Science Friday - Squid Lighting, Tongue Microbiome, Invasive Herbivores. March 27, 2020, Part 2

Episode Date: March 27, 2020

How Humboldt Squid Talk To Each Other In The Dark Cephalopods are masters of changing their bodies in response to their environments—from camouflaging to sending warning signals to predators. The art of their visual deception lies deep within their skin. They can change their skin to different colors, textures, and patterns to communicate with other animals and each other. But how does this play out in the darkness of the deep ocean? That’s the question a team of scientists studied in the deep diving Humboldt squid that lives over 2,000 feet beneath the ocean’s surface. Their results were published this week in the journal Proceedings of the National Academy of Sciences. Biologist Benjamin Burford, who is an author on that study, explains how Humboldt squid use a combination of skin color patterns and bioluminescence to send each other signals and what this might teach us about communication in the deep ocean. See a video and more photos of Humboldt squid communicating with each other from Monterey Bay Aquarium Research Institute.  Mapping The Microbiome Of Your Tongue Your mouth is home to billions of bacteria—some prefer to live on the inside of the cheeks, while others prefer the teeth, some the gums, or the surface of the tongue. Writing this week in the journal Cell Reports, researchers describe their efforts to map out the various communities of bacteria that inhabit the tongue.  In the average mouth, around two dozen different types of bacteria form tiny “microbial skyscrapers” on your tongue’s surface, clustered around a central core made up of individual human skin cells. The researchers are mapping out the locations of the tiny bacterial colonies within those skyscrapers, to try to get a better understanding of the relationships and interdependencies between each colony.  Jessica Mark Welch, one of the authors of the report and an associate scientist at the Marine Biological Laboratory in Woods Hole, Massachusetts, talks about what we know about the microbiome of the human mouth, and what researchers would still like to learn. Rethinking Invasive Species With Pablo Escobar’s Hippos Colombia is home to an estimated 80 to 100 hippos where they’re an invasive species—hippos are native to Africa. But notorious drug lord Pablo Escobar brought four to the country as part of his private zoo. After his death in 1993, the hippos escaped to the wild where they thrived.  Some locals consider them pests, the government has mulled over getting rid of them, and recent studies have shown that their large amounts of waste is changing the aquatic ecology of Colombia. But new research has taken a different view, showing that even though hippos are invasive, they might be filling an ecological hole left by large herbivores killed off by humans thousands of years ago. Erick Lundgren, the study’s lead author and a Ph.D. student at the University of Technology in Sydney, Australia, talks about why we should stop thinking of the phrase “invasive species” as inherently bad, and what may be in store for the future of these hippos.  Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

This is Science Friday. I'm Ira Flato. Just a note, due to the need for social distancing this week, we won't be taking calls during this edition of Science Friday, which was pre-recorded earlier in the week. A bit later in the hour, bacteria on your tongue and Pablo Escobar's hippos. But first, cephalopods, as we know and love, are clever creatures. And one of their most fascinating features is their skin. they can change their skin to different colors, textures, and patterns to communicate with other animals and each other. But how does this play out in the deep ocean where it's total darkness? That's the question a team of scientists was trying to figure out. And for the answer, they looked to the deep diving humble squid that live over 2,000 feet down.

Their results were published this week in the journal Proceedings of the National. Academy of Sciences. Our producer Alexa Limb spoke with Benjamin Burford, a PhD candidate in biology, and an author on that study. Hi, Ben. Welcome to Science Friday. Hey, thanks for having me. You could have picked any animal in the deep ocean. What makes the Humboldt Squit a good candidate for studying communication? One thing that's really cool about squid is that they have these crazy pigmentation patterns that they're able to display on their skin. So it's pretty easy to see their communications. And Humboldt Squid, they're pretty social, right? Highly social. They live in groups. You know, sometimes we see several of them. Sometimes we see hundreds of them. So, I mean,

you could picture in some cases these animals, you know, get up to close to two meters long. So you can picture a pack of about a hundred of those rolling, a hundred two meter long squid roving through the deep sea. And so you were looking at communication in the deep ocean. How much do we know about how animals communicate down there? What's really known about animal communication down there, you know, we're starting to observe these animals in their natural habitat more and more and learn more there. But a lot of what we know is what's been observed when some of these animals migrate

shallower during the night or, you know, by just looking at the animal's anatomy. So a lot of animals in the deep ocean, you know, it's a dark environment by and large. It can be dim light. but a lot of animals visually communicate by making their own light through a process called bioluminescence. And the way they make their own light is they use these organs called photophores. And by looking at how these organs are arranged, you know, we know that some animals are probably able to say things like, this is the species I am, or I'm a male, or I'm a female, or stuff like that. So pretty basic information is what we knew was communicated visual.

