Sleepy Times Under The Sea
If you’re like most people, you sleep. Every so often, your body enters an extended period of little movement and you become less responsive to stimuli. And if you find your sleep regularly disturbed, you become sleepier and sleepier, eventually finding yourself dozing off during the day. Research published this week in the journal Current Biology finds that one species of jellyfish, Cassiopea, has a similar behavior, making it the simplest organism known to nap.
An interdisciplinary team of researchers at the California Institute of Technology found that Cassiopea enter a nightly period of quiescence, in which their rhythmic pulsing slows. They become less likely to respond to stimuli, such as squirts of water, and slower to react to changes in their environment. And if the jellyfish are regularly disturbed during this quiescent period, they become more likely to enter a similar state during times when they’re normally active.
Claire Bedbrook, one of the co-authors of the new study, says that they don’t yet know if there is a genetic component to the sleeplike behavior across species, or what changes might be going on at the neuronal level during the jellies’ quiescent period. However, the presence of a sleeplike behavior in such an evolutionarily ancient species raises questions about what exactly sleep is, and its role in animal life.
Claire Bedbrook is a graduate student in the department of biology and biological engineering at the California Institute of Technology in Pasadena, California.
IRA FLATOW: This is Science Friday. I’m Ira Flatow. What do you I have in common with jellyfish? Hard to think of something we share with a soft, undulating marine creature with tentacles. But we do have something in common and that is sleep. Yes, jellyfish sleep. And the weird part is that jellyfish have no brain and they can still sleep. How is that?
Writing this week in the journal, Current Biology, researchers describe how they discovered this unexpected behavior in an upside down jellyfish. Joining me to tell the tale is one of the authors of that report, Claire Bedbrook, is a graduate student in Viviana Gradinaru’s laboratory in the Division of Biology and Biological Engineering at Caltech. She joins me from the campus there. Welcome to Science Friday.
CLAIRE BEDBROOK: Thank you so much for having me.
IRA FLATOW: This is a really interesting tale. How did you decide to study sleeping jellyfish?
CLAIRE BEDBROOK: Yes, so it really started with my two friends, Ravi Nath and Michael Abrams, and myself wanting to work on a project together. And we were really interested in this basic question of do all animals sleep. And we decided to get at that by actually asking, and hopefully answering the question, which is how conserved is sleep across animals?
IRA FLATOW: And so what did you do?
CLAIRE BEDBROOK: So we studied this one jellyfish called Cassiopea, which is also known as the upside down jellyfish. And we showed that this jellyfish has these three key behavioral characteristics to prove that it actually has a sleep state.
IRA FLATOW: And they are?
CLAIRE BEDBROOK: So the first one is that the animal has to have a period of quiescence, where their activity levels are lower. The second one is that during that quiescent period, the animal responds to sensory stimulus differently. So they don’t respond as quickly and they might require a stronger stimulus to actually wake up or respond.
And the third one is that this quiescent state is homeostatically regulated. So what that means is this quiescent state or this sleep state is actually required for the animal’s well-being and the animal’s survival. So if you prevent the animal from sleeping, they’ll try and compensate by sleeping more afterward.
IRA FLATOW: So did you find that if you disturbed, give it a bad night’s sleep, was it groggy?
CLAIRE BEDBROOK: Exactly, yeah. So we designed a stimulus where we actually pulsed water at the jellyfish for 10 seconds. And we would do this multiple times throughout the night to kind of wake them up and prevent them from going into this quiescent state. And as a result, the following days and nights they actually were less active. And once they’d compensated, they went back to normal levels of activity.
IRA FLATOW: Did they ever take a nap? Could you tell?
CLAIRE BEDBROOK: So they do sometimes have decreases in activity, even in the middle of the day, which is sort of yeah, nap-like.
IRA FLATOW: So you could actually tell in your definition they were sleeping.
CLAIRE BEDBROOK: Yes, so they did fulfill these behavioral characteristics that the sleep literature has really put together after decades of studying sleep in other animals.
IRA FLATOW: In humans when we sleep there are all sorts of things going on in our brain, in serotonin and other chemicals. A jellyfish doesn’t have a brain.
CLAIRE BEDBROOK: Yeah, you’re right. They don’t have a brain, but they do have a nervous system. So they do have neurons. And a lot of the neurotransmitters and neuropeptides that are in even human neurons, they are actually even conserved in jellyfish neurons. So though they don’t have a brain and they don’t have a centralized nervous system, they do have some features that we expect to see in neurons.
IRA FLATOW: Well, with people, if you want to go to sleep, there’s a drug for that.
CLAIRE BEDBROOK: Yeah, yeah. And we actually did test if– so melatonin, which is a molecule that’s known to regulate sleep in humans and many animals, it actually also, if we gave the jellyfish melatonin, they would go into their quiescent state, even in the middle of the day.
IRA FLATOW: You know sometimes you take an antihistamine for an allergy and you get groggy?
CLAIRE BEDBROOK: Yeah, we also tested pyrilamine, which is an antihistamine, and it also caused the jellyfish to go into their quiescent state.
IRA FLATOW: Now I want to go through your thought process on this. I’m trying to put myself in your lab when you go to your supervisor and say, you know, I want to study sleeping jellyfish.
CLAIRE BEDBROOK: Yeah, the three of us started this project and it was a question that really interested us, but we kind of played around with it for a little bit before we went and told our advisors. Because we wanted to show them the cool results. And they were all so supportive and really excited about it.
