Published online 7 January 2008 | Nature | doi:10.1038/news.2008.414


Blind cave fish see the light

Two blind fish can make sighted offspring.

The offspring of crossbred blind cave fish see like their surface-dwelling cousins, shown in the background.R. Bolowsky

By mating blind fish from distant underwater caves, researchers have bred offspring that can see.

The results, published this week in Current Biology1, show that the two populations took different evolutionary paths to blindness.

“We’ve basically shown that these different populations have converged upon the same outward appearance independently, and that they use different genes to do it,” says Richard Borowsky of New York University.

The blind fish, called Astyanax mexicanus, live in isolated limestone caves in northeast Mexico. Over hundreds of millennia of living in darkness, the fish, which have a sighted ancestor, accumulated genetic mutations that affect eye development, and so lost their sight. Today some 29 different varieties of the blind Mexican fish live in isolated caves. Researchers have long wondered whether they all lost their sight the same way or not.

Fishy differences

Borowsky and his assistants descended into the caves and fished out different blind populations to cross in the lab. If the fish had the same developmental mutations, the researchers reckoned they would produce blind offspring. Instead, the experiment produced a number of fry with functioning eyes; in the most successful pairing, 40% of hybrid fry could see. The results suggest fish from different caves have mutations that don’t overlap.

To test for vision, Borowsky and his team immobilized the hybrid fish in viscous goo. They then tracked eye movements while the fish were presented with a rotating pinstripe pattern. A number of the hybrids could track the pattern with their eyes — at least for a while. The young fishes' vision deteriorated with age.

Previous work has shown hybrids of blind fish can have eyes that look to be functional2. But “this is the first study to show that these hybrids have vision,” says biologist William Jeffery of the University of Maryland in College Park, who has studied the genetics of eye development in the cave fish.


Blind evolution

Researchers still do not know exactly what drives the evolution of blindness. Theories differ on why the fish repeatedly changed from a sighted sun-lover to a blind bat-guano eater.

Borowsky notes that the eye requires a lot of energy to maintain, and so a cave-dwelling fish might scrap its eyes in favour of other, more advantageous investments, such as a better system for detecting vibrations. 

  • References

    1. Borowsky R. Current Biology 18, R23 - R24 (2008) | Article |
    2. Wilkens, H. Evolution 25, 530-544 (1971). | Article |
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