Do spiders sleep?

REM sleep is a phase of sleep characterized by rapid eye movements, vivid dreams, involuntary muscle movements, intense brain activity, and rapid breathing and heartbeat. According to multiple studies, it is at this moment that we process memories and knowledge. Humans are not the only ones who go through this ‘trance’: it has been shown that other animals, such as birds, cats or rats, also experience similar experiences. Now, a group of biologists from the University of Konstanz (Germany) has discovered that a new name should be added to the list: spiders. The conclusions of their research have just been published in the ‘ Proceedings of the National Academy of Sciences ‘ (PNAS). Daniela Roessler and her team noticed that, at night, the spiders hung from their threads in the containers of the laboratory. So, they wondered if, indeed, these animals went through the same sleep processes. Thus, they observed the behavior of some jumping spiders, a common species with a hairy brown body and four pairs of large eyes. “It was the most unusual thing I’ve ever seen in my life,” Roessler said of the suspended spiders. Looking at the videos, they saw that the spider pups displayed patterns that closely resembled sleep cycles: their legs twitched and parts of their eyes ‘blinked’. The researchers defined this behavior 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 dreams. Desktop Code Image for mobile, amp and app Mobile Code AMP Code APP Code Research showed that nocturnal movements in spiders closely resembled REM in other species, such as dogs or cats, that tremble in their sleep. And they occurred in regular cycles, similar to the sleep patterns of humans. As for ‘blinking’, it does not occur in the same way in these animals: these spiders do not have eyelids as such, not even moving eyes. However, they do move their retinas to change their gaze while hunting; In addition, young spiders have a transparent outer shell that provides a clear window into their bodies. “We still have to find out if, in this state, the spiders are indeed technically sleeping in this quiescent state,” explains Roessler. “That includes testing whether they respond more slowly, or not at all, to triggers that would normally activate them, for example.” Still, creatures like the jumping spider are a long way from humans on the evolutionary tree. That is why many researchers doubt that this is really a type of REM sleep. “There may be animals that are active in calm states,” explains Jerry Siegel of the UCLA Sleep Research Center, who was not involved in the study. “But are they REM sleep? It’s hard to imagine they could be the same.” For his part, Barrett Klein, an entomologist at the University of Wisconsin-La Crosse, who was also not involved in the study, says, “It’s exciting to find EMR-like signs in such a distant relative. Many questions remain about how widespread REM sleep is and what purpose it might serve for the species.” In Klein’s words, this type of process “remains, to a large extent, a black box.”

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