How to become a parasite

Daniel and Kelly talk about whether or not dinosaurs had parasites, how often parasitism has popped up in the tree of life, and more. See omnystudio.com/listener https://omnystudio.com/listener for privacy information.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Speaker 00

  This is an iHeart Podcast. Guaranteed Human. Hey, I'm Niall Rogers. This fall, I'll be driving across the country, meeting some of today's coolest and most fascinating artists. We'll explore the stories before the moments that changed everything. Because every musician remembers the moment where it all began. Experience Before the Moment. A Lincoln original series on the iHeart Radio app, YouTube, or wherever you get your podcasts.

• 0:36Speaker 01

  Running a small business takes everything you've got. But with Chase for Business, you're not alone. They bring together local support and a broad range of resources to more than 7 million customers. With a deep understanding of your day-to-day needs, they provide products and guidance built to help you thrive. Right now, earn $500 when you open a new Chase Business Complete Checking account for new business checking customers with qualifying activities. Offer expires January 21, 2027. Chase Business Complete Checking has the flexible tools you need to accept payments, make deposits, and manage your finances with confidence. Learn more at chase.com/podcastbizoffer. Chase, make more of what's yours.

• 1:21Speaker 01

  Fees may apply to Chase Business Complete Checking accounts. The $500 offer is available for new business checking accounts with qualifying activities through January 21, 2027. Eligibility and qualification requirements must be met. Additional restrictions may apply. Please speak with a business banker for more information. JPMorgan Chase Bank, N.A., Member FDIC.

• 1:54Kelly Weinersmith?

  Imagine sitting out on a porch on a warm spring evening. You hear the spring peepers calling out to each other in a nearby pond. Birds are chirping in the trees, preparing to turn into their nest for the night. Off in the distance, you see a deer walking with her fawn. It's a beautiful scene, reminding you how wonderful it is to live in Virginia. When I hear and see these denizens of the forest, though, I see something else as well: walking ecosystems for parasites. You see, on average, a bird species harbors more than three species of tapeworm. Nearly three nematode species probably call that frog home.

• 2:35Kelly Weinersmith?

  Those deer are harboring trimatodes, tapeworms, nematodes, and more. Though hidden from sight, parasites are thought to make up over half of the biodiversity of multicellular organisms on our planet. Today, we're going to answer listener questions about the evolution of parasitism. Hope you're not listening to the show while eating dinner. Welcome to Daniel and Kelly's extraordinarily infected universe.

• 3:14Daniel Whiteson?

  Hi, I'm Daniel. I'm a particle physicist, and I'm looking forward to meeting alien parasites.

• 3:19Kelly Weinersmith?

  Hello, I'm Kelly Wiener-Smith. I study parasites in space, but not parasites in space. But maybe one day I'll study. Yeah, maybe one day I'll be studying parasites in space.

• 3:29Daniel Whiteson?

  So my question for you today, Kelly, is what is your favorite depiction of parasites in science fiction?

• 3:36Kelly Weinersmith?

  Probably aliens. Don't need to think about it. Aliens, it's a great parasitoid in there. I went through a phase where I was just loving all of the zombie movies, and I was actually taking notes on like what mechanism was producing the zombies. So for a while, you know, when there were big fears of nuclear bombs getting dropped on the US, for example, you know, nuclear material was the cause of zombies. But then it became like infectious diseases, and I've gotten off course. I was thinking about writing a whole book on this, actually.

• 4:06Daniel Whiteson?

  And why didn't you? It sounds fascinating.

• 4:09Kelly Weinersmith?

  Uh, you know, enough people told me that like the zombie craze is behind us and that this is a book nobody would want to read because it would be too of the time. Yeah, too of the moment, right? Like when people weren't watching the zombie movies, like The Last of Us, or which I guess that's running still now, but.

• 4:24Daniel Whiteson?

  Zombies aren't a moment, they're a movement, you know?

• 4:27Kelly Weinersmith?

  That's right. Well, and I, I gave a talk at the Zombie Apocalypse Medicine Meeting, or I think I forget.

• 4:34Daniel Whiteson?

  That's a meeting?

• 4:35Kelly Weinersmith?

  Yeah, it's, and it's happening in October of this year. I highly recommend folks go to it.

• 4:40Daniel Whiteson?

  These are legit scientists?

• 4:41Kelly Weinersmith?

  These are legit scientists, yes.

• 4:43Daniel Whiteson?

  Wow.

• 4:43Kelly Weinersmith?

  And I gave a talk on that topic and it was like the most fun research I've ever done in my life.

• 4:51Daniel Whiteson?

  Well, I think I speak for the audience in saying that we all want to read your book on the science of zombies. That sounds fantastic.

• 4:57Kelly Weinersmith?

  You know, I've got a link to the talk that I could share if anyone wants to see the talk, but I don't think it's going to become a full-length book, not with, not with what I've got on my agenda right now.

• 5:05Daniel Whiteson?

  All right. Well, today we're not talking about space or science fiction or zombies. We're answering a really fascinating question from a listener about the context, the evolution, and maybe even the future of parasites in our world.

• 5:18Kelly Weinersmith?

  Take it away, Zach.

• 5:19Speaker 04

  Hey there, extraordinaries. The recent episode on the history of Trichinella, I should say, the recent history of Trichinella, got me wondering about the more ancient history of parasites. I assume that being a parasite is a strategy that existed back in the time of the dinosaurs, maybe even further back. I'm curious if we have evidence of that and if parasites tend to become extinct when their host species does as well, or if we're still living with the same kind of parasites that dinosaurs dealt with. I'm also curious if we know about how parasites evolve. How does a organism go from being not a parasite to a parasite? Do we have any idea of that evolutionary history?

• 6:03Speaker 04

  Looking forward to hearing more squishy wormy biology from you guys.

• 6:08Daniel Whiteson?

  Thank you, Zach, for sending in this question. If you have questions about the nature of the universe, or the history of parasites, or anything in this extraordinary universe, we want to hear from you. We want to answer your questions. We want to scratch your itch, because everybody's curious about the universe. So don't be shy. Write to us to [email protected]. Everyone gets an answer.

• 6:28Kelly Weinersmith?

  And I am currently researching why we scratch itches, which is a question sent by a listener. So you even get those kinds of questions answered.

• 6:37Daniel Whiteson?

  Amazing.

• 6:37Kelly Weinersmith?

  Yep.

• 6:38Daniel Whiteson?

  So dig into this for us, Kelly. Tell us about the history of parasites, and why we call something a parasite, and what fraction of species we could classify as parasites.

• 6:47Kelly Weinersmith?

  Well, Daniel, let's pretend that you didn't read the outline, which maybe, maybe you didn't, although you're usually very well prepared. If you had to guess what percent of multicellular organisms were parasites, what percent would you guess?

• 7:00Daniel Whiteson?

  It doesn't seem to me like most things are parasites. Bunnies are not parasites. Flies are not parasites. Whales are not parasites. So, you know, it seems to me unusual. So I guess 1% is my absolutely no information guess.

• 7:13Kelly Weinersmith?

  Are you playing along? Are you really guessing 1%?

• 7:15Daniel Whiteson?

  I'm really guessing 1%.

• 7:16Kelly Weinersmith?

  Oh, wow. That's fantastic. Okay. I love those moments where you can be like, you're totally wrong. So Daniel, you're totally wrong.

• 7:21Daniel Whiteson?

  Yay.

• 7:22Kelly Weinersmith?

