Evolution: a different view with loss of traits; not Behe (Introduction)

by David Turell , Monday, May 02, 2022, 19:51 (935 days ago) @ David Turell

A supportive view of Behe. Gene loss drives innovation:

https://ecoevocommunity.nature.com/posts/do-harmful-mutations-have-a-constructive-role-...

"In our new work (Farkas et al, 2022), we challenge this view and propose that gene loss is an internal driving force in creating new morphologies. This might sound very odd to many readers. It is easier to mess up the normal functioning of a gene than to improve it. Therefore, loss-of-function mutations are prevalent in the genomes of many species, including humans. But losing a molecular function is unlikely to be a good thing. So, how can gene loss be a creative evolutionary force?

"Well, luckily for us, and all other species on the planet, such detrimental, loss-of-function mutations do not remain unnoticed by evolution. So-called compensatory mutations in other genes can fix the damage incurred by gene loss. Therefore, one can envisage this process as a co-evolutionary dance between the harmful and the corresponding compensatory mutations. The central issue is whether this process has any enduring effects on morphological traits. We addressed this issue by studying the evolution of baker’s yeast morphology in the laboratory.

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"...baker’s yeast was an excellent choice. It is not only an important species for humans to make delicious bread, beer, and wine, but also a well-studied model organism in biology. Researchers can readily introduce deleterious mutations into its genome and investigate potential compensatory mutations that spontaneously arise. There are also large collections of baker’s yeast strains, each lacking a single gene, created by geneticists. Some of the gene deletions are harmful, causing slow microbial growth, and thereby serving as a perfect starting point for compensatory evolution.

"Compensatory evolution in the lab occurred immensely rapidly. In no more than 100 days, over half of the slow-growing mutant yeasts recovered their normal growth in an optimal laboratory condition without any external stress. But do these compensated strains also show normal morphology? Or do they change their look as a side-effect of compensatory evolution? The latter scenario is plausible given the many genes that affect morphology in baker’s yeast.

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"It is important to point out that the original, unmutated strain we used, cannot grow invasively or make clumps, and only form a small biofilm. Despite these, it was stunning to see that each of the above multicellular behavior appeared or was enhanced in some of our compensated strains. On top of this, the appearance of the same traits in different strains was caused by mutations in various genes. In the case of invasive growth, the effectiveness of the cells to enter into a surface was comparable to what we saw across natural strains capable of growing invasively. All of these findings suggest that compensatory evolution might also contribute to the emergence of clinically relevant microbial traits.

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"Our work is the first to systematically test this hypothesis and provides empirical evidence that deleterious mutations can frequently contribute to novel phenotypes. A second debate concerns the possible role of large-effect mutations in evolution. According to the dominant view, phenotypic evolution proceeds in small discrete steps, because large-effect mutations often have deleterious side effects. However, our work demonstrates that such deleterious side-effects can be readily alleviated by compensatory evolution while a novel phenotype is being created. Hence, compensatory evolution in the lab can generate “hopeful monsters”, organisms with normal fitness despite having an atypical phenotype. Probably the most exciting open question is whether compensatory evolution really contributes to the morphological diversity seen in nature. By demonstrating that compensatory evolution does have the potential to create new morphologies in the lab, our results can hopefully open an avenue to get closer to the answer."

Comment: this study carries the theory of gene loss influencing evolution by 'compensatory evolution' to a new state of thought. Behne was not wrong. The genome was designed all along to compensate when necessary to carry evolution forward. going backward dos not appear to be allowed.