Speaker 1: Hey you welcome to Stuff to Blow Your Mind. My
Speaker 1: name is Robert.
Speaker 2: Lamb and I am Joe McCormick, and today we're bringing
Speaker 2: you an episode from the vault. This is part two
Speaker 2: of our series on the reptiles of the Galapagos. This
Speaker 2: was originally published December tenth, twenty twenty two.
Speaker 3: Enjoy 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 2: Lamb and I'm Joe McCormick, and we're back with part
Speaker 2: two of our series on the reptiles of the Galapagos Islands. Now,
Speaker 2: in the previous episode, we focused mainly on the marine iguana,
Speaker 2: or as they were often referred to early on, those
Speaker 2: hideous creatures, those stupid, awful, sluggish lizards. We mounted a
Speaker 2: defense of the marine iguana. But today we are here
Speaker 2: to talk about the Galapagos tortoise. And I wanted to
Speaker 2: kick things off by reading a passage from Charles Darwin
Speaker 2: in the Voyage of the Beagle. Darwin, of course, was
Speaker 2: not just a great scientist, but a really wonderful writer,
Speaker 2: and I think this will help set the scene. So
Speaker 2: are you ready to hear about Darwin's first vision of
Speaker 2: San Cristobal Island. Then then what they called Chatham Island.
Speaker 1: Yeah, let's let's hear from from old Charles.
Speaker 2: And this is part of a narrative of when he
Speaker 2: slept ashore one night on the island. So off the boat,
Speaker 2: Darwin writes. The entire surface of this part of the
Speaker 2: island seems to have been permeated like a sieve by
Speaker 2: the subterranean vapors. Here and there the lava, whilstsoft, has
Speaker 2: been blown into great bubbles, and in other parts the
Speaker 2: tops of caverns similarly formed have fallen in, leaving circular
Speaker 2: pits with steep sides. From the regular form of the
Speaker 2: many craters. They gave to the country an artificial appearance
Speaker 2: which vividly reminded me of those parts of Staffordshire, where
Speaker 2: the great iron foundries are most numerous. The day was
Speaker 2: growing hot, and the scrambling over the rough surface and
Speaker 2: through the intricate thickets was very fatiguing, but I was
Speaker 2: well repaid by the strange Cyclopean scene. As I was
Speaker 2: walking along, I met two large tortoises, each of which
Speaker 2: must have weighed at least two hundred pounds. One was
Speaker 2: eating a piece of cactus, and as I approached, it
Speaker 2: stared at me and slowly walked away.
Speaker 4: The other gave a.
Speaker 2: Deep hiss and drew in its head. These huge reptiles,
Speaker 2: surrounded by the black lava, the leafless shrubs and large
Speaker 2: cacti seemed to my fancy like some Antediluvian animals. The
Speaker 2: few dull colored birds cared no more for me than
Speaker 2: they did for the great tortoises. So Darwin transported to
Speaker 2: a time from before Noah's flood by the vision of
Speaker 2: these bizarre, gigantic tortoises crawling around on the on the lava.
Speaker 1: Yes, this is the great sceni paints here and and yeah.
Speaker 1: As I mentioned in the first episode, I was. I
Speaker 1: was fortunate enough to get to travel to the Galapagos
Speaker 1: Islands just a couple of months ago. In San Cristobo
Speaker 1: Island was one of the islands that I got to visit,
Speaker 1: and this was pretty much the the experience I had
Speaker 1: with my family walking through one of the the areas
Speaker 1: they had set aside for these magnificent tortoises. They're just
Speaker 1: they just they walk around as if yeah, if you
Speaker 1: don't matter, unless you get a little too close for
Speaker 1: their liking, in which case there'll often be this hiss
Speaker 1: and this retraction of their head. I mean, their heads
Speaker 1: don't retract in the same way that say, a box
Speaker 1: turtle does, but they're able to sort of pull their
Speaker 1: head in a bit. But that the hissing that Darwin
Speaker 1: is describing here, it does have a very, I don't know,
Speaker 1: pneumatic kind of quality to it. It feels it sounds
Speaker 1: like some sort of machinery. And indeed, that's that's kind
Speaker 1: of more what it is, as opposed to like the
Speaker 1: hiss you might hear from a house cat or something.
Speaker 1: And one of the things that I kept thinking about
Speaker 1: while encountering them is that they already move with this
Speaker 1: kind of herky jerky kind of locomotion. They already move
Speaker 1: like they are elaborate mechanical creatures created for practical effects
Speaker 1: for a nineteen nineties science fiction feature. And then they
Speaker 1: also make this hissing sound to move part of their anatomy.
Speaker 1: So it almost creates this feeling of am I seeing
Speaker 1: real animals or is this an elaborate hoax these animatronics? Yeah, yeah, yeah,
Speaker 1: they feel almost like animatronics, but of course they're they're
Speaker 1: they're they're quite alive, and they're quite, but that's part
Speaker 1: of their strangeness, and they just the awe of watching
Speaker 1: these giant creatures walk arou around, slowly, eat, and occasionally
Speaker 1: have some startling interactions.
