Speaker 1: Hey, welcome to Stuff to Blow Your Mind. My name
Speaker 1: is Robert Lambin. Today we have a vault episode for you.
Speaker 1: Of course, this is going to be our second episode
Speaker 1: in the four part Life in the Hypogean World series.
Speaker 1: So without further ado, let's dive right.
Speaker 2: In Welcome to Stuff to Blow Your Mind production of iHeartRadio.
Speaker 1: Hey, welcome to Stuff to Blow your Mind. My name
Speaker 1: is Robert.
Speaker 3: Lamb and I am Joe McCormick. And hey, we are
Speaker 3: back with part two of our series on cave ecosystems
Speaker 3: and Hypogean biology. Cave biology. In the last episode, we
Speaker 3: talked about some of the characteristic features of cave ecosystems
Speaker 3: and then we ended up discussing how lightless cave environments
Speaker 3: shaped the evolution of a creature called Astianax Mexicanus, or
Speaker 3: the blind Mexican cavefish, also known as the Mexican tetra,
Speaker 3: of which many populations have adapted to life in subterranean
Speaker 3: waterways by losing their eyes and the pigments in their flesh.
Speaker 3: We ended up kind of doing a deep dive on
Speaker 3: the evolutionary logic of this why an animal population that
Speaker 3: once had eyes and skin pigment would adapt over many
Speaker 3: generations to lose those traits in a cave. So if
Speaker 3: you haven't heard part one yet, you should probably go
Speaker 3: back and check that one out first. But we are
Speaker 3: back again today to talk about some more elements of
Speaker 3: cave biology. Specifically, one of the things I wanted to
Speaker 3: get into we didn't really have time for last time,
Speaker 3: was something else about blind Mexican cavefish, which is, if
Speaker 3: they have no sight, what do they do? How do
Speaker 3: they navigate their environment and forage for food?
Speaker 1: And this is key because they've got to eat something.
Speaker 1: These are extreme environments that are generally regarded as not
Speaker 1: being the most bountiful places to scrape out a livelihood
Speaker 1: as an organism.
Speaker 3: Right, and there might be some advantages to living in
Speaker 3: the cave if you are a fish like this, Like
Speaker 3: there might be fewer predators than you would encounter in
Speaker 3: the world above, but there are also fewer food resources,
Speaker 3: so you know, you have to have to kind of
Speaker 3: like shift your specialization.
Speaker 1: Yeah, Like, if I was to decide, again this is
Speaker 1: a non evolutionary example, but if I was to decide
Speaker 1: I am going to now live in my local Ikea store, well,
Speaker 1: you know, I've got to figure out some new things. Right,
Speaker 1: It's going to be easy to find a bed when
Speaker 1: the lights go out, but I'm going to have to
Speaker 1: deal with the night security. My diet is going to
Speaker 1: consist entirely of Ikea food. So if you like Lingenberry, yeah, yeah,
Speaker 1: make sure you don't have a Lingenberry allergy for sure.
Speaker 3: Yeah. So I wanted to explore this question of how
Speaker 3: do blind cavefish since their surroundings, and so I was
Speaker 3: looking into this and I discovered that apparently one major
Speaker 3: sense mechanism that they rely on is what's known as
Speaker 3: the lateral line system. And this is not a sense
Speaker 3: that is unique to blind cavefish. The lateral line system
Speaker 3: is found in lots of aquatic vertebrates, even those that
Speaker 3: can see. Though in blind fish there are usually enhancements
Speaker 3: to this system. So it's a sense that they already have,
Speaker 3: but it gets stronger in the cave evolved variants. As
Speaker 3: a side note, I always really enjoy imagining types of
Speaker 3: senses that humans don't have, Like what it would be
Speaker 3: like to have a different kind of sense, you know,
Speaker 3: like electro reception or magnetic perception or something like that.
Speaker 3: And this sense in particular, I'm very excited to try
Speaker 3: to imagine because it's very spooky trying to imagine it.
Speaker 3: It's something about it feels almost kind of Halloween. This
Speaker 3: might make more sense once I explain it. So, the
Speaker 3: basic function of the lateral line system is to detect
Speaker 3: movements in the water surrounding the animal through high sensitivity
Speaker 3: to changes in water pressure. This system it runs along
Speaker 3: the length of an animal like a fish, so there'll
Speaker 3: be sort of canals of the lateral line sensing organs
Speaker 3: around the head of the fish and then running lengthwise
Speaker 3: along the body. The system uses sensory organs known as
Speaker 3: neuro masts, which contain little hairs suspended within a kind
Speaker 3: of jelly filled capsule that bends in response to changes
Speaker 3: in water pressure and flow. And then these little hairs
Speaker 3: are connected to nerve cells that are strung along the
Speaker 3: lateral line system like Christmas tree lights. Sometimes the neuromasts
Speaker 3: are exposed to the water on the outside of the skin.
Speaker 3: They're just right on the outside of the skin, but
Speaker 3: other times they are contained within a kind of duct
Speaker 3: or canal that is just under the surface of the skin.
Speaker 3: And either way, the purpose of the lateral line system
Speaker 3: is to detect vibrations, movements, and objects within the water
Speaker 3: by sensing these little changes in water pressure and flow.
Speaker 3: So with this system, an animal can get feedback about
Speaker 3: its own movement through the water, for one thing, but
Speaker 3: it can also sense the presence of currents and nearby
Speaker 3: solid masses, either moving or stationary, by the way they
Speaker 3: displace water as the fish moves through it. And this
Speaker 3: is coming back to what I was saying a minute ago,
Speaker 3: something about trying to imagine this is. Oh, it's very
Speaker 3: evocative and a little bit scary, almost so imagining living
Speaker 3: in a place of dark water. But you can sense
Speaker 3: objects around you by the way they move the water,
Speaker 3: or by the way they change how the water moves
Speaker 3: around you.
