Abstract:
Nosema is a microsporidian parasite of the honeybee, which infects the epithelial cells of the gut. In Denmark, honeybee
colonies have been selectively bred for the absence of Nosema over decades, resulting in a breeding line that is tolerant toward
Nosema infections. As the tolerance toward the Nosema infection is a result of artificial selection, we screened chromosome 14
for a selective sweep with microsatellite markers, where a major quantitative trait locus (QTL) had been identified to be
involved in the reduction in Nosema spores in the honeybees. By comparing the genetic variability of 10 colonies of the selected
honeybee strain with a population sample from 22 unselected colonies, a selective sweep was revealed within the previously
identified QTL region. The genetic variability of the swept loci was not only reduced in relation to the flanking markers on
chromosome 14 within the selected strain but also significantly reduced compared with the same region in the unselected
honeybees. This confirmed the results of the previous QTL mapping for reduced Nosema infections. The success of the selective
breeding may have driven the selective sweep found in our study.