  Yay. So if you look at that rabbit, so rabbits are mammals, and on average mammals harbor one to two species of trematodes, one to two species of tapeworms, and four nematode species.

• 7:35Daniel Whiteson?

  Well, I didn't want to eat rabbits before, but I certainly don't want to eat rabbits now.

• 7:39Kelly Weinersmith?

  Well, then let's not talk about more typical food animals like cows and pigs. We'll stay away from those. But it's estimated that, and this was from a 2008 paper, that was estimating about 44,000 host species with vertebrates, and about 77,000 species of trematodes, tapeworms, nematodes, and acanthocephalins. So this is four kinds of parasites, almost twice as many parasites as there are hosts. And that doesn't even include things like lice and ticks and stuff like that.

• 8:09Daniel Whiteson?

  What? Hold on a second. You're telling me that like, every species of critter out there has like, two unique species of parasites? So there's like a two to one parasite to critter ratio?

• 8:21Kelly Weinersmith?

  This is a great question. This is where it gets a little bit complicated. So for example, if you have two different species of rabbit, they might share one of their trematode species, for example. So there are some parasites that are generalists and you can find them in more than one host species. But there are also a lot of parasites that are found in one species. And so in general, when we look at how many parasites are generalists and how many are specialists and are just found in one host, we get this estimate where we feel comfortable saying that probably more than 50% of the multicellular biodiversity on Earth is using the parasitic strategy in some way.

• 8:55Daniel Whiteson?

  Oh my gosh, we're in the minority.

• 8:57Kelly Weinersmith?

  Yeah.

• 8:58Daniel Whiteson?

  For not sucking on some other critter. Like unusual.

• 9:02Kelly Weinersmith?

  We're total chumps, man.

• 9:06Daniel Whiteson?

  We gotta rethink this. Wow.

• 9:08Kelly Weinersmith?

  I know. There's a lot of interesting questions that arise from there. So we know that a bunch of species have this strategy of being a parasite, which essentially means that you rely on another organism where you're extracting their energy. It's not benefiting them and you need them to get the energy.

• 9:24Daniel Whiteson?

  Well, then can I ask a technical question?

• 9:26Kelly Weinersmith?

  Like, yeah.

• 9:26Daniel Whiteson?

  Is a cow a parasite because it relies on grass? And you know, it's extracting the energy from the grass? Why isn't a cow listed as a grass parasite?

• 9:34Kelly Weinersmith?

  So it is eating lots of different blades of grass. And so this is usually an intimate and durable interaction between two individuals.

• 9:45Daniel Whiteson?

  Intimate. Wow.

• 9:46Kelly Weinersmith?

  Intimate. Well, you know, if you're living inside, for example, of something and sharing its dinner with it every night, that's pretty intimate. And so, yeah, cows are eating lots of different grass. We call mosquitoes and lampreys and ticks and stuff, micro predators. So they take little meals from lots of animals. They don't kill them, which predators usually do, but they just take little meals from lots of animals. And so the idea is that to be a parasite, you have to be on one organism for a long time.

• 10:17Daniel Whiteson?

  Okay. So mosquitoes technically not parasites then, right?

• 10:20Kelly Weinersmith?

  You would be amazing how much fur flies at parasitology conferences when the mosquito and the leech people are like, these are parasites. And then some of the community is like, they're micro predators. And the leech people are like, we belong here. And I'm like, they belong here. Don't kick them out.

• 10:35Daniel Whiteson?

  Well, they're parasites in spirit, even if they don't qualify technically.

• 10:39Kelly Weinersmith?

  That's right.

• 10:39Daniel Whiteson?

  Because otherwise, like a giraffe, which nibbles on this tree and then the other tree and the other trees, basically has the same relationship with a tree as a mosquito does with people, right? So.

• 10:47Kelly Weinersmith?

  That's right. Because it's not killing all of them.

• 10:49Daniel Whiteson?

  Yeah.

• 10:49Kelly Weinersmith?

  Yeah. And so sometimes you can get into debates with some folks about to what extent herbivores can be thought of as parasites. So, you know, if like an insect lives on the same tree for a long time, is it a parasite? Or is it a different category altogether? Because it's a plant. And anyway, I guess at the end of the day, nature doesn't care that humans like to have very nice, clear boxes to put things in. She's always giving us edge cases to make things complicated.

• 11:16Daniel Whiteson?

  And life is an ecosystem, right? It's a web and there's nothing isolated. We're all munching on each other and eating each other and being eaten by each other. It's a big party, right?

• 11:26Kelly Weinersmith?

  Hmm. I don't want to go to the parties you go to, Daniel, based on what you just described.

• 11:31Daniel Whiteson?

  We have fun. We have fun. But how useful are these categorizations? I mean, does it matter what we call a parasite or not?

• 11:39Kelly Weinersmith?

  So I think it does. And the main reason I think it does is because often folks will try to model the impact of parasites on populations, or use some modeling to try to understand how to control a parasite population. And those models depend on the assumptions you make about what that organism is doing, how many organisms it's feeding on, how many babies it produces. Like, having these details helps you create models that can describe different groups of strategies. And those models can be important for a lot of things, including epidemiology.

• 12:12Daniel Whiteson?

  I see. All right. And also, it's nice to get like-minded people together, right? And so.

• 12:17Kelly Weinersmith?

  Yeah.

• 12:17Daniel Whiteson?

  You got people want to know, which conference do I go to? Do I go to the zombie conference, or the parasite conference, or the zombie parasite conference, or whatever? And so we got to put names on things so that we can get ourselves organized, even if we admit that the names are fuzzy. You know, is Pluto a planet or not? Does it really matter? We're interested in studying this stuff floating in outer space.

• 12:35Kelly Weinersmith?

  I once organized a symposium called How to Make a Zombie with my friend Zen Fals, who has like the coolest name ever. And then it was me who has the least cool name ever. And it was a very interesting combo. But anyway, it was all about parasites that manipulate host behavior and and how they do that.

• 12:50Daniel Whiteson?

  Right, right. Yeah, parasites and zombies are connected in the end.

• 12:54Kelly Weinersmith?

  Sure.

• 12:55Daniel Whiteson?

  So the bottom line is that there are lots and lots and lots of parasites out there. I was totally wrong. And there's lots of different kinds of parasites out there. But what about by body mass? Are parasites like a tiny fraction of the mass? Or if you made a big pile of all the parasites on the planet, would it be bigger than the pile of non-parasites?

• 13:13Kelly Weinersmith?

  This is a great question. So I didn't necessarily prepare for you to ask this question. So I don't have all the numbers that I want at my fingertips. But there was a system where this question was studied explicitly. And it was the estuaries in Southern California. And essentially, they took the biomass of all of the free living organisms and they extracted the parasites from them. And they took the biomass of them.

• 13:34Daniel Whiteson?

  Yeah.

• 13:34Kelly Weinersmith?

  And in these systems, the main predators are predatory birds. They eat the crustaceans, they eat the fish, they're like the main predator out there. And the biomass of Trematode parasites was equal to, and maybe I think in some cases greater than, the biomass of the top predators in the system, which is to say greater than the biomass of the birds.

• 13:54Daniel Whiteson?

  Wow.

• 13:54Kelly Weinersmith?

  And that's because this system has a lot of Trematode parasites that infect the snails. And when the snails get infected, they get castrated. And all of the energy that would have gone to making baby snails now becomes parasite biomass. And so the ground, it's like a carpet of snails in these estuaries. There's just loads and loads of them.

• 14:12Daniel Whiteson?

