This Podcast Will Kill You - Ep 33 Chytrid: The Silent Forest

Episode Date: August 6, 2019

Walking through a forest at dusk, you’ve likely heard the croaks and groans of frogs and toads forming a chorus in the damp undergrowth. But what if the forest were suddenly, inexplicably, silent? In the 1980s scientists started noticing the forests becoming quieter as amphibian populations around the globe began to decline -- rapidly. Today we are joined by Dr. Taegan McMahon from the University of Tampa to discuss our first ever wildlife disease: chytridiomycosis. Chytrid fungus, or Bd for short, has wreaked havoc on amphibian populations for the last several decades, and researchers are still trying to find a way to stop it.  For more information on Chytrid and Taegan’s research, follow her lab on instagram @mcmahon_lab. For more awesome parasitology pics, check out @uoftampa_parasitology, and for gorgeous biology art, Taegan does watercolors @wandering.ecologist!   See omnystudio.com/listener for privacy information.

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Val, bad fun. Outdo it with Intuit QuickBooks. Feature availability varies by product. I've always loved frogs, toes, salamanders, all amphibians. And my mother also did. She would bring us out. We didn't really have TV or anything along those lines. We spent our entire childhood running around in the woods, which is awesome.

and she would take us out every spring to look at amphibian populations in this local state park called Haley Farm. And so we would go out and we knew where to look for the eggs. There were all these little small ponds. And we would go out every week and we'd watch the eggs develop these tab holes. And then those tab holes developed into Metamorx, the little baby frogs, and then those would grow up. And we did this my entire childhood. When I became a babysitter, that was the activity I took all the kids on. We'd all go out to Haley Farm and look for these amphibians.

And then I taught special needs camps for years, and we would do the same thing to bring the kids out and we'd look for the eggs. Now as an adult, when I go back, the amphibians are not there. You'll see periodically adults, but we just don't see the babies. We don't see the eggs. And so they're probably there. They're just deeper in the pond or further out into the woods, but the populations are not what they used to be when I was younger.

And it's really sad because there's something about going out into the environment and finding a frog in the woods that really fosters a love for that place. Like Haley Farm is one of those really special places for me, and I think for a lot of people. And now that we can't find the eggs, you know, kids aren't growing up in those state parks finding frogs. They're not finding the eggs. They're not trying to catch frogs. This is a huge part of my childhood growing up. But I think it was a huge part of what made me become a conservation disease ecologist because I loved that when I was younger.

And it's just not a thing anymore for kids. Hi, I'm Erin Welsh. And I'm Aaron Alman Updike. And this is, this podcast will kill you. Today we're talking about. Kittred. Kittred. And you just heard a fabulous firsthand account of some of the terrible effects.

that Kitred has had on amphibian communities by our friend Tegan McMahon, Dr. Tagan McMahon. I should introduce her properly. And you will hear more from her later in the episode because she was so kind as to share some of her expert experience and knowledge on the subject. So we didn't have to do as much work. Yes. No, not kidding, though. At least I didn't have to.

Only kind of kidding. But before we get there, we have one very important thing to do. We do. And that means it's quarantine time. What are we drinking this week? Today we're drinking simply croaked. We shouldn't be laughing at this. It's not funny.

It's not funny. Pony. I'm tickled at the name. What's in croaked? There is mango puree, a bit of lime juice, some bubbly fizz water, and rum, of course. Delicious. Rona-boilo, if you can grab it. And the key ingredient in this particular beverage is just a few sprinkles of chia seeds.

To look like frog eggs. You guys. I love it. We'll post the full recipe for this. quarantini as well as our non-alcoholic placebo-rita on our website and all of our social media channels so you can find them there. Do we have any business, Erin? I don't think so.

We have merch. Go. We have merch. Go look at it. You can find our merch at our website. This Podcast Will Kill You.com by clicking on merch. And we've got T-shirts and mugs and pins and the most important of all. Soap.

So it smells so good. I have a bar in my bathroom right now. And every time that I walk in there, I'm like, what smells so good? And it's the soap every single time, legitimately. It makes the whole bathroom smell good. I didn't know soap could do that. Packaging's incredible. Okay. Okay. So enough of that. All right. Kittred. Kittred. Hit me with it. I'll hit you with it in just a minute. Okay. So listen, Kitrid, first off, is a fungus. Our first fungus. Our first fungus. We like briefly talked about fungi on the Biology of Superheroes podcast. Right? That's right. We talked about corticeps. Corticeps. Okay, but this is our first foray into the fungi. Yay. So let's talk about this fungus. It's self first. The fungus that causes the disease known as chitriomycosis in amphibians is called batry coquitrium dendrobatitis. I'm glad that you attempted that because I looked it up

and I wrote out a phonetic spelling for myself in my notes. Oh no, can you quickly send that over to me because I need to do it later. Okay. Batre coquitrium, dendrobatitis. Okay. We'll cross that bridge when we get to it. You could call it BD.

And I do. Okay. And I really hope that this isn't stepping on your history toes too much, Aaron, but I texted you about this because I got so excited. And it blew my mind so much because we just did Gerardia, which I said correctly. No, you didn't. Giardia, I did.

And it blew my mind in that episode that that parasite wasn't fully classified until like the late 80s, right? Mm-hmm. B-D wasn't described as a species until 1999. Yeah. What? Yeah. Oh, my gosh. I did not know that at all.

It was thrilling information. Yeah. And there's another species that infects salamanders. Bacherichotryam salmandrivoreans. That was described in 2013. Uh-huh. Oh, my gosh. The history is still being written, that's for sure.

Oh, big time. Okay, so this is a fungus. We'll call it BD or probably a lot of times through this episode. We might just call it Kittred. but I do want to point out that there's a lot of other fungi in the group known as chitridiomycoda. So even though we'll be probably bad biologists and call it chitrid, I might slip up and call it chitrid.

There are a number of different other chitrid fungi, many of which are free living and happily exist in the environment, digesting cellulose and chitin and keratin. Ding, ding, ding. That word's going to come back. Other chitrids are parasitic on plants or algae or other invertebrates. But the one that we're focusing on today is the only, I guess, two species, BD and B-SAL that are known to infect vertebrates. Specifically, amphibians. Okay.

So today we're talking about an amphibian fungus. Fungi have very cool life cycles in general. and chitrid, chitridiomycota fungi are no exception. They have two life stages. The zoospore and the zoosporangium. So the zoospore is like a spore. So it travels through the environment. That's the point of it.

And it happens to have an adorable little flagellum and it can swim. So the zo spore stage swims through water. water. It doesn't go very far. We're talking like a few centimeters, but it does swim. And it responds to chemotactic signals. So it actually can swim directionally towards a host. In this case, an amphibian. When it finds an amphibian, it releases a bunch of proteolytic enzymes. So it releases a bunch of stuff that digests the protein on the skin of the amphibian. And then it burrows its way into the skin of this, let's call it frog. What cues is it using to find the host?

That's a good question that I don't entirely know the answer to. It's a really good question. But they know that, like, it's not just swimming at random. It swims directionally towards the frogs. But I'm not sure what about the frogs. Like, what are they releasing that they're swimming towards? Great question. So once it's at the frog, it burrows its way into the skin, it forms a little cyst,

and then it forms the sessile or the non-motile stage, the zosporangia, underneath the skin of this little frog. That zosporangia will grow and then produce additional zospores, which will burst forth from the skin and swim along their way, and those zospores can either re-infect the same host, in a new spot, or if they're close enough to another frog, they can infect a new host. Tadda. Life cycle complete.