Speaker 1: Wow, I mean, we're getting right back into that Gollumn territory,
Speaker 1: you know. I'm imagining Gollum sensing that that goblin that
Speaker 1: has come down and is washing its hands in the
Speaker 1: water and so forth on this lightless underground lake. And
Speaker 1: to your point, it is so alien to try and
Speaker 1: imagine this. I'm in the water a fair amount. I
Speaker 1: swim laps most morning, though swimming this morning, and it's
Speaker 1: still you know, it's a very visual exercise. You can
Speaker 1: set you can feel things in the water, obviously you can,
Speaker 1: and Lord knows, there's a lot to see and feel
Speaker 1: in a ymca pool. You know, there are people doing
Speaker 1: exercise classes, there are people swimming laps next to you,
Speaker 1: sometimes very often in the same lane with you, and
Speaker 1: you pick up on those movements, but nowhere near this
Speaker 1: level of detail. You know, this is like compared to
Speaker 1: what we have. This is like a second site.
Speaker 3: Yeah, I kind of ghostly vision through which you can
Speaker 3: sense things around you by the way they move the
Speaker 3: water against your body.
Speaker 1: Yeah.
Speaker 3: So anyway, the astianax fish, the Mexican blind cavefish apparently
Speaker 3: compensate for their lack of vision by having a more
Speaker 3: sensitive lateral line system than their surface dwelling cousins, and
Speaker 3: this helps them navigate, forage and survive in their lightless environment.
Speaker 3: But this way of living depends not just on heightened
Speaker 3: sensitivity to water displacement, but also on changes to behavior.
Speaker 3: For example, one thing I was reading about is that
Speaker 3: when preparing to mate, apparently male and female blind cavefish
Speaker 3: engage in this in these patterns of exaggerated movements of
Speaker 3: various body parts like the mouth and the gills, and
Speaker 3: these movements are thought to perhaps help the mating partners
Speaker 3: find and identify one another without visual cues, does some sense,
Speaker 3: like moving around in the water more so that they
Speaker 3: can locate one another. Of course, the fish also have
Speaker 3: changes to their metabolism to allow them to survive in
Speaker 3: a place where food is less abundant than it is
Speaker 3: on the surface, so they are thought to have slower
Speaker 3: metabolisms to need less food energy. But also I was
Speaker 3: reading about an interesting twenty seventeen study published in PLUS
Speaker 3: one by some researchers associated with the University of Cincinnati,
Speaker 3: and this was on the role of a symmetry in
Speaker 3: blind cavefish evolution. We actually did a whole series on
Speaker 3: asymmetry and animals a while back in which we talked
Speaker 3: about fiddler crabs and such, you know, fiddler crabs having
Speaker 3: one claw much much bigger than the other. But we
Speaker 3: talked about a lot of examples in the animal world,
Speaker 3: and I remember that being a very interesting series.
Speaker 1: Yeah, that was a fun one for sure. You know,
Speaker 1: some of the outrageous examples in some of the less
Speaker 1: obvious examples of asymmetry.
Speaker 3: Apparently there is a bit of hidden asymmetry in the
Speaker 3: blind Mexican cavefish as well. So let's see. This study
Speaker 3: was by Amandicaate Powers Aeronym Davis, Shane A. Kaplan and
Speaker 3: Joshua be Gross, published in Plus one in twenty seventeen,
Speaker 3: and it was called Cranial asymmetry arises later in the
Speaker 3: Life History of the blind Mexican cavefish Astianax Mexicanus. And
Speaker 3: so we were talking in the previous episode about how
Speaker 3: in some of these cavefish populations the fish are not
Speaker 3: without eyes from the very beginning. Rather, they do grow
Speaker 3: eyes initially in embryonic development, but then the eyes go
Speaker 3: through what's called regression where they are absorbed and disappear
Speaker 3: as the fish grows, and then the bone around the
Speaker 3: eye socket collapses in by the time the fish as
Speaker 3: an adult. Young cavefish apparently start life with fairly symmetrical bodies,
Speaker 3: and the surface variants in the rivers above where there's
Speaker 3: plenty of light also have fairly symmetrical bodies even as adults.
Speaker 3: But the young cavefish start out fairly symmetrical, and then
Speaker 3: as they mature, a mismatch develops in how the bones
Speaker 3: on either side of their skull take shape, and this
Speaker 3: asymmetry in their cranial bones seems to match a difference
Speaker 3: in behavior between the cave variant of the tetras and
Speaker 3: the surface variant still has eyes. The surface variant, when
Speaker 3: you place it in a fish tank, will swim in
Speaker 3: more random patterns or will just kind of float without
Speaker 3: moving in the shaded portions of the tank. The cave variant,
Speaker 3: on the other hand, will just keep it'll keep swimming
Speaker 3: in circles around the edges of its tank, and this
Speaker 3: matches with the fact that has been observed in the wild.
Speaker 3: In its natural environment, the cave variant will tend to
Speaker 3: follow the rocky walls of the pool where it lives,
Speaker 3: swimming counterclockwise around these boundaries in an endless loop. And
Speaker 3: one of the studies authors, Amanda Powers, was quoted in
Speaker 3: a press release about the research, explaining quote, you could
Speaker 3: see how asymmetry might be an advantage in navigation. They
Speaker 3: tend to swim in a unidirectional circular motion around their
Speaker 3: tanks to explore their surroundings. Having asymmetry in their skull,
Speaker 3: we think is attributed to handedness. If their skull is
Speaker 3: bent to the left, they could be right handed. They're
Speaker 3: feeling the wall to the right with their sensory structures.
