Viruses of honeybees: Exploring the mechanisms of adaptation

The Honeybee Research Group at SLU specializes in research on honeybee health and pathology, and the expertise of the author within the group is on honeybee viruses. The main research interests of both the group and the author are the interactions and adaptations of pathogens and host to each other, especially in relation to individual bee and colony health.

One major interest is the genetic variability of honeybee viruses within bees and bee colonies and the relevance of this variability for adaptation of the virus to its host. We regularly encounter major sequence polymorphisms in natural populations of deformed wing virus (DWV; our primary study virus), usually consisting of two major strains each with a cloud of minor variants. We were intrigued why this is so, and what forces were responsible for generating and maintaining such polymorphisms. The immediate cause appears to be the large diversity in DWV genetic composition between individual bees in a colony, and between colonies. This points to individual bees and within-colony factors as the major drivers of diversity, but does not identify the mechanisms producing this diversity. One possibility is that the many different DWV transmission routes could produce a polymorphism in the virus population, if different variants are transmitted with different efficiencies through different routes. This relates to the theory of virulence evolution, which contrasts the selective outcomes of horizontal and vertical pathogen transmission. This possibility was particularly interesting, since one of the horizontal transmission routes involves a parasite vector that is also an alternative host for DWV, providing additional selective pressure for DWV genetic adaptation. However, even though the transmission routes affected the amount of DWV in bees, they did not affect the DWV genetic composition in a consistent manner, either in detailed transmission experiments or in long-term host-parasite-pathogen co-adaptation studies. This is consistent with several other studies. Another approach is to compete the different transmission routes against each other, using different variants for different routes, to determine the relative importance of each transmission route for the overall DWV status of the colony, as well as any possible preferences of the DWV variants for different routes. This is a planned future study, subject to funding. Other planned future studies are to analyze the biological, molecular and genetic adaptive responses of both bees and the parasite to virus infection.

/Joachim Rodrigues de Miranda