  I'm imagining stepping on them, which is like crunch, crunch, crunch.

• 14:14Kelly Weinersmith?

  Yeah, it's not crunch, crunch, crunch, crunch, because it's very muddy out there. So you're like squishing them underground, like they're getting covered in mud. So you do feel bad about that. I did feel bad. It was great exercise working in this system, though. This is what I, what I did for my PhD, because every step you take, you need to like steal your foot back from the mud. And anyway, good exercise. Point is, some systems have really, really high parasite biomass. But for example, if you were to collect a deer, the biomass of parasites in a deer is probably a very small percent.

• 14:48Daniel Whiteson?

  Like 1%?

• 14:49Kelly Weinersmith?

  Yeah, I guess probably like 1%. That's where your 1% Came from Daniel.

• 14:53Daniel Whiteson?

  That's what I meant. Yeah, yeah, let's say that.

• 14:56Kelly Weinersmith?

  Oh, man.

• 14:56Daniel Whiteson?

  Let's retcon that.

• 14:57Kelly Weinersmith?

  Totally right. You hit the nail on the head. It was perfect.

• 15:02Daniel Whiteson?

  If we keep asking questions, we'll eventually find one that lines up with my answer.

• 15:06Kelly Weinersmith?

  That's right. And we got there pretty quick. We got there pretty quick. And this biomass question that you asked depends a lot on what the strategy of the parasite is. And in our next segment, we're going to talk about different strategies. But basically, when the strategy involves killing your host, you can take up more of that host biomass because the host is going to die anyway. But now I want to talk about, you know, so we've determined that maybe as much as 50% or more of the number of species on the planet that are multicellular are parasites. But how many times did you get a transition from free living to a parasitic strategy?

• 15:39Daniel Whiteson?

  Right. Like, did this evolve one time? And now we have a huge explosion of parasites? Or is it a common thing that's been developed independently multiple times, like flight, for example?

• 15:49Kelly Weinersmith?

  I mean, do you want to give a, like, guess at how many times parasitism has evolved?

• 15:54Daniel Whiteson?

  This time?

• 15:54Kelly Weinersmith?

  You're such a good sport.

• 15:56Daniel Whiteson?

  I would guess that it's evolved multiple times because it seems like kind of an obvious strategy. And it doesn't require, like, some huge technological innovation, like photosynthesis or the engineering of flight even. So I would guess it's pretty common. I don't know, a dozen times?

• 16:13Kelly Weinersmith?

  When we had Joe Wolfe on the show, she pointed out that the crab body plan has popped up, I think, eight times. I think you undersold the difficulty of parasitism a little bit. So if you are trying to infect a host, you need to find that host. You need to survive its immune system. You're now in a completely foreign environment that is actively trying to kill you all the time. But despite those challenges, we think that parasitism has shown up at least 223 times in Kingdom Animalia.

• 16:44Daniel Whiteson?

  I'm sorry, 223 times?

• 16:48Kelly Weinersmith?

  223 times.

• 16:49Daniel Whiteson?

  Like, you can identify individual moments when something went from non-parasite to parasite in the evolutionary record hundreds of times?

• 16:59Kelly Weinersmith?

  Hundreds of times, yes.

• 17:01Daniel Whiteson?

  Why aren't we all parasites?

• 17:03Kelly Weinersmith?

  Well, you know, there's got to be some hosts.

• 17:06Daniel Whiteson?

  I see. For the grifters to keep grifting, we need some suckers. That's what you're saying.

• 17:10Kelly Weinersmith?

  And you and I are the suckers, I guess. But so sometimes you get this transition to parasitism that results in a lot of additional species. So I think when you ask people about parasites, they usually think about things like tapeworms and trematodes and nematodes and stuff like that.

• 17:28Daniel Whiteson?

  Unfortunately, that is my mental image, and that's why it gives me the willies.

• 17:31Kelly Weinersmith?

  Yeah, I'm sorry.

• 17:32Daniel Whiteson?

  It's intimate, though.

• 17:34Kelly Weinersmith?

  It's very intimate. So in Phylum, Platyhelminthi, so that's where you get the trematodes and the tapeworms and stuff. There were about 13 transitions to parasitism last time we counted. But in Arthropoda, so these are invertebrates with exoskeletons. So we're thinking about like wasps and crustaceans and stuff like that. It evolved 143 times.

• 17:58Daniel Whiteson?

  Wow.

• 17:59Kelly Weinersmith?

  So lots of transitions and lots of times it happened in insects and it happened 60 times in flies. So flies, you often get a transition from free living to parasitic strategies.

• 18:12Daniel Whiteson?

  How do we trace these transitions? Like, I understand we can look at the fossil record and see how whales return to the ocean, this kind of stuff. But insects, we don't have fossils. How do we know this history?

• 18:23Kelly Weinersmith?

  We do have some insect fossils. Often they get trapped in things like amber. And amber actually does a really great job of preserving things and making it so you can still see their features.

• 18:33Daniel Whiteson?

  Yeah.

• 18:34Kelly Weinersmith?

  But we probably are undercounting because there probably are a lot of like transitions that happened and then were lost. Those species went extinct. Or a lot of just instances where there was like a free living host that we just never found. And so these, you should imagine that all of these estimates are very likely to change over time.

• 18:50Daniel Whiteson?

  Yeah.

• 18:50Kelly Weinersmith?

  But we have been lucky to get a fair number of fossils in the record. And the fossils are usually not beautiful, exactly what you want fossils. But for example, there's a lot of tapeworms and monogenines. So these are, monogenines are parasites that you often find on the outside of fish. They have these hooks that they use to hold on to the fish and then they suck like the mucus. Sometimes they suck blood, but they live on the outside.

• 19:17Daniel Whiteson?

  The less intimate side, we'll say.

• 19:19Kelly Weinersmith?

  Yeah, slightly less intimate, but no less durable.

• 19:24Kelly Weinersmith?

  And so they use these hooks and then tapeworms also tend to have these hooks and they use them to hold on inside. So now we've got intimate and durable, but these hooks have very distinctive shapes. And sometimes we can find in fossilized animal poops called coprolites, which we've talked about before, these hooks in like the pairings that you would expect and in the shapes that you would expect and inside of or like very adjacent to organisms that you would expect to find them in. And we found evidence of these sorts of relationships from the Mesozoic area, which was 66 to about 250 million years ago. This includes like the Jurassic period where, you know, Jurassic Park and the Paleozoic

• 20:06Kelly Weinersmith?

  period, which is even later. I think Paleozoic means something like old life. And we found some evidence of these parasites from back then, too. So it's totally reasonable to assume that like T. rex was probably carrying around some nematodes. These are ancient interactions.

• 20:20Daniel Whiteson?

  I love thinking about when things arose because it's a way to figure out like, how hard is it to happen? And also, is it like they happen on alien planets? Like we think about how quickly did we get life after there were the conditions for life on Earth? Pretty quickly. How quickly did we get intelligence after there were the conditions for intelligence? Not that quickly. And it's only n equals one, but it's like a hint as to like, is this likely to happen elsewhere? And so how far back is the evidence of parasitism? How quickly did people start to slurp and munch intimately on each other?

• 20:52Kelly Weinersmith?

  Well, so we are mostly focusing on multicellular organisms going after other multicellular organisms. I think it would be really hard to know if there was like a bacterial parasite going after other organisms in the like primordial soup era of life.

• 21:10Daniel Whiteson?

  I guess bacteriophages could be considered parasites, like viruses that infect bacteria, right?

