A gene that makes cave fish sleep significantly less than their surface counterparts, could shed light on the sleep patterns and disorders in humans, biologists have found.
The study by Erik Duboue, an NYU graduate student, Alex Keene, an NYU post-doctoral fellow, and Richard Borowsky, a professor in NYU's Department of Biology, may shed light on how genetic makeup contributes to sleep variation and disruption in humans.
They examined surface fish in the species Astyanax mexicanus and three cave fish populations, Pachon, Tinaja and Molino, all of which inhabit northeast Mexico.
While surface and cave fish have different physical appearances and behaviours or phenotypes brought about by evolutionary change, the researchers sought to determine whether the sleep patterns of cave fish also changed as they adapted to cave life.
To do so, they examined sleep patterns of both the surface and cave fish using two methods. In one, they determined that fish inactive for 60 seconds or more were sleeping.
The conclusion was confirmed by tapping on the tank. Fish inactive for this length of time were slow to respond to the tapping, a behaviour consistent with being awoken from sleep.
In the second, the researchers deprived the fish sleep as a way of inducing subsequent sleep behaviour.
When animals are deprived the chance to sleep, there is a rebound effect, so at the next opportunity, they sleep for longer than normal periods to make up for the deprivation.
The researchers tested this rebound effect by disturbing the sleep of fish all night by moving their containers once a minute. When observed the next day, they slept significantly increased amounts of time.
Using these methods, the researchers found that, over a 24-hour period, surface fish slept an average of over 800 minutes while cavefish slept an average of between 110 to 250 minutes.
The researchers then sought to determine if genetics played a role in the varying sleep behaviours. To do this, they bred cave and surface fish and examined the sleep patterns of these hybrids.
Their results showed that these hybrid fish nearly matched the sleep patterns of the cave fish, rather than those of the surface fish, demonstrating that cave fish carry a dominant gene for less sleep.
"In some ways, the sleep phenotypes of cave fish are similar to those of humans with sleep disorders," Borowsky explained.
"They go to sleep, but only for relatively short periods, then they awaken and remain awake for relatively long periods.
"The next job is to identify the genes which are responsible for sleep modification in the cave fish. They would be good candidates for the genes responsible for insomnia and other sleep disorders in humans," he added.
The study has been published in the journal Current Biology.