Drosophila}$ immigrans, and speckled wood butterflies ($\textit{Pararge aegeria}$) are all vertically transmitted. We find patterns of vertical transmission that are consistent with those seen in $\textit{Drosophila}$ 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 $\textit{D. immigrans}$ and $\textit{C. capitata}$ had both recently swept through host populations. The viruses were common in nature, with mean prevalences of 12% in $\textit{C. capitata}$, 38% in $\textit{D. immigrans}$ and 74% in $\textit{P. aegeria}$. 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. B.L. is supported by a Sir Henry Dale Fellowship jointly funded by the Wellcome Trust and the Royal Society (grant no. 109356/Z/15/Z). B.L. and F.M.J. are supported by an NERC grant no. (NE/L004232/1 and by an ERC grant (281668, DrosophilaInfection, P.T.L., T.C. and L.A.F. are supported by a BBSRC grant no. (BB/K000489/1).