Creatures that live in the dark may lose their sight over evolutionary time. They may even lose their eyes entirely. Now it (appears) that they also lose sleep. Because a new study shows that cave-dwelling fish spend more time awake than their counterparts at the sunny surface. The finding is in the journal Current Biology. [Erik Duboué, Alex Keene and Richard Borowsky, "Evolutionary Convergence on Sleep Loss in Cavefish Populations"]
Researchers studied three populations of Mexican tetra in the lab. Fish that live in creeks or rivers have two eyes and see just fine. But those that have (adapted) to living in caves lack eyes. What they do have is insomnia. The scientists observed that the tetras that normally spend time in the light do sleep soundly at night, resting on the bottom of their tanks. The cave fish, on the other hand, remain on high alert, (patrolling) their habitats even after hours.
The researchers are working to identify the genes responsible for this fishy restlessness. Not that they’ll reveal how you can get by on (minimal) shut-eye. Because the cave fish may not need less sleep—they may need to stay awake to forage more in an environment where food can be scarce and appear unpredictably. And even a blind fish can see: you snooze, you lose.