Speaker 2: Now I'm greatly envious of the opportunity you got to
Speaker 2: see these animals in person, but I trust that you
Speaker 2: did not do what Darwin did upon encountering these beasts
Speaker 2: and try to ride them.
Speaker 1: Absolutely not, no, no. The only time the times we
Speaker 1: were forced to get uncomfortably close in one of these
Speaker 1: situations of the area that we were walking through had
Speaker 1: a path and you're supposed to stay on the path
Speaker 1: and keep your distance from the tortoises. Sometimes though the
Speaker 1: tortoises will just get on the path. You have to
Speaker 1: find your way around them, and they don't necessarily like that.
Speaker 1: But we kept our distance, and you want to keep
Speaker 1: your distance because, yeah, if you get a little too close,
Speaker 1: they're going to stop interacting with their environment for a
Speaker 1: little bit. And if you don't want to watch that,
Speaker 1: you want to watch them eat and rampage around and
Speaker 1: occasionally have these fabulous stare downs between two males which
Speaker 1: I don't know, we may describe this later, So maybe
Speaker 1: I shouldn't get into that just yet.
Speaker 2: Yeah, yeah, we can talk about the mock fights later on.
Speaker 2: So the Galapagos tortoise is I think you would say,
Speaker 2: originally the dominant land herbivore of the Galapagos Islands, which
Speaker 2: makes them kind of unique because there's pretty much nowhere
Speaker 2: else on Earth now where the dominant land herbivore is
Speaker 2: a reptile. So these are very unique and beautiful creatures,
Speaker 2: and the Glapagos tortoise stands out so much among the
Speaker 2: endemic fauna that it's actually the origin of the archipelago's
Speaker 2: name in one way or another. There's a little bit
Speaker 2: of nitpicking on that, but basically it goes like this.
Speaker 2: By the fifteen seventies, these islands had already appeared on
Speaker 2: at least a couple of European maps. The one I
Speaker 2: saw named was by a Flemish cartographer named Abraham Ortelius,
Speaker 2: and it named the islands Insulae de los galapago or
Speaker 2: meaning Islands of the Tortoises. Now, the nitpicking about the
Speaker 2: terminology I've read is what exactly the word galapago or
Speaker 2: Galapagos originally meant. According to a book that I'm going
Speaker 2: to reference multiple times in this episode, Galapagos and Natural History,
Speaker 2: second Edition by John Creecher and Kevin Laughlin from Princeton
Speaker 2: University Press. That editions out just twenty twenty two. They
Speaker 2: write that the origin of the name of the islands
Speaker 2: is an old Spanish word, galapago, which was a name
Speaker 2: for a specific type of saddle. So there's like, you know,
Speaker 2: a saddle you'd use on a horse. I guess that
Speaker 2: has a kind of upturned front. That was a galapago.
Speaker 2: And some, but not all, of the Galapagos tortoises have
Speaker 2: saddle shaped shells. Others have a more straightforward dome. And
Speaker 2: we can talk about the evolutionary reasons for those differences
Speaker 2: later on. But when Tamas de Berlanga landed on the
Speaker 2: islands in fifteen thirty five, a story we talked about
Speaker 2: in the previous episode. After this, he wrote a letter
Speaker 2: to the king in which he observed describing the animals
Speaker 2: of the island, he observed mucos lobos marinos meaning many
Speaker 2: sea lions, tortugas meaning sea turtles, iguanas, and Galapagos, and
Speaker 2: the authors write that this is probably a reference to
Speaker 2: the tortoises and their saddle shaped shells rather than to
Speaker 2: literal saddles being on the island.
Speaker 1: This is a solid observation that thankfully still holds true today.
Speaker 1: Mucos lobos marinos and tortugas, iguanas and tortoises. Yes, yeah,
Speaker 1: the sea lion, I mean the mucco lobos marinos. That
Speaker 1: was probably the most astounding of all when you're near
Speaker 1: the coast, because they're everywhere and sometimes laying. There'll be
Speaker 1: like a male that's come up and he's like laying
Speaker 1: in the street, or they they love park benches. There
Speaker 1: are a lot of fun to wide.
Speaker 4: Well.
Speaker 2: The difference in the Spanish name. I guess if it's
Speaker 2: lobo marino that would mean see wolf, not sea lion, right,
Speaker 2: But that that heightens the kind of implicit comedy of
Speaker 2: naming these animals after what you would think of as
Speaker 2: a more actively voracious land predator, whereas you know, I
Speaker 2: guess when they're on the land, they're not quite so
Speaker 2: threatening as maybe a wolf for a lion would seem.