And about how long is this all taking place? Oh, gosh. Well, I know that the incubation period from when the zoospore first infects to when the frog start showing symptoms are between 10 and 18 days. Okay. So my guess is that that's about the time frame that it takes for them to start shedding. And I would assume it's variable depending on frog species and temperature or amphibian species and temperature and et cetera, et cetera. Very variable.

Yeah. Okay. So let's talk about the symptoms of a chytrid chytridaomycosis infection. This is going to make me sad. It's so sad. It hit me in the feels, this one. So you can tell by the way that I described the life cycle that. this fungus, it's pretty much just infecting the skin of these amphibians.

So human listeners might be thinking something along the lines of, how can a simple skin infection be so detrimental to an amphibian? It's just skin. Do you think anyone would say that? Maybe. They would? I don't know. But for anyone who's not familiar with frogs and amphibians, their skin is not just a barrier between the frog and the outside world. It's not for us either. But in frogs, it's an especially important organ. It's part of how frogs breathe. It's part of how they hydrate, how they thermoregulate, how they osmo regulate.

So it's a very critical organ. Okay. So any kind of skin infection in a frog you can assume is going to be bad news bears. And that is very true in Kittred. However, because B.D. Kittred can infect so many different species of amphibians, the symptoms really do vary a lot based on the species and how serious the infection is varies hugely across species. And actually, Tegin will talk a little bit more about that because we don't fully understand why it is that some species seem to handle infection so much better than other species. But we can talk about some of the generalized symptoms that you see in a chitriomycosis infection. First off, what's very interesting is that you don't see a lot of inflammation. So the frogs themselves aren't mounting a big inflammatory response when they get infected with this fungus.

But what you do get is something called hypercarotosis, which means that you're making a whole bunch more keratin, which is kind of the protective protein that we have in our skin as well. It's the toughest outermost layer of skin, which for a frog, because their skin has to be able to interact with the environment so much, this is especially bad because that means that this thick extra-carotinized layer is not going to be as permeable to water or air or electrolytes. That's really interesting. I didn't either. Yeah. And then what you also get very, very commonly is sloughing of the skin. So this skin will just start to sluff off in sheets, which is really sad. You can get ulceration and like multiple cyst formation, but you don't always. The skin sloughing is kind of more common than this ulceration formation.

Often also the skin will become very discolored. So you might have seen classic photos of frogs infected with Chitred that are bright red on their bellies and their legs. So that's really common is for their bellies to become discolored. And it's also very in common, it's very common that they get infected at the highest rates or the most intense infection on their bellies and their legs, like the undersides. which to me kind of makes sense because this is a fungus that's in the environment and in the water specifically. So that's kind of the part of the frog that's probably in contact with water the most and in contact with the soil the most, right? But it can infect any part, any keratinized part of the frog. But does the infection tend to be localized in that way or is it pretty much systemic at a point?

Well, that's an interesting question. So it's not systemic in that it doesn't travel throughout their body. This is a very localized skin infection. The zosporangia can produce like these, I don't know if rhizomes is the proper word, but they can sort of spread out a bit where they infect. But really, they also just produce a lot of spores that auto infect that same host on other parts of the skin. So you end up with very. really high burdens of infection where you have spores infecting all over the skin. But it doesn't travel like through their bloodstream. It doesn't invade their organs, et cetera. And that's, I'm going to talk a little bit more about that in a minute because it's a really interesting part of the story. Yeah. Yeah. So any and all parts of the skin can get infected. And then what you see happening in addition to all these skin changes is that the frogs become very low. lethargic. They stop seeking protection. They stop hiding during the day so you can find them just sitting out and about. They're less responsive to stimuli. So if you try and get them to jump or to do

something, they just kind of don't. They just don't really respond. And they can sit in a very kind of characteristic position where they're sitting out and their hind legs, their jumper legs, are not poised underneath them like a frog ought to be, like ready to bounce at any second. They hang there kind of loose and gangly and they hold them away from their body. Isn't that sad? It's really sad. Just this little loose like wamp-womp of a frog? Well, just no, like, yeah, no willingness to river or ability.

And then they tie. Yeah. Sorry. There's no easy way to say that. So then they die. And what's interesting is that one very common cause of death is actually heart attack. Tiny little froggy heart attack. Is this because they can't regulate water? Oh, look at you, Aaron. You're so smart. What? Yeah. So again, this is an infection. that's not actually invading any organs in general. It can in some cases, but in general, it's just in the outermost layer of this frog's skin. And so we don't fully understand exactly how this disease ends up killing frogs. But what it does seem to do, according to a 2018 paper that I found, is that it causes widespread metabolic imbalance. So the electrolytes of the

frogs get completely messed up because they're not able to osmo-regulate through their skin like they're supposed to. They can't regulate the water and electrolytes moving in and out of their skin. And when that happens, other organs can get messed up. So then other important metabolites that your body would normally produce, like say your liver would normally produce these certain metabolites, the liver can't do that because the other electrolytes are so messed up. Does Does that make sense? Yeah. Mm-hmm.

So while Kittred itself doesn't invade frogs, livers, or hearts, the osmotic deregulation that it causes just by infecting the skin to such a degree ends up affecting processes in their internal organs. And that's what ends up causing death. That makes sense and horrible, sad sense. Horrible and sad. And it's, it was really interesting to sort of do the research on this because it's so recent. Because a lot of times when I'm trying to figure out, you know, what's the pathophysiology of a disease?

I just, I find a paper that's relatively recent, like the last 20 years, and they've got pretty much an answer. But in this one, if you go back just five or 10 years, it's all, here's our hypothesis. Here's the best guess we have. And so it's only from these really, really recent papers, like this 2018 paper, which I will post on our website, where they actually found sort of evidence of this. It's still not entirely clear how this happens, but there is good evidence for this widespread electrolyte imbalance. I would bet that that's also just also a factor of it being a wildlife disease versus a human disease.

Definitely, definitely. Funding research, et cetera, et cetera. And another thing I noticed is that so much of what we study in wildlife diseases compared to human diseases is all population level rather than individual level. So like the disease. process that's happening inside each individual frog is not studied to the same extent as a disease in humans might be, if that makes sense. Right. We lack the case studies in wildlife disease cases, yeah.

Yeah. So that's pretty much the biology. The other thing I did want to say that I think is interesting is that so BD, chytrid, amphibian chitrid, only infects keratinized epithelium. So that means that actually tadpoles aren't infected. So tadpoles actually can survive in areas that have BD. The only part of a tadpole that has keratin is the mouth parts. So that's the only part that BD can potentially infect. But then as soon as a tadpole starts to undergo metamorphosis, as soon as they start to change into adults,

then they've got that keratin, then they can be infected. So even the really early, early frogs, but just not tadpoles specifically. Right. But what's also very interesting is that a lot of free-living chytrid fungus also feeds on keratin. And so it's hypothesized that that's exactly what this fungus is feeding on in the frogs. And it's interesting that it's causing this hyper-carotic response where the frogs, they're not mounting an immune response. They're not coming in and fighting off this infection, but rather they're making more and more keratin, and that's potentially what this fungus is feeding on. So it's like the fungus is creating the optimum environment for itself to survive in this frog.

