Ep 33 Chytrid: The Silent Forest

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.

Episode Transcript

Speaker 1 (00:00):
I've always loved frogs, toads, salamanders, all amphibians, and my
mother also did, so 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

(00:20):
called Haley Farm, and so we would go out, and
we knew where to look for the eggs through all
these little small ponds, and we would go out every
week and we'd watch the eggs developed tabholes, and then
those tabholes developed into metamorphs, 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

(00:41):
activity I took all the kids on. So we'd all
go out and the 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.

(01:02):
We don't see the eggs, and so they're probably they're
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 Hayley Farm is one of

(01:24):
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, which is a huge part
of my childhood growing up, and I think it is
with a huge part of what made me become a
concentration disease ecologists, because I loved that when I was younger,

(01:48):
and it's just not a thing anymore for kids.

Speaker 2 (02:33):
Hi, I'm erin Welsh and I'm erin oman Updyke and.

Speaker 3 (02:37):
This is this podcast will Kill You Today.

Speaker 2 (02:40):
We're talking about Kittred Kittred, and you just heard a
fabulous first hand account of some of the terrible effects
that Kittred has had on Amphibian communities by our friend
Tagan McMahon, Doctor Tagan McMahon. I should introduce her properly.

Speaker 3 (03:00):
And you will hear it 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.

Speaker 2 (03:12):
Yes, no, not kidding, though at least I didn't have to.

Speaker 3 (03:17):
Only kind of kidding. But before we get there, we
have one very important thing to do, and that means.

Speaker 2 (03:27):
It's quarantine time time.

Speaker 3 (03:31):
What are we drinking this week?

Speaker 2 (03:33):
Today? We're drinking simply croaked.

Speaker 3 (03:38):
We shouldn't be laughing at this. It's not funny, but
it's not funny punny, I'm tickled at the name. What's
in croaked?

Speaker 2 (03:47):
There is mango puree, a bit of lime juice, some
bubbly fizz water and rum of.

Speaker 3 (03:56):
Course delicious run a boil, oh if if you can
grab it.

Speaker 2 (04:01):
And the key ingredient in this particular beverage is just
a few sprinkles of chia.

Speaker 3 (04:08):
Seeds to look like frog eggs.

Speaker 2 (04:13):
You guys, I love it. We'll post the full recipe
for this quarantini as well as our non Alcoholic Place
Barta on our website and all of our social media channels,
so you can find them there. Do you have any business.

Speaker 3 (04:27):
Erin I don't think so.

Speaker 2 (04:29):
We have merch. We have merch, go look at it.
You can find our merch at our website. This podcast
will kill you dot com by clicking on merch. And
we've got t shirts and mugs and pins and the
most important of all, soap. Soap we have It smells

(04:51):
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.

Speaker 3 (05:03):
Packaging is incredible.

Speaker 2 (05:05):
Okay, okay, so enough of that.

Speaker 3 (05:08):
All right, Kittredgy hit me with it.

Speaker 2 (05:14):
I'll hit you with it in just a minute, Okay,

(05:39):
So listen, kittred First, off is a fungus.

Speaker 3 (05:44):
Our first fungus, Our first fungus.

Speaker 2 (05:46):
We like briefly talked about fung gui on the Biology
of Superheroes podcast. Right, that's right.

Speaker 3 (05:54):
We talked about court.

Speaker 2 (05:56):
Aceps, cordyceps. Okay, but this is our first fora into
the fun guy. Okay, so let's talk about this fungus
itself first. The fungus that causes the disease known as
kytridio micosis in amphibians is called batray coquittrium dendro but titus.

Speaker 3 (06:23):
I'm glad that you attempted that, because.

Speaker 2 (06:27):
I looked it up and I wrote out a phonetic
spelling for myself. Yeah, I know.

Speaker 3 (06:32):
Can you can you quickly send that over to me
because I need to do it.

Speaker 2 (06:36):
Later, Okay, battray coquittrium dendro bade titus, Okay, dendro get
to it. You could call it b D.

Speaker 3 (06:48):
And I do.

Speaker 2 (06:49):
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 Giardia, which
I said correctly, and we didn't Giardia I did, and

(07:11):
it blew my mind in that episode that that parasite
wasn't fully classified until like the late eighties.

Speaker 1 (07:19):
Right.

Speaker 2 (07:21):
B D wasn't described as a species until nineteen ninety nine.

Speaker 3 (07:28):
Yeah what? Yeah, Oh my gosh, I did not know
that at all.

Speaker 2 (07:36):
It was thrilling information. Yeah, and there's another species that
infects salamanders, battery Coquetrium salamandrivorians that was described in twenty thirteen.

Speaker 4 (07:51):
Uh huh, oh my god, this is the history is
still being written. That's oh big time. Okay, So this
is a fungus. We'll call it B D or probably
a lot of times through this episode, we might just
call it kittrid. But I do want to point out
that there's a lot of other fungi in the group
known as kittridio mycoda. So even though we'll be probably

(08:14):
bad biologists and call it kittrid, I might slip up
and call it kittrid. There are a number of different
other kittrid fungi, many of which are free living and
happily exist in the environment, digesting cellulose and kitan and keratin.