in the deep ocean prior to this study. And that's what you're trying to get to at this study. And you used the ROV to take live videos of the squid. What did you see when you turned on the light for the ROV? One thing that make Humboldt squid such great study subjects is they're gregarious, they're inquisitive, they're fairly bold as far as deep sea animals go. I mean, again, they feel pretty confident, it seems, and they'll approach the vehicle. In fact, the vehicle is large and noisy, and it scares a lot of deep sea animals.

but the Humboldt Squid seem to seek it out. So they find us when we're down there. When we dive this thing down hundreds of meters into the ocean, the Humboldt squid find us if they're around. They like the vehicle. They're curious about it, but they also use the lights to forage by. We see these dense feeding aggregations in front of the vehicle,

and they kind of look like feeding frenzies. It looks pretty hectic. But if you pay close attention, you'll notice they're not bumping into each other. They're not fighting amongst each other. They're rarely in competition even for the same prey item. And so in our view, you know, they must have some way of coordinating this activity. And they're visually cute animals.

So presumably the way they signal, we thought, was through a visual pathway using pigmentation patterns like their shallow living counterparts. So what signals did you see? What were they, what patterns were they making to each other? The patterns, in some cases, they resemble patterns that we, we see in shallow living squids, the pigmentation patterns that they would make, you know, would take advantage of most of their body surfaces. So, you know, they might make patterns that involve pigment on their fins, on their head, on their mantle, which is kind of, you know, the central part of a squid. It's where all, it's like the biggest muscular cavity, really,

and it has all the organs inside of it. That is a surface that a lot of the pigmentation patterns use. And so, you know, the squid are using their skin to make these pigmentation patterns. And, you know, an example of a really conspicuous pattern that they might do is they might, you know, make half of their body dark and half of it pale. And it'd be like their left side would be dark and their right side would be pale. There are a lot of other conspicuous patterns like that. There are also some more subtle patterns like, you know, maybe a dark spot between the eyes on top of the head. And I should point out, you know, they can combine these patterns. They can arrange them in sequence and they can transition between them very quickly, like with the snappier finger, you know, they can change

pigmentation pattern from one to the other. So they're actually like stacking these different signals on top of each other? Is that what they're doing? Yeah, in some cases, some signals are compatible to, to put together. They're able to arrange any of them in sequence if they want to. So like do like the half light, half dark, and then they might transition to all dark or all pale or just a dark margin of their fins or something we call model where there, you know, there's this like mosaic of pigmentation that kind of, you know, flows around their body in a way. It's very, it's very cool. What were they using these signals for? Was it like, you know, when you lean into your car horn to say, move out of my way? Or was it more like, you know, you put on your blinker and you're kind of saying, trying to direct traffic and asking to move into a new lane? Yeah.

I think it's pretty similar to like, you know, driving in heavy traffic with a lot of aggressive drivers. And thank goodness, I have turned signals and brake lights and, you know, a horn, things like that on my car that, you know, help me navigate that situation. Because I think, you know, similarly, these squid down in the deep feeding, I think a lot of what they're doing is to essentially prevent catastrophe, just like the turn signals in traffic. You know, it's preventing an accident. I think a lot of their pigmentation patterning is geared at indicating intent and things about their, perhaps their social dominance or things like that.

Stuff that helps the squid avoid antagonistic interactions because those are costly, And if you can avoid those when possible, you know, that'll help you like save energy and resources and prevent unnecessary damage or being eaten, things like that. Right. So, okay, so for the study, you had the ROV lights on so you could see the squid and could see these patterns. But what happens when it lights out? How do the squid see each other's signals? I wish we had the low light cameras during this study to be able to see what we think is going on. But I'll tell you what we think is going on. So Humble Squid, like I mentioned, mentioned earlier, they, like some other deep living animals, have light-producing organs, these photophores. Where the photophores I described earlier in a lot of deep-sea animals,

and even in, you know, many animals that live on land that were familiar with, like fireflies, like a lot of those photophores are designed to project light outward. The light-producing organ, in some cases, will be encased in like a silvery lining. That really helps the light get out. But the photophores of the Humble Squid are a little different. They're really rudimentary. They're very small. They're like little grains of sand or grains of rice, kind of, and they're embedded in the animal's muscle tissue, and a single animal may have hundreds, and will be spread throughout the body. And what these do, instead of projecting light outward, they'll radiate light within the animal's body. So the animals can make themselves glow with

these photophores. And so we think they're basically making their bodies glow, and then projecting pigmentation patterns on top of that glowing backdrop. So if you think of like the classic pigmentation pattern communication paradigm, you know, where the squid in shallow water, when they're making these patterns, you can think of them kind of as like words on a book. And, you know, you need light to be able to read those words, to read the book.