• 21:14Kelly Weinersmith?

  Yeah. I mean, at conferences, we like to joke that the first organism was free living and the second one found some way to exploit it, but. But you know, we don't know that for sure.

• 21:23Daniel Whiteson?

  In this economy, that's just how it works.

• 21:25Kelly Weinersmith?

  That's right. That's right. And so, you know, I think pretty early on, when you start getting multicellular organisms, you get parasites also.

• 21:33Daniel Whiteson?

  And remind us, how early did we get multicellular organisms for those of us who are not evolutionary biologists?

• 21:38Kelly Weinersmith?

  So multicellular life is probably something like 700 million years ago. And I think we have decent evidence of parasites in multicellular organisms from at least 250 million years ago. And I'm guessing that before that, it gets even harder to find evidence of parasites. And you have to be super careful that you're not tricking yourself. So for example, there are these isopods that attach to fish and sometimes they'll like live on top of their gill arches. So like underneath their gill flap and then other times they'll live on their tongue. And so if you find an isopod next to a fish, you might be like, oh, there, there's a parasitic isopod. But how do you know that it wasn't just like fossilized next to the fish? How do you know it was actually a parasitic relationship?

• 22:23Kelly Weinersmith?

  So this stuff can be really difficult.

• 22:25Daniel Whiteson?

  These glimpses into deep time are super fascinating. One of my favorite things in science, you know, to think that like Earth had life on it for billions of years before it had multicellular life. You know, like so many years, so many seasons, so many days passed with just like frothing bacteria and stuff floating in the oceans. Not really very interesting, but it's also kind of depressing because it means like, if you find a planet with life on it, there's a good chance it's just a bunch of single cell organisms. Nobody really to talk to. It's incredible how rapidly things have changed. Like 700 million years ago, we get multicellular life and then, you know, things explode. And only recently have we had intelligence and technology and podcasts.

• 23:07Kelly Weinersmith?

  I promised to not rat you out because you essentially said, there's just bacteria and that's not interesting. I promise I won't tell Katrina that you said that, but, but I agree.

• 23:17Daniel Whiteson?

  Well, this is our way to find out if she listens to the podcast or not, if I get in trouble over there.

• 23:21Kelly Weinersmith?

  That's all right. Well, keep me posted. All right. So when we come back, let's talk about categories that parasites fall into. So we were talking about how do you define and categorize these things? Let's talk about the categories that we think make the most sense.

• 23:45Speaker 00

  Hey, I'm Nile Rodgers, producer, songwriter, guitarist, and co-founder of the group Chic. A great song has a way of defining a moment, a moment of joy, heartbreak, or anything in between. This fall, I'll be driving across the country, dropping in on some of the coolest, most fascinating artists working today. We'll go deep into their lives and careers and hear what it was like before the moment that made them. From hitmakers like Miguel...

• 24:18Speaker 05

  That last year, finishing that record was the hardest experience of my life. Regardless of how everyone else buys into this, I believe in this and I'm gonna push.

• 24:31Speaker 00

  To rising stars like Alex Warren.

• 24:33Speaker 06

  You know, a song is a story and the verse is setting the scene. And for me, at least, it's allowing me to be personal and vulnerable with the audience, whether it's about my wife and I'm being vulnerable about her, or it's about, you know, my parents and I'm being vulnerable to them. And it's almost like a cinematic piece in a way where each song tells that beautiful story.

• 24:52Speaker 00

  It's gonna be one hell of a trip. Experience Before the Moment, a Lincoln Original Series on the iHeartRadio app, YouTube, or wherever you get your podcasts.

• 25:04Speaker 07

  Cash Flow Crunch, OnDeck's small business line of credit, gives your business immediate access to funds up to $200,000 right when you need it. Cover seasonal dips, manage payroll, restock inventory, or tackle unexpected expenses without missing a beat. With flexible draws, transparent pricing, and control over repayment, get funded quickly and confidently. Apply today at ondeck.com. Funds could be available as soon as tomorrow. Depending on certain loan attributes, your business loan may be issued by OnDeck or Celtic Bank. OnDeck does not lend in North Dakota. All loans and amounts subject to lender approval.

• 25:34Speaker 08

  Hey, it's Covino and Rich Davis from Covino and Rich. Buy smart, drive for less, and trade for more. That's Toyota Ford ability. And it starts with a great deal on an off-road, ready Tacoma or half-ton Tundra, two of Toyota's most capable and longest-lasting trucks. Combining power for work... Tech for adventures and style in between. Built on reputation for quality and reliability. Toyota trucks are known for holding their value, which can mean big savings when it's time for your next Toyota. So get a great deal today and great value tomorrow. Shop toyota.com for more. Toyota, let's go places.

• 26:20Daniel Whiteson?

  All right, we are back and we are talking about a very intimate topic today. We're talking about the incredible community of folks that live off of you, that you are supporting, you're parasites and the parasites of everybody else on earth. We're digging deep into the history to understand how often this happens, how it happens, why it happens and what is the future of parasitism? So let's keep digging into the past. Kelly, tell us about like how these things become parasites. How does the species decide from being a maker to becoming a taker?

• 26:52Kelly Weinersmith?

  I love that phrasing. And the answer is really like, we don't have a great handle on this. So, you know, we talked about how this transition has happened probably more than 223 times. And there's this long running belief in the community that what usually happens is that an organism starts specializing on dead stuff. So you go from a decomposer to a parasite. And the idea is you get good at living off of flesh when it's dead. And that sort of lowers the threshold to becoming a parasite and living on that thing and taking its energy while it's still alive.

• 27:27Daniel Whiteson?

  So first you identify like, hey, these corpses are rich in nutrients. I might as well eat them. And then you start eating the living versions of them?

• 27:35Kelly Weinersmith?

  Yeah. And so my friend Dan Metz and I wrote a paper. He was leading this paper. I was just on the support team. But we wanted to find like the papers that showed this, because this is a thing that you can see found in the literature for like 100 years or more. But when you look into the literature, it actually hasn't been tested that often. So I think a lot of us have this gut feeling that, you know, being a decomposer is the step before becoming a parasite. But folks really haven't done the nice kind of analyses you'd need, where you'd need a tree of life. You'd need to know who the free living organisms and the parasites are. And you'd need to know what that free living organism was doing before the transition to parasitism. And then look to see if certain kinds of free living organisms were more likely to transition to parasites.

• 28:19Kelly Weinersmith?

  And you need some control groups too. And that requires a lot of natural history data. And so you and I have talked in the past about, you know, the value of taxonomy and the value of going out and collecting information. And, and I think it's critical because a lot of times we'll want to do these sorts of analyses and then you'll get your tree of life together and you'll be like, oh, we have no idea what any of these species are doing in the wild. And so you can't ask these questions that really help us understand, you know, the paths that life take. You need that natural history data.

• 28:49Daniel Whiteson?

  And you always need data, right? Especially to check your intuitions.

• 28:52Kelly Weinersmith?

  Yeah.

• 28:53Daniel Whiteson?

  Because, you know, science is a story and we're putting together a history of what happened. And when we don't know, we're inclined to like fill in with our intuition and say, well, here's an idea, maybe this is reasonable. And if it sounds natural to us, we accept it. We're like, okay, yeah, I believe that.

• 29:07Kelly Weinersmith?

  Yeah.

• 29:07Daniel Whiteson?

  But sometimes the universe is not intuitive. So you always got to go out there and check, especially when you're telling a reasonable sounding story that doesn't have any actual data to support it. So more science, people, right?