Speaker 1: Yeah, I mean, well, on one hand, yeah, you have
Speaker 1: some of the little tiny islands are at least one
Speaker 1: that's named for the wolves for the lobos, and of
Speaker 1: course that's why, because sea lions are hanging out there
Speaker 1: and yeah, on the on the on the beach. They're
Speaker 1: often quite docile and you see people getting way too
Speaker 1: close to them in some cases. But the big males,
Speaker 1: of course, are very territorial about hanging on to their
Speaker 1: bit of property and their and their females, you know,
Speaker 1: their their their beach real estate, and so there of
Speaker 1: course always they're continuously loudly sending the alarm and occasionally
Speaker 1: chasing off other males. So there's there's a lot of
Speaker 1: drama if you just sit back and watch the sea lions.
Speaker 1: And I imagine that listeners from other parts of the
Speaker 1: world can to this as well.
Speaker 2: Yes, yes, keep your distance, folks, I mean, observe, but
Speaker 2: there's no reason to get in the sea lion space.
Speaker 1: Though sometimes in my experience, sea lion will come for
Speaker 1: your space. I was just seated away from sea lions
Speaker 1: and then here comes this female and she's just howling
Speaker 1: about something and insists on taking my spot on a log,
Speaker 1: and I'm like, it's yours at yours, and then she
Speaker 1: just hangs out on the log for a few minutes
Speaker 1: and then leaves it. I don't know, She's just trying
Speaker 1: to make a point.
Speaker 2: So if you have never seen the Galopagos tortoises before,
Speaker 2: you can easily find lots of pictures of them. But
Speaker 2: to briefly describe the adults, there are many different species
Speaker 2: scattered across the different islands. Maybe we can get into
Speaker 2: the exact numbers on that in a bit, but generally
Speaker 2: what they all have in common is that they're very large.
Speaker 2: They have large shells, some species with rounded dome tops,
Speaker 2: others with the saddle shape that Burlonga probably observed, which
Speaker 2: are typically turned up in the front to have a
Speaker 2: kind of big notch above the animal's head and neck.
Speaker 2: They have long, dry, wrinkly necks which are surprisingly slim,
Speaker 2: almost I dare say snake like in a way. They
Speaker 2: have blunt, round snouts and a beak like mouth with
Speaker 2: no teeth, and everywhere you can see their their skin.
Speaker 2: In between the shell parts there is typically a lot
Speaker 2: of leathery, wrinkly flesh, which just makes them look like
Speaker 2: old people.
Speaker 1: Yeah, they they have this kind of appearance of a
Speaker 1: of acute shriveled old person.
Speaker 4: Vase.
Speaker 1: Uh. They're they're very They're very sweet to look at
Speaker 1: it's it's it's kind of hard to to not anthropomorphize
Speaker 1: them as such even and and that can, of course,
Speaker 1: can become complicated when you start considering like the full
Speaker 1: range of their of their lifestyle and the way that
Speaker 1: they they live and reproduce and so forth. Uh, it
Speaker 1: never pays to anthropomorphize creatures too much.
Speaker 4: Yeah.
Speaker 2: Now, no one thing many of us today might not appreciate,
Speaker 2: even if you go to the Galapagos today or if
Speaker 2: you see Good Nature documentary footage from there, is how
Speaker 2: many tortoises there were when people first arrive, Before the
Speaker 2: animals had any natural predators other than the threat post
Speaker 2: to hatchlings by the Galapagos Hulk, this place was swarming
Speaker 2: with tortoises. And to try to get a picture of that,
Speaker 2: I wanted to cite some basically math work that Creature
Speaker 2: and Laughlin do in their book. So they're talking about
Speaker 2: the reproductive rates of these tortoises. So they say, if
Speaker 2: a female tortoise has more than two young that survive
Speaker 2: into adulthood, the tortoise population will grow, so she has
Speaker 2: replaced both her and her mate. And if she has
Speaker 2: more than one, the population will grow and they say, Now,
Speaker 2: consider that a female tortoise may conservatively lay five to
Speaker 2: ten eggs annually for perhaps eighty years or more. So,
Speaker 2: just for a very conservative estimate, they say, Okay, imagine
Speaker 2: she averages one annual clutch and there's just three eggs
Speaker 2: in it. That's kind of a small estimate. But there's
Speaker 2: just three eggs per clutch. That's more than two hundred
Speaker 2: eggs in a single adult female tortoises lifetime. They say, realistically,
Speaker 2: the number is probably a multiple of that. So they're
Speaker 2: going to have a lot of young and there before
Speaker 2: humans arrive and bring their invasive species with them, before
Speaker 2: they bring dogs and pigs and stuff. There is not
Speaker 2: significant predation at any life cycle. A part of the
Speaker 2: life cycle of a tortoise. There's some minor predation by
Speaker 2: like hawks of the babies, but most of them are
Speaker 2: going to grow and become reproducing adults.
Speaker 1: Yeah, it's pretty amazing. Amazing. I ask one of the
Speaker 1: guides about, you know, how long are the females reproductive?
Speaker 1: Because you see some very who was pointed that My
Speaker 1: guide here was pointing out the various the old tortoises.