You can't read the book in the dark. But the Humble is good, we think, basically turn themselves into e-readers. So as opposed to having to shine light on the Humble, The Humboldt Squid, the Humboldt Squid backlights the words, if you will. Just, you know, so you can read your e-reader in the dark before you go to bed. But, you know, you can't do that with a book. But it seems like the two are linked further in that these light-producing organs,

they're not just randomly spread throughout the squid's body. And what we did is, you know, we kind of mapped where those were. And then we found that those regions of higher than average photo-fore density corresponded to being right underneath where some of the subtle but important communication pigmentation patterns were. We think they might be able to glow a little bit more brightly in some regions of their body more than others. This could help enhance the visibility of some patterns that might be a little bit subtle. So it's like a backlight and a highlighter on your e-rader? Yeah, exactly. I hadn't thought of it. Highlighter, nice. Okay. The Humboldt

squid has complex communication, but would you call it language? I mean, the moral of the story there is like, no, we could definitely not call it a language by any means at this point. Who knows if future research would even show they have the capability for a language. But I think our research hints at them having perhaps some elements that we wouldn't have expected just based on their habitat and their social structure. So then what does this tell us about communication in the deep ocean? I think it expands the possibilities. So the deep ocean, it's this massive habitat that's mostly dark, it's empty, it's not a lot of structural complexity at all. And so, you know, it's been thought that visual signals would be pretty basic, but I think

this expands the possibilities. In theory, these squid can say a whole lot more than we previously thought in the deep ocean. These animals, they're predators, they're really abundant. So Humboldt squid and the group of open ocean squid that they belong to, they're the most abundant and ecologically important squid on the planet. You know, these animals, they're moving about eating stuff, pooping, mating, being eaten, and where they go and what decisions they make are pretty important for processes out in the open ocean. They're probably making decisions based on what they're saying to each other, and that might influence processes in the ocean. I just think it's fascinating to think that as you and I are talking right now, they're probably squid talking to each other in the deep ocean. And yeah, they're probably sharing all sorts of information.

Great. Well, thanks, Ben. Thanks for joining us. Absolutely. Thanks for having me. Producer Alexa Limb, speaking with Benjamin Burford, a PhD candidate in biology at Stanford University. When we come back, what lives on your tongue and why? We'll tackle the tongue microbiome after this. This is Science Friday. I'm Ira Flato. You know when you go to the doctor for a regular checkup, what's one of the first things that happens? Stick out your tongue and say, all right? But when you do

stick out your tongue, you know you're not just showing off one of your body's more useful muscles. You're also showing off a collection of billions of bacteria that make their home within your mouth. Researchers are trying to map out exactly what lives in your mouth and where, hoping that the information could provide clues to health and disease. And writing this week in the journal Cell Reports, a team of researchers has taken a first taste at mapping relationships between the bacterial colonies that live on the human tongue. Sci-Fri director Charles Berkwis spoke with Jessica Mark Welch,

an associate scientist at the Marine Biological Laboratory, one of the authors on that study. Thank you for joining me. It's a pleasure to be here. Thank you. Let's talk about what's going on in the environments in your mouth. Are all mouth bacteria the same? There are a lot of different bacteria that live in your mouth. And in fact, there are different kinds of bacteria that live on your teeth and on your tongue and on your gums and on your cheek cells.

so all the different environments in your mouth have different bacterial communities that live on them. In this particular study, you were looking specifically at the tongue. How are the bacteria arranged there? The bacteria on your tongue build these little skyscrapers. They build these little microbial apartment buildings. When we looked at them through the microscope, we said, wow, there's so much more structure there than we'd expected. It was really amazing. Is it just bacteria stacked up on top of bacteria, or they glommed on to some, I don't

no, support structure. Oh, yeah. So the bacteria on your tongue, they're arranged on your tongue epithelial cells. So there's a core cell at the center of these clusters of bacteria that's human. And onto that human cell, these bacteria grow, and they grow out in little clusters, and different bacteria live in different places in the clusters. So there are some bacteria that seem to like to live right down in with the human skin cell, the human epithelial cell that's on your tongue.

and then there are other bacteria that form a crust on the outside and others that form clumps in the middle. So it's a really very complex, complicated structure. You're developing a map of how the bacteria are organized vertically in those skyscrapers you mentioned. It's sort of who's living on what floor and who's next to the laundry room and all that? Yeah, exactly. What we want to know is how are the bacteria arranged relative to each other at these really fine scales, these micrometer scales, so 1,000th of a millimeter. You know, which bacteria are next to who, which other bacteria are, which bacteria are next to which other bacteria, which are right next to the human cells, and how do they arrange themselves?