• 29:19Kelly Weinersmith?

  So much more science. Yes, so much more science. Okay, so we were talking a little bit earlier about why you would want to try to create boxes to describe what parasites are doing, what different animals are doing. And I was arguing that you need those boxes so that you can create models to help understand what's happening. And there's a couple of different folks who have come up with categories that they think keep popping up as strategies that parasites take. And I saw a quote in one of these papers that made me think, oh, man, this is for Daniel.

• 29:48Daniel Whiteson?

  Uh oh.

• 29:49Kelly Weinersmith?

  So here it is. This is from Poulon 2011. It seems safe to speculate that if life exists on other planets, as long as alien ecosystems show some basic similarities to ours, then parasitism will not only have evolved, but alien parasites would be using exploitation strategies very close to the ones defined here.

• 30:10Daniel Whiteson?

  Wow, parasites in the universe.

• 30:16Kelly Weinersmith?

  So he was really going out on a limb here. Very strongly worded. He believes these categories explained like truths about paths taken by life.

• 30:25Daniel Whiteson?

  I think it's fascinating when scientists do that, when they find something here, they understand it, and then they say, this must be universal. We found it here and therefore it's everywhere. It seems like it could be the only way. And that's so often just reveals like a lack of the broader context. Like you're within a certain set of box of ways of thinking about the universe and it's hard to imagine outside that box. Doesn't mean that outside the box doesn't exist. And like, as I was just saying, like, this is why we gotta go and find alien parasites and blow earthling parasitologists minds about ways that you can suck on other people. Right? There may be even more intimate ways to be a parasite we never even imagined.

• 31:03Kelly Weinersmith?

  Totally true.

• 31:04Daniel Whiteson?

  As you know, and that's why I wrote this whole book about how aliens might do science, trying to think outside the box.

• 31:10Kelly Weinersmith?

  Daniel, what is that book called?

• 31:12Daniel Whiteson?

  It's called Do Aliens Speak Physics? And it's for sale in November. Check it out.

• 31:16Kelly Weinersmith?

  At all fine bookstores. Yeah, no, it is a fantastic book. I got to read it.

• 31:20Daniel Whiteson?

  So I love that this parasitologist is thinking about aliens, but I'm a little skeptical that our earthly categories of parasites are the only ones in the universe. But anyway, walk us through the kinds of parasites we have found here on Earth. And everybody out there, if you're eating dinner, maybe finish up before you dig into all of these intimate details.

• 31:40Kelly Weinersmith?

  Okay. So one of the exciting things about these strategies is that organisms from very different locations on the tree of life seem to have ended up with very similar strategies, which suggests that there's something critical about these boxes that we're creating.

• 31:55Daniel Whiteson?

  Yeah.

• 31:56Kelly Weinersmith?

  So one of the strategies, which we've already talked about, is parasitoids. So the idea here is that you infect one host species, you use all of its energy, you have to kill it as part of your life cycle. And so we get parasitic wasps that do this. We get nematomorphs. So these are sort of nematode looking things that live in cricket. So have you ever seen that video of a cricket that jumps into a pool and a worm that's like 10 times the length of the cricket, maybe even more glides out of its back end?

• 32:25Daniel Whiteson?

  Mm hmm. Nightmare fuel, yes.

• 32:28Kelly Weinersmith?

  Absolute nightmare fuel.

• 32:29Daniel Whiteson?

  There's one with a praying mantis also, I think.

• 32:31Kelly Weinersmith?

  Yeah, yeah, yeah, yeah. So sometimes those animals survive, actually, after they jump into the water, which blows my mind, because you would think something that big comes out of you, you're a goner.

• 32:40Daniel Whiteson?

  Yeah.

• 32:42Daniel Whiteson?

  I think that some mornings, yes.

• 32:44Kelly Weinersmith?

  Oh, God.

• 32:48Daniel Whiteson?

  There's an intimate detail for everybody.

• 32:50Kelly Weinersmith?

  That's right. Intimate. I hope not durable. I hope we can all forget that.

• 32:55Kelly Weinersmith?

  Okay, so, so you get those like wormy things that eat almost everything inside of the organism. And it's kind of amazing because they've managed to take everything from the organism without killing it. So they're able to like, avoid the critical organs, but all the like fat has been slurped out. Anything that's not absolutely critical has been slurped out and turned into parasite. And those zombie ants that you see with the cordyceps fungus, they also are exhibiting a parasitoid strategy. They kill the ant and then they use all of that energy to make their own babies.

• 33:25Daniel Whiteson?

  So explain to me the word here, parasitoid, because as a non-expert, I hear that and I think that's sort of like a quasi parasite or a semi parasite or something. Oid makes me think like, not quite. What does the word mean, parasitoid?

• 33:40Kelly Weinersmith?

  This is a great question. I think the original phrase came from a German scientist. And that doesn't necessarily mean that like their prefixes and suffixes meant something different. You're right. I'm looking up Merriam-Webster and the first definition of parasitoid is resembling a parasite, which must be the oid thing.

• 33:59Daniel Whiteson?

  The way that like our jokes resemble humor, but aren't always right on the money. You know, it's humoroid.

• 34:04Kelly Weinersmith?

  That's right. That's right. We're humoroid kind of podcast, which sounds maybe too close to hemorrhoid. But so.

• 34:12Daniel Whiteson?

  A lot of intimate jokes today.

• 34:13Kelly Weinersmith?

  Yes, right. So many. My guess would be, and I, this is total spitball. Okay, so there are no parasitoids that infect humans. And so I think that when we think of parasites, we think of things that are like living in your guts. Or, you know, like we think of the kind of parasites that we have. And so it's possible that when parasitoid was first named, they were like, oh, like it's living in another thing. We're familiar with that, but then it like kills them and bursts out of them. And it's, this is something different. So let's call it parasitoid. And I'm totally spitballing. You have asked me yet another question. I don't know the answer to, but I'm gonna double down on my answer.

• 34:52Daniel Whiteson?

  All right. So these guys don't live in humans. They infect their host, slurp up all the crucial bits and then eventually kill them.

• 35:00Kelly Weinersmith?

  Yep. That's a strategy.

• 35:02Daniel Whiteson?

  All right. And so if that wasn't gross enough for you, let's hear about the next category, which I shiver to even say parasitic castrators.

• 35:11Kelly Weinersmith?

  Yes. Lovely. So they, uh, they don't kill the hosts, but they do reduce their evolutionary fitness to zero. So essentially they make it so that that organism will never be able to pass down its genes again. It won't be able to have any more of its babies.

• 35:27Daniel Whiteson?

  Oh, sad.

• 35:27Kelly Weinersmith?

  But now the parasites get to live.

• 35:31Daniel Whiteson?

  Cute little parasite babies.

• 35:33Kelly Weinersmith?

  You know, the parasite I studied for my PhD has these two little eye spots and it has like a little suckery kind of mouth that opens and closes. And by the end of my very long PhD, it took a really long time to finish, I kind of thought that they were cute. So I am capable of thinking some parasites are cute.

• 35:50Daniel Whiteson?

  They've infected your brain. See, they're working their magic on you.

• 35:54Kelly Weinersmith?

  That's right. That's right.

• 35:55Daniel Whiteson?

  So tell us about what these guys do.

• 35:57Kelly Weinersmith?

