Migratory beekeeping facilitates genetic admixture in populations of the honeybee parasite Varroa destructor

Abstract

Understanding the rapid evolution of agricultural pests can inform mitigation efforts and provide comprehensive models for natural systems and examples for the consequences of anthropogenic global change. It is suspected that the practice of migratory beekeeping, in which beehives are shipped great distances to meet pollination demands, increases dispersal of honeybee (Apis melifera) pests and parasites, including the highly virulent mite Varroa destructor. Given it has never been explicitly examined in the United States, here we test this hypothesis by studying the population genetics of Varroa mites sampled from migratory and non-migratory hives across the western United States. Using 3RAD to generate a genome-wide dataset for hundreds of samples, we found very low genetic diversity and no population structure across more than one thousand kilometers. Our findings are consistent with the proposed large and fast mite admixture enabled by migratory pollination. Furthermore, hives that avoid migratory pollination are not insulated from the effects of this admixture, as there is evidence for extremely high rates of gene flow into—and a resulting lack of isolation by distance among—these sedentary populations. Our research suggests the genetic variation of Varroa destructor in the western United States is a result of its recent introduction to the region and shows clear signals of high admixture, likely due to management practices. Moreover, it demonstrates how an evolutionary, genetic perspective is crucial in understanding host-parasite dynamics in agricultural systems and shaping management decisions to protect key species