Speaker 3: Oh wow, Yeah, so it seems that the cavefish have
Speaker 3: a type of developmental handedness that correlates to a navigation
Speaker 3: behavior where they follow the walls of their natural enclosure
Speaker 3: in this slow, counterclockwise lapping motion. Though I think it's
Speaker 3: still not fully understood how this system emerges, if it
Speaker 3: helps them survive how, we don't fully know yet, but
Speaker 3: it's interesting to imagine why. Another interesting sort of unrelated
Speaker 3: thing that I was just reading in this press release,
Speaker 3: also quoting the same author of the paper, I mean powers,
Speaker 3: talking about how she and colleagues went into the caves
Speaker 3: to observe these fish, and she says in this article quote,
Speaker 3: whenever you would touch the surface of the water with
Speaker 3: your finger, a swarm of cavefish would come right up
Speaker 3: to it. Not many fish would do that. These cavefish
Speaker 3: have zero predators, so they're not afraid.
Speaker 1: Oh wow, that you know. That reminds me of other
Speaker 1: examples we've talked about in the show, like various birds
Speaker 1: of the Galapagos Islands, for example. It reminds me of
Speaker 1: some stuff I was just reading the other day about
Speaker 1: the dodo bird. You know, where you have these organisms
Speaker 1: that adapt over evolutionary time to an environment where there
Speaker 1: are no predators or there is just an entirely different
Speaker 1: predation situation going on, and yeah, they just lose their fear.
Speaker 1: There's no need to engage in that kind of protective
Speaker 1: behavior because those things don't exist for them until they
Speaker 1: show up on a bub Yeah.
Speaker 3: Yeah, dutch. Okay, So that's lateral line sensations, and then
Speaker 3: the asymmetry of the skull, the kind of the circling behavior,
Speaker 3: all those differences. But there was one more thing I
Speaker 3: wanted to talk about. I mentioned in the previous episode
Speaker 3: another sensory enhancement found in some of these cavefish, and
Speaker 3: that sensory enhancement was taste. It appeared to be involved
Speaker 3: in a pliotropy. Remember that's where a single genetic change
Speaker 3: would result in multiple different changes in the phenotype in
Speaker 3: the body or the behavior. And in this case, the
Speaker 3: idea was that there was a single genetic change that
Speaker 3: would result in both regression of the eyes. So this
Speaker 3: process we talked about where the eyes are sort of
Speaker 3: absorbed and the adult fish doesn't have eyes, and then
Speaker 3: along with that development of a greater number of taste buds. Now,
Speaker 3: we speculated generally in the last episode that you know,
Speaker 3: having enhanced other senses in a cave would probably be
Speaker 3: useful in some way. Taste buds are generally useful. They
Speaker 3: are our body's chemistry set to know what we're putting
Speaker 3: in the digestive tract. But I was wondering if there
Speaker 3: was anything else we could know about that, like how
Speaker 3: do these extra taste buds work in these fish? What
Speaker 3: kind of benefit do they provide? So this is another
Speaker 3: thing where the answer is not fully known yet we
Speaker 3: know a few kind of interesting morsels. So I came
Speaker 3: across a very recent paper addressing this question. It was
Speaker 3: by Daniel Burning and Joshua B. Gross published in Frontiers
Speaker 3: and Ecology and Evolution twenty twenty three, called the Constructive
Speaker 3: Evolution of Taste in astianax Cavefish or Review. And one
Speaker 3: of the things I thought was interesting here, Rob, I've
Speaker 3: attached a I've attached a diagram for you to look at.
Speaker 3: It seems that mostly what we're talking about are what's
Speaker 3: called extra oral taste buds, taste buds that are not
Speaker 3: inside the mouth like hours, but outside the mouth and
Speaker 3: spread out over the jaws in the front of the face.
Speaker 3: So in this diagram, it shows blind cavefish from a
Speaker 3: couple of different populations compared to the surface variant with
Speaker 3: taste buds filled in as red dots on the illustrations.
Speaker 3: And while the surface variant looks like it is wearing lipstick,
Speaker 3: you know, the red dots, the taste buds are on
Speaker 3: the mouth, the cave fish are wearing clown makeup. The
Speaker 3: taste buds are all over the face.
Speaker 1: Yeah, it's quite impressive, And again it makes sense for
Speaker 1: this kind of an environment, you know, you need to
Speaker 1: lean into a different sense situation. It reminds me a
Speaker 1: bit of our past discussions about catfish being super tasters,
Speaker 1: you know, and really when and again it come back
Speaker 1: to that situation where we have our human understanding of
Speaker 1: the senses, but we have a human level understanding of
Speaker 1: those senses. And so when you're talking about something like
Speaker 1: this that is enhanced, it's not taste as we know it,
Speaker 1: it's something different.
Speaker 3: Yeah, exactly. So I was wondering, like, what do we
Speaker 3: know about what kind of difference this makes? What difference
Speaker 3: does it make in the lives of these fish? So
Speaker 3: there were a few things mentioned in this review. One
Speaker 3: is that multiple studies have found what appears to be
Speaker 3: enhanced sensitivity to chemical repellence and taste sources in the
Speaker 3: water in the cavefish when compared to the surface fish.
