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Date: | Sun, 17 Sep 2023 19:38:07 -0500 |
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>I think it's worth questioning what are the significant differences between
evolution (which proceeds in an undirected fashion) and breeding (which is
by definition, goal oriented). Can the results of the two be compared? Would
we expect the results to be similar?
In my very humble opinion, I think the target of our evaluations in
resistance development are in the vein of adaptation- which involves a suite
of malleable genetic, environmental, behavioral and epigenetic factors.
One thing from the Prospects
<https://onlinelibrary.wiley.com/doi/10.1111/eva.13533> paper that struck
me was the recognition of non-genetic (including G X E
<https://coloss.org/gei-experiment/> ) interactions in resistance
development:
As long as the impact of local environment on the ability of the selected
traits to limit infestation remains unknown, progress towards surviving
stock will likely be limited.
The lack of progress towards the selection of honey bee lineages surviving
infestations by V. destructor is probably not due to the generation time of
the honey bee, which is short compared to other livestock such as cattle,
but is likely due to caveats in selection strategies and knowledge gaps in
our understanding of resistance mechanisms.
The literature focusing on resistance traits indicates that several agents
can affect their expression. These agents are the parasite itself, other
pests and the host via its biological attributes or via the interaction
between resistance traits. As a result, only part of the phenotype measured
reflects the ability of a colony to defend itself against the parasite.
It is worth noting that heritability might be confounded by epigenetic
processes. A genetically inherited trait is indistinguishable from a trait
acquired via social learning, when workers have the ability to transmit
acquired knowledge across generations: thus, behaviours may be expressed by
related workers without a genetic causality.
The likely frequent occurrence of genotype-by-environment interactions
indicates that adaptation to local conditions plays a major role in colony
survival and restrains the possibility to export resistant colonies to
regions with different environments. Because of the lack of initial local
adaptation, importing resistant colonies from other regions or environments
bears low chances of success, and selecting local stock is recommended.
This reminds me of a Mondet et al
<https://www.sciencedirect.com/science/article/pii/S002075192030093X?>
paper which observed:
Even though the ability of honey bee colonies to survive varroa without mite
control stands as the ultimate goal of varroa resistance and tolerance
selection, using "survival" as the only phenotype may be dangerous since it
may be dependent on many other factors besides varroa. Our literature review
revealed that low MPG is a common downstream result in surviving
populations. This highlights three important aspects for methodological
development: (i) low MPG can result from many different traits operating
alone or in combination; (ii) it can also be influenced by many
environmental and beekeeping factors; and (iii) standing as a central
feature of varroa-resistant populations, evaluating MPG may be the most
robust phenotyping method to assess mite resistance.
While anecdotal, in my own TF experiment I have found that low MPG is the
only reliable predictor of long-term survival even while I have had colonies
with relatively high mite loads persist for several seasons.
So in answer to the question and based on my own limited vantage point I
would suggest that Mother Nature selects for survival in a specific context,
and breeding should be selecting for low MPG (if we want relatively
consistent results in varied environments).
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