Right. I mean, it's ingenious. Yeah. Huh. I know. What else is keratin? Tell me more about keratin. So keratin is the protein. It's all of our skin, like any skin that you see, it's all keratin. Your hair is keratin. Your nails are keratin. It's a protein that makes, it's like a very tough outer protein. So our skin as it grows and moves like from the basal layers and then it moves up, it becomes keratinized. So by the time that it reaches our outside environment, it's like completely just mostly keratin. There's not really any cell left. So why amphibians and not other animals? Great question. It's a really good question. I'm sure that it's not. the exact same keratin. There's a lot of different types of keratin. So it might just be that they can infest a very specific form of keratin. That's a really good question, though. Yeah. Interesting.

Yeah. So that's the biology. Oh. That was it. What do you think? That was great. It was so fun to learn about. I knew nothing about Kittred coming into this. I knew nothing except sort of like the broad sweeps of it. Right. Like I knew, it's real bad. It's real bad for frogs and it's causing widespread havoc. And that's literally, and like I've seen pictures of ponds where Kittred has just, you know, all these dead frogs.

That's all that I knew. Yeah. So. Oh, so, Aaron, tell me, how did we get here? What's the history of this thing? Okay. I'll see what I can do. Right after this break.

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that we were used to. Something, many somethings, were missing. And it didn't go unnoticed. Herpetologists across different continents began talking amongst themselves. Where have the frogs gone? Where have the salamanders gone? Where have the toads gone? Where there used to be untold numbers of frogs, toads, salamanders, amphibians,

now there were none. Even stranger were the circumstances of the sudden disappearance. Amphibians were going missing in habitats of all kinds from urban streams to remote highly protected conservation regions. And often there were no bodies to be found. What? Yeah. They just sort of disappeared, which makes sense. Okay.

In other places, the sad carcasses of amphibians piled up, which was in itself maybe even more bizarre, because in places like the tropics, something as small as a frog can be quick. dismantled by ants or dispatched by a bird within a matter of minutes or hours. So the sight of these corpses was maybe even more worrying than their absence. What could be causing such widespread devastation? Climate change, habitat destruction, environmental toxins, and infectious diseases were all the immediate culprits. Finding out what was causing these amphibian die-offs was top priority if there was any hope

of saving even some of the species. Extinction happens, but not often like this. This is probably the largest extinction event that modern humans have been witnessed to so far. Wow. Maybe this is pessimistic of me, but I don't think it'll be the last one we see in our lifetime. You're probably right. Yeah. Let's talk about amphibians.

Okay. What does the word amphibian mean? Oh, good question. Tell me. It comes from the Greek for double life, which is a nod to their close dependence on water and moisture and sort of their transformation over their life cycle. Cool. Many species of amphibians need water to complete their life cycle. Tadpoles swimming around in little ponds, stuff like that.

But that's not the only way that eggs develop into tadpoles. then frogs. So frog eggs, amphibian eggs, don't have a hard shell like that of a bird, so they have to be kept moist or they'll dry out. Frogs can do that by laying them in streams or ponds or temporary pools, but some will make their own little foam nest to lay eggs. Some carry the eggs around on their backs or on their legs, and some carry their eggs in their stomachs, eventually giving birth to little frogs out of their mouths. Oh my God. It's so cute. Or at least they used to Because the two species that did this stomach brooding

When extinct in the 1980s And haven't been seen since I know it was cruel of me That was really cruel Are there any in captivity? No Oh Yeah

As of July 16th, 2019 When we're recording this episode there are 8,043 species of amphibians, and that includes frogs, toads, salamanders, and Sicilians, which don't have any limbs and kind of look like giant worms or very slippery small snakes. They're kind of cute in a weird way, kind of creepy cute, I don't know. Frogs and toads make up the biggest chunk of this, and new species of amphibians are being discovered all the time, all the time. So of these over 8,000 amphibian species, 501, which is around 6.5%, have faced serious declines due to Kittred, with at least 90, possibly 122, confirmed or presumed to be extinct in the wild.

God dang. Over the course of a couple of decades. Right. According to the authors of one of the papers I read, we are witnessing, quote, the most. spectacular loss of vertebrate biodiversity due to disease in recorded history. Wow. It's unprecedented for us to observe. Amphibians have been around since before there were humans, before there were mammals, before

there were dinosaurs. There are amphibian species on all continents except Antarctica. There are species that live in the desert like the Sand Hill Frog of Australia, ones that live on mountains, ones that live in rainforests, ones that live above the Arctic Circle, like the wood frog. Yeah. Oh yeah, I knew that, but it's still crazy. Ones that literally freeze solid during winter and emerge again in the spring, little spring peepers. Wow. The diversity of amphibians is amazing.

And they're survivors. They have gone through massive extinction events and live to tell about it. But their long and incredible existence may be coming to an end, and the biggest reason is us, humans. It's maybe a bit difficult to say exactly when the great decline of amphibians began, but I can tell you when it started to be noticed, at least, and that was in the 1980s. And similar to how Tegin described, it was a pretty drastic shift. Researchers were coming back empty-handed from collecting trips where they once could barely avoid stepping on frogs. Amphibian populations had been declining over the past century due to things like overhunting, habitat destruction, etc.

But it was the recognition that it was happening globally and rapidly that really caught scientists' attention. In September 1989, the first world Congress of Herpetology led to a massive gathering of herpetologists from all over the world. Just imagine that room, man. Herpetologists are some of the coolest people. I was just thinking, I was saying this to myself when I was researching this. I was like of all of the, you know, like ornithologists, entomologists, herpetologists, ichthyologists, I feel like herpetologists are. I would go to that international congress. It would be, I mean, I'm not sure.

Like, I think it would be the most fun. It would be pretty fun. I feel like they know how to party, but I don't know. So at this conference, at this world Congress of Herpetology, researchers there began to talk amongst themselves about, like, oh, yeah, I really had a hard time finding my study species this year. And someone would be like, oh, me too. but I was doing research in this other country, this other continent.

And so one instance of not being able to locate your study organism might not be that surprising because fieldwork is unpredictable. And sometimes the animals you want to find aren't where you expect to find them. And that just happens. But this was that times a thousand. Researcher after researcher had a story about the unexpected disappearance of their study species. and people started to pick up on these not being isolated events, but part of maybe like a larger crisis,

one that was taking place across the entire globe. And after this Congress, herpetologists wasted no time. They got right into action. They started holding workshops to present the most likely causes of the amphibian decline, and then they proposed a plan of action to save the frogs. So this plan had basically three focuses. One, save the amphibians, conservation. Two, find out what was killing them, investigation, and three, tell people about it, education.

Because unless you get people who are not researchers interested and passionate about this subject, it's going to be an uphill battle even more than it already is. Absolutely. So to have any shot at long-term success with conservation, scientists, had to get work on uncovering what was causing this rapid decline. What were the clues left behind? The first was that the species that were suffering were the most similar ecologically. They bred or lived near streams or other water sources and had to spend a significant amount of their lives in contact with water. The second was that it was happening rapidly, but still in like a

wave-like pattern. It would start in one geographic area and then go upwards, directionally or go in some direction. The third was the rate of decline, which was super fast, really fast. Within a few years, the population went from normal, or at least what was maybe could be perceived as normal, to empty, done, extinct. The fourth was in the bodies of the amphibians themselves. So in this book that I read, they mentioned how organ, that there were some organs that showed widespread necroses.