Speaker 3: So just one example is a study by Humbach in
Speaker 3: nineteen sixty that found in the cave fish compared to
Speaker 3: the common minno, that the modality for bitter sensation was
Speaker 3: three hundred times more acute roughly, and then the salty
Speaker 3: slash acid slash sweet modality difference was about two thousand
Speaker 3: to four thousand times more acute in the cavefish, so
Speaker 3: much greater, much lower I guess threshold of sensitivity to
Speaker 3: these tastes also protus at all. In two thousand and
Speaker 3: eight found quote amino acids dissolved in system water were
Speaker 3: detected at a much lower concentration in Paschone cavefish. That's
Speaker 3: from one particular cave source paschone cavefish, compared to surface fish.
Speaker 3: And one possible explanation the authors discuss for this heightened
Speaker 3: sensitivity to amino acids could be what they call the
Speaker 3: savory taste receptor T one R one. This is the
Speaker 3: receptor that binds to glutamate and helps us taste savory
Speaker 3: umami flavors. So I wonder if you could really get
Speaker 3: these cavefish going bananas over something in the water, a
Speaker 3: piece of food or whatever is dispersed in the water
Speaker 3: if you hit it with a bit of the good
Speaker 3: old MSG.
Speaker 1: I bet, or maybe one of those little fish shaped soy.
Speaker 3: Sauce. Yeah, we get soy sauce, some parmesan cheese, some tomatoes,
Speaker 3: some MSG, all the good savory things. However, the authors
Speaker 3: do say that several amino acids were used in the
Speaker 3: study that found this, so there could be other explanations,
Speaker 3: possibly also involving old faction rather than taste. But anyway,
Speaker 3: what difference would these these taste bud arrangements and heightened
Speaker 3: sensitivity to flavors make in terms of the behavior of
Speaker 3: the fish the author's right quote. One recent study argued
Speaker 3: that external taste buds are used for preliminary assessment of
Speaker 3: food items during random swimming or targeted searches for food.
Speaker 3: Extra oral taste buds thus carry in importance for determining
Speaker 3: whether to pursue or avoid a food item. So the
Speaker 3: way I understand that is it's heightening the fish's foraging
Speaker 3: efficiency basically by saying, before you even get something in
Speaker 3: the mouth, you're tasting the water around this thing with
Speaker 3: the front of your face, and it helps you zero
Speaker 3: in more quickly on something that is good to eat
Speaker 3: or is not good to eat. Like you're getting you're
Speaker 3: getting an idea about whether you're coming close to a
Speaker 3: good piece of food or not earlier. So that would
Speaker 3: make your foraging more efficient.
Speaker 1: Okay, that makes sense.
Speaker 3: In the end, however, they do say that that this
Speaker 3: is just an area that hasn't had enough research yet.
Speaker 3: They say that the quote precise function of cavefish extraoral
Speaker 3: taste buds remains unclear and largely unexplored, and then they
Speaker 3: also say that future studies need to do things like
Speaker 3: excluding the role of oldfaction or smell and isolating the
Speaker 3: variable of taste. And there are differences that even remain
Speaker 3: that they did examine in the paper that we just
Speaker 3: don't know how to explain yet, but could possibly be
Speaker 3: related to taste. One interesting idea they bring up is
Speaker 3: the feeding angle, so they you know, if you look
Speaker 3: at the cave variants of these fish versus the surface variants.
Speaker 3: One thing you will notice is that they both go
Speaker 3: along the bottom. Might there might be like a stony
Speaker 3: or sandy or pebbly bottom of the water source where
Speaker 3: they are, and they'll go along the bottom with their
Speaker 3: mouth down to the bottom, kind of searching for little
Speaker 3: bits of food to eat or you know, prey in
Speaker 3: the case of you know, carnivory, or just little bits
Speaker 3: of dead organic matter, whatever it is they're coming across
Speaker 3: to eat. They're scouring the bottom for it. For some reason,
Speaker 3: the surface fish have a steeper angle that they forage
Speaker 3: at with their body more it's almost more totally vertical,
Speaker 3: whereas the cave fish tend to forage at a more
Speaker 3: slanted angle that's closer. It's more like fifty five degrees
Speaker 3: from the bottom versus more like eighty degrees in the
Speaker 3: surface variant. They say this could be related to the
Speaker 3: changes in extraoral taste buds. Maybe it's you know, like
Speaker 3: they're tasting things differently, thus they have to orient their
Speaker 3: bodies differently. Don't know, but interesting question.
Speaker 1: Yeah, yeah, I mean this this is fascinating to think about,
Speaker 1: Like it makes one wonder if it has something to
Speaker 1: do with their being more predation opportunities for the surface fish,
Speaker 1: you know, like you've got to come in at that
Speaker 1: steeper angle because there's a greater risk of things, you know,
Speaker 1: on the floor of the of the sea or what
Speaker 1: have you, that might come after them while they're feeding.
Speaker 1: And maybe those are absent in these cave environments. Again,
Speaker 1: you know, we're talking about like a lack of just
Speaker 1: biodiversity in those environments. You know, there's many fewer predators,
Speaker 1: et cetera. But who knows. That's just me spitballing.
Speaker 3: I don't want to act like I'm just look at
Speaker 3: a diagram and a paper and answer the question. But
Speaker 3: just one thing I wonder about is looking at the
Speaker 3: looking again at the diagram of where these extraoral taste
Speaker 3: buds are in the surface fish. Remember they're all like
Speaker 3: right at the mouth, but in the in the cave variant,
Speaker 3: a lot of them tend to be spread out along
Speaker 3: the lower jaw. So I wonder if it can come
Speaker 3: in at this shallower angle because it's sort of like
Speaker 3: feeling and tasting more along the bottom without having to
Speaker 3: get the front of its mouth in contact with it.