  All right. So at the top of the show, we talked about those snails where a bunch of the biomass of those snails is actually going towards the production of parasite babies. That's an example of castration. All of the energy that would have gone towards making snail babies is now making parasite babies. And those snails can live for like, I think it's like a decade after getting infected. And sometimes when the tide comes in on a warm day, they can release up to 2,000 of those parasites into the water column. And so we think of them as essentially like extended versions of parasites at that point. They're not working towards their own evolutionary goals anymore. Also, side note, the parasites that live in the snails have social behaviors. Like, you know how ant communities have different jobs for the different ants and the ants have different shapes?

• 36:42Daniel Whiteson?

  Yeah.

• 36:43Kelly Weinersmith?

  You've got like a million mile stare right now. Is this too much?

• 36:47Daniel Whiteson?

  No, I'm thinking about ants.

• 36:48Kelly Weinersmith?

  Oh, all right. Okay.

• 36:49Daniel Whiteson?

  I was thinking about that time they poured aluminum into an ant farm. I was trying to remember like the shape of it.

• 36:53Kelly Weinersmith?

  That's a mean but informative way of getting that information. Okay, so ants have individuals who have different jobs and they have different shapes. And they have some individuals who never have their own offspring. Their job is just to support the colony. The same thing is happening inside of these snails. So there are attacker morphs that are essentially just like giant mouths that go around. And when a parasite tries to invade the snail, because sometimes a new parasite species will come in, invade a snail that already has parasites living in there. And it could kick out the parasites that are living in there and then take over the gonad.

• 37:31Daniel Whiteson?

  So it's like parasite versus parasite battle inside the snail?

• 37:34Kelly Weinersmith?

  Yes. Yes. And some kinds of tramehtode parasites have essentially these mouths that never reproduce on their own. Their whole job is to just patrol the snail. And if a parasite comes in, they go and they suck a hole into the side of the tramehtode and like suck out the insides and kill it that way.

• 37:52Daniel Whiteson?

  Wow, this is like gang violence. This is our territory.

• 37:55Kelly Weinersmith?

  Yes. Yeah, they have like more interesting social lives than I do. They're fascinating.

• 38:00Daniel Whiteson?

  How high a bar is that, Kelly? Tell me.

• 38:02Kelly Weinersmith?

  Oh, my God, it's like, it's like on the ground. You don't have to lift your foot up much at all. I don't go out much. But anyway, okay. Parasitic castrators, tramehtodes. Let's do one other example. There are barnacles. And so like, if you've been to the ocean, you've probably seen barnacles. There are barnacles that stick to the sides of like whales and turtles. There are also barnacles and isopods. These are these little crustacean things that are both able to castrate crustaceans like crabs. So the barnacle in particular does this very interesting thing where it has a sack where female crabs would usually have their babies. And it sets up shop there and females usually will use their claws. So this is on like the underside of what you'd think of as like the crab's belly.

• 38:45Kelly Weinersmith?

  They use their claws to like pass water over it to make sure that their eggs stay oxygenated. They will do that when the barn- Barnacles down there to keep the barnacle oxygenated.

• 38:54Daniel Whiteson?

  Wow.

• 38:55Kelly Weinersmith?

  And males will start doing that, too. So it looks like not only do they castrate male and female crabs, but they get the males to start acting like females to take care of the barnacles. We call this feminization and it's kind of poorly understood. But anyway, so barnacles are castrating crabs. Trematodes are castrating snails and there's insects castrating other insects. This is another very common strategy.

• 39:21Daniel Whiteson?

  You just said the word castrating way too many times for my comfort. Let's move on.

• 39:27Kelly Weinersmith?

  There's a total of six categories, but rather than making you all sit through all six, let's pick one more to give you a flavor of the amazing strategies that parasites have taken on.

• 39:39Daniel Whiteson?

  Let's do vector transmitted parasites because that sounds physicsy. Vectors.

• 39:43Kelly Weinersmith?

  Ooh, all right. Well, you can try to connect this with physics at the end. We'll see. But so what we mean by vector transmitted is that you have one animal that is bringing a parasite to another animal and essentially injecting it into that other animal. Probably the most famous vector transmitted parasite is malaria. So mosquitoes will take a blood meal from a person who has malaria. They suck the parasite up. The parasite does some developing inside of the mosquito and eventually goes to live in the mosquito's salivary glands. And then when a mosquito goes to take a blood meal from another human who isn't infected yet, the parasite ends up in that person's blood and then that person gets infected and the cycle starts again.

• 40:25Daniel Whiteson?

  I think it's fascinating you call this a blood meal. It makes it sound so wholesome, you know, like it's just going home to have dinner after a long day of work, you know, it deserves it, but like this thing is sucking my blood.

• 40:36Kelly Weinersmith?

  You know, I've read stories from the early 1900s in the Journal of Parasitology, where they sort of mentioned in an offhanded way that like the mosquitoes and the lice in the colonies were fed blood meals by volunteers, which means somebody was like sticking their arms in the mosquito cage. Anna Phillips was telling us in the leech episode that now you can like fill medical gloves up with blood from, you know, a hospital or something and feed them that way. But I love the faces you make when we talk about parasites. It's so entertaining for me, but, but my, you know, Mike, if I could tell you my big goal here, I feel like when you start learning about parasites, you can't get over the disgust hump.

• 41:15Daniel Whiteson?

  Yeah.

• 41:15Kelly Weinersmith?

  It's just like so upsetting, but the more you learn about it. This doesn't happen for everybody, but maybe you'll get there. I feel like the more you learn about it, the more kind of amazing it is that evolution has resulted in this super complicated strategy. Like, I mean, imagine being able to live in environments as different as a mosquito and a human, like to conquer both of those hosts in a way that like human ingenuity has just not been able to outsmart. There's good evidence that malaria is able to essentially like change the proteins on the outside so that our immune system can't recognize it. Like, we start to get a handle on it and then it shows up again in like a whole different outfit and our body's like, where did the malaria go? But it's still there and it's like racing us.

• 41:59Kelly Weinersmith?

  And, you know, we have, we've created all of these vaccines that keep, you know, not quite keeping up. These are kind of incredible creatures. You can hate them and I wish there was no malaria because I don't want to see any child with malaria ever again. But you kind of have to respect sort of the amazing strategies that they've been able to come up with, with the help of natural selection.

• 42:19Daniel Whiteson?

  Yeah, I totally appreciate you leaning into the wonders of the universe. And, you know, that's our whole brand and the universe is extraordinary and these things are incredible. And I guess I'll try to think about that next time I see a mosquito biting me. I'll be like, wow, think about all the amazing science going into this itch that I'm going to be suffering for the next three days.

• 42:38Kelly Weinersmith?

  Well, that's a micro predator, Daniel. I'm not interested.

• 42:45Kelly Weinersmith?

  Just kidding.

• 42:45Daniel Whiteson?

  All right, so let's take another break and when we come back, let's hear some good news about how parasites can go extinct.

• 43:01Speaker 00

  Hey, I'm Niall Rogers, producer, songwriter, guitarist and co-founder of the group Sheik. A great song has a way of defining a moment, a moment of joy, heartbreak, or anything in between.

• 43:17Speaker 00

  This fall, I'll be driving across the country, dropping in on some of the coolest, most fascinating artists working today. We'll go deep into their lives and careers and hear what it was like before the moment that made them. From hitmakers like Miguel...

• 43:34Speaker 05

  That last year, finishing that record was the hardest experience of my life. Regardless of how everyone else buys into this, I believe in this and I'm gonna push.

• 43:46Speaker 00

  To rising stars like Alex Warren.

