Speaker 1: Welcome to Stuff to Blow Your Mind, a production of iHeartRadio.
Speaker 2: Hey, Welcome to Stuff to Blow Your Mind. My name
Speaker 2: 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 evolution mary logic of this why an animal population
Speaker 3: that once had eyes and skin pigment would adapt over
Speaker 3: many generations to lose those traits in a cave. So
Speaker 3: if you haven't heard part one yet, you should probably
Speaker 3: go back and check that one out first. But we
Speaker 3: are back again today to talk about some more elements
Speaker 3: of cave biology, specifically One of the things I wanted
Speaker 3: to 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 site, what do they do? How do
Speaker 3: they navigate their environment and forage for food?
Speaker 2: And this is key because they've got to eat something.
Speaker 2: And these are extreme environments that are generally regarded as
Speaker 2: not being the most bountiful places to scrape out a
Speaker 2: livelihood as an organism.
Speaker 3: Right, And there might be some advantages to living in
Speaker 3: a 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 you have to kind
Speaker 3: of like shift your specialization.
Speaker 2: Yeah, Like, if I was to decide, again, this is
Speaker 2: a non evolutionary example, but if I was to decide
Speaker 2: I am going to now live in my local Ikea store, well,
Speaker 2: you know, I've got to figure out some new things. Right,
Speaker 2: It's going to be easy to find a bed when
Speaker 2: the lights go out, but I'm gonna have to deal
Speaker 2: with the night security. My diet is going to consist
Speaker 2: entirely of Ikea food.
Speaker 3: So if you like Lingenberry.
Speaker 2: Yeah, yeah, make sure you don't have a Linenberry allergy
Speaker 2: 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 and see. Though in blind fish there are usually
Speaker 3: enhancements to this system, so it's a sense that they
Speaker 3: already have, but it gets stronger in the cave evolved variants.
Speaker 3: As a side note, I always really enjoy imagining types
Speaker 3: of senses that humans don't have, like what it would
Speaker 3: be 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 halloweeny. 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 nals 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 that the purpose of the lateral line
Speaker 3: system is to detect vibrations, movements, and objects within the
Speaker 3: water by sensing the 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 2: Oh wow, I mean, we're getting right back into that
Speaker 2: Gollumn territory, you know. I'm imagining Gollum sensing that goblin
Speaker 2: that has come down and is washing its hands in
Speaker 2: the water, and so forth on this lightless underground lake.
Speaker 2: And to your point, it is so alien to try
Speaker 2: and imagine this. I'm in the water a fair amount.
Speaker 2: I swim laps most mornings. They'll swim in this morning,
Speaker 2: and it's still you know, it's a very visual exercise.
Speaker 2: You can send You can feel things in the water,
Speaker 2: obviously you can. And Lord knows, there's a lot to
Speaker 2: see and feel in a Ymca pool. You know, there
Speaker 2: are people doing exercise classes, there are people swimming laps
Speaker 2: next to you, sometimes very often in the same lane
Speaker 2: with you, and you pick up on those movements, but
Speaker 2: nowhere near this level of detail. You know, this is
Speaker 2: like compared to what we have. This is like a
Speaker 2: second site.
Speaker 3: Yeah, I kind of ghostly vision through which you can
Speaker 3: you can sense things around you by the way they
Speaker 3: move the water against your body.
Speaker 2: Yeah.
Speaker 3: So anyway, the astyanax 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 that
Speaker 3: make sense, like moving around in the water more so
Speaker 3: that they can locate one another of course, the fish
Speaker 3: also have changes to their metabolism to allow them to
Speaker 3: survive in a place where food is less abundant than
Speaker 3: it is on the surface, so they are thought to
Speaker 3: have slower metabolisms to need less food energy. But also
Speaker 3: I was reading about an interesting twenty seventeen study published
Speaker 3: in Plus one by some researchers associated with the University
Speaker 3: of Cincinnati, and this was on the role of a
Speaker 3: symmetry in blind cavefish evolution. We actually did a whole
Speaker 3: series on asymmetry and animals a while back in which
Speaker 3: we talked about fiddler crabs and such, 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 2: Yeah, that was a fun one for sure, you know,
Speaker 2: with some of the outrageous examples in some of the
Speaker 2: less 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 Amandicate Powers, aeronam 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 a Stianax Mexicanus.