Speaker 1: But because you can sort of tell by looking at
Speaker 1: their shells the way that the line, like, for a while,
Speaker 1: you can sort of it's not like you can count
Speaker 1: the rings exactly, but you can sort of see the
Speaker 1: rings and the patterns on their shell. But eventually there's
Speaker 1: kind of like a smoothing out that occurs, and those
Speaker 1: are the really old ones. And the guy was like, yeah,
Speaker 1: we're not entirely sure, but it seems like they're reproductively
Speaker 1: active for pretty much most of their lives, which is
Speaker 1: the astounding.
Speaker 2: Yeah, it's amazing. And so the authors of this book
Speaker 2: end up concluding that before humans arrived and brought these
Speaker 2: invasive predators with them and started harvesting the tortoises themselves,
Speaker 2: which is a sad fact we'll talk about in a moment,
Speaker 2: the tortoises.
Speaker 4: Were just.
Speaker 2: Profuse.
Speaker 4: They were everywhere.
Speaker 2: They say, there's a conserva estimate of a total population
Speaker 2: of two hundred and fifty thousand tortoises just on this
Speaker 2: small group of islands. But of course, today all of
Speaker 2: these tortoise populations are at least vulnerable, and some are
Speaker 2: up to critically endangered, and that's after a significant bounce
Speaker 2: back in some cases, you know, after conservation efforts kicked in.
Speaker 2: So what happened to these tortoises. Well, one thing that
Speaker 2: happened is is something Darwin talks about in his Passage
Speaker 2: and Voyage of the Beagle. Before he even really gets
Speaker 2: to ecological observations about the tortoises, he writes at length
Speaker 2: about people eating them. So, in describing the small human
Speaker 2: colony on what was then Charles Island what today is
Speaker 2: called Floriana Island, so Darwin writes, in the woods there
Speaker 2: are many wild pigs and goats. Now remember those are
Speaker 2: not native to the islands, but introduced by humans. Darwin
Speaker 2: goes on, But the staple article of animal food is
Speaker 2: supplied by the tortoises. Their numbers have of course been
Speaker 2: greatly reduced in this island, but the people yet count
Speaker 2: on two days hunting, giving them food for.
Speaker 4: The rest of the week.
Speaker 2: It is said that formerly single vessels have taken away
Speaker 2: as many as seven hundred, and that the ship's company
Speaker 2: of a frigate some years since brought down in one
Speaker 2: day two hundred tortoises to the beach. And this brings
Speaker 2: us to a very sad fact about the human use
Speaker 2: of tortoises. Here that tortoises were, of course very good
Speaker 2: meat sources for sailing vessels, but this was especially due
Speaker 2: to the fact that because turtles have a very slow metabolism,
Speaker 2: and they could be loaded into the ship alive and
Speaker 2: then would survive for an extremely long time without food
Speaker 2: or water in the hold. And it's important to remember that,
Speaker 2: of course, ships at the time didn't have refrigerators or
Speaker 2: freezers or other sophisticated food preservation techniques beyond things like
Speaker 2: the nuclear option salting.
Speaker 1: Yeah. Yeah, so this is quite sad to picture, because
Speaker 1: on one hand, it's not like these tortoises were wandering
Speaker 1: around on deck. They were stuffed below I think generally
Speaker 1: upside down and just stored away as living casks of
Speaker 1: food because they could live for up to a year
Speaker 1: without food or water, which is just crazy to think about,
Speaker 1: but also just unimaginately cruel to imagine them down there.
Speaker 1: And on top of this, one of the other troublesome
Speaker 1: things about this for the tortoises is that the sailors
Speaker 1: would tend to grab the tortoises they could easily carry
Speaker 1: back to the ship, which meant that they tended to
Speaker 1: focus on the smaller tortoises and leave the bigger ones.
Speaker 1: This meant that they were favoring female tortoises over male tortoises,
Speaker 1: and I guess to a certain extent also younger male tortoises,
Speaker 1: but certainly skewing more towards female tortoises, thus destabilizing the
Speaker 1: species even more than if they had managed more of
Speaker 1: a fifty to fifty split between the tortoise genders.
Speaker 2: Yeah, so unfortunately a lot of tortoises were removed from
Speaker 2: the islands that way, but also they just remained a
Speaker 2: live meat source for hunting by the locals, and Darwin
Speaker 2: tells many interesting stories about this. For example, he writes
Speaker 2: about a time that he went up to one of
Speaker 2: the highland regions of one of the islands, and he
Speaker 2: hung out in a hovel that had been built by
Speaker 2: two men there who spent their time hunting tortoises. And
Speaker 2: so he visits these guys and he sleeps there in
Speaker 2: the hovel one night, and what did he eat while
Speaker 2: he was there, Well, exclusively tortoise meat. That was the
Speaker 2: entire menu, about which he says, quote the breastplate roasted
Speaker 2: as the gauchos do carne conquero, which I think means
Speaker 2: meat with leather with the flesh on. It is very good,
Speaker 2: and the young tortoises make excellent soup, but otherwise the meat,
Speaker 2: to my taste, is indifferent.