• 43:49Speaker 06

  You know, a song is a story and the verse is setting the scene. And for me at least, it's allowing me to be personal and vulnerable with the audience, whether it's about my wife and I'm being vulnerable about her, or it's about, you know, my parents and I'm being vulnerable to them. And it's almost like a cinematic piece in a way where each song tells that beautiful story.

• 44:07Speaker 00

  It's gonna be one hell of a trip. Experience Before the Moment, a Lincoln original series on the iHeartRadio app, YouTube, or wherever you get your podcasts.

• 44:20Speaker 07

  OnDeck is built to back small businesses like yours. Whether you're buying equipment, expanding your team, or bridging cash flow gaps, OnDeck's loans up to $400,000 help make it happen fast. Rated A+ by the Better Business Bureau and earning thousands of five-star TrustPilot reviews, OnDeck delivers funding you can count on. Apply in minutes at ondeck.com. Depending on certain loan attributes, your business loan may be issued by OnDeck or Celtic Bank. OnDeck does not lend in North Dakota. All loans and amounts subject to lender approval.

• 44:49Speaker 09

  This is Colin Cowherd from the Colin Cowherd Podcast. Buy smart, drive for less, and trade for more. That's Toyota Ford ability. All starts with a great deal on an off-road ready Tacoma or a half-ton Tundra, two of Toyota's most capable and longest-lasting trucks. Built on a reputation for quality and reliability, Toyota trucks are known for holding their value, which could mean big savings when it's time for your next Toyota. For a great deal today to a great value tomorrow. Shoptoyota.com. Toyota, let's go places.

• 45:32Daniel Whiteson?

  Okay, we're back and Kelly is grossing me out with intimate details of how parasites infect their hosts, castrate them, and pass on diseases. Yay, we're all supposed to think.

• 45:44Daniel Whiteson?

  So let's turn to some good news. We heard about how parasites have evolved many, many times in their record. Do parasites also go extinct? Do we have evidence for parasites disappearing? How does that happen?

• 45:55Kelly Weinersmith?

  They do go extinct. And so, you know, we talked about how parasitism as a strategy popped up, you know, over 200 times in the tree of life. It appears it's also been lost a few times.

• 46:05Daniel Whiteson?

  Oh.

• 46:06Kelly Weinersmith?

  I know. So sometimes it's hard to get a handle on those losses because if an animal loses it and then doesn't end up in the fossil record, it can just be kind of complicated. But yeah, parasites go extinct. And in fact, some parasites are more susceptible to extinction than their hosts. And I know that's not sad for you, but we're losing diversity. So one parasite strategy that we didn't talk about in the last section are trophically transmitted parasites.

• 46:31Daniel Whiteson?

  What does trophic mean?

• 46:33Kelly Weinersmith?

  So like, think about trophic levels in a food web. And so trophic transmission is essentially a predator consumes an animal that was infected and the parasite gets into the predator. So the trophically transmitted system I studied for my PhD was California killifish. They're these small fish in Southern California estuaries and they get eaten by predatory birds like egrets. And the parasite goes from living on top of the fish's brain to living in the egret's gut.

• 47:00Daniel Whiteson?

  I wouldn't want to live in either of those places. I mean, you're in Southern California. There's lots of beautiful places to live. Why would you choose a fish brain? But hey, you do you.

• 47:08Kelly Weinersmith?

  I mean, I'd rather live in Virginia, but it's all right. So everyone knew that was coming. But this parasite actually has an even more complicated life cycle. So parasites can have different strategies depending on where they are in the life cycle. So there you've got trophic transmission from fish to bird. The parasites then find love in the bird's gut and they make eggs that pass with the bird species into the salt marsh, where they're accidentally consumed by those snails that we talked about that get castrated. And then.

• 47:39Daniel Whiteson?

  This is such a horror movie. This whole thing is a horror.

• 47:42Kelly Weinersmith?

  I, I love it. I eat it up. My mom loved horror movies. Maybe that's what set me up for all of this.

• 47:47Daniel Whiteson?

  It's her fault. Yes.

• 47:48Kelly Weinersmith?

  Yeah. Yeah. So anyway, in order for this parasite, this tree toad parasite to complete its life cycle, you need to have the fish, you need to have the birds and you need to have the snail. If you lose any of those hosts in the cycle, or any of them falls to numbers that are small enough where it's hard for the parasite to find them, then that animal can go extinct. And so parasites have all of these extra requirements that depend on what's happening with their hosts. And so in some cases, we think that parasites might be more susceptible to extinction than a lot of free living animals, because there's so many different components that need to work well for the parasite to complete the life cycle.

• 48:23Daniel Whiteson?

  It's kind of a fragile system.

• 48:25Kelly Weinersmith?

  A bit of a fragile system. And so parasites can be used as what we call ecological indicators. So if you go to an estuary and you find a lot of parasites, that probably means a lot of host species are there and they're there in pretty high numbers. And so a lot of parasites can be indicative of a healthy ecosystem, which I think is counterintuitive to some people, but makes perfect sense to my parasitologist heart.

• 48:47Daniel Whiteson?

  Like if you go to a new neighborhood and you discover there's lots of gangs there, you're like, oh, wow, this must have a thriving economy for the gangs to be siphoning money off of.

• 48:59Kelly Weinersmith?

  Wow. Where do I go with that? I mean, I guess, I guess it means that the police aren't really doing their job, which maybe means there's immune systems and hosts that are compromised, perhaps by pollutants, but maybe we're pulling this analogy a little bit too tight. So let's, let's move on.

• 49:14Daniel Whiteson?

  All right. So they do go extinct and maybe even more often than their hosts, because they rely on like a complex system and getting passed from one to the other. But then they're everywhere and they're very common and they've evolved many, many times. How do we understand that all together?

• 49:27Kelly Weinersmith?

  I mean, there's a lot of hosts also, and you can be losing a lot of hosts, but you still look around and there's a lot of birds outside and stuff. It's just, you know, hard to keep track of all of this stuff. But if I can just for one second, try to convince you that you should care about parasites going extinct and I won't.

• 49:41Daniel Whiteson?

  You can try.

• 49:44Kelly Weinersmith?

  So parasites are important parts of ecosystems. So we mentioned that those snails that are castrated can release up to 2,000 parasites into the water. Those parasites are free swimming bags of energy that get eaten by a lot of organisms. So they provide food to the system. Also, you know, we talked about those crickets that have those long worms in them and the crickets are forced into jumping into the river and then the worms, the nematomorphs come out the back of them. Those crickets are terrestrial organisms that jump into creeks. And in Japan, there's this endangered trout where a lot of the food that it gets comes from crickets that are jumping into the creek that they wouldn't have access to otherwise. And so these parasites often make lots of food available to other animals or make that

• 50:28Kelly Weinersmith?

  food easier to catch. They play important roles in ecosystems that we don't always understand very well. And if you lose them, that could be bad in some cases.

• 50:37Daniel Whiteson?

  Yeah, I totally appreciate that. And it's sort of curious to me, like, why do parasites have this ick factor that like predators don't, you know, like a jaguar, it's still like finding another critter and taking it and eating its resources. Why is it somehow grosser to be like living inside as you consume somebody? For some reason, it is definitely grosser, though like morally, it's not any better or worse. So I don't know, there's just some sort of like human ick factor there. And maybe when we meet the aliens, they'll be like, yay, parasites. And Kelly will be like, I found my people.

• 51:08Kelly Weinersmith?

