>. this suggests the possibility that these bees and these mites have
co-evolved, meaning we are looking at distinct populations of bees -and-
mites.
It seems that much of the research coming out studying resistant populations
in Europe would lend some credence to this hypothesis:
Population genetics of ectoparasitic mites suggest arms race with honeybee
hosts <https://www.nature.com/articles/s41598-019-47801-5.pdf> (2019
Beaurepaire et al):
The mites from the mite-resistant population on Gotland were compared with a
geographically neighboring mite population from managed mite-susceptible
honeybees that have not experienced natural selection pressures. The changes
in the genetic diversity and genetic structure was compared over time using
microsatellites to compare historic mite samples collected in 2009 with
current mite samples collected from the same populations in 2017 and 2018.
. these . analyses clearly indicate that V. destructor populations have
changed within the eight years separating the collection of the current and
historical samples. These changes led to a higher level of differentiation
and an increased diversity of mite genotypes in the resistant colonies
compared to the susceptible ones.
This observation suggests that a strong selection against the most common
mite genotypes is occurring in the resistant colonies. To conclude, the
above-mentioned evidences strongly suggest that the main factor responsible
for the temporal changes in the genetic structure of V. destructor measured
here are caused by the strong selection pressures induced through the
co-evolution of the mite with its host, rapidly leading to observable
genetic changes in the parasite population, potentially aiding their
survival in adapted mite-resistant A. mellifera colonies.
In conclusion, the observed changes over time in the genetic structure of V.
destructor suggest adaptations of the parasite, in a host-parasite
coevolutionary arms race, most likely in response to selection pressures
applied by the adapted resistant traits of the host. The magnitude of these
changes between the historic and current samples of this study demonstrate a
relatively fast response.
Selection for outbreeding in Varroa parasitising resistant honey bee (Apis
mellifera) colonies
<https://www.researchgate.net/publication/342637280_Selection_for_outbreedin
g_in_Varroa_parasitising_resistant_honey_bee_Apis_mellifera_colonies> (2020
Conlon et al):
. investigated the potential for the evolution of counter resistance traits
and selection for outbreeding in Varroa infesting resistant honey bee
colonies near Toulouse, France.
Having identified colonies which exhibited unusually high rates of
nonreproducing Varroa, we investigated the reproductive success of Varroa
between singly and multiply infested cells. We then used genetic analyses to
test if reproductive success was linked to genetic polymorphism in founding
females. Selection for increased recombination, via outbreeding, could
increase evolutionary rates in this Varroa population and indicate it is
engaged in a co-evolutionary arms race with its host.
We screened four honey bee colonies, three (Mother; Daughter 1; and Daughter
2) resistant and one (Daughter 3) susceptible. The mother colony was
produced in 2015 while the 3 daughters came from 2016. None of the resistant
colonies varied significantly from a 50:50 distribution of
resistant:susceptible pupae.
.only the nonresistant colony exhibited significant variation from a 50:50
ratio of Resistant:Susceptible pupae, with no intermediate levels of
resistance, supported the previous identification
<https://www.researchgate.net/publication/332047687_A_gene_for_resistance_to
_the_Varroa_mite_Acari_in_honey_bee_Apis_mellifera_pupae> of a single
resistance-linked locus in this population and suggests Mendelian
inheritance of the resistance trait.
Our results show that, when Varroa resistance is allowed to develop by
natural selection, it is possible for a host-parasite relationship to
evolve. The increased reproductive success we identify when Varroa
co-infests the drone pupae of resistant honey bee colonies means that, in
contrast to acaricide-treated colonies, there may be selection for outbred
offspring. This, combined with a small proportion of Varroa reproducing in
each generation, could reduce the selective pressure for the evolution of
more virulent counter resistance traits and result in a more stable
host-parasite relationship.
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