Speaker 1: Oh well, there you go. Also taking the harvesting the
Speaker 1: young tortoises, that's great as well.
Speaker 2: But they apparently these the adult tortoises, are an amazing
Speaker 2: food source because of their immense size, and Darwin recounts
Speaker 2: a story told to him by a mister Lawson, who
Speaker 2: is an Englishman who is vice governor of the Charles
Speaker 2: Island Colony, saying that some tortoises, when caught, required six
Speaker 2: to eight men just to lift them off the ground
Speaker 2: and would provide up to two hundred pounds of meat.
Speaker 2: Darwin also later describes a strange operation performed by the hunters.
Speaker 2: He says that you know they didn't always kill a tortoise.
Speaker 2: He says that, well, the tortoises meat is used both
Speaker 2: fresh and salted. The tortoises are also important for providing oil.
Speaker 4: That's right, reptile lard.
Speaker 2: And oil that I think could be used for food purposes,
Speaker 2: but also for just like lamp purposes.
Speaker 1: I believe yeah, it's said that in the old days,
Speaker 1: the larger towns of the Galapagos would have their streets
Speaker 1: would have been lit with tortoise oil.
Speaker 2: Bizarre though, I guess we're more familiar with that from.
Speaker 4: Like whale oil and stuff.
Speaker 2: But yeah, so if a tortoise will not provide enough oil,
Speaker 2: it is apparently not worth killing to the hunters. So
Speaker 2: Darwin writes, quote, when a tortoise is caught, the man
Speaker 2: makes a slit in the skin near its tail so
Speaker 2: as to see inside its body whether the fat under
Speaker 2: the dorsal plate is thick. If it's not, the animal
Speaker 2: is liberated, and it is said to recover soon from
Speaker 2: this strange operation. In order to secure the tortoise, it
Speaker 2: is not sufficient to turn them like a turtle, for
Speaker 2: they are often able to get.
Speaker 4: On their legs again.
Speaker 2: And I think this is something that will come up later,
Speaker 2: because there are some situations where these tortoises often do
Speaker 2: end up flipped on their backs, even under natural circumstances,
Speaker 2: and they need to be able to flip back over
Speaker 2: and get back to business.
Speaker 1: I did not get to see that happen, thankfully. I
Speaker 1: don't want to see a tortoise in distress.
Speaker 2: No, we're not going to ask you the quiz from
Speaker 2: the blade runner test. So what do these tortoises eat
Speaker 2: to grow so big? Well, it turns out in reality,
Speaker 2: they just they eat plants. These are entirely herbivorous creatures.
Speaker 2: There are turtles and tortoises that eat other things, but
Speaker 2: these tortoises are entirely plant eaters. And so especially in
Speaker 2: the lowlands, especially the saddlebacked tortoises, will eat succulent cactus.
Speaker 2: This is something Darwin identifies. He says they especially favor
Speaker 2: the cactus if they live in the low and arid
Speaker 2: parts of the islands where there is little or no water.
Speaker 2: Of course the cactus becomes a principal water source, but
Speaker 2: also they eat tree leaves and berries as well as
Speaker 2: green lichen, and their diet somewhat depends on which species
Speaker 2: they are and which part of the islands which microclimate
Speaker 2: they inhabit. Like the ones that live higher up in
Speaker 2: the highlands with more lush vegetation probably feed on more
Speaker 2: leafy stuff, and the ones that live more in the
Speaker 2: arid regions probably feed on more cactus.
Speaker 1: Yeah, the ones I got to actually observe in the
Speaker 1: wild as it were on San Cristobo on Santa Cruz Island.
Speaker 1: They they were definitely eating the leafy green stuff. But
Speaker 1: I got to see plenty of the cacti, which of
Speaker 1: course have coexisted with the tortoises long enough that they
Speaker 1: have particular adaptations, like they have been changed by cohabitation
Speaker 1: with the tortoise as well. And the most remarkable of
Speaker 1: these are the ones that they basically seem to grow
Speaker 1: up like trees and then branch out because they're trying
Speaker 1: to reach and reaching an optimal height at which they're
Speaker 1: hopefully above the reach of the tortoise.
Speaker 2: There is one type of cactus there's a great picture
Speaker 2: of in this book by Creature in Laughlin I've been
Speaker 2: talking about. It's called a candelabra cactus, and I thought
Speaker 2: it was beautiful because the branches look to me like
Speaker 2: giant green tarantula legs. They kind of have these lobes
Speaker 2: that look like little hairy leg segments on a large spider.
Speaker 1: Yeah. Yeah, And this is a nice picture too, because
Speaker 1: you got a flamingo in there. I did get to
Speaker 1: see a few flamingos on Seymour Island, I.
Speaker 2: Believe, But the tortoises just generally seem to eat all
Speaker 2: kinds of foods that would look to us quite hostile.
