Recurrent evolution of high virulence in isolated populations of a DNA virus

Abstract

Hosts and viruses are constantly evolving in response to each other: as a host attempts to suppress a virus, the virus attempts to evade and suppress the host’s immune system. Here we describe the recurrent evolution of a virulent strain of a DNA virus which infects multiple Drosophila species. Specifically, we identified two distinct viral types that differ 100-fold in viral titer in infected individuals, with similar differences observed in multiple species. Our analysis suggests that one of the viral types appears to have recurrently evolved at least 4 times in the past ~30,000 years, 3X in Arizona and once in another geographically distinct species. This recurrent evolution may be facilitated by an effective mutation rate which increases as each prior mutation increases viral titer and effective population size. The higher titer viral type suppresses the host immune system and an increased virulence compared to the low viral titer type.