Speaker 3: And so we were talking in the previous episode about
Speaker 3: how in some of these cavefish populations, the fish are
Speaker 3: not without eyes from the very beginning. Rather, they do
Speaker 3: grow eyes initially in embryonic development, but then the eyes
Speaker 3: go through what's called regression where they are absorbed and
Speaker 3: disappear as the fish grows, and then the bone around
Speaker 3: the eye socket collapses in by the time the fish
Speaker 3: is an adult. Young cavefish apparently start life with fairly
Speaker 3: symmetrical bodies, and the surface variants in the rivers above
Speaker 3: where there's plenty of light also have fairly symmetrical bodies
Speaker 3: even as adults. But the young cavefish start out fairly symmetrical,
Speaker 3: and then as they mature a mismatch develops in how
Speaker 3: the bones on either side of their skull take shape.
Speaker 3: And this asymmetry in their cranial bones seems to match
Speaker 3: a difference in behavior between the cave variant of the
Speaker 3: tetras and the surface variant still has eyes. The surface
Speaker 3: variant when you place it in a fish tank, will
Speaker 3: swim in more random patterns or will just kind of
Speaker 3: float without moving in the shaded portions of the tank.
Speaker 3: The cave variant, on the other hand, will just keep
Speaker 3: it'll keep swimming in circles around the edges of its tank,
Speaker 3: and this matches with the fact that has been observed
Speaker 3: in the wild. In its natural environment, the cave variant
Speaker 3: will tend to follow the rocky walls of the pool
Speaker 3: where it lives, swimming counterclockwise around these boundaries in an
Speaker 3: endless loop. And one of the studies authors, Amanda Powers,
Speaker 3: was quoted in a press release about the research, explaining, quote,
Speaker 3: you could see how asymmetry might be an advantage in navigation.
Speaker 3: They tend to swim in a unidirectional circular motion around
Speaker 3: their 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,
Speaker 3: powers talking about how she and colleagues went into the
Speaker 3: caves to observe these fish, and she says in this
Speaker 3: article quote, whenever you would touch the surface of the
Speaker 3: water with your finger, a swarm of cavefish would come
Speaker 3: right up to it. Not many fish would do that.
Speaker 3: These cavefish have zero predators, are not afraid.
Speaker 2: Oh wow, that you know. That reminds me of other
Speaker 2: examples we've talked about in the show, like various birds
Speaker 2: of the Galapagos Islands, for example. It reminds me of
Speaker 2: some stuff I was just reading the other day about
Speaker 2: the dodo bird. You know, where you have these organisms
Speaker 2: that adapt over evolutionary time to an environment where there
Speaker 2: are no predators or there is just an entirely different
Speaker 2: predation situation going on, And yeah, they just lose their fear.
Speaker 2: There's no need to engage in that kind of protective
Speaker 2: behavior because those things don't exist for them until they
Speaker 2: show up on a bub Yeah yeah, speaking.
Speaker 3: Dutch, Okay, So that's lateral line sensations, and then the
Speaker 3: 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 plyotropy. 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 yeah, 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. A 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 ours, 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
Speaker 3: lip stick, you know, the red dots, the taste buds
Speaker 3: are on the mouth, the cave fish are wearing clown makeup.
Speaker 3: The taste buds are all over the face.