Speaker 2: So of course the ones in the lowlands are going
Speaker 2: to eat a lot of cactus, but they also apparently
Speaker 2: eat plenty of poison apple or men's in illo, which
Speaker 2: is toxic. It has a sap that is poisonous to
Speaker 2: other creatures, and I think it can cause blistering if
Speaker 2: you touch it. But apparently the tortoises just chow down
Speaker 2: on this stuff, doesn't bother them.
Speaker 1: Yeah. On San Cristobo Island, the area where we were
Speaker 1: encountering the tortoises, they had signs everywhere, do not touch
Speaker 1: the apples. Do certainly do not eat the apples. Leave
Speaker 1: this to the tortoises.
Speaker 2: Now, coming back to Darwin's writing on the tortoises, he
Speaker 2: also observes their relationship with water. He says, they are notable,
Speaker 2: of course for their ability to survive without water for
Speaker 2: a very long time. But when they get out access
Speaker 2: to water, they go hog wild. They love it, the
Speaker 2: spring water and the mud puddles. They'll just get in
Speaker 2: there and settle in, sometimes for days at a.
Speaker 4: Time, and when.
Speaker 2: They're drinking they will just gulp huge mouthfuls of water
Speaker 2: for a long time. And Darwin even this leads into
Speaker 2: him writing a really bizarre anecdote that I had to share.
Speaker 2: So he says, quote for some time after a visit
Speaker 2: to the springs, their urinary bladders are distended with fluid
Speaker 2: which is said to gradually which is said to gradually
Speaker 2: decrease in volume and to become less pure. The inhabitants,
Speaker 2: when walking in the lower district and overcome with thirst,
Speaker 2: often take advantage of this circumstance and drink the contents
Speaker 2: of the bladder if full. In one tortoise I saw killed,
Speaker 2: the fluid was quite limpid and had only a very
Speaker 2: slightly bitter taste. The inhabitants, however, always first drink the
Speaker 2: water in the pericardium, which is the membrane of belief
Speaker 2: that surrounding the heart tissue, which described as being best.
Speaker 2: So that's right, drinking the water from a tortoise's heart
Speaker 2: or from a tortoise's bladder. And Darwin tasted the tortoise
Speaker 2: bladder water.
Speaker 1: I guess I should be happy for this, that they're
Speaker 1: using all parts of the tortoise conceivably in doing this.
Speaker 1: But of course this is still kind of sad to imagine. Yeah,
Speaker 1: but also from just a purely anatomical level, this is
Speaker 1: of course amazing.
Speaker 2: Now, Darwin goes on to talk about how impressed he
Speaker 2: is by the long determined journeys that some of these
Speaker 2: tortoises make between He believes what the point of these
Speaker 2: journeys is is between highland water sources and usual breeding
Speaker 2: grounds in the lower districts. I don't know if that
Speaker 2: holds up as the main reason for these journeys today,
Speaker 2: though I do think some of these tortoises do make
Speaker 2: journeys between the highlands and the lowlands for the purpose
Speaker 2: of depositing eggs the females do after mating season. But
Speaker 2: there are also journeys I think having to do with
Speaker 2: food resources in the different seasons and so forth. But anyway,
Speaker 2: Darwin says, you know, although the tortoises are pretty slow
Speaker 2: in their movements, you would be surprised how much ground
Speaker 2: they cover over time due to sheer determination. He estimates
Speaker 2: that they're going to move sixty yards in ten minutes,
Speaker 2: which is three hundred and sixty yards in an hour,
Speaker 2: or about four miles a day.
Speaker 1: Yeah, it's pretty remarkable, and of course nowadays of course
Speaker 1: that everything has been shifted around a bit. You know,
Speaker 1: all these invasive species, not only the such harmful invasive
Speaker 1: species as pigs and goats that were introduced and then
Speaker 1: their populations have been dealt with to varying degrees. But
Speaker 1: you also have, of course, have plants to think about,
Speaker 1: and so in some cases you have things like berries
Speaker 1: that are now grown in the Galapagos and may occur
Speaker 1: wild in some cases, and of course the tortoises love
Speaker 1: those even though they are not native, and so you
Speaker 1: may see that interfere with their movements. So that but yeah,
Speaker 1: basically through modern conservation and through modern tracking technology, you
Speaker 1: can actually see all of these tortoise movements plotted out
Speaker 1: on maps and it's quite impressive. I think they are
Speaker 1: movements in these cases help illustrate why they're so crucial
Speaker 1: for the island ecosystem that they thrive in. They eat
Speaker 1: so much and while they're slow, they do cover a
Speaker 1: lot of ground and defecate to spread speeds spread seeds rather,
Speaker 1: and this is very much in line with other megafona
Speaker 1: that you encounter in other ecosystems as well as the
Speaker 1: remember if you think back to our episode on or
Speaker 1: episodes on the giant moa bird, which of course is extinct,
Speaker 1: but would have we still see like the footprint of
Speaker 1: their ecological importance in the areas that they occupied, because
Speaker 1: they were vital for consuming plants and then spreading those
Speaker 1: seeds through defecation.