Speaker 3: It can kind of taste with the slope of its
Speaker 3: lower jaw.
Speaker 1: Yeah, that would make a lot of sense.
Speaker 3: But yeah, again don't know interesting questions about Usually when
Speaker 3: you when you think about fish and taste together, you're
Speaker 3: thinking about what a fish tastes like to you, not
Speaker 3: what it's like to taste as a fish.
Speaker 1: Yeah, which again it can put you an entirely different
Speaker 1: sense realities, especially considering things like a catfish. But also
Speaker 1: you know, getting into taste and smell. When whenever I
Speaker 1: read information about, you know, the distances at which fish
Speaker 1: in the ocean can detect other things going on, say
Speaker 1: blood in the water or some sort of rotting shoe,
Speaker 1: I'm always just amazed because again it is an experience
Speaker 1: of the ocean that is just unlike anything we can
Speaker 1: experience when we venture into it. And the same holds
Speaker 1: true of the cave. Like when we enter into the cave,
Speaker 1: our experiences are rather different compared to the organisms that
Speaker 1: have evolved to thrive there. Now the place I'd like
Speaker 1: to turn to next. This gets into something that was
Speaker 1: probably one of the key reasons I decided this would
Speaker 1: be a good series for us to do, you know,
Speaker 1: to return to cave biology. This and the fact that
Speaker 1: I was also inspired by some environment related stuff at
Speaker 1: the Bishop Museum on a Wahuo recently when I returned
Speaker 1: there and got to take in their natural history section
Speaker 1: in addition to their cultural and historical sections. But yeah,
Speaker 1: this is the revelation that really pushed me over the
Speaker 1: edge that for many cave environments, batguano is sunlight. Ooh, batguano,
Speaker 1: that's bat poop if you will, if you're not familiar
Speaker 1: essentially in these environments, yes, this is the light of
Speaker 1: the sun. This plays a vital role in the food
Speaker 1: chain because remember light is the first step in the
Speaker 1: food chain of the Epigean world. Sunlight reaches the surface
Speaker 1: where photo autotrophic organisms create food via sunlight, carbon dioxide
Speaker 1: and water. These are autotrophs, and we call this the
Speaker 1: trophic level of the food chain.
Speaker 3: Right, So yeah, this came up in the last episode
Speaker 3: that almost all of the food chain where we're really
Speaker 3: familiar with is happening where the base layer of the
Speaker 3: food chain is using energy from the sunlight to make
Speaker 3: its food and then we of course you know, other
Speaker 3: organisms eat those organisms and on and on it goes.
Speaker 3: But if you don't have the sunlight to power the
Speaker 3: food synthesis at the base layer of the food chain,
Speaker 3: what do you do.
Speaker 1: That's right, yeah, yeah, most of it depends on sunlight.
Speaker 1: Plants are autotropes, as are seaweed phytal blanked in some
Speaker 1: kinds of bacteria, including bacteria that produce their own food
Speaker 1: vio chemosynthesis around volcanic vents. But most of the producers
Speaker 1: are producing their own food via the process of photosynthesis
Speaker 1: and therefore require the bounty of sunlight. The next trophic
Speaker 1: layer of the food chain is, of course the primary
Speaker 1: consumers who eat the producers, the herbivores being chief among them.
Speaker 1: And then the predators compose the third trophic layer, the
Speaker 1: secondary consumers, followed by the tertiary consumers and on up
Speaker 1: to the apex predators. And then you have you know,
Speaker 1: you also have the other roles in there, the you know,
Speaker 1: the scavengers, the decomposers, and so forth. Now, it's pointed
Speaker 1: out by sakoy at All in The Life Hidden Inside Caves,
Speaker 1: published twenty twenty in the International Journal of Ecology. Cave
Speaker 1: ecosystems are intrinsically devoid of primary productivity due to the
Speaker 1: absence of light. Again, light may enter the opening of
Speaker 1: a cave to different degrees, and other caves may feature
Speaker 1: open areas or areas with sort of like naturally occurring skylights.
Speaker 1: But past those pools of light there is only darkness,
Speaker 1: and that means again no photo autotrophic organisms.
Speaker 3: Right, So this raises a question of how could there
Speaker 3: really be anything like an ecosystem inside a cave unless
Speaker 3: I don't know, it was just like unless things were
Speaker 3: coming and going from the outside to the inside constantly
Speaker 3: and eating each other in between. You know, how could
Speaker 3: there really be anything sustained within the cave purely in
Speaker 3: the dark.
Speaker 1: And that's where bats enter the picture. We've of course
Speaker 1: talked about bats before. You have various species of bats
Speaker 1: that roost in cave and viral and do so in
Speaker 1: vast numbers. So batguano instead offers a major food source,
Speaker 1: a kind of alternate sunshine, brown sunshine if you will,
Speaker 1: that falls upon the floor of caverns where insectivore or
Speaker 1: frugivorous bats roost. So yeah, batsidiat insects bats that eat fruit.
Speaker 1: So we're talking about bat species that are generally nocturnal
Speaker 1: or crepuscular, that go out and feed and then return
Speaker 1: to the seclusion of their caves where they roost on
Speaker 1: the ceiling and when they poop, they poop on the
Speaker 1: floor below them, and that poop brings in quite a
Speaker 1: few nutrients.