Speaker 2: Yeah, it's quite impressive. And again it makes sense for
Speaker 2: this kind of an environment, you know, you need to
Speaker 2: lean into a different sense situation. It reminds me a
Speaker 2: bit of our past discussions about catfish being super tasters,
Speaker 2: you know, and really when and again it come back
Speaker 2: to that situation where we have our human understanding of
Speaker 2: the senses, but we have a human level understanding of
Speaker 2: those senses. And so when you're talking about something like
Speaker 2: this that is enhanced, it's it's not taste as we
Speaker 2: know it, 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 are a few things mentioned in this review. One
Speaker 3: is that multiple studies have found what appears to be
Speaker 3: in enhanced sensitivity to chemical repellence and taste sources in
Speaker 3: the 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. You know, something in the water.
Speaker 3: A piece of food or whatever is dispersed in the
Speaker 3: water if you hit it with a bit of the
Speaker 3: good old MSG.
Speaker 2: I bet, or maybe one of those little fish shaped
Speaker 2: soy soy sauce.
Speaker 3: Yeah, we get some soy sauce, some parmesan cheese, some tomatoes,
Speaker 3: some MSG all the good, all the good savory things. However,
Speaker 3: the authors do say that several amino acids were used
Speaker 3: in the study that found this, so there could be
Speaker 3: other explanations, possibly also involving old faction rather than taste.
Speaker 3: But anyway, what difference would these these taste but arrangements
Speaker 3: and heightened sensitivity to flavors make in terms of the
Speaker 3: behavior of the fish the author's right quote. One recent
Speaker 3: study argued that external taste buds are used for preliminary
Speaker 3: assessment of food items during random swimming or targeted searches
Speaker 3: for food. Extra oral taste buds thus carry in importance
Speaker 3: for determining whether to pursue or avoid a food item. So,
Speaker 3: the way I understand that is it's heightening the fish's
Speaker 3: foraging efficiency basically by saying, before you even get something
Speaker 3: in the mouth, you're tasting the water around this thing
Speaker 3: with the front of your face, and it helps you
Speaker 3: zero in more quickly on something that is good to
Speaker 3: eat or is not good to eat, Like you're getting,
Speaker 3: you're getting an idea about whether you're coming close to
Speaker 3: a good piece of food or not earlier. So that
Speaker 3: would make your foraging more efficient.
Speaker 2: Okay, that makes sense in the And.
Speaker 3: However, they do say that this is just an area
Speaker 3: that hasn't had enough research yet. They say that the
Speaker 3: quote precise function of cavefish extraoral taste buds remains unclear
Speaker 3: and largely unexplored. And then they also say that future
Speaker 3: studies need to do things like excluding the role of
Speaker 3: old faction or smell and isolating the variable of taste.
Speaker 3: And there are differences that even remain that they did
Speaker 3: examine in the paper that we just don't know how
Speaker 3: to explain yet, but could possibly be related to taste.
Speaker 3: One interesting idea they bring up is the feeding angle.
Speaker 3: So they say, you know, if you look at the
Speaker 3: cave variants of these fish versus the surface variants, one
Speaker 3: thing you will notice is that they both go along
Speaker 3: the bottom. There might be like a stony or sandy
Speaker 3: or pebbly bottom of the water source where they are
Speaker 3: and they'll go along the bottom with their mouth down
Speaker 3: to the bottom, kind of searching for little bits of
Speaker 3: food to eat or you know, prey in the case
Speaker 3: of you know, carnivory or just little bits of dead
Speaker 3: organic matter, whatever it is they're coming across to eat.
Speaker 3: They're scouring the bottom for it. For some reason, the
Speaker 3: surface fish have a steeper angle that they forage at
Speaker 3: with their body more it's almost more totally vertical, whereas
Speaker 3: the cavefish tend to forage at a more slanted angle
Speaker 3: that's closer. It's more like fifty five degrees from the
Speaker 3: bottom versus more like eighty degrees in the surface variant.
Speaker 3: They say this could be related to the changes in
Speaker 3: extraoral taste buds. Maybe it's you know, like they're tasting
Speaker 3: things differently, thus they have to orient their bodies differently.
