A recurrent adaptive mutation in the transmembrane 2B protein of an insect picorna-like virus in a nonnative host

The forces driving virus evolution are central to understanding cross-species transmission and virus emergence. It is well established that the adaptive immune system drives virus evolution in mammals, but whether innate responses likewise drive virus evolution upon host shifts is less well understood. In this manuscript, we used <i>Drosophila melanogaster</i> as a model to study the evolution of a native and a nonnative pathogen under conditions in which innate antiviral immunity is either abolished or enhanced. Using an experimental evolution approach, we find little evidence for adaptive evolution of the natural pathogen Drosophila C virus. In contrast, we observed a recurrent adaptive mutation in the viral nonstructural 2B protein in the nonnative cricket paralysis virus, independent of the antiviral cGAS/STING pathway. Our work provides insights into viral adaptation to new hosts and the characteristics of the 2B protein of dicistroviruses, a family comprising important model insect viruses.