And then there was just the behavior of the diseased frogs themselves acting sluggish and not being able to move. Yeah. And the fifth thing is that these are a lot of clues was that there were some species that seemed to escape the effects of whatever this was while their neighbors died in droves. So all of these things together kind of shouted to researchers, this is an infectious disease. All of those things are very characteristic of a widespread virulent pathogen. And a couple of years after this disease hypothesis had been fully flushed out,

researchers across different continents detected a fungal pathogen on the skin of dead and dying amphibians. Amphibians from different continents from Australia, Europe, North America all seem to harbor this pathogen. and so the researchers who were like, hey, so do you see this thing? Because I have a fungus on my frog. Do you have a fungus on your frog? I just want to say that Erin is using her phone hands. Like she's calling someone on the phone to chat across global waters. Well, and they didn't have to chat across global waters much longer.

They were like, you know what, let's meet up in person. Let's take a real peek at this. So they met. Herpetology meeting. Another herpetology meeting. this one in Champaign, Illinois. No, uh.

Yeah. Stop it. In 1998, a bunch of researchers who had found this pathogen gathered in champagne to compare their findings to say, is this fungus the same, is my fungus the same as your fungus?

That's adorable. I also should say I didn't mean to throw shade on the other ologists earlier. They're all cool. You're going to get in trouble for that. I know, right? Especially from like, other entomologists. It's cool. We're all cool.

Nerds. Everyone's cool in their own nerdy way. That's just how it is. Yes. Anyways, we're in Champaign. We're comparing fungi. I love it. Well, the fungi, I always say fungi, but I think it's supposed to be fungi. That's what my high school biology teacher would kill me for saying fungi. Maybe that's why I say it. But these fungi were all the same. They looked and they were like, But how is this possible? These are the same, these look to be the same species. And they were like, okay, well, what kind of fungi is this? Kittred. And that's not that surprising, maybe, because Kittred is everywhere. So, you know, okay, that makes a little bit of sense. But like you said, this was unprecedented in its ability to infect and cause disease in vertebrates. And the other thing

was that it looked brand new. This was a different kind of Chitred. And so not only was a new species named, it was a new entire genus that was created to house this BD species. It's so exciting. Yeah. It's so exciting.

This chitrid fungus seemed to be an unstoppable force. It tore through populations and then just sat there waiting because Chitred doesn't need amphibians to survive. It's content to just, chill waiting. Finding out what was responsible for at least a good bit of the amphibian declines was great news, right? But it also raised a ton more questions and even some skepticism. No single pathogen had been the cause of so many extinction events or population declines in modern history. And blaming the decline on Kittred might make people ignore the other causes

of amphibian decline, such as environmental pollutants and climate change. And it still left this massive question of how do we stop it? The story of amphibians in Kitrid shouldn't be looked at in isolation, because it's raised all kinds of questions about what the role of humans is in conservation intervention. Some people have argued that Kitrit is a natural pathogen, so maybe these extinctions and population declines are natural as well. Yeah, that expression you're making, I'm also like, no, I'm not, I don't buy that. It's a highly skeptical expression, everyone. Well, because what it does is that, I mean, that viewpoint fails to consider or acknowledge the role that humans have played in the spread of Kittred around the globe.

Like, diseases don't just pop up everywhere at once out of nowhere. Nope. That's not, yeah. Nope. And there's also some Kittred emergence and climate change seem to be, in some cases. acting in conjunction with each other. So, again, and humans, this is human-induced climate change. This is humans have caused climate change.

Right. That's a fact. Anyway. But the other reason that you can't tell the story of amphibian decline as one single event is because it's part of a massive and terrifying trend that's happening globally right now. We're in the middle of and the cause of the sixth extinction. I want to talk.

just a little bit about extinctions. Good. Let's make this a more depressing episode. I mean, one of my favorite courses in college was called dinosaurs and disasters. So this is really going back to my roots. Yeah. Okay. So you might have heard this term, the sixth extinction or the Holocene extinction, used a lot quite a bit lately, particularly in talking about climate change impacts or exploitation of natural resources, and often along with the word anthropocene. But what is it? What is the sixth extinction? Basically, since the first vertebrates evolved, there have been five massive extinction events. And we can see these in the fossil record. The first one took place 450 million years ago, which is just an incomprehensible amount of time.

Yeah. And the most recent one happened at the end of the Cretaceous period, around 6,000. 65 million years ago. That's the one that wiped out all the dinosaurs and terrorsors and pleasiosaurus and all the other cool animals. And based on the population declines and extinction rates of not just amphibians, but many other species, some researchers believe that we are in the midst of the sixth great extinction event. And the really, the only debate that seems to be left is where to actually put the starting point of that, because a lot of people believe that humans were responsible for the extinction of the prehistoric megafauna, like the giant ground sloth and mastodons and all of the amazing cave bears and Irish elk.

I love prehistoric fias. Erin's face is getting so sad talking about this. I wish I could time travel so much. But what makes a mass extinction a mass extinction? Because animals do go extinct for various reasons occasionally. And by looking at the fossil record, paleontologists can estimate about how many species of a certain group of animals, like, let's say mammals, go extinct over a long period of time. And that is what we would call a background extinction rate, just a normal baseline level of

extinction. And it's when that extinction rate skyrocketed beyond the normal background rate that we call it a mass extinction, particularly if there are multiple groups that are undergoing higher extinction rates at the same time. So I'm going to borrow a metaphor from paleontologist Michael Benton. He suggests you think of it as the tree of life. As the tree grows, you have little twigs or branches that may break off along the way, just as part of the growth process, part of the normal weathering.

And a mass extinction event is like a tornado coming through and ripping off an entire half of the tree or huge branches at random, places. that won't grow back. The background extinction rate for amphibians is hard to estimate, since there are fewer fossils than there are for something like mammals. But researchers think it's very low, probably around one amphibian species going extinct every thousand years. Wow.

Whoa. That's, yeah. Oh, dear. The extinction rate currently is estimated to be 211 times higher. than the background rate, or if you take into account endangered species as much as 45,000 times higher. Oh, no. Yeah. Assuming that endangered species are very unlikely to bounce back and are going to go extinct imminently.

Right. Yeah. Amphibians are the most endangered class of animals. And even though this episode is about kitrid and amphibians, I want to bring us even further down by mentioning that they're not the only ones in an extinction crisis. So this is basically taken pretty much verbatim from the sixth extinction. An estimated one-third of reef-building corals, one-third of freshwater mollusks, a third of sharks and rays, a quarter of all mammals, a fifth of all reptiles, and a sixth of all birds

are headed towards extinction. Oh no. Oh, no. Yeah. This might be one of our top most depressing episodes because it's like everything on the planet is going to die. Yeah. I know that I'm sounding alarmist, but there's cause for alarm. This is happening and humans are the cause of it. and it's going to cascade, I think, much more rapidly and much more powerfully than we could possibly anticipate. At the root of these extinctions is humans. But, you know, I also just said that extinction is a natural process, right? And there were five massive extinction events before humans existed. So maybe we're just due for another extinction event and humans aren't to blame at all.

that's wrong, flat out wrong. There's no such thing as being due for extinction. Let's look at the case of Kittred and amphibians. Climate change, human caused, habitat destruction, human cause, environmental contaminants, human caused. These have all contributed a ton, but the key role that humans have played in this particular event is transport. Yeah.