Speaker 2 (08:31):
Ding ding ding. That word's gonna come back. Other kittreds
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 B D and B. Sal that
are known to infect vertebrates, specifically amphibians. Okay, so today

(08:58):
we're talking about an amphibian. Fur Fungi have very cool
life cycles in general, and kitrid Kytridiomycota fungi are no exception.
They have two life stages, the zospore and the zo sporangium.
So the zospore is like a spore, so it travels

(09:22):
through the environment, that's the point of it. And it
happens to have an adorable little flagellum and it can swim.
So the zospoor stage swims through 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

(09:42):
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,

(10:02):
and then it burrows its way into the skin of
this let's call it frog.

Speaker 3 (10:08):
What cues is it using to find the host?

Speaker 2 (10:12):
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.

(10:32):
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 zo spores which will
burst forth from the skin and swim along their way,

(10:57):
and those zospores can either reinfect the same host in
a new spot, or if they're close enough to another frog,
they can infect a new host. Today, life cycle complete.

Speaker 3 (11:11):
And about how long is this all taking place?

Speaker 2 (11:14):
Oh gosh, Well, I know that the incubation period from
when the zospor first infects to when the frog starts
showing symptoms are between ten and eighteen days. Okay, So
my guess is that that's about the timeframe that it
takes for them to start shedding.

Speaker 3 (11:30):
And I would assume it it's variable depending on frog
species and temperature, or amphibian species and temperature and et cetera,
et cetera very variable.

Speaker 2 (11:40):
Yeah, okay, so let's talk about the symptoms of a
kittrid kytritiomycosis infection.

Speaker 3 (11:49):
This is gonna make me sad.

Speaker 2 (11:50):
It's it's so sad. It hit me in the feels
this one. So you can tell by the way that
I describe 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

(12:12):
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.

Speaker 3 (12:24):
I don't know.

Speaker 2 (12:26):
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

(12:47):
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 kittrid. However,
because B. D. Chytrid can infect so many different species
of amphibians, the symptoms really do vary a lot based

(13:08):
on the species and how serious the infection is varies
hugely across species, and actually, Tagan, we'll 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

(13:28):
kytrideo micosis 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 hyper keratosis, which means that you're making a

(13:50):
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 extra keratinized layer is not

(14:15):
going to be as permeable to water or air or electrolytes.

Speaker 3 (14:19):
That's really interesting.

Speaker 2 (14:20):
Yeah, I know that. Why didn't neither? Yeah, And then
what you also get very very commonly is sluffing of
the skin, So this skin will just start to slough
off in sheets, which is really sad. You can get
ulceration and like multiple cyst formation, but you don't always.

(14:43):
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 kittred that are bright red on their belly and
their legs. So that's really common, is for their bellies

(15:04):
to become disccolored, 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

(15:27):
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.

Speaker 3 (15:40):
But does the infection tend to be localized in that
way or is it pretty much systemic at a point?

Speaker 2 (15:46):
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,

(16:08):
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 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

(16:30):
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 lethargic.
They stop seeking protection, they stop hiding during the day,

(16:54):
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

(17:15):
are not poised underneath them like a frog ought to be,
like ready to bounce at any second. They hang their
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 wop of a frog.

Speaker 3 (17:33):
Well just no like yeah, no willingness to yeh ever, yeah, ability.

Speaker 2 (17:40):
And then then they die. 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, ty, any little froggy heart attack?

Speaker 3 (18:04):
Is this because they can't regulate water?

Speaker 2 (18:06):
Oh look at you airon you're so smart?

Speaker 3 (18:10):
Yeah.

Speaker 2 (18:11):
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

(18:31):
seem to do, according to a twenty eighteen 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,

(18:55):
other organs can get messed up. So then other important
metabolites that you're body would normally produce, like say your
liver would normally produce these certain metabolites that liver the
liver can't do that because the other electrolytes are so
messed up. Does that make sense? So while kittred itself

(19:16):
doesn't invade frog's livers or hearts, the osmodic 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.

Speaker 3 (19:32):
That makes sense and horrible sad sense, Yeah.

Speaker 2 (19:35):
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 path of physiology of a disease,
I just I find a paper that's relatively recent, like
the last twenty years, and they've got pretty much an answer.

(19:56):
But in this one, if you go back just five
or ten 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 twenty eighteen 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

(20:18):
widespread electrolyte imbalance.

Speaker 3 (20:20):
I would bet that that's also just also a factor
of it being a wildlife disease versus a human disease.

Speaker 2 (20:26):
Definitely definitely funding research, etc. Right, 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

(20:49):
that makes sense.

Speaker 3 (20:50):
We don't have we lack the case studies in wildlife, Yeah,
exactly these cases.

Speaker 2 (20:54):
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 kittred amphibian Kittrid only infects
keratinized epithelium, so that means that actually tadpoles aren't infected,

(21:15):
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 b
D 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

(21:37):
they can be infected, so even really early early frogs,
but just not tadpoles specifically.

Speaker 1 (21:44):
Right.

Speaker 2 (21:44):
But what's also very interesting is that a lot of
free living Kittrid 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 hyperkeratotic response where the frogs they're not mounting an

(22:06):
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.

Speaker 3 (22:22):
Right, I mean, it's it's ingenious. Yeah, and huh, I
know where what else is keratin? Tell me more about keratin.

