Impact of vector-mediated transmission on the evolution and ecology of a bee virus
The emergence of novel transmission routes is likely to have profound impacts on the ecology and evolution of infectious diseases, with potentially dramatic effects on host populations. This might be particularly drastic when transmission changes from direct to vector-borne transmission, where prevalence and virulence are expected to increase. Despite its importance for disease control, we lack empirical and theoretical understanding of this process. The emergence of Varroa destructor in honeybees provides a unique opportunity to study how a novel vector affects pathogen ecology and evolution: this ectoparasitic mite is a novel vector for Deformed Wing Virus (DWV), a disease linked to severe increases in hive mortality. To study the fundamental evolutionary ecology of emerging vector-borne diseases, I will exploit a unique natural experiment, the presence of Varroa-free island refugia, to test how this novel vector affects epidemiology and evolution in the field. I will adapt cutting-edge single molecule sequencing to guide  controlled lab experiments by viral evolution in the wild, establishing novel reverse genetics approaches in DWV to test causal links between phenotypic and molecular evolution. Like all emerging diseases, DWV is a multi-host pathogen that also infects wild bee species not infested by Varroa, such as bumblebees. This raises an additional question, highly relevant for zoonotic diseases: does this specialist honeybee vector impact disease in wild bee populations? I will model the impact of vector acquisition and evolving pathogens on host populations and test potential prevention and mitigation strategies to safeguard these crucial pollinators. This system will not only provide fundamental insights into the evolutionary ecology of disease, but is also of immediate applied importance: bees are key pollinators of crops and wildflowers, and halting population declines facilitated by infectious disease is crucial for food security and biodiversity.