So this isn't a map of the tongue in terms of who's living on the tip of the tongue versus the sides of the tongue versus... Exactly. What we were interested in was really the fine scale structure of, at the bacterial scale, the scale at which the bacteria are really living and interacting with each other. What's the structure and what's the map there? Looking at the pictures in the paper, it doesn't look like there's a ton of large-scale patterns or organization. Does it really matter who's living where? So the reason it matters is that bacteria interact with whatever's right next to them. So the bacteria are taking up nutrients

and then they're secreting other nutrients. They take up molecules and secrete molecules. And And they do that most dramatically, most importantly, with all the bacteria that are right next to them. And the bacteria that are right next to the human cells are also in the best position to influence human cell biology. Are these bacteria living on what we would call the taste buds? Or are they influencing how we, are the flavors we're experiencing? Yeah. So if these clusters of bacteria that we see aren't right on the taste buds, they're certainly right next

to the taste buds. and it's certainly possible that exactly what kind of bacteria you have on your tongue influences how you taste food. Now, on the other hand, the food comes through your mouth really quickly just in a few seconds. So the bacteria would have to be acting pretty fast to make a difference for your taste. The food's moving through my mouth, the saliva is sloshing around. What's keeping the bacteria in place? Is there some kind of glue or, I don't know, tendrils or something that they have? Yeah, exactly.

So all the bacteria that are in your mouth, they have to be hanging on to something or else they're going to end up in your stomach. And they don't want to be in your stomach. They want to stay in the mouth. So every bacterium in your mouth is adhered to something. It's either adhered to your cells or to your teeth or it's adhered to other bacteria that are hanging on to your teeth. We ask our volunteers to basically just clean their tongues and then we collect the stuff that they've scraped off their tongue and we look at it under the microscope. and we see these flumps and clusters that stick together really pretty well through all of our experimental manipulations because they're sticking together in the mouth with the way they grow.

So the volunteers are using one of those tongue scraper things that some people use for oral care? Yeah, exactly. They're just using a little ridged plastic tongue scraper like your dentist might hand you and say, here, you should scrape your tongue. And should people scrape their tongues? Do you have any sense of whether it makes a difference? So when you scrape your tongue, it certainly reduces the number of bacteria in your mouth, and that does seem to be a good thing. You can't get rid of all of them. There's always more of them coming up behind, but when you scrape your tongue, the same as when you brush your teeth and floss your teeth, you can reduce their numbers, and that's probably good. What about mouthwash?

So the interesting thing about mouthwash and the bacteria on the tongue and the rest of the mouth is that using mouthwash seems to have an effect on your blood pressure because of the bacteria. Right? So what these bacteria can do that your body doesn't do very well is they take a certain nutrient that's in your food. It's called nitrate. The bacteria can convert nitrate to nitrite, which your body doesn't do very well. Then your body takes the nitrite and turns it into nitric oxide.

And that has a lot of effects, including regulating your blood pressure. So the interesting finding is, and this is other people's work, it's not our own, is that if you eat a diet that's rich in green leafy vegetables and other healthy foods, that will lower your blood pressure by a little bit, small but measurable amount, but not if you're using an antiseptic mouthwash. So the bacteria are an important part of that effect of the healthy diet. So, wait, using mouthwash can alter my blood pressure, with all those other things taken into account.

Yes, so all those things taken into account. Yes, using mouthwash. So there have been scientific studies where people have shown that, yes, if you consume a high nitrate diet and then use mouthwash, that will alter your blood pressure, just a little bit. Zooming out from just the tongue, how many different species of bacteria are in an average mouth? Yeah, there are about, oh, a couple hundred species of bacteria in the average mouth. there about 500 species of bacteria, 500 or 700 or 700 that are known from the human mouth as a whole in all the people all over the world, than any one person has, maybe a couple hundred.

