Comparative studies of genetic diversity and population structure can shed light
on the ecological and evolutionary factors governing host–parasite
interactions.
Even though invasive parasites are considered of major biological importance, little
is known about their adaptative potential when infesting the new hosts. Here, the
genetic diversification of Varroa destructor, a novel parasite of Apis mellifera originating
from Asia, was investigated using population genetics to determine how the
genetic structure of the parasite changed in distinct European populations of its new
host. To do so, mites infesting two categories of hosts in four European regions were
compared: (a) adapted hosts surviving through means of natural selection, thereby
expected to impose strong selective pressure on the mites, and (b) treated host populations,
surviving mite infestations because acaricides are applied, therefore characterized
by a relaxed selection imposed by the host on the mites. Significant genetic
divergence was found across regions, partially reflecting the invasion pattern of V.
destructor throughout Europe and indicating local adaptation of the mite to the host
populations. Additionally, varying degrees of genotypic changes were found between
mites from adapted and treated colonies. Altogether, these results indicate that V.
destructor managed to overcome the genetic bottlenecks following its introduction
in Europe and that host-mediated
selection fostered changes in the genetic structure
of this mite at diverse geographic scales. These findings highlight the potential of
parasites to adapt to their local host populations and confirm that adaptations developed
within coevolutionary dynamics are a major determinant of population genetic
changes.