Speaker 3: Don't know, but interesting question.
Speaker 2: Yeah, yeah, I mean this this is fascinating to think about,
Speaker 2: Like it makes one wonder if it has something to
Speaker 2: do with their being more predation opportunities for the surface fish,
Speaker 2: Like you've got to come in at that steeper angle
Speaker 2: because there's a greater risk of things, you know, on
Speaker 2: the floor of the of the sea or what have you,
Speaker 2: that might come after them while they're feeding, and maybe
Speaker 2: those are absent in these cave environments. Again, you know
Speaker 2: we're talking about like a lack of just biodiversity in
Speaker 2: those environments. You know there's many fewer predators, et cetera.
Speaker 2: 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 extra oral
Speaker 3: taste buds are in the surface fish. Remember they're all
Speaker 3: like right at the mouth, but in the in the
Speaker 3: cave variant, a lot of them tend to be spread
Speaker 3: out along the lower jaw. So I wonder if it
Speaker 3: can come in at this shallower angle because it's sort
Speaker 3: of like feeling and tasting more along the bottom without
Speaker 3: having to get the front of its mouth in contact
Speaker 3: with it. It can kind of taste with the the
Speaker 3: slope of its lower jaw.
Speaker 2: Yeah, that would make a lot of sense.
Speaker 3: But yeah, again, don't know. Interesting questions about Usually when
Speaker 3: you think about fish and taste together, you're thinking about
Speaker 3: what a fish tastes like to you not what it's
Speaker 3: like to taste as a fish.
Speaker 2: Yeah, which again it can put you an entirely different
Speaker 2: sense realities, especially considering things like a catfish. But also
Speaker 2: you know, getting into taste and smell. Whenever I read
Speaker 2: information about, you know, the distances at which fish in
Speaker 2: the ocean can detect other things going on, say blood
Speaker 2: in the water or some sort of rotting tissue, I'm
Speaker 2: always just amazed because again it is an experience of
Speaker 2: the ocean that is just unlike anything we can experience
Speaker 2: when we venture into it. And the same holds true
Speaker 2: of the cave. Like when we enter into the cave,
Speaker 2: our experiences are rather different compared to the organisms that
Speaker 2: have evolved to thrive there. Now the place I'd like
Speaker 2: to turn to next. This this gets into something that
Speaker 2: was probably one of the key reasons I decided this
Speaker 2: would be a good series for us to do, you know,
Speaker 2: to to return to cave biology.
Speaker 3: Uh.
Speaker 2: This and the fact that I was also inspired by
Speaker 2: some cave environment related stuff at the Bishop Museum on
Speaker 2: a Wahuo recently when I returned there and got to
Speaker 2: take in their natural history section in addition to their
Speaker 2: their cultural and historical sections. But yeah, this is the
Speaker 2: revelation that really pushed me over the edge that for
Speaker 2: many cave environments, bat guano is sunlight. Ooh, bat guano,
Speaker 2: that's bat poop if you will, if you if you're
Speaker 2: not familiar essentially in these environments, yes, this is the
Speaker 2: light of the sun. This plays a vital role in
Speaker 2: the food chain because remember light is the first step
Speaker 2: in the food chain of the Epigean world. Sunlight reaches
Speaker 2: the surface where photo autotrophic organisms create food via sunlight,
Speaker 2: carbon dioxide and water. These are autotrophs, and we call
Speaker 2: this the 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 2: That's right? Yeah, yeah, most of it depends on sunlight. Plants,
Speaker 2: our autotrophs, as our seaweed phytal blanked in some kinds
Speaker 2: of bacteria, including bacteria that produce their own own food
Speaker 2: vio chemosynthesis around volcanic vents. But most of the producers
Speaker 2: are producing their own food via the process of photosynthesis
Speaker 2: and therefore require the bounty of sunlight. The next trophic
Speaker 2: layer of the food chain is of course the primary consumers,
Speaker 2: who eat the producers, the herbivores being chief among them.
