It appears that much of this discussion hinges upon definitions of
"evolution."
One meaning of the term is "change in heritable
<https://en.wikipedia.org/wiki/Heredity> traits
<https://en.wikipedia.org/wiki/Phenotypic_trait> of biological
<https://en.wikipedia.org/wiki/Biology> populations
<https://en.wikipedia.org/wiki/Population> over successive generations
<https://en.wikipedia.org/wiki/Generation>." I prefer this broad
definition, since it is about observable traits, rather than limiting
itself strictly to genetics (of which we are only recently gaining a better
understanding). This definition allows for heritable
environmentally-influenced traits, such as behaviors, inherited resistance
to specific parasites, or phenotypic adaptation to the environment (larger
body size, color, etc). This broad definition would thus apply to the
development of locally-adapted populations or races of honey bees, all
occurring within the species *Apis mellifera. *Such local populations
continually *evolve* in response to non-static environments.
The extreme result of such adaptation is *speciation*, in which
reproductive isolation occurs between two or more populations of a single
species (little breeding between the different populations), and the
populations diverge into different species (or some go extinct), either
through physical isolation due to geography, morphological isolation, or
behavioral isolation. At this point of evolution, certain alleles of
certain genes become "fixed" in the populations, and they can be
distinguished by our current genetic analyses. Had mankind not intervened
in Europe, such speciation may have eventually occurred between some of the
races of bees that had apparently evolved since the retreat of the ice
sheet.
Recent studies of feral and managed populations of honey bees, such as the
one cited in this thread, indicate that such reproductive isolation is
indeed occurring (and has long occurred) between the managed and feral
populations of bees in the U.S. Such reproductive isolation has the
potential to lead to either rapid or slow evolution of "races" or
"subspecies" of bees, with different morphology, behaviors, and resistance
to various parasites.
It is not common knowledge that speciation can happen with great
rapidity--over the course of only tens of generations, rather than
thousands (see The speed of ecological speciation
<http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2605086/>). But in the case
of honey bees, full divergence into distinct species appears to be
uncommon, as evidenced by the paucity of species in the genus *Apis.* This
is likely due to the extreme adaptability of the *Apis* genus as a whole,
as well as the mating system, which works strongly against complete
reproductive isolation. Rather, honey bees tend to form many
locally-adapted races of any species.
I guess that it is all up to our individual interpretation of the evidence
in the literature. Some of us (such as myself) see bees as continually and
rapidly *evolving* to adapt to ecological changes (such as the introduction
of varroa). Others can justifiably claim that the species *Apis mellifera *is
simply one huge interbreeding population, and is thus not "evolving."
One example of interpretation has to do with the evolutionary success of
the Africanized hybrid (AHB) of *A. mellifera*. This hybrid formed in South
America when races of bees introduced from Africa crossed with the
established, but poorly adapted races that had been previously introduced
from Europe. In relatively few years, a dominant form of the hybrid
(consisting mainly of African mitotypes, but containing a fair proportion
of European genotype) completely displaced the preexisting honey bee
populations. This now-fixed hybrid was more swarmy, more defensive,
generally formed smaller colonies, used smaller cavities, favored
reproduction over honey storage and wintering, and adapted more quickly to
the invasion of varroa.
Few would claim that they were not a very different bee. Yet they were
still *Apis mellifera. *So did evolution take place? It all depends upon
your definition of "evolution."
--
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com
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