Daniela Rößler: From a research perspective, the whole visual being of jumping spiders really excited me. They have eight eyes and two really big ones that are forward facing. They totally hunt like cats. So they will stalk their prey and pounce on it. And when something is moving and jumping, spider will turn towards it to investigate. You get that feeling of the spider is actually looking right back at you, and no other spider will do it.
For hundreds of years, people have looked at them and studied them, but obviously it's the times where we tend to not look at our animals that the interesting stuff happens. For example, when they're sleeping. I'm Daniela Rößler and I'm a behavioral ecologist, and I study spider sleep. There's a lot of evidence that sleep is crucial for learning and memory formation.
Sleep has been associated also with lots of health benefits. It's like, if you don't sleep, you will not function normally. And I think that is something we know across species. So sleep is incredibly important and super universal. And that includes animals like jellyfish which has not really a brain. But the truth is really is so far lacking an understanding of sleep evolution and where it originated and how the components of sleep evolved.
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Because usually the way we sleep is study is, is like in single species and with different methods. So what I'm really trying to do is to study sleep with the same methods across spiders. So we can really link back how sleep sleep components, how they evolved. Do we see differences? Is there anything then that would hint at association between sleep and sensory processing?
I have only very recently jumped into this endeavor. In the middle of the pandemic, I was forced to be at home, and that's when I found Evarcha. And they were rather big, easy to find. So I caught a bunch of them and I put them on the windowsill. And then one night I was just quickly glancing into the boxes and all of them was hanging like Christmas decorations suspended on a silk thread from the lid.
And I got super curious what the hell they are doing? So the first clue was that this whole suspended position was exclusively something we see at night in these spiders that are only active during the day, hinting at them actually engaging in a sleep behavior. And the first night we saw those twitches, which was very in line with what you probably used to see in dogs and cats when they dream.
And the twitches came in very regular intervals of about 20 to 30 minutes. That's when we said, okay, let's have a look at baby spiders because they're transparent and we could actually see the retinal tube. When we saw that all those twitching always occurred with movements of the retinas, that's when we were like, okay, well yeah, this could really be REM sleep.
The definition of REM sleep is the atonia of muscles. So muscles are not active during this phase. Whereas we see increased activity in the brain, which is fundamentally different from deep sleep states when the brain is not active in animals that have movable eyes, you would see eye movements of sorts and muscle twitches generally not in a controlled way.
From an evolutionary perspective, up to then it was the mammals, birds, reptiles and cephalopods. Here we have the spider, where it all looks very, very similar. But from a research perspective, proving that this is actually happening is a whole different idea. Spiders are notoriously difficult to study in terms of brain activity, because the hydraulic pressure of the spider just does not really allow that to be done easily.
But we can demonstrate that this is actually REM sleep in a behavioral way. During REM sleep, you will find a big range of animals. You need much higher stimulus to wake up and react. So it is very important right now that we actually demonstrate a reduced responsiveness during this leg curling time that we think is like our REM sleep before we really will be able to say something definite.
We see the leg curling behavior in orb web spiders. So we went out in the field and tested whether there are times where they are less responsive. So we went with a sound stimulus that is actually the wing beat frequency of wasps and bees. So the nice thing about this stimulus with common orb web spider Arenus diadimatus is that it will robustly display an anti-predator signal and what we see is that during the night when they're immobile, they need much higher stimulus to wake up and react at the same time.
In the lab, we're starting to look at Portia. So Portia is really extremely special compared to other jumping spiders. So she's specialized in eating other spiders. And depending on the spider type, she will adjust her hunting strategy, which is obviously outrageously cool and comes with outstanding cognitive abilities. So we get a lot more information by studying this pair.
So we make them fall asleep in little vials, and then we put them on top of the speaker, and we watch them and wait until they show one of those REM like behaviors before we apply the stimulus. You can just see the moment when the spider senses the stimulus and starts to move the grid, just starting this line of research and then putting the pieces together.
I think we're going to know a lot more in a few years. So there are a lot of different experiments we could do to test the effect of sleep and sleep deprivation on cognition. So maybe if we sleep-deprived Portia, will it be as efficient in hunting other spiders as a Portia that got a lot of sleep. So it's very easy to look at these videos and immediately fall into, ‘Oh my god! Yes! Look at that. Look, it's dreaming,’ which is fair because obviously a lot of people will associate REM sleep with dreaming. But from a research perspective, we will never be fully able to prove that a non-human animal is dreaming. Like even in humans, the only evidence for dreams are basically dream reporting, and no other animals can actually do this.
But I think research is showing us again and again, again that all these complex things have always been there in other forms. And it's not just that they evolve with humans, like, boom, everything's super complicated and complex and no one else does this. And seeing that, it's also present probably in dogs and cats and other animals, there's probably an evolutionary story behind it.
Obviously their sensory systems are super different, so we have no clue what a dream could feel or look like. But to me, the most meaningful would be for a spider to dream about prey capture or running away from predators. But in the bigger picture of things, whatever version of dreaming could be present would also potentially have an evolutionary ecological purpose and benefit.
So for me, obviously there's something here that needs to be explored.
For a long, long time, REM sleep was really in the realm of complex brains mammals. But since the paper was published, we've looked at about 15 other families of spiders to see whether we see those REM like behaviors. And so far we do in all of them, completing this picture of no, this is really something much more universal, but I still can't believe that this has not been seen or documented before.
This just a huge, vast knowledge gap because no one ever looked. And I totally want to tap into that.