Do mutations that drive evolution improve many traits or few? Does this change over the course of evolution? Excited to share our work in PLOS Biology exploring these questions in the first 2 adaptive steps w/ Yuping Li, @gsherloc.bsky.social, @petrovadmitri.bsky.social 🧵 doi.org/10.1371/jour... - ThreadSky

grantkinsler.bsky.social • 167 days ago

Do mutations that drive evolution improve many traits or few?

Does this change over the course of evolution?

Excited to share our work in PLOS Biology exploring these questions in the first 2 adaptive steps w/ Yuping Li, @gsherloc.bsky.social, @petrovadmitri.bsky.social 🧵

https://doi.org/10.1371/journal.pbio.3002848

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grantkinsler.bsky.social•167 days ago

Theory predicts that adaptation should be slow and gradual, driven by mutations that incrementally improve the organism one trait at a time.

However, work from microbes, cancer, and other fields often find LARGE mutations that improve multiple traits at once. 2/n

grantkinsler.bsky.social•167 days ago

For instance, Yuping previously found that ~85% of first-step adaptive mutations improved yeast's performance in both fermentation and respiration growth phases under selection in this environment. 3/n

grantkinsler.bsky.social•167 days ago

We wondered whether this pattern might continue over further adaptive steps, suggesting that mutations that improve multiple traits at once are common (left).

Or if we begin to run out of these mutations, mostly finding mutations that improve one trait or the other (right). 4/n

grantkinsler.bsky.social•167 days ago

To do this, we conducted a series of 2nd-step evolution experiments.

We constructed barcoded populations from five 1st-step mutations and evolved them in the same environment as the 1st step.

We then isolated 100s of mutants and quantified their performances in growth phases. 5/n

grantkinsler.bsky.social•167 days ago

While 85% of 1st-step mutations improve both fermentation and respiration performances, only 35% of second-step mutations do so.

This suggests that already in the 2nd-step of evolution, we have begun to run out of mutations that improve both growth phases to a large extent. 6/n

grantkinsler.bsky.social•167 days ago

This suggests that mutations that improve multiple performances at once may be relatively rare and may be expected to arise early in adaptation.

However, once they are exhausted, organisms then must improve traits one at a time, consistent with some of the theory. 7/n

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