Short Wave - Save The Parasites

Episode Date: August 14, 2020

Saving endangered species usually brings to mind tigers or whales. But scientists say many parasites are also at risk of extinction. Short Wave's Emily Kwong talks with Chelsea Wood, an Assistant Professor in the School of Aquatic and Fishery Sciences at the University of Washington, who tells us about the important role parasites play in ecosystems and a new global plan to protect them.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Meet the nematomorphs, a type of parasite you can find in some streams of Japan. There are these long round worms that just squirm around and kind of tie themselves into knots. And they have this awful habit of bursting out of living insects that doesn't at all endear them to people. Yeah. But for a parasitologist like Chelsea Wood, the strategies nematomorphs used to survive illustrates just how unexpectedly interconnected different species in ecosystems are. And the vital role played by, you guessed it, parasites. We're specifically talking here about metazone parasites, so things like flatworms, tapeworms, that kind of thing.

See, nematomorphs often jump back and forth between freshwater and an invertebrate host, usually an insect. In its larvae baby stage of life, a nematomorph can get ingested by a cricket where it starts to grow. So it has this important problem to solve where it's hanging out in a cricket, and it needs to find a way to get into an aquatic habitat. Back into the stream. So our parasitic nematomorph does something I find both disturbing and fascinating. It induces in its cricket host what's called a water drive, which is essentially a suicidal impulse on the part of the cricket to drown itself.

in nearby freshwater bodies. Obviously, real bad for the cricket, it dies in this process. It dies in the process? The cricket dies in the process. It's not the nicest thing to do to your host. But in the process, what the nomadamorph does is deliver this cricket into a freshwater habitat where it can be food for an endangered species of trout. Chelsea says without the nomadamorphs, this endangered trout would be in big trouble.

And this is just one example of the countless ways parasites benefit ecosystems around the world. In the absence of parasites, our ecosystems would fall apart. So conserving them is an insurance policy. It makes sure that we've got ecosystems to depend on for our livelihoods moving forward. If we want to continue to enjoy ecosystems, we need to invest in figuring out ways to preserve the parasites that exist within them. Because Chelsea says some parasite species are actually vulnerable to extinction, just like the giant panda, the lion, the polar bear. Although parasites, maybe not as camera-ready. What it lacks in beauty, it makes up for an ecological importance.

And they have a fierce public relations manager in Chelsea Wood. So today on the show, we talk about animal parasites and a global plan to save them. Chelsea and a group of parasitologists published their plan in the journal Biological Conservation this month. So Parasite Week, anyone? I'm Emily Kwong, and this is Shortwave, the Daily Science Podcast from NPR. So today we're speaking with Chelsea Wood, assistant professor in the School of Aquatic and Fishery Sciences at the University of Washington about parasites, organisms that live on or in a host, and thrive at the expense of the, their host. But before we get to the plan to conserve them, let's tell one more parasite story, Chelsea's

favorite. I know I'm not supposed to play favorites. It's all right. You're in safe territory. I do have a favorite clade of parasites. And they're tapeworms in the order Trapanarinka. I call them Trapanorinx for short. She came across them starting out as little larvaled tapeworms inside fish, just hoping to continue their life cycle in the gut of a shark. So many. Many of them just lay in wait invisibly all over the coral reef, hoping that they'll be the one to hit it big and wind up in a shark intestine. Don't we all? The other thing she loves about them, their tentacles. They each have four tentacles on their head end.

So imagine the monster from stranger things. Terrifying. Except, imagine that rather than having this like gaping maw full of teeth out of that head end poked these. four tentacles, which could each be averted from the head rapid fire, just like a bullet right out of the head. And imagine that each of those four tentacles was armed with thousands and thousands of rows of backward-facing hooks. And now you've got kind of an idea of what the tropanerinks are like. Honestly, it makes the Stranger Things monster seem kind of lame. It does. They should have gone all the way. I'm going to write to them next time, maybe next season.

I remember the first time I learned about parasites in biology being creeped out and amazed, equally. Yeah, that's common. And I think reasonable, we can't help but take the perspective of the host, right? We're host to over 300 species of parasites. And I think when most people encounter parasitism for the first time, they can't help but imagine what it might be like to have a worm living inside you. And of course, that's not a pleasant thought. But only 4% of the parasites. species on the face of the planet affect people. And that is probably an overestimate because we spend a lot of time on the taxonomy of parasites that affect people and not a lot of time describing the parasites that don't affect people. And so the vast majority of parasitic life is out there in nature having literally nothing to do with humans. And those are the parasites that we're

thinking about in this plan. So what made you go in the opposite direction of some people who are just like, ugh, slimy worm. I'll be honest and say that I started that way. That was the same attitude that I took to parasites when I first started studying them. But I think when you start to learn about them, you really can't help but be, if not in awe of them, at least impressed. They are so different from the rest of what we learn in our biology education. There are 40% of animal species, and yet you can.