And how much do different people have in common? How similar are my mouth bacteria to your mouth bacteria? What we've found, and this is something we're learning only just recently, what we've found is that different people have pretty much the same species of bacteria. So we all have pretty much the same species. And in fact, the bacteria on your tongue are the same as the bacteria on my tongue. The bacteria on your teeth are the same as bacteria on my teeth, pretty much. But we all have slightly different proportions of those bacteria. So somebody will have a lot of one kind, somebody else will have a lot of another kind. And we also have slightly different

strains of bacteria. So if I take a sample from your mouth and then a year later you come back, I can identify you. At least I could pretty much guess, you know, which, which person you are based on what bacteria I find in your mouth. So you could actually, I mean, would this be a reliable forensic technique? Could you identify somebody based on, I don't know, scraping off their tongue? It's certainly not as reliable as your genome would be, but one could certainly make a good guess based on the bacteria that you have, your specific strains of bacteria. You're developing this map of the bacteria that are there, and I guess there are people that are working on sort of the microbial census of the mouth. Do we have any sense yet of what is healthy, what is normal, what is a standard mouth? We're starting to get a sense, I think, of what is, what's the range of normal that you find in the mouth. The human microbiome project did a lot of sequencing, DNA sequencing, from the brain.

bacteria in the mouth, and they've shown what bacteria tend to be there. So what we're still working on on the imaging side is finding out what kinds of structures are normal. What's the range of normal in the structures of bacteria that you see in the mouth? What does that get you? I mean, what's the goal in knowing that information? Yeah, so the goal really is to be able to understand how the bacteria work, how these communities work. First of all, why are there so many different kinds of bacteria. Why aren't there just two or three or four? Why do we have hundreds? What are they all doing in the mouth? And we know that some people's microbiomes, some people's sets of bacteria can work well for them, seem to promote health. But then other sets of bacteria, other microbiomes

can cause disease or can contribute to disease. And we'd like to understand what are the characteristics of a healthy microbiome? What are the characteristics of disease? And then, really, the ultimate goal is to be able to shift the microbiome from a disease state into health. So if we can really understand how these bacteria work together, then we can understand what conditions the good bacteria need to grow. So the reason to look with imaging is to see exactly what environment a good bacteria needs to live in. You know, who does it have to be next to? And then how can we tweak the environment, tweak the community to push it toward health? Are these things that grow in a petri dish? Can you do some of these experience? What nutrients do

they need? What other supports do they need in the lab? Yeah. So one really interesting thing about bacterial communities that we've been learning is that if you go out and sample bacteria from the soil, say, or from the ocean, really only a tiny fraction of them will grow on your petri dish in the lab, right? They need something that we don't know how to give them, and probably they need to be next to some other bacterium. And we don't know what it is. That's another reason we want to do the imaging and find out who's next to who. In the human mouth, it turns out that about half of the bacteria can be grown in a petri dish. And for those other half, there is probably, again, there's something that they need or somebody that they need to be next to that we don't know yet.

So that's one of the things we're trying to learn. I can't help but notice you're at the Marine biological laboratory, what relation do tongues have to do with marine life? Yeah, that's a great question. We do a lot of really basic biological research at the marine biological lab. So we started using the giant axon of the squid to ask questions about neurobiology, using the great big oocytes and surf clams to ask questions about cell divisions. So what we've really been about for more than 100 years is using these marine model organisms to ask basic science questions. But because of that, we have a a lot of innovative microscopy that you can really see put to work in this project.

And then we also have a lot of experts who study bacterial communities anywhere in the world, in the Arctic and the deep sea, in coastal marshes. And here we're just applying that to an environment that's a little bit closer to home. And then I'm doing that with my colleagues at the Forsyte Institute, who are real experts in oral microbiology as well. Are there marine organisms that have tongues that you've looked at? That's a good question. You know, there are marine organisms with tongues, and I haven't looked at them yet, but I'd love to.

Yeah, I'd love to find out where else besides the human mouth you find such fantastic structure. So it's amazing bacterial structures that these bacteria build. You're listening to Science Friday from WNIC Studios. I'm Charles Bergquist talking with Dr. Jessica Mark Welch from the Marine Biological Laboratory at Woods Hole. We're talking about tongue bacteria. When I go to the dentist and I leave with those nice, clean-feeling teeth, How long does it take for them to get recolonized by the bacteria communities in my mouth? Minutes.

So when the dentist cleans your teeth, your teeth are really pretty clean, the dentist do a great job of getting all the bacteria off, at least 90% of the bacteria. But then within seconds, your nice, clean enamel of your teeth gets coated with saliva. There's a coating called the salivary pellicle that goes on to the enamel in a different coating called the mucosal pellicle goes on your tongue and your cheeks. And bacteria within minutes start attaching to that pellicle. The bacteria start reattaching to your teeth. And there are initial colonizers that are really good at binding to those pretty clean teeth with a little coating of saliva. And then there are other bacteria that come in and bind to the initial colonizers. So it's a whole ecological succession really going on in your mouth. And actually it goes on