  That's right. That's right. I understand you guys. You know, I agree, there's definitely a judgment call. People think of parasites as like these super degenerate organisms. They have fewer sort of abilities to like sense the exterior environment, but they do manage to thrive in really complicated systems where they're being attacked. And yeah, anyway, people do tend to find parasites to be much grosser than lions. I get that some people could look at a lion and be like, that looks much nicer than a tapeworm. But if you know what to look for in a tapeworm, some of them are quite beautiful. I've got my tapeworm picture right here.

• 51:41Daniel Whiteson?

  Oh, wow. Do you know anybody who like has a coat made out of tapeworms or something like that, you know, tapeworms? Maybe we need a fashion industry, you know, to replace fur with parasites somehow.

• 51:52Kelly Weinersmith?

  I think that any parasite themed fashion that is available is found at the American Society of Parasitologists Student Travel Auction. We bring it in and we all pay way too much for it to try to pay for student travel so that they can come to our conferences. But anyway, we're getting off track. We've got one more question from the listener and the question is, do parasites go extinct with hosts? So there's a number of different things that can happen when hosts go extinct or when hosts sort of split into multiple species. And so, yes, often when a host goes extinct, the parasite can go extinct also. If the parasite was infecting lots of other host species, then maybe it will be fine. But we already talked about complex life cycles where if you lose one host in the system, you can lose the parasite too. But there's also examples where you get these

• 52:37Kelly Weinersmith?

  splits in the tree of life. And as you get those splits in the hosts, the parasites also split into new species over time because you now get like separations of parasite populations. And over enough time, they become their own species. And so there's a sort of famous example where pelicans, as they sort of speciated over time, their lice speciated with them. So pelicans, if you like create the tree of life for pelicans and then you create the tree of life for their lice, you could almost lay them on top of each other. They follow very similar paths. But you can also get cases where the parasites don't seem to be tracking what's happening with their hosts. So for example, guppies, they're these tiny little fish. They get infected by monogenians. These are these external parasites we were

• 53:21Kelly Weinersmith?

  talking about that have the hooks and they hold on to the outside of the fish. They don't seem to be following the evolutionary trajectory of their hosts. And right now, we don't have a really good framework for when you should expect the tree of life for parasites and species to essentially mirror one another and when you shouldn't. But we get all of these different options because nature is amazing and it depends. But we don't always know on what.

• 53:45Daniel Whiteson?

  And the incredible variety of strategies we see helps us explore like the space of possibilities and maybe even helps us think outside the box to like what might be happening elsewhere in the universe.

• 53:55Kelly Weinersmith?

  Absolutely. Yes, I would love to find a planet that was rich with free living hosts and dissect a bunch of them to see if they have parasites. But

• 54:07Kelly Weinersmith?

  Only if it was humane and ethical.

• 54:09Daniel Whiteson?

  All right, aliens, if you're listening, come on by. Kelly wants to look inside you.

• 54:14Kelly Weinersmith?

  Kelly wants to say hi.

• 54:15Daniel Whiteson?

  In an intimate sort of way.

• 54:17Kelly Weinersmith?

  All right, well, thank you so much to Zach for sending in his questions. Let's see if Zach feels like we've answered the many questions he posed about the evolution of parasitism.

• 54:26Speaker 04

  Hey, there, Extraordinary's. Thank you so much for this incredible primer on parasites and their history. I feel like I got way more than I bargained for, which is awesome. You definitely answered my essential question that, yes, T-Rex probably had tapeworms or something like it, though we can't be totally sure. I also really enjoyed hearing about all the different categories of parasite strategies and really appreciated hearing that there are no parasitoids or castrating parasites for humans, so I can sleep a little better at night. I was also definitely convinced that parasites have an important role to play in our ecosystems, so I'll try to be a little bit more appreciative and a little less grossed out. I am still a little curious.

• 55:08Speaker 04

  Seems like it's still an open question how something goes from being a free-living organism to being a parasite, even if we can count when it happens. I'm also curious if anything has ever gone from being a parasite back to being a free-living organism. In any case, you guys rock. Thank you again so much.

• 55:26Kelly Weinersmith?

  All right. Thank you so much to Zach for all of his many questions. If you would like to send us questions, we would love to hear from you. Send them to [email protected]. And I hope that you enjoy your meal, or you ate it before we began this conversation.

• 55:40Daniel Whiteson?

  And before you heard Kelly say the word "castrate" uncountable number of times.

• 55:44Kelly Weinersmith?

  I don't think there's a limit on how many times you can say "castrate." It's a great word.

• 55:48Daniel Whiteson?

  All right, everyone. Thanks for joining us on this tour of one more aspect of our extraordinary universe.

• 56:01Kelly Weinersmith?

  Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We would love to hear from you.

• 56:07Daniel Whiteson?

  We really would. We want to know what questions you have about this extraordinary universe.

• 56:13Kelly Weinersmith?

  We want to know your thoughts on recent shows, suggestions for future shows. If you contact us, we will get back to you.

• 56:19Daniel Whiteson?

  We really mean it. We answer every message. Email us at [email protected].

• 56:26Kelly Weinersmith?

  Or you can find us on social media. We have accounts on X, Instagram, Blue Sky. And on all of those platforms, you can find us at D and K Universe.

• 56:35Daniel Whiteson?

  Don't be shy. Write to us.

• 56:39Speaker 10

  With ChatGPT, you can do more than get answers. You can get things done. Whether you're leading a big project, planning an elaborate trip, or trying to balance work and life, ChatGPT can help. Give it a goal, plus things like files, notes, or project plans. Develop a trip itinerary with daily updates, or create a prioritized schedule. So you can spend less energy sorting out the details and more on bringing your biggest ideas to life. Get started at chatgpt.com.

• 57:07Speaker 07

  Cash flow crunch? OnDeck's small business line of credit gives your business immediate access to funds up to $200,000 right when you need it. Cover seasonal dips, manage payroll, restock inventory, or tackle unexpected expenses without missing a beat. With flexible draws, transparent pricing, and control over repayment, get funded quickly and confidently. Apply today at ondeck.com. Funds could be available as soon as tomorrow. Depending on certain loan attributes, your business loan may be issued by OnDeck or Celtic Bank. OnDeck does not lend in North Dakota. All loans and amounts subject to lender approval.

• 57:37Speaker 11

  Hey, it's Lunchbox from the Bobby Bones Show. Buy smart, drive for less, and trade for more. That's Toyota affordability, and it starts with a great deal on an all-wheel-drive Camry, Corolla Cross, or a Corolla sedan with the latest features in tech. Or test drive a spacious Grand Highlander or an adventure-ready RAV4. And with so many hybrid models available, you can enjoy longer trips without all the stops. While Toyota's legendary resale value means you could get more at trade-in. Get a deal today and great value tomorrow. Shop toyota.com for deals and details. Toyota, let's go places.

• 58:15Speaker 12

  Breathe in and reset with Lincoln Rejuvenate. An available multisensory feature in the 2027 Lincoln Navigator SUV. Experience the luxurious massage, visuals, and sense to help you relax in the driver's seat. It's your time for a reset. Visit Lincoln.com to learn more. Lincoln Rejuvenate does not operate unless the vehicle is in park. When the vehicle is off or if any doors open, do not use the feature in a closed garage or in other enclosed areas. See owner's manual for important operating instructions. Lincoln and Navigator are trademarks of Ford or its affiliates. All rights reserved.

• 58:45Speaker 07

  This is an iHeart Podcast. Guaranteed Human.