Speaker 2 (22:31):
So, keratin is the protein. It's all of our skin,
Like any skin that you see, it's all keratinized. 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.

(22:52):
So by the time that it reaches our outside environment,
it's like completely just mostly keratin. There's not really any
cell left.

Speaker 3 (22:59):
So why amphibians and not other animals.

Speaker 2 (23:02):
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.

Speaker 3 (23:19):
H Yeah, interesting.

Speaker 2 (23:21):
Yeah, so that's the biology.

Speaker 3 (23:24):
Oh that was it? What do you think? That was great?

Speaker 2 (23:28):
It was so fun to learn about. I knew nothing
about Kittrid. Oh yeah, no, I.

Speaker 3 (23:33):
Knew nothing except sort of like the broad sweeps.

Speaker 2 (23:37):
Of it, right, Like I knew 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 Kittrid is just
you know, all these dead frogs. That's all that I knew.

Speaker 1 (23:51):
Yeah.

Speaker 2 (23:51):
So, oh so, Aaron, tell me, how did we get here?
What's the history of this thing?

Speaker 3 (23:58):
Okay, I'll see what I can do.

Speaker 2 (24:01):
Right after this break.

Speaker 3 (24:30):
In the nineteen eighties, all over the world, the forest
started to go silent. Oh no, it started to become static.

Speaker 2 (24:40):
Still.

Speaker 3 (24:41):
This was not the vibrant, dynamic forest 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

(25:04):
untold numbers of frogs, toads, salamanders, amphibians, Now there were none.
Even stranger were the circumstances of this 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

(25:26):
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 quickly dismantled
by ants or dispatched by a bird within a matter

(25:48):
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

(26:09):
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

(26:30):
of me. But I don't think it'll be the last
one we see in our lifetime.

Speaker 2 (26:36):
You're probably right.

Speaker 3 (26:38):
Yeah, let's talk about amphibians. Okay, what does the word
amphibian mean?

Speaker 2 (26:45):
Oh, good question. Tell me.

Speaker 3 (26:48):
It comes from the Greek for double life, oh, which
is a nod to their close dependence on water and
moisture and sort of their transformation over their life cycle.

Speaker 2 (27:00):
Cool.

Speaker 3 (27:00):
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
and then frogs. So frog eggs and 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

(27:22):
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

(27:46):
two species that did this stomach brooding went extinct in
the nineteen eighties and haven't been seen since. Oh, I know,
it's cruel of me.

Speaker 2 (27:55):
That was really cruel. Are there any in captivity?

Speaker 4 (27:59):
No?

Speaker 1 (28:02):
Yeah.

Speaker 3 (28:04):
As of July sixteenth, twenty nineteen, when we're recording this episode,
there are eight and forty three 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

(28:28):
weird way, kind of creepy cute.

Speaker 1 (28:30):
I don't know.

Speaker 3 (28:32):
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 eight thousand amphibian species,
five hundred and one, which is around six point five percent,
have faced serious declines due to kittred, with at least
ninety possibly one hundred and twenty two confirmed or presumed

(28:56):
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.

Speaker 2 (29:15):
Wow, it's.

Speaker 3 (29:19):
Unprecedented, yeah 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,

(29:39):
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 frog.

Speaker 4 (29:49):
Yeah.

Speaker 2 (29:50):
Oh yeah, I knew that, but it's still crazy.

Speaker 3 (29:53):
Ones that literally freeze solid during winter and emerge again
in the spring, little spring peepers. The diversity of amphibians
is amazing, and their survivors they have gone through massive
extinction events and lived to tell about it. But their
long and incredible existence may be coming to an end,

(30:16):
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
nineteen eighties, and similar to how Tegan described it was
a pretty drastic shift researchers were coming back empty handed

(30:39):
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 science into the tension. In September

(31:03):
nineteen eighty nine, the first World Congress of Herpetology led
to a massive gathering of herpetologists from all over the world.

Speaker 2 (31:12):
Just imagine that room, man, herpetologists are.

Speaker 3 (31:16):
Some of the coolest people.

Speaker 2 (31:17):
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.

Speaker 3 (31:33):
It would be I mean, I'm not sure, Like I
think it would be the most fun.

Speaker 2 (31:38):
It would be pretty fun.

Speaker 3 (31:40):
I feel like they know how to party, but I
don't know. So at this conference that this World Congress
of Herpetology, researchers there began to talk amongst themselves about like,
oh yeah, I really had a hard time finding this
my study species this year, and someone would be like, oh,
me too, But I was doing research in this other country,

(32:03):
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

(32:27):
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

(32:48):
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

(33:12):
unless you get people who are not researchers interested and
passionate about the 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

(33:34):
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

(33:56):
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

(34:17):
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

(34:39):
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. A couple of years

(35:00):
after this disease hypothesis had been fully fleshed 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 seemed to harbor this pathogen. And so
the researchers who were like, hey, so do you do

(35:23):
you see this thing? Because I have a fungus on
my frog. Do you have a fungus on your frog?

Speaker 2 (35:27):
I just wanted to say that Aaron is using her
phone hands like yes, calling someone on the phone to
chat across global waters.

Speaker 3 (35:37):
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 peak at this.
So they met herpetology meeting another herpetology meeting, this one
in Da Da Champagne, Illinois.