Speaker 3: So it's not like the base the photo autotroflayer outside,
Speaker 3: because in that case it is that would be organisms
Speaker 3: that are fundamentally synthesizing chemical food energy out of what
Speaker 3: was originally inorganic sunlight energy. In this case, they are
Speaker 3: bringing energy in already in the form of chemical food
Speaker 3: energy pooping it out on the floor, but it becomes
Speaker 3: like a new base layer of a food chain within
Speaker 3: the cave.
Speaker 1: Exactly. Yes, And I will also add it is like
Speaker 1: sunlight in that you can replace the word sun or
Speaker 1: sunlight with bat guano in any song lyric and it
Speaker 1: will work just as well. So please feel free to
Speaker 1: try that on your own time.
Speaker 3: I'm walking on guano.
Speaker 1: Yeah, yeah, yeah, it works.
Speaker 3: It works perfectly, don't I feel good?
Speaker 1: So this guano often serves as the primary renewable organic
Speaker 1: resource of these caves, and a whole food chain extends
Speaker 1: from this, supporting various bacteria, fungi, uh protus, and small arthropods. Now,
Speaker 1: according to Sokoi, at all, the exact blend of nutrients
Speaker 1: is going to vary depending on broad category and specific
Speaker 1: species of bat. But the end result is that the
Speaker 1: fields of poop beneath the bats just become teeming with life,
Speaker 1: life enough to support an ecosystem of organisms, including those
Speaker 1: visiting from the outside, other creatures that spend part of
Speaker 1: their time in the caves, and also of course obligate
Speaker 1: cave dwellers that are there all the time. Also, this
Speaker 1: was interesting, the fermentation of the biomass, along with the
Speaker 1: presence of all those warm blooded bat colonies actually heats
Speaker 1: up the caves.
Speaker 3: Oh that's interesting. You know, that's a difference that is
Speaker 3: acknowledged in some of the literature I've looked at, but
Speaker 3: we haven't really talked about much. Which is a difference
Speaker 3: between cave environments and the surface is not only the
Speaker 3: lack of sunlight, but a much more constant temperature than
Speaker 3: you get on the surface. Though I guess this could
Speaker 3: be changed if yeah, you're bringing in a lot of biomass,
Speaker 3: and that's sort of like warming up the cavern.
Speaker 1: Yeah, like at base level, it's like life in the
Speaker 1: wine cellar. But then if you get enough life in
Speaker 1: the wine cellar, well things they can have elevated temperatures,
Speaker 1: but still going to be pretty dependable. It sounds like, though,
Speaker 1: I guess you do have to factor in that there
Speaker 1: are sometimes fluctuations in these the occupation by bats and
Speaker 1: so forth.
Speaker 3: I do have to apologize I'm only half following the
Speaker 3: conversation now because my brain is just running through song
Speaker 3: lyrics like I've been waiting so long to be where
Speaker 3: I'm going in the guano of your love of.
Speaker 1: Guano on my shoulder shoulders makes me happy. Yeah, yeah,
Speaker 1: I'm want to read a quote here from the sequoiad
Speaker 1: All paper that gets into some of the details here
Speaker 1: of the guano quote. For example, small metazoins such as mites, pseudoscorpions, beetles, thrips, mites,
Speaker 1: and flies inhabit the guano of insectivorous bats, whereas the
Speaker 1: guano of frugivorous vat bats is frequented by spiders, mites, isopods, millipedes, centipedes, waiters,
Speaker 1: bark lice, and insects. Salamander and cavefish populations and invertebrate
Speaker 1: communities also rely heavily on nutrients from the bat guano.
Speaker 1: They also point out that bat guano constitutes a niche
Speaker 1: of several varieties of micro organisms. Includeing fungi, protus, lichen viruses,
Speaker 1: and bacteria.
Speaker 3: I wonder if the bat guano is primarily sweet or savory.
Speaker 1: I guess we'd have to ask those blind cavefish from earlier.
Speaker 3: Yeah, though, to be fair, in that quote, it just
Speaker 3: said that the cavefish populations rely on nutrients from bat guano.
Speaker 3: I don't know if that means they eat it directly
Speaker 3: or they eat other things that eat it, or what.
Speaker 1: True true that that is essential and I believe that
Speaker 1: something sakoy at All point out is that it's yeah,
Speaker 1: there aren't necessarily there are organisms that depend on the
Speaker 1: guano that are not directly eating the guano, but they
Speaker 1: are able to thrive on the things that do consume
Speaker 1: and thrive on the guano directly. Now, it's it's also
Speaker 1: worth noting that the presence of the bats themselves also
Speaker 1: produces feeding and opportunities for either scavengers or predators. I'm
Speaker 1: going to probably have more on this particular tidbit in
Speaker 1: the next episode. And yeah, there's another interesting thing that
Speaker 1: they point out is all of this can potentially change
Speaker 1: over time as well, you know, stable environments but not
Speaker 1: necessarily eternal. I was reading a CBC Radio story about
Speaker 1: a University of Ottawa study of bat guano in a
Speaker 1: specific Jamaican cave or cave system. I believe this cave
Speaker 1: is known as Home Away from Home cave. It's very
Speaker 1: remote and it has been a subject of some scientific
Speaker 1: study and they were looking at it and they were
Speaker 1: able to observe a shift over in the past from
Speaker 1: insect eating bats to fruit eating bats, though it was
Speaker 1: unclear as of twenty twenty one if this was a
Speaker 1: change in diet by a specific species or perhaps more
Speaker 1: likely the influx of a different bat species that had
Speaker 1: a different diet. They also found increased guano levels of cadmium, mercury, lead,
Speaker 1: and zinc present during the same time as the Industrial Revolution,
Speaker 1: so they were getting into like, you know, we can
Speaker 1: see this change, We can see this environmental change brought
Speaker 1: on by the Industrial Revolution in the of these bats
Speaker 1: in this remote Jamaican cave.
