Local adaptation of a major honey bee virus, deformed wing virus, to an alternative spillover host, a bumble bee

In a serial passage experiment, we explore the adaptability of DWV genotypes A and B to an alternative host, the bumble bee Bombus terrestris, and investigate associated consequences for DWV virulence in B. terrestris and when re-infecting its presumed reservoir host, A. mellifera. Both DWV-A and DWV-B selected in B. terrestris increased in their speed of viral growth in the bumble bee host, indicative of viral adaptation, though viral virulence in B. terrestris remained largely unaffected. Moreover, DWV selected in the bumble bee host showed no attenuated virulence when reintroduced into the honey bee host, suggesting that viral adaptation to B. terrestris did not incur a fitness cost when re-infecting A. mellifera. High-throughput sequencing of experimentally evolved DWV-A and DWV-B showed that viral populations were characterised by modest genomic alterations on the consensus level. The adaptive landscapes of DWV-A and DWV-B appear to be flat plateaux, possibly permitting each to be generalist pathogens of a range of invertebrate species.