Speaker 2 (35:53):
Not ah, yeah, stop it.

Speaker 3 (35:56):
In nineteen ninety eight, a bunch of researchers who've 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?

Speaker 2 (36:08):
That's adorable. I also should say I didn't mean to
throw shade on the other ologists earlier. They're all going
to get in trouble for they know, I know, right,
especially for like other entomologists. It's cool. We're all cool nerds.

Speaker 3 (36:23):
Everyone's cool in their own nerdy way. That's just how
it is.

Speaker 2 (36:26):
Yes, anyways, we're in Champagne. We're comparing fungi.

Speaker 3 (36:31):
I love it, well, the fungi. The I always say fungi, but.

Speaker 2 (36:36):
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.

Speaker 3 (36:44):
But these fungi were all the same. They looked and
they were like, how 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 kittrid And that's not that surprising, maybe because
kittred is everywhere, so you know, okay, that makes a

(37:06):
little bit of sense. But like you said, this was
unprecedented in its ability to infect and cause disease and vertebrates.
And the other thing was that it looked brand new,
like this was a different kind of kittred, and so
not only was a new species named, it was a
new entire genus that was created to house this bd.

Speaker 2 (37:28):
That's so exciting. Ugh, yeah, so exciting.

Speaker 3 (37:33):
This kittrid fungus seemed to be an unstoppable force. It
tore through populations and then just sat there waiting, because
kittred 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,

(37:55):
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

(38:16):
and climate change, and it still left this massive question
of how do we stop it. The story of amphibians
and kittred 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

(38:38):
kittred 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 you, No, I don't buy that.

Speaker 2 (38:49):
Highly skeptical expression for everyone.

Speaker 3 (38:51):
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.

Speaker 2 (39:00):
Like diseases don't just pop up everywhere at once, out
of nowhere. Nope, that's not yeah, nope.

Speaker 3 (39:08):
And there's also some catrid emergence and climate change seem
to be in some cases acting in conjunction with each other.
So yeah, again, and humans, this is human induced climate change.
This is humans have caused climate change. Yeah, yeah, that's
a fact anyway. But the other reason that you can't
tell the story of amphibian decline as one single event

(39:30):
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.

Speaker 2 (39:46):
Good, let's make this a more depressing episode.

Speaker 3 (39:49):
I mean, one of my favorite, one of my favorite
courses in college was called Dinosaurs and Disasters. So this
is really gone back to my my roots.

Speaker 2 (40:00):
Yeah.

Speaker 3 (40:00):
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 anthropiscene.

Speaker 2 (40:15):
But what is it?

Speaker 3 (40:16):
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 four hundred and fifty 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

(40:38):
around sixty five million years ago. That's the one that
wiped out all the dinosaurs and pterosaurs and plesiosaurs and
all the other cool animals, and based on the population
declines and extinction rates of not just the amphibians but
many other species, some researchers believe that we are in
the midst of the sixth Great Extinction event, and the

(41:00):
really is 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 mastdons and you know, all of the
amazing cave bears and Irish elk all I love parents.

Speaker 2 (41:22):
Face is getting so sad talking about this, you guys, I.

Speaker 3 (41:26):
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, 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

(41:49):
would call a background extinction rate, just a normal baseline
level of extinction. And it's when that extinction rate skyrockets
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 palaeontologist Michael Benton. He

(42:12):
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

(42:37):
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.

Speaker 2 (42:52):
Wow. Whoa, oh that's yeah, oh dear.

Speaker 3 (42:58):
The extinction rate currently is estimated to be two hundred
and eleven times higher than the background rate, or if
you take into account endangered species, as much as forty
five thousand times higher.

Speaker 2 (43:13):
Oh oh no, yeah, assuming that endangered species are very
unlikely to bounce back and are going to go extinct eminently.

Speaker 3 (43:21):
Yeah right, Yeah, Amphibians are the most endangered class of animals.
And even though this episode is about kittrid 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

(43:45):
sixth Extinction and estimated one third of rebuilding 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.

Speaker 2 (44:03):
Oh no, oh, yeah, this might be one of our
top most depressing episodes because it's like everything on the
planet is going to die.

Speaker 1 (44:16):
Yeah.

Speaker 3 (44:17):
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

(44:39):
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.

(45:03):
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,

(45:26):
Kittred itself doesn't seem to be brand new to amphibians,
and I mean like we've found it in I think
the earliest museum specimen is from nineteen thirty eight, 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

(45:47):
such widespread geographic distributions, something must have brought Kittred from
point A to point B. Amphibians can't cross oceans, but
humans can. For a while, while, the leading hypothesis of
where Kittred came from was that during the nineteen fifties
and sixties, the African Claude frogs that were being shipped

(46:09):
around the world for pregnancy tests carried the fungus. Do
you know that they were used for pregnancy tests?

Speaker 2 (46:17):
I you know, I didn't until we started researching this.
I knew rabbits were used, I didn't know that frogs
were used. Yeah, I found that very interesting.

Speaker 3 (46:26):
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 twenty eighteen, seems like the evidence is
pointing towards East Asia as the point of origin of

(46:47):
the bead fungus.

Speaker 2 (46:48):
I read two of the same papers as you are in.

