Daniela Roessler: From a research point of view, the whole visual creature of jumping spiders really impressed me. They have eight eyes and two really big, forward looking ones. They hunt exactly like cats. So they will chase their prey and pounce on it. And when something is moving and jumping, the spider will turn to investigate. You get the sensation of the spider actually looking at you, and no other spider will.
For hundreds of years, people have looked at them and studied them, but of course interesting things happen when we are not looking at our animals. For example, when they are asleep. i am Daniela Roessler and I am an ecological behaviorist, and I study spider sleep. There is a lot of evidence that sleep is essential for learning and memory formation.
Sleep has also been linked to many health benefits. If you don’t sleep, you won’t function normally. And I think that’s something we know across species. So sleep is incredibly important and very universal. And that includes animals like jellyfish that don’t really have a brain. But the truth is, until now, understanding of the evolution of sleep and where it originated and how the components of sleep evolved is lacking.
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Because it is usually to study the way of sleeping, as in a single species and with different methods. So what I’m really trying to do is analyze sleep through spiders with the same methods. So we can really relate how the sleep components of sleep have evolved. Do we see the differences? Is there something then that would suggest a relationship between sleep and sensory processing?
I have recently joined this endeavor. In the middle of the pandemic, I was forced to stay at home, and that’s when I found Evarch. And they were quite large, easy to find. So I caught a bunch of them and put them on the window. And then one night I was looking through the boxes and they were all hanging like Christmas decorations hanging from the ceiling on a silk thread.
And I was curious what the hell are they doing? So the first clue was that this suspended position was something we see at night in these day-only spiders, suggesting that they actually have a sleeping behavior. And the first night we saw those thrills, which were very similar to what you probably saw in your dreams of dogs and cats.
And the twitches came at very regular intervals of about 20 to 30 minutes. So we said, okay, let’s look at spiders because they’re transparent to babies and we could actually see the retinal tube. When we saw that all of these circulations were always occurring with retinal movements, that’s when we had, okay, yes, this could be REM sleep.
The definition of REM sleep is muscle atony. So the muscles are not active in this phase. While we see increased activity in the brain, which is fundamentally different from deep sleep states when the brain is not active in animals with mobile eyes, you will see eye movements and generally not see muscle contractions in a controlled manner.
From the point of view of evolution, until then they were mammals, birds, reptiles and cephalopods. Here we have the spider, where everything is very, very similar. But from a research point of view, proving that this is actually happening is another idea. Studying spiders in terms of brain activity is very difficult, as the spider’s hydraulic pressure does not allow this to be done easily.
But we can demonstrate behaviorally that this is actually REM sleep. During REM sleep, you will find a wide variety of animals. You need a much greater stimulus to wake up and react. So it’s really important right now to demonstrate a reduced reaction to this leg-curling time, which we think is like REM sleep, before we say anything definitive.
We observe the leg curling behavior of orb web spiders. So we went out into the field and tested whether there are periods of less response. So we went with a sound stimulus that is the frequency of the wingbeats of wasps and bees. So it’s a nice thing with the normal orb spider around this stimulus Arenus diademed it will show a strong anti-predator signal and what we see is that, when they are mobile at night, they need a much greater stimulus to wake up and react at the same time.
In the laboratory, we are starting to look at Portia. So Portia is very unique compared to other jumping spiders. So it specializes in eating other spiders. And depending on the type of spider, it will adapt its hunting strategy, which is obviously incredibly cute and has excellent cognitive abilities. So we get a lot more information by looking at this pair.
So we put them to sleep in little bowls, and then we put them on top of the speaker, and we watch them and wait until they show one of these REM-like behaviors before we apply the stimulus. You just watched the moment the spider senses the stimulus and starts moving the web, starting this line of research and putting the pieces together.
I think we’ll know a lot more in a few years. So we could do a lot of different experiments to test the effect of sleep and sleep deprivation on cognition. So maybe if we sleep without Portia, she’ll be just as effective at hunting other spiders as a Portia that slept a lot. So it’s very easy to watch these videos and immediately think, ‘Oh my god! Yes! look at that Look, he’s dreaming’, which is fair, of course, because many people will associate REM sleep with dreaming. But from a research point of view, we will never be able to fully prove that a non-human animal is dreaming. As in humans, the only evidence of dreams is essentially dream reporting, and no other animal can do that.
But I think research is showing us over and over again that all these complex things have always existed in other forms. And it’s not just that they evolve with humans, like, boom, it’s all very complicated and complex and no one else is doing this. And given that it’s probably present in dogs and cats and other animals, there’s probably an evolutionary story behind it.
Of course, their sensory systems are very different, so we have no clue what a dream might feel or look like. But to me it would be most significant if a spider dreams of catching prey or running away from predators. But in the larger picture of things, any version of the dream would have an evolutionary purpose and ecological benefit as well.
So to me, it’s clear that there’s something to be explored here.
For a long time, REM sleep was actually in the realm of complex mammalian brains. But since the paper was published, we’ve looked at about 15 other spider families to see if we see these REM-like behaviors. And so far we do it in everything, no completing this picture, this is actually something much more universal, but I still can’t believe this hasn’t been seen or documented before.
It’s just a big, wide knowledge gap because no one ever looked. And I want to take full advantage of that.