every time you brush your teeth every day. And when bacteria start to colonize apart, is it just sort of luck of the draw who happens to get into that niche first and start multiplying and growing outwards? Or are there ones that really like the squishy places and other ones that like the not-so-squishy places or some other environmental variable that they're looking for? Yeah. So some bacteria are really good at attaching to that first salivary coating on the teeth. So to some extent, it's which bacteria are particularly good at being the first colonizers,

but then there is also probably a lot of chance involved. So for these structures on the tongue, when a new piece of human tongue cell becomes available in the mouth, when it shows up in the mouth to be colonized, whichever bacteria land on it first probably have a pretty big influence on what kind of community grows out over time. Where else are you planning to go with this? Do you want to develop a map of what lives on my tip of my tongue versus the sides, or is that not of interest? Or what other directions do you have for this? Yeah, so we'd love to know what kinds of bacteria live exactly where on your tongue.

So what kinds of structures we see if you look at the very back of the tongue or in the crevices between the papilli versus on the front of your tongue or the sides. We'd also really love to push this forward to looking at the dynamics of the communicative. So so far, everything we've looked at, we've had to take the sample out and fix it. It's all dead. We'd love to be able to watch these bacteria growing and see how they grow, how they accrete. I think that'll tell us a lot about how they're working together. And how would you go about doing that? Is it, you know, looking at, I don't know, cadaver tongues or peeling pieces of tape off my tongue surface, or what are you doing?

Right. So, yeah, to discover how the bacteria are arranged on the tongue, it would. So one thing, the simplest thing we can do is just. take little scrapings from all over the tongue and look at them. We have certainly thought about trying to get cadaver tongues or to put tape on the tongue and peel it off and see exactly what's where. We've also thought about going to piercing parlors where people are having their tongues pierced

and collecting little samples. This is all in the future. We haven't tried this yet. But yeah, but then for the live imaging, to image these microbial communities live, we'd really have to change the whole way that we're labeling them. So it's another whole transformation of how we're doing the science, but we're really excited to try to push the microscopy in that direction. It's tough to paint fluorescent probes all over somebody's time.

Yes, we have a little trouble getting permission to do that from our human subjects review board. Yeah, it's true. Well, thank you very much for taking time to talk about it with me today. Thank you so much. It was a pleasure. That was Cy Frye Director Charles Berkwist speaking with Jessica Mark Welch, Associate Scientist at the Marine Biodic. biological laboratory in Woods Hole. When we come back, we'll talk about invasive herbivores and how a drug lord's hippos.

You heard me right, hippos are changing the environment in one South American country. Stay with us. This is Science Friday. I'm Ira Flato. Columbia is home to somewhere between 80 and 100 hippos. These huge mammals spend most of their time eating plants on land and staying cool in the world. the water. But they're an invasive species native to Africa. Some locals consider them pests. The

government has mulled over getting rid of them. And recent studies have shown they're having a negative impact on the Colombian environment. But now new research has taken a different view, showing that even though hippos are invasive, they might be filling an ecological hole left by herbivores killed off by humans thousands of years ago. Producer Kathleen Davis spoke with Eric Lungren, the lead author on this new study. He's a PhD student at the University of Technology in Sydney, Australia.

So, Eric, what does the study about invasive species have to do with Colombian drug lord Pablo Escobar? Well, that's a great question. Pablo Escobar is an infamous character. He was a very successful drug lord in Colombia. And he loved animals. He had his own private zoo in his stronghold fortress. And in that zoo were his favorites, which were hippos.

And when Pablo Escobar was killed, those hippos were left to be. And they have bred and they have left the zoo and are showing up as far as 200 miles away in the river system there. And they estimate that there's now between 80 and 100 of these animals, which is they are the largest introduced species to be flourishing in the world. And hippos are, of course, endangered in their native range and present some really interesting ecological questions in Colombia where they've been introduced. So what kind of impact do these hippos have on the Colombian environment? Well, that's an open question. A paper was recently published that found that much like in Africa, these hippos are feeding in the terrestrial environment. They're leaving the water. They're going

upland and they're grazing. And then they come back to the water and they definitely, in the water. And in Africa, that plays a really amazing keystone role in fertilizing water bodies, increasing productivity. In Africa, hippos are responsible for vastly boosting fish production and water birds, et cetera. We know that they're moving nutrients in Colombia, but we don't know what the downstream effect of this is going to be. So in this new study, you and the other researchers say hippos might actually act as a substitute for, or another large herbivore that was wiped out by people thousands of years ago. What did this animal look like and how are hippos acting like them in a way?

