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It turns out that spiders also dream

Time:2023-03-20 14:40:43 author:Bird Read:528次
It turns out that spiders also dream

A bowhunting spider (Evarcha arcuata) perches on a flower. These arachnids appear to experience visual dreams—maybe even nightmares. PHOTO: STEPHEN DALTON, MINDEN PICTURES TEXT: ELIZABETH ANNE BROWN For ecologist Daniela Rößler of the University of Konstanz, "field" research often means traveling to the far reaches of the Brazilian Amazon. But during the 2020 pandemic lockdown, she discovered the mystery in a bush near her home in Trier, Germany, which has become the best place to study. Rößler was soon fascinated by the little jumping spiders in the fields. After nightfall, some jumping spiders about the size of her pinky fingernails slid into silky pouches known as "Hermitages." She found the other jumping spiders motionless, hanging upside down on a silk thread, with their legs tucked neatly and occasionally moving. "The way they twitched reminds me of the reactions of cats and dogs when they dream," says Rößler. Before long, Rößler set up a nursery in her lab for baby jumping spiders to watch them hang at night. Her new research, published Aug. 8 in the Proceedings of the National Academy of Sciences, reveals that jumping spiders experience a sleep-like state with rapid eye movements similar to those observed in dreaming humans. During REM sleep, the jumping spider's legs twitch and curl up as shown. Photo credit: DANIELA C. RÖSSLER REM sleep is also characterized by muscle relaxation and changes in brain waves, which are important for memory consolidation and may play a role in the development of important survival skills. Confirming REM-like sleep in jumping spiders could change our understanding of when and how it evolved - so far, REM-like sleep has only been found in vertebrates (reptiles, birds, fish and large animals) found in most mammals). "The intelligence of spiders -- and the dreams of spiders -- may be very different from ours in most ways," said Nate Morehouse, an associate professor at the University of Cincinnati who studies vision and decision-making in jumping spiders, who was not involved in the study. "I can't wait to see what window this new study opens up for us to understand jumping spiders." Spider Eyes You can't do brain scans of spiders the way you do humans or other large animals, and you can't ask them how they're sleeping, But with baby spiders, you can see their heads. In their first ten days of life, the exoskeleton covering the jumping spider's small head has not yet produced pigment, and this part of the space is almost completely occupied by their eyeballs. "They're basically walking retinas," Morehouse said. Morehouse explained that the six smaller eyes provide a 360-degree monochromatic view of the world and are very sensitive to movement, while the main eyes — "big, round and lovely" — provide a height similar to that of a domestic cat. Resolution vision. While their eyeballs are fixed and cannot rotate in their sockets like ours, the boomerang-shaped retinas move around the back of the dominant eye, changing the jumping spider's field of vision. In her lab, Rößler began experimenting with recording napping spiderlings with magnifying glasses and night-vision cameras to learn about their sleeping habits. She focused on the spiders' eye and body movements, which provide clues to what's going on when they're at rest. She quickly discovered that they went through periods of rapid retinal movement that increased in duration and frequency throughout the night, lasting about 77 seconds and occurring roughly every 20 minutes. It was during REM-like sleep that Rößler observed uncoordinated body movements -- their bellies swaying, their legs curled or relaxed. The spider's spinneret, the organ at the top of their abdomen that produces silk, periodically "goes crazy," says Rößler. Like the rhythmic foot twitches of sleeping puppies, these spiders appear to be "practising" a behavior they do when they're awake. "Although jumping spiders don't make webs, they leave small silk anchors wherever they go," she explained. "They always leave silk as they walk, so whenever they jump, there's always a spare line, like a bungee cord." Morehouse says one of the main theories about REM sleep is that it allows animals to grind Practice basic survival skills. "Occasionally things happen that I can only explain with the theory that they are nightmares," Rößler said. "They just hang there silently, with their legs neatly curled up, and suddenly all of them stick out at the same time, like they're startled." There are also times when jumping spiders stop to stretch, adjust their dangling threads, or clean themselves. A period of coordinated movement. Judging by the lack of retinal movement, the spiders appear to be waking up only briefly to get themselves comfortable before returning to sleep. Sleeping, or dreaming? Rößler emphasizes that we have not yet shown that this period of inactivity in spiders can be considered sleep. To do this, several aspects need to be examined - including demonstrating that the spiders are low arousal, or slow to respond to stimuli, and "rebound sleep" if they are sleep-deprived. Based on her observations outside, "they seem to really be able to distinguish between what's a real distraction and what's not," Rößler said. For example, if "there are vibrations on the plants or silk, they will respond immediately," she said. "But when it's windy, they sway with the breeze and don't care at all." Scientists are sure that all animals sleep, despite their odd appearances. Some birds and marine mammals rest only half their brains each time they sleep, while hibernating animals can sleep for weeks or months almost continuously. Defining "dreaming" is more difficult -- but rest periods like REM sleep do mean the animal is visual dreaming. Seizing the opportunity to learn from other jumping spider researchers called Rößler's research very exciting. "It's a clever idea, with a relatively simple approach that yields very profound results," says Alex Winsor, a doctoral student at the University of Massachusetts Amherst who studies vision in jumping spiders. He and his advisor, who studies jumping spiders, Beth Jakob, who has been with spiders for decades, said they were eager to contact Rößler for ideas for follow-up research. "We're interested in whether they respond to visual stimuli in this sleep-like state, after all, they don't have eyelids," Jakob said. Winsor is already developing a system to monitor brain activity in jumping spiders, which may provide more evidence for their dreaming. "I use a tungsten electrode -- a very thin wire that is placed on the outside of the head to detect electrical activity," Winsor said. The team also plans to combine it with a device previously used to monitor retinal movement in spiders watching tiny televisions. Jumping spiders, such as the arch-hunting spider, the species featured in this study, are found throughout Eurasia and are oddities among the arachnids because of their good eyesight. While jumping spiders choose to go to bed (or dangling) when it's dark because they can't see well enough to hunt, other families of spiders are more likely to be "nappers," with short stretches during the day and night Time is inactive. Non-jumping spiders generally have much poorer vision and rely primarily on sensing motion in their webs to perceive the world around them, so more research is needed to determine what their sleep might look like. "Maybe they dream in vibrations," Rößler said. Arachnid Ambassador With nearly 6,000 species of jumping spiders in the world, and they're found on every continent except Antarctica, you'll almost certainly have a jumping spider in your backyard or block. Jumping spiders, with their oversized, expressive, cartoon-like eyes, extremely diverse color patterns and elaborate courtship dances, are the key to keeping people out of fear of spiders, Rößler said. There is a community of jumping spider lovers on TikTok and YouTube - some of whom also have previous arachnophobia. Jumping spiders can make strategic decisions, think ahead, calculate, and maybe even dream. Morehouse says it's often both challenging and comforting to learn about jumping spiders' cognitive abilities -- making them less alien and more worthy of respect or empathy. "If they dream, I mean, what can you do? You can't smash a dreaming spider," Rößler said. (Translator: Flowers on Moshang)

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