Post by Pro Plyd2nd attempt
Longish article. May be of interest to others.
https://www.sciencedaily.com/releases/2024/10/241011140950.htm
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
Second attempt to post:
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