get an undergraduate degree in biology and never hear about parasites. And so when you do finally start wading into the world of parasites, it's just, it's like landing on a different planet. You know, the body structures are different. The life cycles are different. The evolution is different. But in fact, they live all around us all the time just below the surface of everything that's familiar. I think that's part of what made me fall in love with them. Wow. Hmm. The fundamental, idea undergirding parasites is that is an organism that benefits itself to the detriment of its host. Is that part of why it's hard to want to conserve them for some people who haven't fallen in love with parasites? Because why would you want to conserve something that harms others, including humans?

Yeah, I think that is a big part of it. But the counter argument to that is we are all completely in love with predators, right? Like we're in the middle of Shark Week right now, and people can't get enough of it. You know, there have been generations of Discovery Channel specials on the lions of Africa, the tigers of Asia. We are obsessed with predators. And yet for a predator, when it has an interaction with prey, that prey is dead, right? It's game over for that prey. Meanwhile, parasites do cause negative fitness effects for their hosts, but not all of them

kill those hosts, right? They're just kind of sucking a little blood or rasping a little mucus or maybe stealing a part of your dinner. So I don't understand why we put predators up on this pedestal when their negative effects on their prey are far, far worse than the negative effects of parasites. And I think that there are some parallels between the journey that parasites are going through from a public relations perspective and the journey that predators have gone through. because a couple generations ago, none of us would have liked predators, right? They have undergone a major revolution in public perception just in the past several decades. We went from seeing them as things that are dangerous to us and certainly dangerous to our livestock to these beautiful charismatic organisms worthy of conservation. That's a really good counter argument. Why are parasites so important for ecosystems? A couple reasons. The first is population regulation of hosts. And a great way to think about this is invasive species, right? Like species that we bring from their native range and put into a new place. They often increase in abundance exponentially because they've landed in a new range where they don't have any parasites. That's what a world without parasites would look like. A lack of regulation of hosts. that we might not want quite so many of.

Number two, every day, parasites of many different species are pushing prey into the jaw of predators and in that way, making the existence of predators possible and increasing the number of predators that can exist on a given landscape. So if we enjoy the presence of birds or lions or tigers or bears, we have parasites to thank for that. I want to snap. This is like a campaign speech for Save the Parasites.

So just to summarize, two of the key ecological benefits of parasites is population control and driving energy, aka food, up the food pyramid to the top. Yep. Yeah, and then we can also talk a little bit about a third that comes from studies of food webs. So trying to understand the connections among all the species in an ecosystem where there's, is a suggestion that the presence of parasites in food webs actually makes those food webs more stable. So it makes them better able to bounce back after disturbance. It makes them more resilient because the parasites do this job of connecting up species. So think about a web with just a few strands in it. That web is very, very weak. But if you add more strands into that web, the stronger it becomes.

And that's the function that parasites serve. And it's thought that that's how they make food webs more stable than they might be in the absence of parasites. Fascinating. Okay. Let's get into the plan. So you and several other scientists recently published a global parasite conservation plan about how some parasites are threatened, endangered, or going extinct from their host species being endangered or their habitats being endangered by climate change and human activity. what are two key points from the plan you want to share with our listeners? One of our moonshot goals, one of our goals that is extremely ambitious and we hope achievable,

is to describe 50% of parasite biodiversity in the next 10 years. Now, that's a tall order because we think that only 10% of parasite species are currently described, but you cannot conserve what you haven't yet named. And we think that the very first step in parasite conservation is for us to take an inventory and understand what we've got so that we can work to make sure we don't lose what we've got. The second, and I think this one is super important, is figuring out ways to increase public literacy about parasitology. figure out ways to get more parasite ecology into K through 12 education and higher education and figure out ways to increase public literacy through museums or documentaries the way that people have been educated about the importance of predators.

We got to figure out ways to make that same strategy work for parasites. Do you think there should be a parasite week on the animal planet? Yes. I mean, Discovery Channel is going to have to really invest in their microscopic videography videography department, because it's certainly a different skill set than taking beautiful video of predators. But I have faith that it can be done and that when it is done, people will see the absolutely striking beauty and wonder of the world of parasites. Chelsea, this has been a total pleasure, like, talking to you.

Yeah, thanks so much for your interest in this work. It has been such a pleasure talking to you. Today's episode was produced by Abby Wendell, edited by Viet Le, and fact-checked by me, Emily Kwong. You're listening to Shortwave, the Daily Science Podcast from NPR.