Speaker 2: And then the predators compose the third trophic layer, the
Speaker 2: secondary consumers, followed by the tertiary consumers and on up
Speaker 2: to the apex predators. And then you have you know,
Speaker 2: you also have the other roles in there, you know,
Speaker 2: the scavengers, the decomposers, and so forth. Now it's pointed
Speaker 2: out by sakoy at All in The Life Hidden Inside Caves,
Speaker 2: published twenty twenty in the International Journal of Ecology. Cave
Speaker 2: ecosystems are intrinsically devoid of primary productivity due to the
Speaker 2: absence of light. Again, light may enter the opening of
Speaker 2: a cave to different degrees, and other caves may feature
Speaker 2: open areas or areas with sort of like naturally occurring skylights.
Speaker 2: But past those pools of light there is only darkness,
Speaker 2: 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 2: And that's where bats enter the picture. We've of course
Speaker 2: talked about bats before. You have various species of bats
Speaker 2: that roost in cave environments and do so in vast numbers.
Speaker 2: So batguano instead offers a major food source, a kind
Speaker 2: of alternate sunshine, brown sunshine if you will, that falls
Speaker 2: upon the floor of caverns where insectivore or frugivorous bats roost.
Speaker 2: So yeah, bats that eat insects, bats that eat fruit.
Speaker 2: So we're talking about bats species that are generally nocturnal
Speaker 2: or crepuscular, that go out and feed and then return
Speaker 2: to the seclusion of their caves where they roost on
Speaker 2: the ceiling, and when they poop, they poop on the
Speaker 2: floor below them, and that poop brings in quite a
Speaker 2: few nutrients.
Speaker 3: So it's not like the base the photo autotrop layer 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 and pooping it out on the floor, but it
Speaker 3: becomes like a new base layer of a food chain
Speaker 3: within the cave.
Speaker 2: Exactly. Yes, And I will also add it is like
Speaker 2: sunlight in that you can replace the word sun or
Speaker 2: sunlight with baguano in any song lyric and it will
Speaker 2: work just as well. So please feel free to try
Speaker 2: that on your own time.
Speaker 3: I'm walking on guano. Yeah, yeah, yeah, it works perfectly,
Speaker 3: don't I feel good?
Speaker 2: So this guano often serves as the primary renewable organic
Speaker 2: resource of these caves, and a whole food chain extends
Speaker 2: from this, supporting various bacteria, fungi, protus, and small arthropods. Now,
Speaker 2: according to Sokoya at all, the exact blend of nutrients
Speaker 2: is going to vary depending on broad category and specific
Speaker 2: species of bat, but the end result is that the
Speaker 2: fields of poop beneath the bats just become teeming with life,
Speaker 2: life enough to support an ecosystem of organisms, including those
Speaker 2: visiting from the outside, other creatures that spend part of
Speaker 2: their time in the caves, and also of course obligate
Speaker 2: cave dwellers that are there all the time. Also, this
Speaker 2: was interesting, the fermentation of the biomass, along with the
Speaker 2: presence of all those warm blooded bat colonies actually heats
Speaker 2: 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.
Speaker 2: Though.
Speaker 3: I guess this could be changed if yeah, you're bringing
Speaker 3: in a lot of biomass, and that's sort of like
Speaker 3: warming up the cavern.
Speaker 2: Yeah, like at base level, it's like life in the
Speaker 2: wine cellar. But then if you get enough life in
Speaker 2: the wine cellar, well, things they can have elevated temperatures,
Speaker 2: but still going to be pretty dependable, it sounds like, though,
Speaker 2: I guess you do have to factor in that there
Speaker 2: are sometimes fluctuations in these the occupation by bats and
Speaker 2: 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 guano.
