Re: "Evolution in real time Scientists predict -- and witness -- evolution in a 30-year marine snail experiment"

On 10/13/2024 10:50 PM, Pro Plyd wrote:

2nd attempt
 Longish article. May be of interest to others.
 https://www.sciencedaily.com/releases/2024/10/241011140950.htm
 Summary:
Snails on a tiny rocky islet evolved before
scientists' eyes. The marine snails were
reintroduced after a toxic algal bloom wiped
them out from the skerry. While the
researchers intentionally brought in a
distinct population of the same snail species,
these evolved to strikingly resemble the
population lost over 30 years prior.
  Paper is here
http://dx.doi.org/10.1126/sciadv.adp2102
 

It looks like they may be dealing with one semi qualitative trait in shell color.  There are multiple color loci segregating, but they may be due to single genes each.  The other two traits are quantitative. Hundreds of genes can contribute to these traits and multiple alleles for each gene.
It looks like all the alleles needed to create the wave phenotype was segregating within the Crab infested population.  Even though the phenotype has changed drastically, no trait has gone to zero (been totally lost).  You can probably reconstruct the original phenotype from the new selected population.
This means that the variation that can be selected to adapt to the Wave environment existed within the Crab environment population.  This variation has existed for a very long time, and is likely maintained by selection in different environments and limited gene flow between environments.
If you look up the literature on the divergently selected Siegel White Rock chicken lines that were divergently selected for more than 50 generations.
https://pubmed.ncbi.nlm.nih.gov/23776258/
Quantitative trait loci for body weight were mapped in these populations using intercrosses between the lines and it was found that the quantitative trait alleles had not been fixed within each line.  The low weight line still had high weight alleles and vice versa.  This is because body weight is a quantitative trait like the snail phenotypes. There are many genes that contribute to the trait, and genetic variation is such at each gene that different combinations of alleles can produce similar phenotypes.  The same alleles can combine in different ways. There is the additive gene model where each allele at each gene contributes a bit to the over all phenotype, but you also have to deal with gene interactions.  Certain combinations are not additive.  You might have to combine certain alleles at different genes in order to produce a phenotype.  Certain alleles of one gene may cover or mask the phenotype of the alleles of another gene.  So even when the alleles under selection are present they do not express the phenotype if that individual has not inherited the needed combination or in the presence of the covering or epistatic gene alleles.
The same thing is happening in these snails.  The evolution is predictable because they started with the same alleles segregating that were needed to produce the new adaptive phenotype.  They still have the alleles needed to go back to the original phenotype even though they have recreated the extreme Wave phenotypes.  Allele frequencies have changed, but very few alleles have gone to fixation.
Ron Okimoto