C.H.U.D. Slumber: The Sleep Cycles of Subterranean Creatures

Another day on the subway. (Mario Tama/Getty Images)

We’ve all watched enough sci-fi and horror films to know how life underground goes. Your skin and hair turn pale, you go blind and before long you’re probably prowling around naked for the great taste of human flesh. Ah, but what is sleep like for these strange creatures of the underdark?

As reported today in Current Biology, the Mexican Blind Cave Fish (Astyanax mexicanus) offers some excellent insight into the question. See, despite what the name might have you think, the species exists in both subterranean and surface populations. The surface fish swim about with the benefit of sighted eyes while they’re underground kin go about blindly.

In laboratory populations, the surface fish slept while the cavers darted around all night. As New York University’s Richard Borowsky details, the recent research put this to the test by breeding the two varieties of cavefish. They discovered that the differing sleep behavior hinges on a few dominant gene mutations that became fixed in the cave populations when they took to the dark. After all, food is scarce in subterranean waters, so natural selection favors the scavengers willing to work long, late hours.

The research brings to mind the 1995 account of researcher Cristina Lanzoni who spent a whopping 269 days of solitary confinement in the subterranean Underlab in the Frasassi caves in central Italy. Granted, she didn’t have to swim about all night scavenging for food, but her sleep patterns altered significantly. On average, Lanzoni’s waking “days” stretched on for 54 to 56 hours, followed by 14 to 16 hours of sleep. Furthermore, that sleep was much like that of an infant, as she’d fall immediately into REM and dream of wide open spaces.

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