Kittred itself doesn't seem to be brand new to amphibians. And I mean like, we found it in, I think the earliest museum specimen is from 1938, and it's probably been around longer than that. But what is new are these massive global die-offs. For these extinctions to happen over such a short period of time with such widespread geographic distributions, something must have brought Kittred from point A to point B. Amphibians can't. can't cross oceans, but humans can. For a while, the leading hypothesis of where Kittred came from was that during the 1950s and 60s, the African-clawed frogs that were being shipped around the world for pregnancy tests carried the fungus. Do you know that they were used for pregnancy tests? You know, I didn't until we started researching this. I knew rabbits were used. I I didn't know that frogs were used. Yeah. I found that very interesting.

Very interesting. These frogs are one of the species that can carry the fungus without being negatively impacted. So it would have been harder to detect that there was anything going on. Right. More recently, however, so in a paper that came from 2018, seems like the evidence is pointing towards East Asia as the point of origin of the BD fungus. I read two of the same papers as you, Aaron. That doesn't happen very often. It doesn't.

Well, I mean, we don't have a pathogen that often that is discovered within the past 30 years. It's true, yeah. With this ease and speed of travel, we are basically living in a new pangia. And that's a very serious threat to the planet species. Yeah. Because species evolve in geographic isolation. and invasive species are a hugely, hugely troublesome problem. Pangaea, for those who might have forgotten their science class from fifth grade

when we learned what Pangia was, was when all of the current continents were one giant massive supercontinent. That was known as Pangaea. So now we're saying that it's like all of the continents are touching again because humans move things across bodies of water. Yep. Yeah. So researchers estimate that around 5 to 15% of Earth species have been described.

Wow. So there are 85. Most of the undescribed ones are like bugs. Probably. Probably. Bugs, bacteria, et cetera. Who knows? Archaia.

But probably many of these will live an entire. higher existence before ever being described. Yeah. But why do we care about biodiversity, Erin? Oh. Like if someone were to ask you, why does biodiversity matter? What would you say? Oh, gosh.

Don't ask me to answer that on a podcast because I need a scripted answer and I don't have one. Well, it's a, that's the thing. It is a hard, it's a hard question to answer because it seems so self-apparent, it seems so obvious that of course biodiversity matters, like why, why does the why matter? Why do you have to know why it matters? Of course it matters. Yeah. But unfortunately, it does matter because we need to convince people that maintaining or improving biodiversity is important and worthwhile and worth their money and their time. Right. That's the only way to get funding or enact the policies that will actually protect biodiversity or improve it.

Basically, humans have to be convinced not to kill off other species. Isn't that sad? Yeah, it's sad. And the other sad thing is that the most common line of reasoning is that you should care about biodiversity because biodiversity benefits you economically. Right. It's like, oh, that's how we find new drugs or that's how we find new whatever. And we can make money off of that.

So that's why we care about biodiversity. I hate those arguments. I hate those arguments too. Yeah. I hate them. And I understand that they are what is needed, but it's just, yeah, it's very difficult. Yeah. Okay.

So let me ask you a slightly different question. Okay. Why should we care about amphibian species going extinct? Ooh, amphibians are good sentinels, aren't they? Actually, so I read something that they're not. Oh, okay. So that the image of the frog as the canary in the mine is actually not a good indicator because they are pretty resilient. That does make sense, yeah.

And also that their baseline levels aren't well established in anywhere. So it's hard to detect a change. There's often a lot of seasonality and their population densities, et cetera, et cetera. Then how about their important parts of the ecosystem and they do a lot of things? There you go. ecosystem services. Yes. When I was looking into this, there were four reasons that were proposed as to why amphibians are important. Why do they matter? Gosh. One, and I'm sure that you could find a whole number of different listicles for this kind of thing. But one is economic. So we use

tons of amphibians for medical and teaching purposes and also for consumption pets. ecosystem services, like you mentioned, amphibians help cycle nutrients and they're really great prey species. They transfer energy upstream. And they're also great predators eating tons of insects and insect eggs and arthropods and whatnot. Another reason that was proposed is aesthetics. Yeah. They're adorable. They're cute.

Yeah. And they've inspired thousands of years of folklore and mythology and tales. And also the final one, which is my favorite. favorite is ethics. As humans with our big brains and our ability to manipulate the environment, we have a responsibility not to destroy the things around us. I feel like that's a really, really good argument, actually. That's the one I'm going to use from now on, I think. Because, yeah, it's like, yeah, sure, you can say it doesn't matter how much we destroy. The planet will keep going. But it's like, dude, are you kidding me? That's a crappy argument. Like, be

better. Be better. Care a little bit. Just like why why is it better to rejoice in your power over things rather than respect things around you? It just is baffling. Yeah. And appreciate them. Yeah. Yeah. But I think that the sad truth of all of this is that we're only going to know how important biodiversity is to humans once it's too late. There's a great quote from Paul Erlich, that puts this nicely. In pushing other species to extinction, humanity is busy sawing off the limb on which it perches. In the scheme of things, and I mean like the big geologic scheme of things, humans are nothing.

Go watch the cosmic calendar from Carl Sagan's cosmos to give you an idea of just how brief a moment in time humans have occupied. And yet we've had this enormous. impact on everything around us, much reaching before humans and extending long into the future when humans are gone. And there are consequences that we are only now beginning to see and feel. By the time that Kitrid was identified as the great amphibian killer, it was already clear that there was no way to stop it. But at the very least, an escape attempt could be made. A huge effort was started to establish amphibian populations in labs and conservation centers

and freezing tissue to create this arc, preserving species while wild populations died out. But that's not a long-term solution. The goal of conservation should not be to have a species exist solely in a zoo for the rest of eternity or in a freezer, but to reestablish it in the wild, to restore ecosystem of functionality and health. But with Kittred still there and not at all bothered by the absence of its hosts, it's not safe to release these amphibians back into the environment. So what do we do now, Erin?

Oh, just that small question you want me to answer? Okay. Well, I might need a break first. Okay. Anyone who works long hours knows the routine. Wash, sanitize, repeat. By the end of the day, your hands feel like they've been through something. That's why O'Keefe's Working Hands hand cream is such a relief.

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So we'll do a quick little recap. Bring it back to Kittred specifically. Focus just on the depressing parts of amphibian decline. Okay. rather than everything. Yeah. You know, small things. So like you had mentioned, it's estimated that at least 500 species have declined, at least in part, due to Chitred.

And one thing, this is the paper that we both read, Aaron, that I thought was really interesting in this paper, is that this is, this puts B.D., Kittred fungus. among the most destructive invasive species of all time ever. Yeah. Like more destructive than rodents, more destructive than cats, who I love but are the worst. By the way, so this is outdoor cats. Outdoor cats, people who keep their cats outdoors and feral cats and so on, have caused the extinction of 63 species. And they threaten 430.

Yeah. So please, if you have an outdoor cat, don't have an outdoor cat. Bring your cat inside. Train it to be on a leash and only let it out on a leash like Mr. Norris and or build a catio. Yeah. Feral cats, man. So anyways, yeah, so Kittred is, is major. It's way more major than the other high profile wildlife pathogens. things like white nose, West Nile, etc. This has affected a hugely more species, which is very depressing. And all but one, it's specifically BD. So, but no, I'm not going to do it again, BD. I didn't even attempt it if you noticed.

