When Mexican tetra fish moved into dark caves long ago, they evolved to deal with the dark by becoming albino…and going blind. And new research shows that the changes various cave fish populations went through occurred repeatedly—a massive, textbook example of convergent evolution. The study is in the journal BioMed Central Evolutionary Biology. [Martina Bradic et al., "Gene flow and population structure in the Mexican blind cavefish complex (Astyanax mexicanus)"]
To determine how the dark-dwelling fish evolved their sightlessness, researchers tested the DNA of 11 Mexican cave fish populations. They compared the genes with those of tetra populations that lived out in the light. Originally, researchers had believed that all of the cave populations were descended from a single group of tetra fish that went underground and then went blind. But the cave fish genes told a different story: the 11 populations had five separate evolutionary origins, with different groups independently experiencing and selecting an eyeless mutation.
Although the surface- and cave-dwelling fish frequently mix, interbreeding has not eradicated cave fish blindness. Which means that evolution is actively selecting blindness. Perhaps because investing bodily resources in sight is a waste of energy in the dark.
[The above text is a transcript of this podcast.]