Well, it's not one specific animal that they seem like in the past. But if you broaden our perspective of what nature is to begin, not when Christopher Columbus discovered the new world, but towards the larger evolutionary context of Earth's history, before humans arrived in South America, South America was full of giant, strange animals. And many of those are quite similar to hippos, although sometimes in different combinations of traits. So hippos are strangely most similar when you look at all their traits in total to a giant llama, which is kind of a ludicrous comparison.

But they're also very similar to these rhino-like noto-ungulets, which were probably semi-aquatic. And so hippos are kind of like a Greek chimera of all these different extinct species. And there's a real strong chance of what they're doing in Colombia in these rivers resurrect certain processes that were once widespread on that continent for 30 to 40 million years. Do we know why these llama-type animals and the other big herbivores that were living in South America, why they were killed by ancient people? Well, I think people were hungry. And this is a topic of debate for decades now. But as humans left Africa, pretty much everywhere we went, the large animals disappeared shortly afterwards. And in some places this happened really recently, like 800 years ago in New Zealand, the giant flightless birds, the moa is when disappeared when humans arrived.

In Australia, like 80,000 years ago, a huge pantheon of bizarre animals, giant wombats and hoofed horse-like kangaroos. all disappeared when humans first arrived. And similar in Europe, Africa is really the only place where the type of herbivory that is really characteristic of the earth still survives today. What else do we know about these early humans? Well, we know that they were sophisticated hunters. And those that came into North and South America came through Eurasia, where there was a culture of hunting mammoths.

And, you know, there's a lot of speculation. about a lot of people that push back on the idea that humans could have caused these extinctions. Although the evidence is increasingly clear that they were the driver, I personally wonder if these people, and this is just a wondering, if these people came in a state of some degree of chaos and persecution, that would lead to perhaps overusing natural resources, as we have done in the modern world. But it really remains unknown.

I wish we could have a teleport into the cultures and minds of the people back then. That's really interesting. I want to play a clip from a conversation I had with Jonathan Shuren, who wrote the study that you mentioned earlier about the ecological effects that hippos are making to the aquatic environment in Colombia. Jonathan is a professor at the University of California, San Diego. In the actual case of the hippos, their most similar extinct species, not very similar. So, I mean, I would say what that really says is that, you know, there wasn't anything very similar to a hippo.

So hippos are not sort of replacing anything that used to be there. Eric, can you respond to this point that Jonathan raises? Of course. I mean, it is, hippos are a very unique species. They are quite unlike anything else. But they are bulk grazers. They are able to eat tons of dry, fibers, grass matter. And so can other species like these extinct llamas and many other

grazers in South American place to slate place the scene. Hippo's unique uniqueness is also that they're semi-aquatic. And to the best of our knowledge, no do ungulates in South America, some of them may have most likely were semi-aquatic. Now we can't unfortunately go back in a time machine, but many species that we don't even consider to be semi-aquatic often use wetlands strongly. Near where I live, wild horses are constantly feeding and defecating in the Salt River of Arizona. So this process, if you look at the sum total on these broad evolutionary timescales of herbivores affecting the environment, the effects of hippos do not seem so novel. They seem awfully novel when you compare their effects to native species in South America,

which are all small-bodied and all the ones that have survived these dramatic extinctions. So we're conditioned to think of the term invasive species as bad. It seems like here you're trying to reframe how we think about that phrase. Yes, the term invasive species carries a great deal of emotional connotation. It implies almost as if these organisms built ships and came over here with the intent to rape and pillage. And with that kind of branding, that branding from the beginning, it really constricts our ability to ask questions about what these animals are doing. If these organisms are harmful by definition, then how will we ever ask questions that might find

that they do other things, like facilitated things? And so across the field of ecology and conservation biology, the term invasive seems to be increasingly problematic when you look at the nuances of how organisms interact with each other. In fact, it's been said by many that if we came to this place in South America and you tried to determine what species were native or invasive simply by how they were affecting each other without any knowledge of the history of those species, you would have no clue. And so I think that broadening our perspective, especially in this time of mass extinctions and global change, is really necessary to make informed, effective and ethical decisions. when it concerns life on Earth. Is there still a lot that we don't know about how human introduced big herbivores play into their new environments?

Oh, there's so much we don't know. For the most part, these introduced species have been studied, as we've mentioned, with the assumption that they are by definition harmful. And if we ask different types of questions, we find out all sorts of different stories. So for instance, wild boar, wild hogs, are maybe the most vilified of introduced species.