You know, we said it twice at the beginning, so it's fine. And one of the things that's so interesting about this pathogen is that, that because it's so, so new, we know still so little about it. There are so many open questions that still remain. One of them is, how old is this really? So like you mentioned, the most recent paper from 2018 estimates that this fungus likely originated in Asia. So based on their data, which seems to me, even though I'm not a geneticist and I don't know how to read these papers that well, it seems pretty comprehensive. They sampled samples of chytrid fungus from every single continent where it's found and like hundreds and hundreds of samples. And based on

their studies, it seems like the Korean peninsula is likely where chitrid originated. So that's where it's from. And they estimate that in the early 1900s is when it likely began spreading across the globe. And they specifically point to the pet trade out of Asia that is a driving factor in spreading this fungus. Yeah. So one of the things that a lot of people are working on and that they pointed out really needs to happen even more is to sequence more species in Asia to really understand what the genetic diversity of Kittred is where it originated so that we can get a better handle on how old it is and how long species in Asia might have been co-evolving with this pathogen. Yeah. There's there's that really interesting map in that 2019 paper that shows

continent by continent the number of like depressed populations or extinct populations or near threatened, et cetera, et cetera. And you can see how much that varies. across these continents. And it makes sense that there would be an East Asian origin because that is one of the lower rates of population declines. Right. Yeah, it's really interesting. But since the early 20th century, if that's when BD began spreading, it has spread everywhere. Australia and Central America and South America seem to be overall the most hard hit in terms of population decline, but the fungus itself is found across the globe and has contributed to declines in populations across the globe as well.

So there are a few major questions that are still unclear in terms of the ecology and understanding this pathogen. First, obviously, is where it came from, but I just talked about that. So it's also very unclear what the impact of amphibian biodiversity and the impact of humans and human-mediated environmental changes have been on chytrid in amphibians and what they will continue to be on chytrid abundance and distribution. We don't really know, does amphibian biodiversity help spread chitrid and make it like a worse pathogen or is it protective in some way like the dilution effect? It's unclear at this point. The effects of climate change, which as we talked

about is human-mediated, though not the only human-mediated environmental change, but a big one. The overall effects of climate change on amphibians are not great, likely. But the effects of climate change and BD combined on amphibians also seems to not be great in a lot of cases. It's really complicated. And at this point, we don't fully understand what the combination of the combination of climate change. So increasing temperatures and more variable temperatures on top of this fungal infection are going to have on amphibian populations. But there are some studies that suggest that

for some populations, it's really not good. And the combination of increasing temperatures and infection is actually really detrimental. So that makes sense. Yeah. What else do we not know? A lot of things. In fact, there are so many things that I just feel that I'm not going to be able to do a good job of explaining it. And on top of that, I actually don't want to end this episode on a really depressing note. And there are some aspects of research on Kittred that are really exciting and promising. So at this point, I want to introduce who you heard in our first-hand account, Dr. Tegan McMahon from the University of Tampa, who's been studying Kitrid for a number of years and from a multitude of different perspectives.

She's going to tell us more about the status of Kitrid research, including the importance of understanding the effects that Kitrid has had on other species. Because guess what, folks? As it turns out, Kitrid can infect more than just amphibians. What? Does that blow anyone else's mind? It blew my mind. She's also going to talk about work on understanding why some populations are so detrimentally affected and other populations seem to do okay when they're infected or seem to even clear the infection entirely and what that means for conservation efforts and some really exciting work on vaccine development just so we can end on a happy note.

Take it away, Tegin. My name is Tegin McMahon and I am a biology. professor and parapsophologists at the University of Tampa, and I've been there for about five years now. But I've been doing amphibian decline research for about 10 years, and I have been in love with amphibians, frogs and toads, especially since I was a really little kid. There's something about frogs that are just extremely charming. They're really diverse in color.

They're these little gems in the rainforest, and out in New England, you'd find this bright green frog calling the top of his lungs. I think they're just wonderful creatures. So you work with Kittred fungus, and so that's obviously what this episode is going to be about. So could you tell us what Kittred is exactly and why people like you are studying it or why it's being researched? Kittred fungus is a very weird fungus. So typically when people think of fungus, they might think of like portobella mushrooms or the type of mushroom that makes a little mushroom cat that they see in the forest growing out of a tree or out of a log. And this is sort of the same group of organisms, but it's a particular kind of fungus that

lives in water and specifically is attacking frogs and living off the frog as its food resource. The fungus has probably been around for an extremely long time, but in the last few decades, notice that it's been causing massive declines in amphibian populations. Some populations are able to handle the infections relatively well, while other populations are totally decimated and or are completely wiped out in a matter of weeks. So there are a handful of groups of amphibians. For example, atalopis is a particular genus of frogs that has been completely and totally decimated by this fungus. So it's wiped out dozens and dozens of species within this group

completely out of the environments. They're now being maintained in captivity, but you don't find them in the wild at all. Wow. So I have a how question and a why question for you. The how question is how did it all of a sudden, if you said it's been around for such a long time, what were the, what was the sequence of events or how did it all of a sudden become more? prevalent or causing these, I guess, pandemics, almost. And then the Y question is why some groups seem to be more vulnerable to Kittred than other groups. Big question. Sorry. Absolutely. Fortunately, I can't give you the super concrete answer on those questions. We'll start off with the idea that it's probably been around for a really long time and yet only recently has been causing massive declines.

there's a lot of groups that are doing research on this in a whole variety of different ways and you have a huge conservation crisis like this. You have dozens of scientific groups that are looking at how and why questions surrounding this

particular disease outbreak. What we've found is that we find chitrid basically globally. Anywhere you find amphibians, you find the chitrid fungus. And in addition to that, people have looked through historical records and been finding these preserved amphibians

with traces of chytchid fungus on them from the 1800s. And so it's been around for a lot longer than we had originally predicted when we first saw the big massive declines and amphibians and discovered that a lot of those declines were due to the chitre fungus. Connecting that history to what's happening today is really difficult because we weren't searching for the fungus that whole time, so we don't have a very good story at death. Why it's been around forever, but suddenly it's now wreaking havoc. One of the main ideas is that amphibians are sort of threatened with a whole bunch of different challenges

because they're found both in the water and on land. So anything that's contaminating the water impacts them, and anything that is contaminating or destroying the land also impacts them. So the thought is that with habitat loss, with habitat fragmentation, over-exploitation of our population, introduction of exotic species that are eating the native species, pollution, climate change is a huge one, and other diseases all coming in that these amphibium populations,

which were very strong, might have been able to handle one parasite infection coming in like Chitred, but now that they're dealing with pollution, climate change, and the disease, their populations aren't resilient enough to be able to handle all of those threats at the same time. There are other ideas that are out there that the strains that were around earlier in time were less virulent, meaning that they were less damaging to the host when they came through a host population, so they didn't destroy entire populations than the infidians, and that now we're having this really virulent strain that is moved around the world.