Speaker 3 (46:51):
Haha.

Speaker 2 (46:52):
That doesn't happen very often, It doesn't.

Speaker 3 (46:55):
Well, I mean, we don't have a pathogen that often
that is discovered in the past thirty that's true.

Speaker 2 (47:00):
Yeah.

Speaker 3 (47:01):
With this ease and speed of travel, we are basically
living in a new Pangaea. 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.

Speaker 2 (47:27):
For those whom might have forgotten their like science class
from fifth grade when we learned what Pangaea was was
when all of the current continents were one giant, massive
super continent 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.

Speaker 3 (47:52):
Yeah, So researchers estimate that around five to fifteen percent
of Earth species have been described.

Speaker 2 (48:02):
Wow, so there are most of the undescribed ones are
like bugs.

Speaker 3 (48:07):
Probably probably bugs, bacteria, et cetera. Who knows, ar kia. Uh,
but probably many of these will live an entire existence
beforeever being described. Yeah, but why why do we care
about biodiversity? Aaron? Oh, if someone were to ask you

(48:28):
why does biodiversity matter? What would you say?

Speaker 1 (48:31):
Oh?

Speaker 2 (48:31):
Gosh, don't ask me to answer that on a podcast
because I need a scripted answer and I don't have one.

Speaker 3 (48:38):
Well, that's that's the thing. It is 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?

Speaker 1 (48:52):
Right?

Speaker 3 (48:52):
Do you have to know why it matters? Of course
it matters, But unfortunately it does matter because you we
need to convince people that maintaining or improving biodiversity.

Speaker 2 (49:03):
Is important, is importantile and worth their money.

Speaker 3 (49:07):
And I'm 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.

Speaker 2 (49:20):
Isn't that sad?

Speaker 3 (49:22):
Yeah, it's sad. And the sad thing is that the
most common line of reasoning is that you should care
about biodiversity because biodiversity benefits you economically.

Speaker 2 (49:33):
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.

Speaker 3 (49:43):
I hate those arguments too. Yeah, I hate them, and
I understand, 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?

Speaker 2 (50:02):
Ooh, amphibians are good sentinels, aren't they?

Speaker 3 (50:06):
Actually? So I've read something that they're not, so that
the image of the frog is the canary in the
mind is actually not a good indicator because they are
pretty resilient.

Speaker 2 (50:21):
That does make sense.

Speaker 3 (50:22):
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 in their population densities, et cetera,
et cetera.

Speaker 2 (50:34):
Also important parts of the ecosystem, and they do a
lot of things that very.

Speaker 3 (50:38):
Important ecosystem services. Yes, when I was looking into this,
there are four There are four reasons that were proposed
as to why amphibians why do they matter? Yes, one,
and I'm sure that you could find a whole number
of different listicles for this kind of thing, But one
is economics. So we use tons of amphibians for medical

(51:00):
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 esthetics. Yeah, yeah,

(51:24):
and they've inspired thousands of years of folklore and mythology
and tales. And also the final one, which is my 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.

Speaker 2 (51:46):
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 is it better to

(52:11):
rejoice in your power over things rather than respect things
around you?

Speaker 3 (52:16):
It just yeah, fling and appreciate them, and 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 Erlick that puts this nicely. In

(52:37):
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

(52:58):
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 Kittred was identified as the Great Amphibian Killer, it

(53:22):
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

(53:44):
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 re establish it in the wild, to restore ecosystem
functionality and health. Kittred's still there and not at all
bothered by the absence of its hosts. It's not safe

(54:05):
to release these amphibians back into the environment. So what
do we do now, Aaron?

Speaker 2 (54:15):
Oh, just that small question you want me to answer?

Speaker 1 (54:17):
Question?

Speaker 2 (54:20):
Okay? Well I might need a break first. Okay, So

(54:50):
that was depressing. So we'll do a quick little recap,
bring it back to kittred specifically, focus just on the
depressing parts of amphibian decline rather than everything. Yeah, you know,
small things. So, like you had mentioned, it's estimated that

(55:13):
at least five hundred species have declined, at least in
part due to Caittred. And one thing this is the
paper that we both read herein that I thought was
really interesting in this paper is that this puts BD

(55:33):
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.

Speaker 3 (55:50):
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 sixty three species.

Speaker 2 (56:02):
And they threaten four hundred and thirty.

Speaker 3 (56:04):
Yeah, so please, if you have an outdoor cat, don't
have an outdoor cat.

Speaker 2 (56:10):
Bring your cat inside, train it to be on a
leash and only let it out on a leash like
mister Norris, and or build a cadio. Yeah feral cats, man.
So anyways, yeah, so kittred is major. It's way more
major than the other high profile wildlife pathogens, things like

(56:31):
white nose, west nil, et cetera. Like this has affected
a hugely more species, which is very depressing, and all
but one it's specifically BD. So but true, No, I'm
not going to do it again b D.

Speaker 3 (56:49):
I didn't even attempt it if you if you noticed,
you know.

Speaker 2 (56:52):
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 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

(57:12):
is this really? So, Like you mentioned, the most recent
paper from twenty eighteen 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.

(57:34):
They sampled samples of kittred 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 kittred originated, so that's where it's from,
and they estimate that in the early nineteen hundreds is

(57:56):
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 fungusah. 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

(58:18):
really understand what the genetic diversity of kittrid 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.

