Cave life is known to favor the evolution of a variety of traits, including blindness and loss of eyes, loss of pigmentation, and changes in metabolism and feeding behavior. Now researchers reporting online on April 7 in Current Biology, a Cell Press publication, have added sleeplessness to that list.
"Cave-adapted fish sleep lessmuch lessthan closely related surface fish," said Richard Borowsky of New York University. "In some ways, their sleep phenotypes are similar to those of humans with sleep disorders."
The fish do sleep, but only for relatively short periods, Borowsky explained. Once they wake up, they remain active for a relatively long time. That sleep-and-wake cycle is repeated throughout the continued darkness of the cave.
The discovery was made by studying three cave populations of Mexican Blind Cave Fish (Astyanax mexicanus), a species ideal for such studies because it includes eyed surface and numerous blind cave populations. Although most of those cave populations have been founded independently by individuals living on the surface, they have nonetheless converged over the course of evolution on similar traits suitable to their new environments.
Borowsky and Erik Dubou, lead author of the study, got the idea that the transition from surface to cave might be associated with less sleep based on anecdotal, nighttime observations of fish in their laboratory. Their surface fish clearly sleep at night. They could be found inactive at the bottom of their tanks with fins drooping. The cavefish, on the other hand, actively patrol their laboratory homes through the wee hours.
To further study the basis of those behavioral differences, the researchers allowed surface and cave individuals to mate in the lab and studied their hybrid offspring. Those studies yielded evidence showing that cavefish differ from surface fish in sleep behavior because of a few dominant gene mutations that became fixed in the cave
|Contact: Elisabeth Lyons|