Liz Ponisi, Sarah Crespi, Matthew Mclaughlin discussed on Science Magazine Podcast
This is the science podcast for October 29th, 2021. I'm Sarah crespi, each week we feature the most interesting news and research published in science and the sister journals. First up this week we have, why brainless animals sleep? Jellyfish, Hydra, roundworms. They all have a version of sleep. Liz ponisi is a staff writer for science. She talks about what we can learn from these simple sleepers. Next, we're gonna look at centuries of alien invasions or put more simply invasive insects moving around the planet with trade. Matthew McLaughlin is a research economist at the USDA economic research service. He wrote in science advances about how long it takes us to realize an invader is already here. Finally, a book on racism and search algorithms. Angela saney is the host for a series of interviews on race and science. This month, she talks with safiya noble about her book. Algorithms of oppression, how search engines reinforce racism. Did you know that jellyfish can sleep? Brainless creatures, like Hydra, roundworms, these things seem to need sleep, or something like sleep. This week, we have a special issue on sleep, and there are a ton of open questions in this area. Liz ponisi is a staff writer for science. She wrote about what simple sleepers can tell us about the big sleep questions. Hi Liz. Hi. I love the way you open your piece with these really existential sleep thoughts. How can something without a brain or even neuron sleep? And why do they need to sleep? My favorite, though, is this idea of sleep as the default state and that wakefulness is the evolved state. Can you expand on that? For a long time, people just thought about sleep in terms of something that you need for the brain. And now recently they've been finding sleep like or sleep behavior in ever simpler creatures. And that's led some researchers to speculate when sleep evolve and to think that it evolved in the very, very beginning of life. And so there's one idea out there that life started out as a pretty dormant thing and that wakefulness. In other words, the ability to respond to the environment and adapt to the environment is a secondary state, whether or not this is true, I have no idea. But it's an interesting way to think about it because it kind of puts the burden of wakefulness on us rather than the burden of sleep when we're trying to figure out how it evolve. Exactly. If we start with brainy creatures, maybe it's a little easier here. How do we define sleep in animals with brains? The definition of sleep has shifted over time, depending on the technology we have for measuring sleep. So of course, early on, it was just what happens when you go to sleep. You lay down. You become oblivious to the world around you. You wake up noises, but you might not wake up if someone walks by you. So what they call unresponsive to stimuli. And another key thing is if you don't get the sleep you need, you have to make up for it. So that was one definition that held sway up until the 50s or 60s. Then researchers developed ways to put electrodes, which measure electrical activity on their surface of the brain or the scalp. So, you know, you can think about those little wires attached by little adhesive tape. They attach electrodes to the surface of the head and they watch what happens in the brain and they notice that when people sleep, they have two kinds of sleep that have active sleep or rem sleep and then quiet sleep or non rem sleep. And so for a period of time, that's how researchers really knew that people were asleep and really defined sleep in that way by the electrical activity in the brain. So what happens after looking at the brainwaves? What have we done new things since then? Since then, people began to think about, well, maybe something besides mammals sleep. For the longest time we thought only mammals and maybe birds went to sleep and needed to sleep. Because they have big brains and they always brains need to rest and rejuvenate. But then at the turn of the 21st century, some researchers started looking at fruit flies and lo and behold, found they sleep. But because they didn't have electrodes to put on the scalps of these fruit flies. So they turned to the older definition of sleep, which is based on the behavior laying down, stopping moving, becoming unresponsive, needing to have makeup for deprived sleep. And using those criteria, they figured out that, yes, fruit flies sleep. And so do crayfish and octopus and roundworms and a whole bunch of other things. How can you even detect sleep in something like a jellyfish, which I think is one of the examples that you bring up in the story? They focused on a behavior and started videoing whether or not that behavior changed. So with these jellyfish, which are called upside down jellyfish because they hang out with their tentacles facing the surface of the water. They notice that they tend to spend time at the bottom of an aquarium say if you watch them in the lab where the bottom of the shallow area where they're saying. And so they realized since these jellyfish sort of stay put in are not constantly floating around. They could actually video them over a 24 hour period to see if they change what they did and what they watched is how often the jellyfish pulse and move their tentacles in a uniform way to get water to pass over them. And what in a video them over the day in the night, they noticed that the pulse rate changes from about 60 beats a minute to about 39 beats a minute. And so they thought, okay, that might be sleep. So to further test that, they then looked at whether or not the jellyfish were unresponsive. In other words, like you, when you're asleep, you don't notice when somebody walks by. This jellyfish notice when you do something that might disturb them. And the way they tested that is they made a false bottom in their aquarium and basically pulled the bottom out from underneath them. Now during the day, as soon as you do that, the jellyfish swim down to the nu bottom. No hesitation. But at night when they're posting only 39 beats and are maybe asleep, it takes them quite a long while to sort of recognize that they're not at the bottom anymore and move back down. And what if you deprive them of their slow beat time? Then what you notice the next night that they sleep the sleep more soundly. In other words, they pulse even more slowly and they pull slowly for an ever long period of time. So I want to sense they're making up for lost sleep. Can we call that sleep or is this just a circadian rhythm? Is this just syncing up with the processes of the world that are all synced up to the sun and the darkness and the light periods? Well, you know, that's a difficult question and there's some debate in the research community about whether jellyfish.