So there's a whole bunch of theories out there as to how it's been around for a really long time, but we're only really seeing these massive decline in the last few decades. And some of these groups are completely wiped out, and some seem to be immune. Is it immunity or is it something else? And does the existence of immunity suggest a longer, like a history of exposure over time or anything like that, historical epidemics maybe? Yeah, this is sort of a newer line of research in this field. As I said, you know, with a conservation crisis, everybody's focused on what is happening

and why. And now that we've had enough time to answer some of those questions, we have a lot of researchers who are starting to ask some of these other, sort of more tangential or connected questions about immunity and things along those lines. what we're finding is that some groups are either tolerance of the fungus or resistance of the fungus. So if a group is tolerant, then they can have the fungus in their skin. The fungus does just fine, gets nutrients from them, but it doesn't kill the host. So there are a few groups that are really well known for this.

One are the African thawed frogs, the Xenopus laivis, for example. They're the frog that you see in pets. stores all over the United States that are fully aquatic, and so they swim along under the water. That particular frog totally does fine with citrus fungus. So it can have a really strong infection, but it's absolutely tolerant of it and it doesn't harm the frog at all. That means if that frog were to get into the wild, it would be shedding the fungus out into the wild, and then the less tolerant species might be impacted by the fungus.

We also have species that are resistant, meaning that if they come in contact to the fungus or come in contact with the fungus, they don't really get the infection. It's something about their system. Maybe it's the bacterial fauna on the outside or their immune system is able to identify it and get rid of it before it can establish. And those populations just don't ever really get strong infections. So again, those populations are resilient and able to move through that epidemic and not be destroyed. And there's some really cool research just starting to come out now that there are populations, many of which are in Central America, that we thought were basically totally wiped out. These are species that had really big populations.

Chittred came through, wiped them out to essentially nothing. and in some cases we thought they were extinct. And now we're starting to see those populations come back. So my hope is that those populations as they come back are going to be either resistance or tolerance of the fungus. The idea there is that everybody, all the individuals in the populations that were susceptible to the fungus were killed off, the few that could handle the infection or the few that completely resisted the infection.

survived and those are the few that we're there to make the next generation. The hope is that we're seeing some potential reestablishment of populations that will be long-term reestablishment. Wow. It's like antimicrobial resistant frogs. Yeah. Yeah. In the best way.

Yeah. We could be really excited about. Yeah, that's so cool. That's cool. And so you mentioned briefly, too, that you've worked on a number of different communities. not just amphibians, even though frogs are maybe the most well-known for getting infected with Kittred. So can you tell us a bit about what it is that you've seen in terms of the effects that this fungus has had on other communities aside from amphibians?

This is a really, to me, a really exciting line of research because for so long we have focused strictly on the Kittred fungus and amphibians. And to the extent where in a lot of the papers, you'll see the Kittred fungus. as being called the amphibian chytrid fungus. And the reality is that it's found in other hosts, which changes how we have to handle that whole system from a management perspective. If it's only found in one host, you can focus on that one host. If it's found in several or even potentially dozens of hosts that are all taxonomically

different, you have to really focus your models in a much broader. So the main host that I have done work with so far are crayfish, or crawfish or crawdad. And this is a group that is also found so occurring with amphibians. In many cases, crayfish will dig burrows, and then frogs will overwinter in those burrows. So they'll actually crawl down into the crayfish hole and hang out with the crayfish in that hole over winter. And then they reemerge in the spring. So these frogs end up spending an extreme amount of time really interacting with crayfish. In addition to that, the tabpools of amphibians will eat the feces of crayfish and things like that.

So what we found is that you have crayfish that are infected with the fungus, and they actually poop out the fungus, and then the amphibians go along and eat that poop, and then they become infected themselves. What? Right. So it changes the system and how we think about it, right? If it's only an amphibians, then we have to worry about amphibians. If it's in crayfish, that can be a really, really huge change to our management state. Does it have like a detrimental effect to the crawfish communities as well?

Or do they just seem to tolerate the infection? So we have only looked at one genus of crawfish. We've looked at a handful of different species within that. But what we found was that in the lab, about 35% of individuals that were exposed to the fungus died. Wow. The ones that did not die maintained the fungus for a really long time. So, like, they were a viable host

and a pretty strong host. And then, um, they just kept living and living. There was no issue at all with them. Wow. So they ate and had no trouble. No, no trouble. The gains weight. They were totally healthy. So about

35, 36% die, and then the rest are just fine. One of the, um, Other issues of this system is that crayfish are invasives around the world. So they have, we've moved, humans have moved crayfish populations all over the world. And for example, when I lived in Costa Rica, I'd go hiking. Sometimes you would see people who had put, you know, a dozen crayfish into a big plastic jug, basically. Like a big juice jug, for example.

And they'd close the juice jug and they'd carry it to the top of the mountain. and they dump all the crayfish out in the stream at the top of the mountain, and within the next year, that entire stream would be populated with crayfish. And they did this because they're a good food resource for people, and they're really good for fishing. So people collect them and use them as bait. And so that becomes a really big issue, because we're not tracking those invasive expansions of the crayfish populations.

And because the population is already invasive, nobody's generally speaking in many places people aren't. out there actively tracking how strong that population. So we don't know if 35% of the individuals that were there died off because nobody's actually looking at those numbers. So it's possible we're being declined in the crayfish population from the fungus, but there was no one out there to ask those questions. Wow.

Wow. That's fascinating. Yeah. I also, I really love the image of a little crawdad and frog. just hold up together. Yeah. There's got to be a kid's book about this. They're really cute.

They're really, really cute little gray frogs that typically go down at since those furrows. That's very adorable. That's fascinating. So to try and maybe end on a slightly happier note, I saw that you've done some work on vaccine development, which is really thrilling. So can you tell us a little bit about that. research and where the vaccine development might be in the in the whole process and scheme of things?

Yeah. This is sort of a newer line of research course and I'm really excited about it, partly because when you work on a really sad topic like amphibian decline, it feels like you are helpless a lot of the time. Everything you look at is dying and declining populations left and right. And this particular line of research gives me a lot of hope that we will be able to help some populations reestablish. So we're basing enough the idea of herd immunity, which you guys did an amazing job describing in your vaccine episodes. I was really excited about that.

But to brief, it's the idea that if we can vaccinate enough individuals in the population, then they will protect the sick and unexposed individuals from any individuals that are sick and contagious. So the first sort of bit of research we did with this, we took amphibians and we gave them the live fungus. And that fungus, as I said, grows into their skin. And it takes a few weeks in many groups for the infection to ramp up enough to actually cause really strong damage in the frog. So we can let them have the live infection

for a few days and then we move them over to a hot chamber and that kills the fungus but doesn't harm the frog. So it allows us to basically give them the live disease and then clear them of the disease. So the first round of

this vaccine work was giving them actual infection and clearing them. And so challenge the body, their immune systems made a nice, robust response to the fungus. And so when we gave them the fungus again, they had a lower infection. So that was really cool work. It was amazing to see that they could acquire this immune response to the fungus.

However, we're not going to be able to effectively do this in the wild because we can't give them the fungus, clear them of it, give them the fungus, clear them of it in the wild. That's just not feasible. So we developed a non-infectious vaccine. In the beginning, we were using the dead fungus, so we took it and we killed it with liquid nitrogen, and then we just squirt it on the frog's back. It's the easiest vaccine to give anything because you just have a frog in a little container and you squirt this liquid on their back and they absorb it through their skin.