Speaker 3 (58:31):
There's that really interesting map in that twenty nineteen 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

(58:53):
Asian origin because that is one of the lower rates
of population declines.

Speaker 1 (58:57):
Right.

Speaker 2 (58:58):
Yeah, it's really interesting. But since the early twentieth century,
if that's when bad began spreading.

Speaker 3 (59:04):
It has spread everywhere.

Speaker 2 (59:07):
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,

(59:32):
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 caittred in amphibians and
what they will continue to be on kittred abundance and distribution.

(59:56):
We don't really know. Does amphibian biodiverse city help spread
catrid 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

(01:00:16):
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

(01:00:36):
of cases. It's really complicated, and at this point we
don't fully understand what 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

(01:01:00):
and infection is actually really detrimental.

Speaker 3 (01:01:04):
So that makes bomber.

Speaker 2 (01:01:05):
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

(01:01:31):
this point I want to introduce who you heard in
our first hand account, doctor Tagan McMahon from the University
of Tampa, who's been studying Kittred for a number of
years and from a multitude of different perspectives. She's going
to tell us more about the status of kittred research,

(01:01:53):
including the importance of understanding the effects that kittred has
had on other species, because guess what, folks, As it
turns out kittred 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

(01:02:15):
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.

Speaker 3 (01:02:35):
Take it away, Tagan.

Speaker 1 (01:02:50):
My name is Tagan McMahon, and I am a biology
professor comparatipologist 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 ten 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

(01:03:14):
that are just extremely charming. They're really diverse in color,
They're these like little gems in the rainforests and out
in New England, you'd find this bright green frog calling
at the top of his lungs. I think they're just
wonderful creatures.

Speaker 3 (01:03:27):
So you work with kittured fungus, and so that's obviously
what this episode is going to be about. So could
you tell us what kittrid is exactly and why people
like you are studying it or why it's being researched.

Speaker 1 (01:03:42):
Hey, kiddrid fungus is a very weird fungus. It's so
typically when people think of fungus, they might think of
like Bordebella mushrooms or the type of mushroom that makes
a little mushroom cats 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

(01:04:04):
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 we've noticed that it's been causing massive declines
in amphibian populations. Some populations are able to handle the

(01:04:28):
infections real 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,
Adylopus is a particular genus of frogs that has been
completely and totally decimated by this fungus. So it's wiped

(01:04:52):
out dozens and dozens of species within this group completely
out of the environments. They're now being maintained in captivity.
You don't find them in the wild at all. Wow.

Speaker 3 (01:05:04):
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 say 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 also,
you know almost. And then the why question is why

(01:05:27):
some groups seem to be more vulnerable to kittrid than
other groups? Big question?

Speaker 1 (01:05:33):
Sorry, absolutely, and unfortunately 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 there's a lot of groups that are doing research
on this in a whole variety of different ways. And

(01:05:54):
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 kittred basically globally, anywhere you find amphibians,
you find the kittured fungus. And in addition to that,

(01:06:18):
people have looked through historical records and been finding these
preserved amphibians with traces of kittrid fungus on them from
the eighteen hundreds, 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 just discover
that a lot of those declines for food to the

(01:06:39):
kitchen pungus. 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
as to why it's been around forever, but we but
suddenly it's now freaking habits. One of the main idea

(01:07:00):
is 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

(01:07:22):
with habitat loss, with habitat fragmentation over exploitation of our population,
introduction and exotic species that are eating the native species, pollution,
climate change is a huge one, and other diseases all
coming in that these amphibian populations, which were very strong,
might have been able to handle one parasite infection coming

(01:07:45):
in like catred, 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

(01:08:08):
the host when they came through a host population, so
they didn't destroy entire population sympathians, 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 declines in the
last few decades, and.

Speaker 3 (01:08:29):
Some of these groups are completely wiped out and some
seem to be immune. Is it 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.

Speaker 1 (01:08:48):
Yeah, this is sort of a newer line of research
in this field. As I said, you know, the conservation crisis,
everybody's focused on what is happening and why, And now
that we've had enough trying to answer some of those questions,
we have a lot of researchers who are starting to
ask some of these other they're more tangential or connected
questions about immunity and things along those lines. What we're

(01:09:12):
finding is that some groups are either tolerance of the
fungus or resistance of the fungus. So the group is tolerant,
then they can have the fungus in their skin. The
fungus does just fine get 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

(01:09:34):
African flawed frogs, the Xenopus latis, for example. They're the
frog that you see in pet 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 the kitchen's fungus, so it can have a really
strong infection, but it's absolutely tolerant that and it doesn't

(01:09:55):
harm the frog at all. That means if that frog
were to get into the wild, it would be shedding
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,

(01:10:16):
they don't really get the infection. It's something about their system,
maybe it's the bacterial fawn 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

(01:10:38):
not be destroyed. And there's some really cool research just
starting to come out now that there are populations, many
which are in Central America, that we thought were basically
totally wiped out. So these are species that had really
big populations. Kitchard came through, wiped them out to essentially nothing.

(01:10:59):
In some case we thought they were extinct, and now
we're starting to see those populations come back. But my
hope is that those populations, as they come back, are
going to be either resistance or tolerance of the fungus.
The idea there's that everybody, all the individuals and the
populations that were susceptible to the fungus were killed off.

