
Monarch Butterflies Evolved to Eat Poison - sohkamyung
https://www.nytimes.com/2019/10/02/science/monarch-butterflies-milkweed.html
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sohkamyung
The companion website put out for the study is also worth a read [1].

[1] [http://www.noahwhiteman.org/monarch-
fly.html](http://www.noahwhiteman.org/monarch-fly.html)

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rockarage
Read the companion website, the authors cherry-picked their findings, good
thing they link to another independent study:

[https://elifesciences.org/articles/48224](https://elifesciences.org/articles/48224)

“Surprisingly, we find that frequently observed adaptive substitutions at two
sites, 111 and 122, are lethal when homozygous and adult heterozygotes exhibit
dominant neural dysfunction. We identify a phylogenetically correlated
substitution, A119S, that partially ameliorates the deleterious effects of
substitutions at 111 and 122. Despite contributing little to cardiac
glycoside-insensitivity in vitro, A119S, like substitutions at 111 and 122,
substantially increases adult survivorship upon cardiac glycoside exposure.”

Essentially the study found 2 mutations (substitutions at 111 and 122) give
the treatment fruit fly(Drosophila ) an immunity to milkweed poison(cardiac
glycosides), the mutation has a lethal side effect: it causes a neural
dysfunction that kills the treatment fly(adult heterozygotes). A third
mutation(A119S) is immediately needed to correct the side effect. If we are
being honest an adaptive walk is essentially impossible for the Monarch. An
honest critic refutes the Whiteman Laboratory & NYTimes assertion that an
adaptive walk occurred.

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redofrac
Could you explain how the need for two mutations refutes the idea of an
adaptive walk? The elife article just seems to suggest that walk may have been
a more complex process.

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inkaudio
Not two, but three mutations. The first & second induced mutations gives the
fruit fly immunity to the poison but the mutations are also lethal, which
means the fly could not survive long enough for the third needed mutation to
occur in an adaptive walk. The third mutation is like a stabilizer of the
first & second mutation, it does not give immunity. In the test all three
mutations are needed simultaneously for the fly to have the immunity and
survive, that is not an adaptive walk, that is incredible engineering. So
essentially you can engineer a monarch butterfly, but an adaptive walk is
impossible in this case. (Writing on the go, may edit later)

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ceejayoz
I'm not sure where you're getting that info. The linked source indicates the
third mutation in question precedes the first two.

> In multiple lineages, the substitutions A119S and A119N preceded
> substitutions to 111 and 122 (Hemiptera, Hymenoptera, Diptera). In
> Drosophila, where we have the greatest phylogenetic resolution, A119S was
> established before substitutions to sites 111 and 122 in the evolutionary
> lineage leading to D. subobscura, which appears to be polymorphic with
> respect to CG-insensitivity.

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netman21
I have been encouraging milkweed to grow in my yard for a couple of years now.
There is a woodchuck that comes by and eats all the leaves off each plant with
relish. So much for toxins.

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babuskov
Poison for one species, food for other.

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k_sze
For me, the most interesting bit of the article is the way the researchers
found the downside of mutation 122 without the other two mutations. Why did
the researchers decide to spin the flies in a centrifuge in the first place?
Is that a standard procedure in studying fruit flies? But since normal fruit
flies usually just walk away from the “carnival ride” as though nothing
happened, what do scientists usually expect to gain from such a procedure?

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k_sze
So I asked on Biology SE and it turns out that the author of the article
confused “centrifuging” with “vortexing”:
[https://biology.stackexchange.com/a/88111/1114](https://biology.stackexchange.com/a/88111/1114)

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JohnFen
They didn't evolve fast enough, maybe.

In my area, I remember monarch season when I was young, when clouds of
monarchs were everywhere.

I haven't seen a single one in about 20 years now.

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jmpman
I spent the last few years building up an immunity to iocaine powder.

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sohkamyung
Sadly, you can't pass on that immunity to your descendants, unless it causes a
beneficial mutation in your reproductive organs. :-)