When we vaccinated them that way, they got just as strong a response immune system-wise. and they had a lower infection when they were exposed to the live fungus. So that's super exciting because that means that we can expose individuals to non-infectious vaccine, and then they'll have less infection when they're exposed to the actual fungus. So we now have an NSF grant, which is super exciting to work on all of this. So we're looking at the most effective form of the vaccine. seen. So how can we most effectively and efficiently vaccinate individuals? We're looking at different species to make sure that we can actually vaccinate across a wide variety of different species.

We're looking in the field to see how effective it is in the field because you don't want to ever say, hey, everybody go out and dump a bunch of dead chitrid in the pond. It's going to save everything without actually knowing that it's going to be effective and do what we expect it to do. So we're looking at the impact on other organisms in the pond and really trying to make sure we have a good idea of what's happening out in the field before we start promoting this vaccine campaign itself. That's so cool. It's really promising work. We've had some really fantastic responses from the different species we're looking at. And so there is certainly the possibility that we could go out and vaccinate some of these.

frog populations that have been removed from the environment that live in really small, isolated ponds. We could vaccinate those groups and then repopulate those ponds back to their more natural species abundance, which would be absolutely amazing. Wow, that is so cool. Oh, my gosh. So I have a question that's a little bit more general or maybe a little bit more about you. So you describe yourself as a conservation disease ecologist, which is the coolest job title.

So it really is. What kind of advice would you have for somebody? I would imagine a lot of our listeners would be very interested in pursuing a career like that, or at least learning a bit more about it. So do you have just like a brief snippet of advice on how you would go about to either learn more about that field or to become a conservation disease ecologist? Yeah. A young person kind of work I wanted to do, this is it.

It's fun and exciting. It's very hard to keep my brain really stimulated. And it feels really meaningful because you get to see actual changes happening in the field and in the environment of your work, which is absolutely incredible. My suggestions are the sort of two-fold. From a more practical side is

reach out to people who are doing research that you think is cool. You can find out what people are doing by Googling scientific papers, by looking at articles. If you see an article in National Geographic and you think it's amazing, look for the author that they interview and look at their research. Reach out to them. Most people doing this work want to talk to you about it, and they're really excited to share what they're doing.

And if you happen to be living near those people, you can ask if you can volunteer and help. If you are in school, reach out to your faculty, and find someone to do research with, it doesn't have to be the research that you wanted to do or that you want to do in the long run. Just getting experience in a lab, getting experience in the field,

will tell you do you like field work, do you like lab work. We'll let you know what you find exciting, what you don't find exciting, and that will help you sort of decide what career routes to go. great great pieces of advice absolutely fantastic are there any organizations or websites or anything like that that you would like to give a shout out to in regards to kitrid or your research there are a lot of research organizations and a lot of conservation organizations that are doing a ton of work with amphibian decline and with kitrid fungus one of the groups the Smithsonian Tropical

Research Institute and their part of the Smithsonian, which has connections in the U.S. as well as in Panama, does an incredible job of connecting scientists to permits and to the environment of getting them out into Panama. That's the group that I work with when I go down into Panama. They also have this huge facility of amphibians that have been pulled from the wild because the populations were in rapid decline due to the chytrid fungus, and they're maintaining these populations in captivity in hopes to be able to re-release them at some point in time

back to where they're supposed to be. That's an incredible amount of money and an incredible amount of time and effort put in to try to maintain this diversity. And it's something I think a lot of people don't realize it's happening is really... I'm very hopeful that some of the vaccine work will be valuable in that space.

There are other groups like, amphibian arc and save the frogs to do a lot of work as well trying to promote amphibian conservation excellent jinks one last question this might be an unfair question but do you have a favorite frog species oh man yeah this i guess and it is a really hard question because i want to tell you yes but then i also want to list five or six different species as long as i think about it the list gets longer, and I am well known for having many favorites in my life. I think I have favorite groups that I've worked with. Generally speaking, all my favorites come in the Tree Frogs group.

But one of my very favorites is the Common Toad. There's a picture of me as a two-year-old kissing the Toad, and the facial expression is me being very aware that maybe I'm not supposed to be kissing the Toad. but I figured it was back in the days of film and my mom ran inside to get the film camera. She probably wasn't very mad at me for kissing the toes. So I'm going to have to think I'm going to go with the Tommy Toad. I think that that's probably my favorite of all of the groups. I love it.

That's adorable. Yes. Oh, excellent. Erin, do you have anything? Any other questions? No, this was so. much fun. Oh my gosh. Thank you so much for coming on and chatting with us about this. And also, we have to give a big thanks to Umat for being Umat and putting us in touch in the first place.

This is, yeah. Awesome. Cool. Thank you guys so much. Thank you. Thanks so much. That was great. She's, she's amazing. She's so fantastic. It was one of the funest. We've had a lot of really fun interviews on this show. We have. How thrilling for us. And you, listeners. I am glad that we ended it on a bit more of an upbeat note. And that's the thing is that like it's really easy to get very bogged down and fatalistic and sort of like, well, nothing matters. Yeah.

The world is going to end, et cetera, et cetera. And I get that feeling. I get it when I think about climate change, when I think about what humans have done to the Earth. But I think that there's also so much to be, to give us hope. or at least give us some sort of optimism. You know, there are people like Tagan working on these amazing systems. There are species that are being turned around. There are people who are making an effort.

And you, if you want to make an effort, if you want to do something, there are many different outlets or resources for you to do that. Conservation societies, volunteering, just reading more about it. It's talking to people about Kittred. It's great. If you want to learn more about Tagan's work, you can find her Lab Instagram at McMahon Lab. So that's MCM-A-H-O-N-U-N-U-N-U-N-U-Skore Lab. She also curates the parasitology Instagram at U of Tampa underscore parasitology.

So fun. And another one at Wandering Ecologist, which is a lot of really fun watercolors of wildlife and diseases. things like that. Yay. Go check those out. Yeah, definitely. And we'll post a bunch of her recent papers on our website as well so that you can read some of her work. And then if you live near her, bother her to go volunteer with her because she's awesome. Yeah. Other sources? Sources, yeah. So I want to shout out a couple of books I read. One is called Extinction in Our Times, Global Amphibian Decline. And this was an invaluable resource. I think this is, even though it published in 2009. There's such

amazing information in there on the emergence of Kittred and also just the global amphibian crisis in general, and that's by James Collins and Martha Crump and Thomas Lovejoy. And then I also read the Sixth Extinction by Elizabeth Colbert,

and that was great. A very interesting book. And then a few papers quickly. Kretzen from 2002 paper. Scarrett at all

2007 paper Wake and Vrendenburg 2008 paper O'Hanland 2018 paper and Sheel 2019 paper

some of those are etals I have several other papers as well and we post all of these as well as links when we can

on our website this podcast will kill you.com under each episode you can find the sources from this and all of our

episodes so check those out yes please do And we also have a good reads list. So you can find these books on our good reads list. These books will kill you. Also a link to it on our website.

Well, thank you first to Tegin for agreeing to be on the podcast and sharing her amazing brain with us. Yeah. We loved it. It was so much fun. And thank you to listeners. Thank you to you all for listening and for, yeah, being you. We really love doing this and you make it worth it all. so much more fun than talking just to ourselves.

Yeah. And thank you also to Bloodmobile for the music in this and all of our episodes. And wash your hands. You filthy animals. Wash your hands before you touch a frog. Ooh, that's a good one. Yeah. Don't touch a frog.

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