Speaker 2: On my shoulder shoulders makes me happy. Yeah, yeah, I
Speaker 2: want to read a quote here from the sequoiad All
Speaker 2: paper that gets into some of the details here of
Speaker 2: the guano quote. For example, small metazoins such as mites, pseudoscorpions, beetles, thrips, mites,
Speaker 2: and flies inhabit the guano of insectivorous bats, whereas the
Speaker 2: guano of frugivorous bat bats is frequented by spiders, mites, isopods, millipedes, centipedes, waiters,
Speaker 2: bark lice, and insects. Salamander and cavefish populations and invertebrate
Speaker 2: communities also rely heavily on nutrients from the bat guano.
Speaker 2: They also point out that batguano constitutes a niche of
Speaker 2: several varieties of micro organisms, including fungi, protus, lichen viruses,
Speaker 2: and bacteria.
Speaker 3: I wonder if the batguano is primarily sweet or savory.
Speaker 2: 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 that eat it, or true.
Speaker 2: Sure that that is essential, and I believe that something
Speaker 2: Sekoy at All point out is that it's yeah, there
Speaker 2: aren't necessarily there are organisms that depend on the guano
Speaker 2: that are not directly eating the guano, but they are
Speaker 2: able to thrive on the things that do consume and
Speaker 2: thrive on the guano directly. Now, it's It's also worth
Speaker 2: noting that the presence of the bats themselves also produces
Speaker 2: feeding and opportunities for either scavengers or predators. I'm going
Speaker 2: to probably have more on this particular tidbit in the
Speaker 2: next episode. And yeah, there is another interesting thing that
Speaker 2: they point out is all of this can potentially change
Speaker 2: over time as well, you know, stable environments, but not
Speaker 2: necessarily you know, eternal. I was reading a CBC radio
Speaker 2: story about a University of Ottawa study of bat guano
Speaker 2: in a specific Jamaican cave or cave system. I believe
Speaker 2: this cave is known as home away from home cave.
Speaker 2: It's very remote and it has been a subject of
Speaker 2: some scientific study, and they were looking at it and
Speaker 2: they were able to observe a shift over in the
Speaker 2: past from insect eating bats to fruit eating bats, though
Speaker 2: it was unclear as of twenty twenty one if this
Speaker 2: was a change in diet by a specific species or
Speaker 2: perhaps more likely, the influx of a different bat species
Speaker 2: that had a different diet. They also found increased guano
Speaker 2: levels of cadmium, mercury, lead, and zinc present during the
Speaker 2: same time as the Industrial Revolution, so they were getting
Speaker 2: into like, you know, we can see this change. We
Speaker 2: can see this environmental change brought on by the Industrial
Speaker 2: revolution in the guano of these bats in this remote Jamaican.
Speaker 3: Cave, heavy metal guano.
Speaker 2: Yeah. Now, of course we have various other creatures besides
Speaker 2: the bat, but also from the era of bats to
Speaker 2: consider that are now extinct that would have entered into
Speaker 2: caves and would have defecated. We have like the cave
Speaker 2: bear that is extinct, the extinct cave hyena. Copy lights
Speaker 2: from both of these species. Fossilized fecal matter has been
Speaker 2: discovered in caves. Now, another tidbit, and this is something
Speaker 2: you could definitely go in deeper on. We could come
Speaker 2: back to another episode in the future at some point Sequoiad.
Speaker 2: I'll point out that the other thing about batguano is
Speaker 2: that human beings figured out that, hey, this stuff has value.
