Vertical transmission and sweeps

Figure 2

We have found sigma viruses that infect several Drosophila species, Mediterranean fruit flies and a butterfly are all vertically transmitted (see here and here). Unlike bacterial symbionts, sigma viruses are transmitted vertically through both sperm and eggs, so are able to spread through populations despite being costly to infected flies.

Four out of the five sigma viruses tested to date have recently spread through their host populations (e.g. Figure 2). This could be due to selective sweeps of an advantageous mutation through an exiting viral population or the spread of new viruses from a different species or population through an uninfected population. It seems that vertically transmitted rhabdoviruses may be common in insects, and they can have very dynamic interactions with their hosts.