IRA FLATOW: So they didn’t think you were crazy at the beginning?
CLAIRE BEDBROOK: No, no. I mean, this is Caltech. They’re pretty used to it.
IRA FLATOW: Richard Feynman would have thought it’s a great idea.
CLAIRE BEDBROOK: Yeah, no they all thought it was really fun, and a fun collaborative project. And they were all 100% behind it.
IRA FLATOW: Well, you said you did this at night, so there were a lot of sleepless nights? Did you take the jellyfish home with you?
CLAIRE BEDBROOK: Well, we took a lot of the data home with us to actually do the analysis and stuff, but all of the studies we did at the beginning were just iPhone videos in lab late at night to try and capture this different state. And yeah, we would get home, sit on the couch, and all watch these jellyfish videos, and manually count their pulses. Yeah, so at the beginning.
IRA FLATOW: So you didn’t have a tank in your living room.
CLAIRE BEDBROOK: No, no. Not yet.
IRA FLATOW: You must have had to build the equipment, because no one’s counted the pulses of a jellyfish, right?
CLAIRE BEDBROOK: Yes, we set up these recordings where we would have the tanks. And part of the reason we actually chose these specific jellyfish, these upside down jellyfish, is because they’re really easy to track their behavior. They actually put their bell on the bottom surface of the tank and pulse in place. So they’re not moving around in the water in three dimensions. So we can just record them, take video recordings from a bird’s eye view, and then just wrote software to be able to actually count the jellyfish pulses.
IRA FLATOW: Did you do anything else besides squirt them with water? Did you sort of like push them to wake them up? You know, they discover, oh no, something’s happening.
CLAIRE BEDBROOK: Yeah, we’ve tested so many different perturbations. Poking them, squirting water at them, we even put them in shakers so they would kind of be constantly agitated. But another one that worked was these particular jellyfish they, like I said, they like to rest their bell on the bottom surface of the tank. And you don’t see them swimming around in the tank. So when you actually pick them up and you drop them into the water, they’ll really quickly pulse and try and orient themselves towards a surface. So that was another environmental stimulus that we tested to see how they would respond to it.
IRA FLATOW: So just like poking him in their sleep. Did they sort of startle? Did they have to startle and wake up?
CLAIRE BEDBROOK: Sometimes, yeah. When you poke them in the night or even actually feed them, that’s another stimulus we tried, they will respond. It’s just often that their response is a bit delayed.
IRA FLATOW: Now I have to ask you this question as a researcher. Did you have any empathy for these jellyfish that you kept waking up in the middle of their sleep?
CLAIRE BEDBROOK: I mean, for us to wake them up in the middle of the night also meant we had to wake up in the middle of the night. So honestly, not really. Yeah it was kind of constantly sleep perturbation. both human and jellyfish.
IRA FLATOW: So would you say that this is the simplest organism that has been shown to sleep?
CLAIRE BEDBROOK: Yeah, I think simple is kind of a controversial term in biology. No one wants to know that the organism they study is simple. But it is the first example of a sleep state in an animal without a brain or without a centralized nervous system, and one that is evolutionarily very distant from humans.
IRA FLATOW: So this must tell us something about if this goes so down on a list of animals, there must be some reason why we sleep and why these sleep. What does it tell us about why sleep is very important?
CLAIRE BEDBROOK: Yeah, exactly. I’d say this study that shows that this state is conserved, at least in this jellyfish, then it opens up possible hypotheses for why is it that something as simple as a jellyfish would need a sleep state? But we haven’t really gotten an answer to that, and I really hope that future studies will address this.
A hypothesis that could come out of this work and also previous work in sleep fields is that maybe any animal that has neurons will sleep. Maybe it’s an intrinsic property of neurons.
IRA FLATOW: Is this going to be your PhD paper?
CLAIRE BEDBROOK: It’s definitely one of them. So one fun part of this project is we all, all three of us, have our own separate main focus projects. And this was a side project that really just took over.
IRA FLATOW: Well, is it going to continue to take over?
CLAIRE BEDBROOK: So I think we are interested in continuing to pursue related questions. But we are also all hopefully graduating soon, so we’ll see.
IRA FLATOW: So who’s going to do your jellyfish work? I’m serious. Is this the last we’re going to hear of this?
CLAIRE BEDBROOK: No, I hope not. I think the labs could continue to pursue these questions. And also I really hope that this gets people in fields who are studying other Cnidarian animals excited and interested in looking to see whether or not other animals on in the same phylum have sleep states. Because that would really further support the idea that this is a conserved state.
IRA FLATOW: So Claire Bedbrook is moving on to larger things.
CLAIRE BEDBROOK: Well, we’ll see.
IRA FLATOW: Well, I don’t know how you can after all this publicity you’ve got.
CLAIRE BEDBROOK: I know. I never expect it ever again.
IRA FLATOW: People must be throwing money soon at you to do more.
CLAIRE BEDBROOK: Not yet, though you should tell them that.
IRA FLATOW: You just did. A couple of million people will be listening to this and maybe you’ll get a phone call when we’re done. Thank you, Claire.
CLAIRE BEDBROOK: Thank you so much.
IRA FLATOW: Fascinating. Claire Bedbrook is a graduate student in the Department of Biology and Biological Engineering at Caltech. Sweet dreams to you and maybe more research money will be coming in.