Somewhere in the quiet hours of the night, a small jumping spider hangs upside down in her silk and begins to twitch, her legs curling and her eyes moving beneath closed lids, much as a dreaming mammal's might. Researchers working with Portia fimbriata, a spider of northern Australia, have shown in a study published in the Proceedings of the National Academy of Sciences that these tiny animals move through distinct sleep phases, one quiet and one resembling the restless dreaming stage known in people as REM. The discovery invites a larger question that the team's colleagues have begun to ask a
Jumping Spiders Show REM-Like Sleep, Study Finds, Reshaping Ideas About Animal Slumber
Some spiders did not respond at all.
Mark
So what did the researchers actually see?
Mimi
Two phases on video. First a quiescent stage, where the spiders groomed and slowly drooped. Then a REM-like stage with leg curls, eye movements and twitching.
Mark
Why Portia fimbriata?
Mimi
Nadja Geiger says it sleeps upside down in a little web at night, a clear posture, so it's easy to tell when she's asleep.
Luke
Video of twitching isn't proof of sleep, though. What backs the claim?
Mimi
The wake test. They used a loud noise and compared quiescent, REM-like and awake spiders. Sleeping ones responded more slowly, and in the REM-like phase some didn't respond at all.
Luke
Fair. But note the wording is REM-like. Nothing here says the spiders dream.
Mimi
Right. The source links REM to human dreaming, but the study shows movement and delayed response, not experience.
Mark
Thomas White said the idea is only sort of controversial. Why?
Mimi
Spiders are very distant from us, but we already infer similar sleep in dogs, cats and reptiles. He asks why stop there.
Luke
And he's an outside voice, which helps. He calls it the most complete behavioural case for sleep in any arachnid, but that's one species, in a lab.
Mark
Which is what the fieldwork is for?
Mimi
Yes. Queensland and Western Australia, looking at artificial light and habitat disturbance.
Luke
Whether wild spiders sleep the same way is still unknown.
The Pulse
- A spider that sleeps upside down in a tiny web is turning out to be the sharpest window yet into how animals far removed from us rest.
- Video footage shows legs curling, eyes flickering and front limbs twitching during a stage that scientists are now calling REM-like, pushing a long-running debate into new territory.
- When researchers jolted the spiders awake with a loud noise, the sleepers reacted slowly or not at all, echoing the grogginess of a person pulled from a nap.
- Skeptics question whether such similar behaviour can be stretched across half a billion years of separate evolution, while the evidence keeps piling up.
- The team is now heading into the wild of northern Queensland and Western Australia to see whether artificial light and disturbed habitat are disrupting spider sleep.
Somewhere in the quiet hours of the night, a small jumping spider hangs upside down in her silk and begins to twitch, her legs curling and her eyes moving beneath closed lids, much as a dreaming mammal's might. Researchers working with Portia fimbriata, a spider of northern Australia, have shown in a study published in the Proceedings of the National Academy of Sciences that these tiny animals move through distinct sleep phases, one quiet and one resembling the restless dreaming stage known in people as REM. The discovery invites a larger question that the team's colleagues have begun to ask aloud: how far back in the history of life does the rhythm of sleep reach, and what does it tell us about why we sleep at all?
Overnight, a small jumping spider hangs upside down in a little web, and on the video her legs begin to curl and her eyes flicker. Her limbs twitch. According to a study in the Proceedings of the National Academy of Sciences, these movements mark a REM-like sleep stage, and the researchers describe their work as the most comprehensive of its kind so far.
The animal is Portia fimbriata, found across northern Australia. Co-author Nadja Geiger calls it a "dream species" for sleep research, because it rests in a clear, predictable posture that makes sleep easy to recognise.
The team recorded the spiders through the night and identified two phases. In the first, the spiders groomed themselves and slowly drooped. In the second, the REM-like stage, leg curls, eye movements and front-limb twitches appeared. To confirm these were true sleep, they woke the spiders with a loud noise. The sleepers responded more slowly, and in the REM-like phase some did not respond at all, much like a person roused from a nap.
Thomas White of the University of Sydney noted that attributing sleep to animals so distant from us may draw objections, since spiders diverged about 500 million years ago from other vertebrates. Yet he observed that we readily grant the same inference to dogs twitching in their sleep, and asked what stops it from reaching animals unlike us. Daniela Rößler of the University of Bonn suggested the findings may reveal that the basic architecture of sleep is far older than thought, and that comparing species could show which features are ancient.
Next, the team plans fieldwork in northern Queensland and Western Australia, to learn how artificial light and habitat disturbance shape spider sleep beyond the laboratory.
Overnight, a small jumping spider hangs upside down in a little web, and on the video footage her legs begin to curl. Her eyes flicker. Her limbs twitch. According to a study published in Proceedings of the National Academy of Sciences, these movements are the signature of a REM-like sleep stage, and the research is being described as the most comprehensive of its kind to date.
The animal is Portia fimbriata, a jumping spider found across Northern Australia. Study co-author Nadja Geiger calls it a "dream species" for sleep research. The reason is practical: the spider has a very clear night-time resting posture, sleeping upside down in a small web, which makes it far easier to tell when she is asleep.
The team recorded the spiders through the night and then analysed the footage to pick out distinct stages. In the first, which the researchers called quiescent, the spiders groomed themselves and slowly drooped over the course of the night. That was followed by the REM-like stage, with leg curls, eye movements and twitching of the front limbs while the spiders dozed.
Having identified two phases, the researchers tested whether they were really sleep. Geiger notes that a hallmark of sleep is responding more slowly, or not at all, to external stimuli. So the team used a loud noise to wake spiders in three conditions: after they had been still for more than 15 minutes in the quiescent stage, during REM-like sleep, and when they were visibly awake.
The results resembled what happens when a person is woken from a nap. Spiders took longer to react in both the quiescent and REM-like states. Geiger said the effect was particularly strong in the REM-like phase, where responses were significantly delayed and some spiders did not respond at all. Co-author Daniela Rößler, a behavioural ecologist at the University of Bonn, said the spiders have distinct sleep stages and that the architecture of their sleep mirrors key features of vertebrate sleep far more closely than anyone expected.
Thomas White, an entomologist at the University of Sydney who studies invertebrate behaviour, said some people might find it controversial to attribute similar behaviours to animals so distantly related to us, noting that spiders diverged 500 million years ago from all other vertebrates. But he pointed out that scientists are growing less hesitant as evidence accumulates. We readily accept that a dog with twitching eyes and kicking paws is doing something similar, he said, and if that inference extends to dogs, cats and even reptiles, he asked what stops it extending to animals very unlike us.
White said the work builds on research from the same team a few years ago that found possible REM-like sleep in jumping spiders. This paper goes a step further by mapping different behavioural facets of sleep-like behaviour, and in his words it is far and away the most complete behavioural case for sleep in any arachnid.
Rößler said the findings may help explain why sleep exists at all. If animals with such different brains and sensory worlds show structured sleep with REM-like phases, she said, the basic architecture of sleep may be far older and more widespread than thought. Comparing species could show which features are ancient and what different stages may be for.
The team now plans to study spiders sleeping in the wild, with fieldwork in northern Queensland and Western Australia. Rößler said this will let them ask how artificial light and habitat disturbance affect sleep outside the laboratory.
Notable Quotes
This paper is far and away the most complete behavioural case for sleep in any arachnid.— Thomas White, University of Sydney
The basic architecture of sleep may be far older and more widespread than we thought.— Daniela Rößler, University of Bonn
Want the full story?
Read the original at ABC News & Headlines – Australian Broadcasting Corporation ↗
Science & Space