Speaker 2: So cave environments have also long been exploited by human
Speaker 2: beings due to its economic value as a fertilizer and also,
Speaker 2: for at least for a while there, it was harvested
Speaker 2: to produce gunpowder, and all of this can impact these
Speaker 2: cave environments. Here's another interesting thing. Bats, the bats that
Speaker 2: enter into these caves. These caves, they are not set
Speaker 2: in stone. They are changing. We just discussed how these
Speaker 2: caves form over geologic time in the first episode. But
Speaker 2: the bats by roosting in the caves physically change them
Speaker 2: roosting on the ceiling with their little claws, so that
Speaker 2: physically changes the cave. And then also there's chemical augmentation
Speaker 2: of the caves via their urination, because yeah, they're going
Speaker 2: They're going both number one and number two in that
Speaker 2: 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 2: I believe it is more dissolving. Yeah, okay, Again, we're
Speaker 2: dealing often with limestone cave systems and so forth. So
Speaker 2: that's my understanding here, because I know what you're thinking.
Speaker 2: Do we end up with with actual.
Speaker 3: Like bat piece stalagmites, Yeah, bat piece stalagmites.
Speaker 2: I do not have an answer to that, but I
Speaker 2: think it is more of a dissolving of the cave
Speaker 2: 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 stalacti.
Speaker 3: Since stalagmites have crystallized bat urine occasionally form.
Speaker 2: Well there you go. Okay, so that is also possible.
Speaker 2: It's just a wonderful world down there. It's a whole
Speaker 2: 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 2: Yeah, there was another art. I didn't get into this
Speaker 2: article a lot. Maybe I could come back more in
Speaker 2: the next episode, but there was a twenty twenty one
Speaker 2: article in The New York Times titled how bats and
Speaker 2: their poop erase ancient cave art, and that one got
Speaker 2: into this issue of it because again they're changing the
Speaker 2: caves and sometimes that can change things that prehistoric humans did. Wow.
Speaker 2: They point out that large quantities of the urine and
Speaker 2: the guano it ferments, it can saturate the air with
Speaker 2: quote aerosolized particles of phosphoric acid. So it's a rich
Speaker 2: world down there. Goodbye horsetoodle. Now an interest and largely
Speaker 2: unanswered question for me, They would get some answers on it.
Speaker 2: Pertains to the question what might cave environments have been
Speaker 2: like before the evolution of cave roosting bats, Because again,
Speaker 2: bats are mammals, and mammals have not in their highly
Speaker 2: successful mammals. They've been around for a while, but they
Speaker 2: haven't always been around. So what would have potentially pooped
Speaker 2: up these caves and sustained these ecosystems before bats.
Speaker 3: That's a good point. So if like the base layer
Speaker 3: of the food, the food web within the cave is
Speaker 3: emerging from back guano and there were at a time
Speaker 3: no bats to bring the guano in, could there be
Speaker 3: an ecosystem in the cave at all?
Speaker 2: Exactly? Yeah, And I think by and large. The answer
Speaker 2: is yes, there would have been things that have done that.
Speaker 2: And we know that in part because even today bats
Speaker 2: are not the only trogs to poop in a cave.
Speaker 2: They are considerable factors, but crickets are often brought up.
Speaker 2: Is another major cave cooper that allows the sun to
Speaker 2: shine in these lightless places. So it would seem that
Speaker 2: prebat organisms would have taken advantage of the cave niche
Speaker 2: to do, you know, to whatever degree they could. One
Speaker 2: of the things about investigations into cave fossils is that
Speaker 2: fossils that you find in deep caves aren't necessarily telling
Speaker 2: you about subterranean life. Tracks in the floor or even
Speaker 2: ceilings of deep caves may actually be insightful about life
Speaker 2: along shorelines of the surface. You know. That's the degree
Speaker 2: of time that we're dealing with, and considering the lights
Speaker 2: of for instance, a five hundred meter deep that's a
Speaker 2: third of a mile deep cavern in France. I was
Speaker 2: reading about this is and I may be butchering French.
Speaker 2: Here likely am castel book cave. Here, for instance, you'll
Speaker 2: find dino footprints that were first etched in mud or
Speaker 2: sand on a beach one hundred million years ago and
Speaker 2: they've 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 2: Yeah, and kind of similar to like, oh, you can't
Speaker 2: find a trillobyte in a mountain and be like, these
Speaker 2: were the mountain trilobites, Like, it's not really what's happening.
