for National Geographic News
It's a miracle! Blind cavefish, despite having adapted to their lightless environment for more than a million years, can produce sighted offspring in just a single generation, a new study reveals.
The ability was discovered when researchers mated fish from distinct populations that had been isolated in separate caves.
In some cases the first-generation offspring of such unions could see.
The find shows that the genetic mutations causing blindness are different in different lineages of the fish.
"Evolution's palette is varied," said study author Richard Borowsky of New York University in a statement.
"Restoration of the ability to see comes in a single generation because the populations residing in different caves are blind for different reasons—i.e., different sets of genes are nonfunctional in the different populations."
The research, which was recently published in the journal Current Biology, focused on several of the 29 known blind cavefish (Astyanax mexicanus) populations found in northeastern Mexico.
The fish evolved from surface-dwelling ancestors during the past million years. (Related: "Eyeless 'Ghost Fish' Haunts Ozark Caves" [October 29, 2003].)
They have sightless eyes as embryos, but the organs decay as the animal ages and are eventually scaled over by the fish's body.
Previous work had suggested that the evolution of blindness, a loss of pigmentation, and other underground adaptations occurred independently in several locations and via mutations of different genes.
The new work "nailed down" this concept, said biologist William Jeffery of the University of Maryland in College Park.
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