Speaker 3: Heavy metal guano.
Speaker 2: Yeah.
Speaker 1: Now, of course we have various other creatures besides the bat,
Speaker 1: but also from the era of bats to consider that
Speaker 1: are now extinct that would have entered into caves and
Speaker 1: and would have defecated. We have like the cave bear,
Speaker 1: that is extinct, the extinct cave hyena copy lights from
Speaker 1: both of these species. Fossilized fecal matter has been discovered
Speaker 1: in caves. Yeah, now another tidbit, and this is something
Speaker 1: you could definitely go in deeper on. We could come
Speaker 1: back to another episode in the future at some point.
Speaker 1: Sequoiat All point out that the other thing about bat
Speaker 1: guano is that human beings figured out that, hey, this
Speaker 1: stuff has value. So cave environments have also long been
Speaker 1: exploited by human beings due to its economic value as
Speaker 1: a fertilizer and also, for at least for a while there,
Speaker 1: it was harvested to produce gunpowder. And all of this
Speaker 1: can impact these cave environments. Here's another interesting thing. Bats,
Speaker 1: the bats that enter into these caves, these caves, they
Speaker 1: are not set in stone. They are changing. We just
Speaker 1: discuss how these caves form over geologic time in the
Speaker 1: first episode. But the bats by roosting in the caves
Speaker 1: physically change them roosting on the ceiling with their little claws,
Speaker 1: so that physically changes the cave. And then also there's
Speaker 1: chemical augmentation of the caves via their urination. Because yeah,
Speaker 1: they're going both number one and number two in that
Speaker 1: cave system and it does have an impact.
Speaker 3: Oh do you know if the urination does it primarily
Speaker 3: like build structures or dissolve parts of the cave.
Speaker 1: I believe it is more dissolving. Yeah, okay, And again
Speaker 1: we're dealing often with limestone cave systems and so forth.
Speaker 1: So that's my understanding here, because I know what you're thinking.
Speaker 1: We end up with actual like.
Speaker 3: Bat piece stalagmites.
Speaker 1: Yeah, bat piece stalagmites. I do not have an answer
Speaker 1: to that, but I think it is more of a
Speaker 1: dissolving of the cave system that is in play here.
Speaker 3: Wait a minute, hold on, I just googled bat piece
Speaker 3: stalagmites with large numbers of bats, thick and hard stalactites
Speaker 3: and stalagmites of crystallized bat you'rein occasionally form.
Speaker 1: Well, there you go. Okay, so that is also possible.
Speaker 1: It's just a wonderful world down there. It's a whole
Speaker 1: new world.
Speaker 3: Sorry, I should say, since I read that directly, that
Speaker 3: was from something called the Internet Center for Wildlife Damage Management.
Speaker 3: I don't know what that is, but that's what they claim.
Speaker 1: Yeah, there was another art. I didn't get into this
Speaker 1: article a lot. Maybe I could come back more in
Speaker 1: the next episode. But there was a twenty twenty one
Speaker 1: article in The New York Times titled how bats and
Speaker 1: their poop erase ancient cave art, and that one got
Speaker 1: into this issue of it because again they're changing the caves,
Speaker 1: and sometimes that can change things that prehistaric humans did.
Speaker 3: Wow.
Speaker 1: They point out that large quantities of the urine and
Speaker 1: the guano it ferments, it can saturate the air with
Speaker 1: quote aerosolized particles of phosphoric acid. So it's a rich
Speaker 1: world down there. Goodbye horsetoodle. Now an interesting and largely
Speaker 1: unanswered question for me, they would get some answers on it.
Speaker 1: Pertains to the question what might cave environments have been
Speaker 1: like before the evolution of cave roosting bats, because again,
Speaker 1: bats are mammals, and mammals have not in their highly
Speaker 1: successful mammals, they've been around for a while, but they
Speaker 1: haven't always been around. So what would have potentially pooped
Speaker 1: up these caves and sustained these ecosystems before bats.
Speaker 3: That's a good point. So like the base layer of
Speaker 3: the food, the food web within the cave is emerging
Speaker 3: from back guano, and there were at a time, no
Speaker 3: back to bring the guano in. Could there be an
Speaker 3: ecosystem in the cave at all?
Speaker 1: Exactly? Yeah, And I think by and large the answer
Speaker 1: is yes, there would have been things that have done that.
Speaker 1: And we know that in part because even today bats
Speaker 1: are not the only trogs to poop in a cave.
Speaker 1: There are considerable factors, but crickets are often brought up
Speaker 1: as another major cave pooper that allows the sun to
Speaker 1: shine in these lightless places. So it would seem that
Speaker 1: prebat organisms would have taken advantage of the cave niche
Speaker 1: to do, you know, to whatever degree they could. One
Speaker 1: of the things about investigations into cave fossils is that
Speaker 1: fossils that you find in deep caves aren't necessarily telling
Speaker 1: you about subterranean life. Tracks in the floor or even
Speaker 1: ceilings of deep caves may actually be insightful about life
Speaker 1: along shorelines of the surface. You know. That's the degree
Speaker 1: of time that we're dealing with, and considering the likes of,
Speaker 1: for instance, a five hundred meter deep that's a third
Speaker 1: of a mile deep cavern in France. I was reading
Speaker 1: about this is and I may be butchering French here,
Speaker 1: likely am castle book cave. Here, for instance, you'll find
Speaker 1: dino footprints that were first etched in mud or sand
Speaker 1: on a beach one hundred million years ago, and they've
Speaker 1: just been gradually forced underground over time.