(01:11:23):
The few that could handle the infection or the few
that completely resisted the infections survived, and those are the
few that were there to make the next generation. See,
the hope is that we're seeing some potential re establishment
of populations that will be long term reestablishments.

Speaker 2 (01:11:43):
Wow, it's like antimicrobial resistant frogs.

Speaker 1 (01:11:47):
Yeah, yeah, like yeah, we could be really excited about.

Speaker 2 (01:11:53):
Yeah, that's so cool. Cool. And so you mentioned briefly
too that you've worked on a number of different communities,
not just in phibians. Even though frogs are maybe the
most well known for getting infected with Kittrid 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.

Speaker 1 (01:12:14):
If this is a really really exciting line of research,
because for so long we have focused strictly on the
kittrid tungus and amphibians, and to the extent where in
a lot of the papers you'll see the kittrien fungus
being called the amphibian kittrid fungus, And the reality is

(01:12:34):
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 house, you can focus
on that one host. If it's found in several or
even potentially dozens of posts that are all taxonomically different,
you have to really focus your models in a much

(01:12:56):
broader aspect. So the main house that I have done
and work with so far are crayfish or crawfish or crawdads,
and this is a group that is also found to
occurring with amphibians. In many cases, crayfish will dig burrows
and then it frogs will overwinter in those burrows, so

(01:13:16):
they'll actually like crawl down into the crayfish hole and
hang out with the crayfish in that hole over winter,
and then they re emerge in the spring. So they
frogs end up spending an extreme amount of time really
interacting with crayfish. In addition to that, the temples of
amphibians will eat the feces of crayfish and things like that.

(01:13:38):
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. That changes
the system and how we think about it. Right, if
it's only in amphibians, then they have to worry about amphibians.
If it's in crayfish, that can be a really really

(01:14:00):
huge changed to our management.

Speaker 2 (01:14:04):
Does it have like a detrimental effect to the to
the crawfish communities as well, or do they just seem
to tolerate the infection.

Speaker 1 (01:14:12):
So we have only looked at one genus of Profiss,
who's looked at a handful of different species within that.
But what we found is that in the lab, about
thirty five percent of individuals that were exposed to the
fungus died. Wow. The ones that did not die maintain
the fungus for a really long time, so like they
were a viable host and a pretty strong host. And

(01:14:35):
then they just kept living and living. There was no
issue at all of them. Wow. So they ate and
had no trouble to gain weight. They were totally healthy.
So about thirty five thirty six percent die and then
the rest are just fined. One of the other issues

(01:14:55):
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,

(01:15:17):
for example, and they'd close the juice jug and they
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

(01:15:38):
big issue because we're not tracking those 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 is. So we don't
know if thirty five percent of the individual that were

(01:16:00):
there died off because nobody's actually looking at those numbers.
So it's possible declined in the crayfish populations from the fungus,
but there was no one out there to ask those questions. Wow.

Speaker 3 (01:16:13):
Wow, that's fascinating. I also, I really love the image
of a little crawdad and frog just for real, hold
up together. Yeah, there's got to be a kid's book
about this.

Speaker 1 (01:16:27):
They are really cute. They're really really cute, little little
gray frogs that typically go down it and so furrows.

Speaker 2 (01:16:32):
That's very adorable.

Speaker 3 (01:16:36):
That's that's fascinating.

Speaker 2 (01:16:38):
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.

Speaker 1 (01:16:56):
Yeah, this is sort of an newer line of research
for us, 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

(01:17:17):
and right. And this particular line of research gives me
a lot of hope that we will be able to
help some populations re establish. So we're basing an off
the idea of herd immunity, which you guys did an
amazing job describing in your vaccine episodes. I was really
excited about that. But a brief it's the idea that

(01:17:39):
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 line fungus, and that fungus,

(01:18:02):
as they said, brows 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 froth, so we can let them have the live
infection for a few days, and then we moved them
over to a hot chamber and that kills the fungus

(01:18:25):
but doesn't harm the froth, so it allows us to
basically give them the live disease and then clear them
of the disease. And 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

(01:18:47):
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 while because we can't give them the fungus,
clear them of it, give them the fungus clear them

(01:19:09):
of it in the wild. That's just not feasible. So
we developed a non infectious vaccines. So 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

(01:19:30):
and 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 live hungus. So that's
super exciting because that means that we can expose individuals

(01:19:51):
to non infectious vaccine and then they'll have less infection
when they're exposed to the actual we'll funkus. So we
now have an NSF France, which is super exciting to
work on all of this. So we're looking at the
most effective form of the vaccine, So how can we

(01:20:13):
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 kittrid in the pond.
It's going to save everything without actually knowing that it's

(01:20:35):
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.

Speaker 3 (01:20:54):
That's so cool.

Speaker 1 (01:20:55):
It's really promising work, and we've had some really fantastic
responses from the different species we're looking at, and so
there is certainly the possibilities that we could go out
and vaccinate some of these frog populations that have been
removed from the environments that live in really small, isolated ponds.
We could vaccinate those groups and then repopulate those ponds

(01:21:20):
back to their more natural vac abundance, which would be
absolutely mean.