Speaker 2: Yeah, there is a great passage in the book by
Speaker 2: Creature and Laughlin where they talk about the importance of
Speaker 2: the tortoise in spreading a type a species of wild
Speaker 2: Galapagos tomato plant, which apparently it only the seeds only
Speaker 2: germinate under very specific conditions, such as being exposed to
Speaker 2: acid for a long period of time.
Speaker 4: Now, how does that happen, Well.
Speaker 2: It happens in the digestive system of the tortoise. So
Speaker 2: like they take this in, the seed gets exposed to
Speaker 2: the acid within the digestive juices, and then it gets
Speaker 2: it travels with the tortoise a long ways away from
Speaker 2: its original location, so that's also good for dispersal. And
Speaker 2: then once the tortoise poops it out, it of course
Speaker 2: has a bunch of nutritious fecal matter surrounding it to
Speaker 2: help it grow.
Speaker 1: Yeah, yeah, I've got I did get to poke some
Speaker 1: tortoise dung with a stick. My son and I did,
Speaker 1: and we got to look all in there. It's, you know,
Speaker 1: quite fascinating. I think some stats would really help drive
Speaker 1: home though, why the tortoise is so great at this.
Speaker 1: And I got these from Seed Dispersal by Galapagos Tortoises
Speaker 1: by Blake at All, published in the Journal of Biogeography
Speaker 1: from twenty twelve. So, in this particular survey, the researchers
Speaker 1: looked at one hundred and twenty fresh dung piles in
Speaker 1: both agricultural and national parkland. They found seeds from more
Speaker 1: than forty five plant species in these dung piles, eleven
Speaker 1: of which were from introduced species, you know, like various
Speaker 1: berries and whatnot. A per tortoise average of four hundred
Speaker 1: and sixty four seeds and two point eight species per
Speaker 1: dung pile was detected. Now, this is where it gets
Speaker 1: kind of interesting, because, okay, we've already established that, yes,
Speaker 1: they eat a lot, they travel farther than you might think,
Speaker 1: But how long does it take for them to process
Speaker 1: their food? Things go a little slower with the Galapagos tortoises.
Speaker 1: The mean digesta retention time for a tortoise is twelve days,
Speaker 1: but twenty eight day retention times have been reported, so
Speaker 1: that's the time time it takes for the food that
Speaker 1: they've consumed to process through their body and become dung, so.
Speaker 2: They can really cover some ground in that time.
Speaker 1: Yeah. During that time, according to this paper, the tortoise
Speaker 1: may travel between three hundred and ninety four and four
Speaker 1: three hundred and fifty five meters on the high end,
Speaker 1: that's two point seven miles or four point three kilometers.
Speaker 2: So you can see how these tortoises would play an
Speaker 2: incredibly important role in helping the reproduction and dispersal of
Speaker 2: local flora.
Speaker 1: Yeah. Absolutely. I mean, as with any species, they don't
Speaker 1: they're not existing in isolation in their ecosystem. They have
Speaker 1: a roll, they have a place in it. And if
Speaker 1: you disrupt them, if you disrupt their numbers, or in
Speaker 1: the very worst case scenarios, if their extinction is brought about,
Speaker 1: then there is there's something missing. There's a you end
Speaker 1: up pulling the carpet out from everything, and unlike with
Speaker 1: the parlor trick, all the plates and the dishes are
Speaker 1: not necessarily going to stay standing up.
Speaker 2: Now we've been talking about a lot of the predation
Speaker 2: and hunting of these tortoises. But barring that, how do
Speaker 2: tortoises die?
Speaker 4: What happens?
Speaker 2: Well, Darwin writes, quote the young tortoises as soon as
Speaker 2: they are hatched, fall preying great numbers to the carryon
Speaker 2: feeding buzzard. I think that would actually be referring probably
Speaker 2: to the Galapago's hawk, unless he's talking about some other
Speaker 2: species that came in after humans arrived. But and Darwin
Speaker 2: goes on, the old ones seemed to die generally from accidents,
Speaker 2: as from falling down precipices. At least several of the
Speaker 2: inhabitants told me that they never found one dead without
Speaker 2: some evident cause, which, oh, that kind of gave me
Speaker 2: a shiver.
Speaker 1: Yeah, yeah, I mean, it's just impressive how long they live.
Speaker 1: That and I did the first point about P's worth
Speaker 1: pointing out that the tortoise sanctuaries that are up and
Speaker 1: running now they care for the little ones to protect
Speaker 1: them from you know, not only the hawk, but also
Speaker 1: all these introduced species that may be about once they
Speaker 1: get big enough. Though, Yeah, there's only really three ways
Speaker 1: they're going to die old age eventually, accident, vehicular especially
Speaker 1: of course being the main threat, though on the Galapico
Speaker 1: sidelands today a lot of you know, laws and messaging
Speaker 1: have been put in place to prevent this from occurring.