Speaker 3: So it's not like they were formed in the cave.
Speaker 3: These are rocks that were formed on the surface and
Speaker 3: then they later emerged in a cave.
Speaker 1: Yeah, and kind of similar to like, oh, you can't
Speaker 1: find a trillobte in a mountain and be like these
Speaker 1: were the mountain trilobites. It's not really what's happening. But
Speaker 1: of course this doesn't mean we don't have evidence of
Speaker 1: dinosaur age cave dwellers. As reported by Nature in twenty twenty,
Speaker 1: cockroaches preserved in amber from ninety nine million years ago
Speaker 1: are likely the oldest evidence we have of organisms evolved
Speaker 1: for life in a cave environment.
Speaker 3: Million year old cave cockroaches. What were they like?
Speaker 1: Oh, they were they were kind of scary. I included
Speaker 1: an image here of one for you, Joe. This is
Speaker 1: one of the species that they were looking at, and
Speaker 1: you'll see that it has front appendages, these kind of
Speaker 1: like raptorial four legs, much like a praying mantis, which
Speaker 1: means they were likely a highly predatory species in their
Speaker 1: cave environments. MM. So that's that's one of the features
Speaker 1: that they found on these these amber preserved specimens. There's
Speaker 1: lost coloration, there's reduced wing and eye size, elongated antennae,
Speaker 1: and and reduced leg spines for passive defense. So two
Speaker 1: species were discovered in amber in this cave from me
Speaker 1: and mar, one of which apparently had these raptorial four legs,
Speaker 1: meaning it was it was likely primarily a predator. And
Speaker 1: according to a paper in Cosmos magazine by James Urckhart,
Speaker 1: one of the one of the interesting things about this
Speaker 1: find is that the specimens in question would seem to
Speaker 1: have mid Cretaceous origins, but all cave animals living today
Speaker 1: have a late Sinozoic origin. Now, why these older cave
Speaker 1: organisms died out is apparently a mystery, because it would
Speaker 1: seem like an ideal place to shelter and survive surface
Speaker 1: world extinction events, but obviously that's not the case. The
Speaker 1: article also stresses that it's not impossible that these cockroaches
Speaker 1: may have survived even into modern times in one form
Speaker 1: or another, because our understanding of living insects is of
Speaker 1: course incomplete, so it's not impossible even though we're gazing
Speaker 1: backwards through time with this particular specimen, its genetic legacy
Speaker 1: could still be alive today. The article here is quite good.
Speaker 1: It also stresses some of the larger challenges of understanding
Speaker 1: such ancient cave environments in figuring out what they consisted of.
Speaker 1: Other Mesozoic cave organisms, it certainly existed, but either we
Speaker 1: get into the same problems we encounter with the inherent
Speaker 1: incompleteness of a fossils in general on the fossil record,
Speaker 1: because either a cave system collapsed long ago or key
Speaker 1: to this example, didn't allow fossil preservation. This case, amber
Speaker 1: containing cave organisms is rather unique because a tree is
Speaker 1: not going to grow in said cave. They say this
Speaker 1: is kind of like a one in a million fine
Speaker 1: because it probably depended on resin from a tree growing
Speaker 1: directly in the mouth of a cave, like in exactly
Speaker 1: the right place, exactly the wrong right time, in order
Speaker 1: to capture this creature that otherwise would not be venturing
Speaker 1: out of the caves to climb around on trees.
Speaker 3: Yeah, that's interesting, and I was wondering I was going
Speaker 3: to ask about exactly that like, how does a cave
Speaker 3: cockroach get trapped in amber? So I guess the answer
Speaker 3: is probably very rarely happened. We're incredibly lucky to have
Speaker 3: this unique find.
Speaker 1: Yeah, and it just raises the question, like what else
Speaker 1: would have been down there that we didn't crawl into
Speaker 1: the amber. You know, there's again just so many mysteries
Speaker 1: within within the fossil record, and back to the earlier point,
Speaker 1: so many mysteries remaining and just sort of the in
Speaker 1: the the existing organic world. You know, we're still making
Speaker 1: discoveries regarding insects, cave environments, of cave ecosystems. It's I mean,
Speaker 1: it's really exciting.
Speaker 3: No doubt, And you know what, I think we're going
Speaker 3: to have to end today's episode there, but we've got
Speaker 3: more cave stuff to talk about. So we're going to
Speaker 3: be back with part three definitely.
Speaker 1: That's right. We're gonna get into some cave creditors and
Speaker 1: who knows what else. All right, stuff to blow your mind.
Speaker 1: As you know. Core episodes are on Tuesdays and Thursday.
Speaker 1: We're primarily a science and culture podcast, and then on
Speaker 1: Mondays we do listener mail. On Wednesdays we do a
Speaker 1: short form episode, and then on Fridays we set us
Speaker 1: on most serious concerns to just talk about a weird
Speaker 1: film on Weird House Cinema. We bust out a rerun
Speaker 1: on the weekends.
Speaker 3: Huge thanks as always to our excellent audio producer JJ Posway.
Speaker 3: If you would like to get in touch with us
Speaker 3: with feedback on this episode or any other, to suggest
Speaker 3: a topic for the future, or just to say hello,
Speaker 3: you can email us at contact at stuff to Blow
Speaker 3: your Mind dot com.
Speaker 2: Stuff to Blow Your Mind is production of iHeartRadio. For
Speaker 2: more podcasts from my heart Radio, visit the iHeartRadio app,
Speaker 2: Apple Podcasts, or wherever you're listening to your favorite shows.