Re: Science has a news article up about "living fossils"

On 3/11/2024 6:28 PM, John Harshman wrote:

On 3/11/24 4:17 PM, RonO wrote:

https://www.science.org/content/article/these-gars-are-ultimate-living-fossils
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Open access article:
https://academic.oup.com/evolut/advance-article/doi/10.1093/evolut/qpae028/7615529?login=false
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These researchers looked at Gar, but it also applies to sturgeons. These two bony fish lineages seem to have a very slow rate of molecular evolution.  The changes in their DNA accumulate so slowly that two lineages separated for over 100 million years can still form fertile hybrids.  3 million years is pushing it for species like lions and tigers that can still form hybrids, but the hybrids are sterile. Bonobos and chimps are around 3 million years divergent and can still form fertile hybrids, but the claim is that these fish evolve orders of magnitude more slowly than mammals.
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The Science news article claims that mammals accumulate 0.02 mutations per site per million years, while these fish averaged only 0.00009 mutations per million years.  For the 1100 coding exons that they looked at for this study these fish evolve much more slowly than mammals.
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The news article notes that other "living fossils" such as coelacanths (0.0005) evolve faster, but slower than amphibians (0.007).  It sounds like terrestrial animals evolve faster than fish.

 If it's repair mechanisms they hypothesize as the cause of slow evolution, they really should be looking at junk sequences rather than just 4-fold degenerate sites. I suggest introns. And if the introns aren't alignable, well, that kills the theory right there.
 

The article claims that these fish have better control of their transposons, and that chromosomal structural changes are also accumulating more slowly.  The decrease in structural mutations is likely what is allowing the interbreeding and interfertility to be extended back to such a distantly lineages.  Structural changes are a big reason why functional gametes do not form from hybrids.  If their chromosomal number is different or they have too many translocations very few viable gametes can form complete haploid genomes.
Ron Okimoto