Abstract
Comparative studies of genetic diversity and population structure can
shed light on the ecological and evolutionary factors governing
host–parasite interactions. Even though they are considered of major
biological importance, little is known about the adaptation potential of
invasive parasites in their new ranges. Here, the genetic
diversification of Varroa destructor, a novel parasite of
Apis mellifera originating from Asia, was investigated using
population genetics to compare how the genetic structure of the parasite
changed in response to its interactions with distinct European
populations of its new host. To do so, mites infesting two categories of
hosts in four European regions were compared: (i) adapted hosts
surviving through means of natural selection, thereby expected to impose
strong selective pressure on the mites, and (ii) susceptible host
populations, surviving because acaricides are applied, therefore
characterized by a relaxed selection imposed by the host. Significant
genetic divergence was found across regions, reflecting partially the
invasion pattern of V. destructor throughout Europe, but also
local adaptation of the mite to the host populations. Additionally,
varying degrees of genotypic changes were found between mites from
adapted and susceptible 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
geographical scales. These findings highlight the potential of parasites
to adapt to their local host populations and confirm that adaptations
developed within co-evolutionary dynamics are a major determinant of
population genetic changes.