Speaker 2 (01:21:26):
Wow, that is so cool.

Speaker 3 (01:21:28):
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 what it really is,
what kind of advice would you have for somebody. I

(01:21:50):
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.

Speaker 1 (01:22:08):
Yeah, I love my job. This is if I could
have described to you as a young person what kind
of work I wanted to do. This is it. It's
fun and exciting. It's very hard, so it keeps my
brain really stimulated and it feels really meaningful because you
get to see actual changes happening in the field and
in the environment because of your work, which is absolutely incredible.

(01:22:32):
My suggestions are the sort of too bold. 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 and National
geographic and you think it's amazing, look for that the

(01:22:53):
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.

(01:23:14):
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 fieldwork?
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's career route to go.

Speaker 2 (01:23:36):
Great great pieces of advice, Absolutely fantastic.

Speaker 3 (01:23:39):
Are there any organizations or websites or anything like that
that you would like to give a shout out to
in regards to Kittrid or your research?

Speaker 1 (01:23:49):
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 tittrid fungus. One of the
groups the Smithsonian Tropical Research Institute, and they're part of
the Smithsonian, which has connections in the US and as
well as in the Panama, does an incredible job of

(01:24:12):
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 caytrid fungus, and they're maintaining these populations in

(01:24:36):
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

(01:24:58):
valuable in that space. There are other groups like Amphibian
Arcs and Save the Frogs that do a lot of
work as well trying to promote amphibian conservation.

Speaker 2 (01:25:10):
Excellent jinks.

Speaker 3 (01:25:13):
One last question. This might be an unfair question, but
do you have a favorite frog species?

Speaker 1 (01:25:19):
Oh?

Speaker 5 (01:25:19):
Man, Yeah, so this I get asked this question a lot,
and it is a really hard question because I want
to tell you yes, but then I also want to
list five.

Speaker 1 (01:25:30):
Or six different species. As longer 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 with all
my favorites come in the tree frogs groups, but one
of my very favorites is the common toad. There's a

(01:25:53):
picture of me as a two year old toad, and
the facialst question is me being very aware that maybe
I'm not supposed to be kissing. But I figured it
was back in the days of film and my mom
ran inside to get this film camera. She probably wasn't
very mad to me for kissing the toad. I'm gonna

(01:26:14):
have to think I'm gonna go with a tom toad.
But that's probably my favorite of all the groups.

Speaker 3 (01:26:20):
I love it.

Speaker 2 (01:26:21):
That's adorable.

Speaker 3 (01:26:23):
Yes, oh excellent, Aaron, Do you have anything any other question?

Speaker 2 (01:26:30):
No, this was so much fun.

Speaker 3 (01:26:32):
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.

Speaker 1 (01:26:44):
This is yeah, awesome, cool. Thank you you so much,
Thank you, thanks so much much.

Speaker 3 (01:27:10):
That was great. She's amazing, She's so fantastic.

Speaker 2 (01:27:14):
It was one of the funnest we've had a lot
of really fun interviews on this show. We have how
thrilling for us and you listeners.

Speaker 3 (01:27:24):
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, every
the world is going to end, etcetera, etcetera. 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

(01:27:49):
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,

(01:28:13):
conservation societies, volunteering, just reading more about it, it's talking
to people about Kittred. It's great.

Speaker 2 (01:28:22):
If you want to learn more about Tiggin's work, you
can find her lab Instagram at McMahon lab. So that's
mcmaho n Underscore Lab She also curates the parasitology instagram
at You of Tampa Underscore Parasitology so fun, and another

(01:28:44):
one at Wandering Ecologist, which is a lot of really
fun watercolors of wildlife and diseases and things like that.

Speaker 3 (01:28:52):
Yay, go check those out.

Speaker 2 (01:28:54):
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.

Speaker 1 (01:29:04):
Yeah.

Speaker 3 (01:29:08):
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 was
published in two thousand and nine. There's such amazing information
in there on the emergence of Kittrid and also just
the global amphibian crisis in general. And that's by James

(01:29:32):
Collins and Martha Crump and Thomas Lovejoy. And then I
also read The Sixth Extinction by Elizabeth Colbert and that
was great, very very interesting book. And then a few
papers quickly cretson from two thousand and two paper, Scaret

(01:29:53):
two thousand at All two thousand and seven paper, Wake
and Vandenberg two thousand and eight paper, Oh ham In
twenty eighteen paper and Shield twenty nineteen paper. Some of
those are eduls.

Speaker 2 (01:30:05):
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 dot com.
Under each episode you can find the sources from this
and all of our episodes, so check those out.

Speaker 3 (01:30:20):
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 Yeah, also a
link to it on our website.

Speaker 2 (01:30:30):
Well.

Speaker 3 (01:30:30):
Thank you first to Tegan for agreeing to be on
the podcast and sharing her amazing brain with us. Yeah,
we loved it.

Speaker 2 (01:30:39):
It was so much fun.

Speaker 3 (01:30:41):
And thank you to listeners. Thank you to you all
for listening and for yeah being you.

Speaker 2 (01:30:47):
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.
Oh that's a good one.

Speaker 3 (01:31:08):
Yeah, don't touch a frog. Don't touch a frog, don't
don't pick them up, just leave them there. They're chilling.