NEW YORK (AP) – It’s a question that keeps some scientists up at night: Do spiders sleep?
Daniela Roessler and her colleagues trained cameras on baby jumping spiders at night to find out. The recordings showed patterns that closely resembled sleep cycles: the spiders’ legs twitched and parts of their eyes flickered.
The researchers described this pattern as a “REM sleep-like state.” In humans, REM, or rapid eye movement, is an active phase of sleep when parts of the brain light up with activity and is closely related to dreaming.
Other animals, including some birds and mammals, have been shown to experience REM sleep. But creatures like the jumping spider haven’t received as much attention, so it wasn’t known whether they got the same kind of sleep, said Roessler, an evolutionary biologist at the University of Konstanz in Germany.
Their findings were published Monday in the journal Proceedings of the National Academy of Sciences.
Roessler and her team delved into the question of sleep after she discovered the spiders hanging at night from silk threads in their laboratory containers. She had recently picked up some jumping spiders to study, a common species with a furry brown body and four pairs of large eyes.
“It was just the most unusual thing I’ve ever seen,” Roessler said of the suspended spiders.
The research showed that the spiders’ movements during the night were very similar to REM in other species, she said – like dogs or cats twitching in their sleep. And they occurred in regular cycles, similar to human sleep patterns.
Many species similar to spiders actually do not have movable eyes, making it difficult to compare their sleep cycles, explained study co-author Paul Shamble, an evolutionary biologist at Harvard University.
But these jumping spiders are predators that move their retinas around to change their gaze as they hunt, Shamble said. In addition, the young spiders have a transparent outer layer that provides a clear window into the body.
“Sometimes as a biologist you’re just very, very lucky,” Shamble said.
The researchers still need to determine whether the spiders are technically asleep while in these resting states, Roessler said. That includes testing whether they respond more slowly – or not at all – to triggers that normally set them off.
Critters like the jumping spider are very far from humans on the evolutionary tree. Jerry Siegel, a sleep scientist who was not involved in the study, said he doubts the spiders can actually experience REM sleep.
“There may be animals that have activity in quiet states,” said Siegel, of the UCLA Center for Sleep Research. “But are they REM sleep? It’s hard to imagine they could be the same.”
But Barrett Klein, an entomologist at the University of Wisconsin-La Crosse who was also not involved in the study, said it was exciting to find REM-like signs in such a distant relative. Many questions remain about how widespread REM sleep is and what purpose it might serve for species, he said.
REM sleep is “still very much a black box,” Klein said.
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