Host shifts result in parallel genetic changes when viruses evolve in closely related species

Ben Longdon; Jonathan P Day; Joel M Alves; Sophia CL Smith; Thomas M Houslay; John E McGonigle; Lucia Tagliaferri; Francis M Jiggins

When a pathogen infects a novel host species, it finds itself in a new environment to which it must 142 adapt [4, 8, 10, 44] . When DCV was passaged through different species of Drosophilidae, we found 143 the same genetic changes arose repeatedly in replicate viral lineages in the same host species. Such 144 repeatable parallel genetic changes to the same host environment are compelling evidence that 145 these changes are adaptive [20] . We then examined whether these same genetic changes might 146 occur in closely related host species, as these are likely to present a similar environment for the 147 virus. We found that viruses evolved in closely related hosts were more similar to each other than 148 viruses that evolved in more distantly related species. Therefore, mutations that evolve in one host 149 species frequently arise when the virus infects closely related hosts. This finding of parallel genetic 150 changes in closely related host species suggests that when a virus adapts to one host it might also 151 become better adapted to closely related host species.