Monarch Butterflies Evolved to Eat Poison | Hacker News Reader

Monarch Butterflies Evolved to Eat Poison

nytimes.com

69 pointssohkamyung17 comments

The companion website put out for the study is also worth a read [1].

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

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

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.

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.

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)

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.

> A third mutation(A119S) is immediately needed to correct the side effect.

Or, that third mutation came first.

These are sequential, it could not have naturally.

The linked source states otherwise.

That is a hypothetical used to promote a narrative, all the test & observations presented show all mutations must be present for specialization. The Monarch only feeds on milkweed, but somehow it survived the A119s phase feeding on milkweed plant (CG-containing plant)without the needed 111& 122 mutation?

In an hypothetical adaptive walk. A119S does NOT provide sufficient CG-insensitivity so an insect with just A119S will die specializing in CG. The are other mutations needed for survival.

Moreover u left out: “A119S is a common substitution among taxa that do not specialize on CG-containing hostplants“

Natural selection is undefeated. Therefore the need for immediate substitutions to sites 111 & 122 in order to specialize on “CG-containing hostplants“

An adaptive walk has to show adaptation in the environment. If all the mutations occur outside the natural environment, without natural selection, it is not an adaptive walk.

Nice layout on that website, I liked the 2 column format. Less distracting than the usual "jump up and down between text and pictures".

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.

Poison for one species, food for other.

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?

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

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.

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

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

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