The trait may have evolved independently twice
Do octopuses dream? Scientists haven’t cracked that mystery, but they have come a bit closer. A new study reveals that, like us, our eight-legged friends experience both an active and a quiet sleep stage. Because humans and octopuses are separated by more than 500 million years of evolution, the discovery suggests a two-stage sleep pattern evolved independently twice.
“We haven’t shared an ancestor with an octopus since we were just single cells in the ocean,” says Marcos Frank, a neuroscientist at Washington State University who was not involved with the research. “It’s incredible, if this holds up.”
To make the discovery, researchers filmed four octopuses of the species Octopus insularis, found off the coast of Brazil, while they slept in tanks in the lab. They checked whether the animals were awake or asleep by showing videos of live crabs on a screen facing their tank or gently hitting the tank wall with a rubber hammer to see whether they stirred. During their “quiet” sleep, the octopuses’ skin was pale and their pupils narrowed to a slit; they were mostly still, and their suckers and arm tips sometimes moved gently and slowly. But during “active sleep,” their skin turned darker and stiffened; they moved their eyes and muscular twitches contracted their suckers and body (see video above).
The active sleep, which typically lasted about 40 seconds, usually occurred after a long quiet sleep, and the cycle repeated every 30 to 40 minutes, the researchers report today in iScience.
These two states are akin to the two major stages in mammalian sleep: rapid eye movement (REM) sleep, in which the eyes move quickly and dreams happen, and “slow-wave” sleep, in which electrical activity synchronizes across the brain. This alternating cycle, also present in birds and possibly in reptiles, is thought to be important for consolidating memories and clearing waste from the brain.
Still, the researchers are cautious about drawing too many similarities.[…]
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