In today’s Academic Minute, Dr. Richard Borowsky of New York University explains the connection between sleep and the loss of vision in cave-dwelling fish species.
Richard Borowsky is a professor of biology at New York University where he studies the evolution and genetics of cave fish with an emphasis on understanding the molecular and developmental bases of adaptation and the "eyeless" condition. He holds a Ph.D. in biology of Yale University.
Dr. Richard Borowsky - Sleep and Blind Cave Fish
Most of us sleep when it’s dark. But what would we do if it were always dark and had been for eons? We can’t answer this for humans, but we can for fish. Cave fish live in constant darkness. Do they sleep more than surface fishes? No, they sleep less, much less!
Eyes are useless without light and animals lose them as they adapt to cave life. We’ve known this for a long time, but only recently we learned that cave fish also lose sleep. While patterns vary, many species of surface fish sleep at night as we do, but for up to twelve hours. In contrast, our research established that individuals of all six cave species we studied slept just two or three hours nightly. In one species, the blind Mexican tetra, we studied three different populations, each of which adapted to cave life independently. All of them had the same reduced sleep pattern. So, just as with eye loss, sleep loss seems basic to cave life, at least for fishes.
How do we know when fish sleep? We know it from their behavior. When they are motionless for as little as sixty seconds, they are asleep and need extra stimulation to take notice. Remember, when you are asleep, someone might need to call your name several times or shake you to get your attention. Also, when we deprive them of sleep the whole night, the next day they sleep a lot more than they normally would have, just as you would if you pulled an all-nighter cramming for an exam.
Why are cave fish more wakeful than surface fish? We think it has to do with a low and unpredictable food supply in the cave. You never know when something tasty will float by. If you are asleep and your neighbor is awake, he gets fed, you go hungry. We study the genes that control sleep patterns in cave fish in order to learn more about insomnia and other human sleep disorders.