And we read about them every day and how they wreck and reap havoc on native ecosystems. But if you study them with a different perspective, recognizing that what they do by rooting soils is something that many species have done for millions of years in both Australia and North and South America. In North America, there were giant peckeries, giant pig-like animals that until the late places

seen were rooting soils. And that rooting behavior is actually really interesting. So in Tennessee, researchers found that tree growth rates are increased by rooting because the pigs are turning leaf litter into the soil and increasing decomposition rates. They're acting like giant fertilizers. In Australia, a study found that while birds will avoid pigs at the moment that pigs are in a place,

the birds will flock to those areas and feed on the excavated soils because the pigs have made termites and fruits and seeds more available for consumption. So if you study them only, these animals only from the perspective of harm, you find one type of question and one type of answer that is always proven right. If anything these animals do is harmful, then it's just a matter of showing that they do anything. But if you ask questions about these animals as megafauna, as herbivores, and in terms of the deep paleoecology of this planet, you find different types of questions and different types of answers. How common is this type of situation for big herbivores? So are these Colombian hippos one example of just a few times humans have moved around big plant eaters?

Or is this something that's happened many times before? Well, that's really the focus of the study is that this is in some ways a countercurrent force to the extinctions we have brought around the world. we have replaced almost 50% of this lost species richness in some continents with introduced species. 33 introduced herbivores in total. And this effect appears to be counteracting the legacies of these prehistoric extinctions. So in Australia, Australia is probably the most rich in terms of these introduced herbivores. They have donkeys and horses and several species of deer and water buffalo and the world's only population of wild Dramidary camel. And these animals are doing really fascinating things in the landscape,

but are subject to the most brutal eradication campaigns you can imagine. What kind of eradication campaigns are we talking about here? Well, they're a lot of aerial gunning of camels, for instance. They do something really, really tragic to wild donkeys called the Judas technique, some biblical undertones there, where they collar a female donkey with a radio collar, and then they release her. And then donkeys are, of course, very social and intelligent animals. And that female will find a herd of friends,

and then two months later, a helicopter will come and shoot all of those other donkeys and let the female go find another herd, and then two months later, the helicopter will come back. And eventually this Judas donkey, this female with the collar, will give up, and which point she will be shot and the call will be put on another donkey. And using this technique, they've eradicated, I think the estimates are around a million

donkeys in northwestern Australia. And this is in the pursuit of restoring nature to some semblance of how it was found by Europeans when they arrived. But that term nature is what needs to be interrogated. You're listening to Science Friday from WNYC Studios. What do you think it'll take for people to reframe this idea of invasive? Well, I think it'll take shows like this and conversations, many of which will be quite contentious. I'm expecting a pretty fierce reply to what we just published.

And I think it's part of culture. It's part of everyday people thinking about these questions of what is the term belong mean that we so often use and hear when we think about the natural world. And what is change when we see a wetland that's crisscrossed with trails from an introduced herbivore? Is that harm or is that maybe the restoration of how wetlands looked for 40 million years? And so I think a little bit of mindfulness and humility and how we think nature should be will go a long ways to changing this situation. To bring it back around to these Colombian hippos, some people consider them pests. And I know the government has considered killing them. What do you hope for the future of these hippos?

Well, I think it would be fascinating to study them without any notion of them being good or of them being bad, but to study them as megafauna. What is the effect of their grazing in the uplands in the riparian meadows in Colombia and then defecating the rivers? Is it facilitating fish or not? And Shuren, in that paper you mentioned, is a great first step, but there's so much more to learn. And I think we learn it best when we drop the idea that these animals are either saviors of the environment or pests of the environment. And when we do science in a more objective way, free from these labels, I think we'll find more interesting stories, not only to fill us with wonder and curiosity, but also to help us go forward and make decisions that may be difficult to make. Eric, thank you for joining me. Thank you so much, Kathleen.

Science Friday producer Kathleen Davis, speaking with PhD student, Eric Lundgren, from the University of Technology in Sydney, Australia. That's about all the time we have for this hour. If you missed any part of this program or you would like to hear it again, subscribe to our podcast or ask your smart speaker to play Science Friday. Every day now is Science Friday. And on our Science Friday Vox Pop app, we want to keep fact-checking your feed. What have you seen reported about coronavirus that you think needs a closer look? Send us your questions on the Science Friday Vox Pop app wherever you get your apps. Charles Berkwist is our director.

Our producers are Alexa Lim, Christy Taylor, Katie Feather, and Kathleen Davis. We had technical and engineering help today from Rich Kim, Kevin Wolfe and Lisa Goslin. B.J. Liedeman composed our theme music. Of course, we're active all week on Facebook, Twitter, Instagram, all social media, or you can email us. The address is SciFri at ScienceFriD.com. Send feedback and tell us what you'd like us to cover. I'm Ira Flato in New York.