Adaptive degeneration in cave fish
Astyanax mexicanus is a variety of blind cave fish which live in harsh conditions where food is scarce. They regularly experience short periods of abundant food, followed shortly after by a long period of scarcity. Yet, these fish don’t just survive, they thrive.
Through the deletion of DNA in the gene hpdb, they have lost the ability to make the ‘sunscreen’ pigment melanin. This is unnecessary in a dark cave, so the damaged gene is not eliminated by natural selection. It actually gives these albino fish an advantage in their environment. An ingredient (tyrosine) normally used to make melanin can instead become an additional nutrition source.
But this example of mutation giving a survival advantage does so by removing information from the genome. Obviously, one cannot go from a microbe to a human over millions of years by deleting genetic information.
- Callier, V., Blind cave fish may trade color for energy, scientificamerican.com, 1 Sep 2022.
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