Speaker 2: But of course this doesn't mean we don't have evidence
Speaker 2: of dinosaur age cave dwellers. As reported by Nature in
Speaker 2: twenty twenty, cockroaches preserved in amber from ninety nine million
Speaker 2: years ago are likely the oldest evidence we have of
Speaker 2: organisms evolved for life in a cave environment.
Speaker 3: One hundred million year old cave cockroaches. What were they like?
Speaker 2: Oh, they were kind of scary. I included an image
Speaker 2: here of one for you, Joe. This is one of
Speaker 2: the species that they were looking at, and you'll see
Speaker 2: that it has front appendages these kind of like raptorial
Speaker 2: fore legs, much like a praying mantis, which means they
Speaker 2: were likely a highighly predatory species in their cave environments.
Speaker 2: M So that's one of the features that they found
Speaker 2: on these these amber preserved specimens. There's lost coloration, there's
Speaker 2: reduced wing and eye size, elongated antennae, and reduced leg
Speaker 2: spines for passive defense. So two species were discovered in
Speaker 2: amber in this cave from me and Mar, one of
Speaker 2: which apparently had these raptorial four legs, meaning it was
Speaker 2: likely primarily a predator. And according to Paper and Cosmos
Speaker 2: magazine by James Urkhart, one of the interesting things about
Speaker 2: this find is that the specimens in question would seem
Speaker 2: to have mid Cretaceous origins, but all cave animals living
Speaker 2: today have a late Cinozoic origin. Now, why these older
Speaker 2: cave organisms died out is apparently a mystery, because it
Speaker 2: would seem like an ideal place to shelter and survive
Speaker 2: surface world extinct events, but obviously that's not the case.
Speaker 2: The article also stresses that it's not impossible that these
Speaker 2: cockroaches may have survived even into modern times in one
Speaker 2: form or another, because our understanding of living insects is
Speaker 2: of course incomplete, so it's not impossible that even though
Speaker 2: we're gazing backwards through time with this particular specimen, its
Speaker 2: genetic legacy could still be alive today. The article here
Speaker 2: is quite good. It also stresses some of the larger
Speaker 2: challenges of understanding such ancient cave environments and figuring out
Speaker 2: what they consisted of. Other mesozoa, cave organisms certainly existed,
Speaker 2: but either we get into the same problems we encounter
Speaker 2: with the inherent incompleteness of fossils in general on the
Speaker 2: fossil record, because either a cave system collapsed long ago
Speaker 2: or key to this example, didn't allow fossil preservation. This case,
Speaker 2: amber containing cave organisms is rather unique because a tree
Speaker 2: is not going to grow in said cave. They say
Speaker 2: this is kind of like a one in a million
Speaker 2: fine because it probably depended on resin from a tree
Speaker 2: growing directly in the mouth of a cave, like in
Speaker 2: exactly the right place, exactly the wrong right time, in
Speaker 2: order to capture this creature that otherwise would not be
Speaker 2: venturing 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 this unique find.
Speaker 2: Yeah, and it just raises the question, like what else
Speaker 2: it would have been down there that we didn't crawl
Speaker 2: into the amber. You know, there's again just so many
Speaker 2: mysteries within within the fossil record, and back to the
Speaker 2: earlier point, so many mysteries remaining and just sort of
Speaker 2: the in the the existing organic world. You know, we're
Speaker 2: still making discoveries regarding insects, cave environments, of cave ecosystems.
Speaker 2: It's I mean, 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 2: That's right. We're going to get into some cave creditors
Speaker 2: and who knows what else. All right, stuff to blow
Speaker 2: your mind. As you know, Core episodes are on Tuesdays
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Speaker 3: Huge thanks, as always to our excellent audio producer JJ Posway.
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