Speaker 1: And then of course in the past human hunting was
Speaker 1: the big thing.
Speaker 2: Now you mentioned they can die of old age, of
Speaker 2: course they do, but that can take.
Speaker 4: A good long while.
Speaker 2: I was reading about this in a Creature in Laughlin
Speaker 2: and they say that it's possible, though we have no
Speaker 2: way to know for sure, that there may be tortoises
Speaker 2: still alive on the islands that were present when Darwin
Speaker 2: visited in eighteen thirty five, and a Galopago's tortoise named
Speaker 2: Harriet lived to an estimated age of one hundred and
Speaker 2: seventy five before she died in an Australian zoo in
Speaker 2: two thousand and six, so they can live a long
Speaker 2: long time.
Speaker 1: Yeah, I was doing some crunching on this as well.
Speaker 1: I think one of the sources I was looking at
Speaker 1: had listed like one hundred and seventy one years as
Speaker 1: being one of the oldest stage is known for the tortoises.
Speaker 1: And even if you're just going to go with that,
Speaker 1: if you consider the idea that you have a tortoise
Speaker 1: born in eighteen thirty five when Darwin is visiting, if
Speaker 1: it lived one hundred and seventy one years, it would
Speaker 1: live to the year two thousand and six. Wow, which
Speaker 1: is just crazy to think about the idea that just
Speaker 1: one tortoise lifetime would bridge our time to the time
Speaker 1: of Darwin, and that a single tortoise lifetime could encompass
Speaker 1: basically the two worst centuries of the impact of humanity
Speaker 1: on Galapago's tortoise numbers as well. Now, again not to
Speaker 1: come back too much to the horrors of human tortoise interaction,
Speaker 1: but yeah, there are these accounts read too of like
Speaker 1: times when roads to various villages were just lined with
Speaker 1: like the bones or the shells of these creatures. It
Speaker 1: was it was a rough time to be a Galapagos tortoise.
Speaker 2: Yes, no, I now I think it's worth talking about
Speaker 2: Galapagos tortoise mating and reproduction, which there's some interesting stuff.
Speaker 2: For one thing I was reading about Maybe we can
Speaker 2: get to the actual mating in a minute, But first
Speaker 2: I was reading a section in Creature in Laughlin about
Speaker 2: the nests and egg laying of the Glopagos tortoise. So
Speaker 2: mating season typically occurs during the rainy season, and after
Speaker 2: having mated, a female tortoise will generally travel toward the
Speaker 2: arid lowlands to build a nest. Darwin has a section
Speaker 2: about this where he correctly observes that they will seek
Speaker 2: out arid sandy soil to dig a nest in, but
Speaker 2: then he says others. He says, sometimes they will just
Speaker 2: drop their eggs where like in a precipice, like in
Speaker 2: a crevice in the rocks. I didn't find any other
Speaker 2: evidence of that, so maybe that was true when he
Speaker 2: was there, but I'm not aware of other evidence for
Speaker 2: that other than what Darwin says. But generally what they
Speaker 2: do is they're going to dig down in the arid regions. Now,
Speaker 2: for the saddleback tortoises, which tend to live more in
Speaker 2: the lowlands, this is not much of a trip. But
Speaker 2: for the domed tortoises it can be a really great
Speaker 2: journey down from the highlands into the place where they're going.
Speaker 4: To lay the eggs.
Speaker 2: And the eggs are laid sometime between June and December.
Speaker 2: A clutch can contain anywhere from like two to twenty eggs.
Speaker 2: The eggs are sort of billiard ball sized or maybe
Speaker 2: a little bit larger. And the nest building process is
Speaker 2: what interested me because apparently it involves a good bit
Speaker 2: of pa. So the tortoise will find a spot in
Speaker 2: the soil and she will dig a hole about thirty
Speaker 2: centimeters deep, scooping the earth out with her hind legs,
Speaker 2: and this is an involved process that can take up
Speaker 2: to about twelve hours, and the tortoise will often urinate
Speaker 2: on the soil in order to soften it for digging.
Speaker 2: But the mother tortoise, after she lays her eggs in
Speaker 2: the hole and covers it up, then also peas on
Speaker 2: the soil again to form a kind of cement layer
Speaker 2: in it.
Speaker 1: This is interesting. We've discussed a number of different nest
Speaker 1: building egg laying scenarios over the years, but I don't
Speaker 1: remember one that was so urine intensive.
Speaker 2: Yeah, there may be other species that do pie cement,
Speaker 2: but this is the first time I remember reading about this.
Speaker 2: So anyway, the eggs incubate in the cemented earth for
Speaker 2: like four to eight months, where the sex of the
Speaker 2: hatchling is ultimately determined by the temperature which the egg incubates.
Speaker 2: That's kind of interesting. It's not chromosomally determined as it
Speaker 2: is for some other animals, and so afterwards they dig
Speaker 2: their way out of the nest to begin their lives,
Speaker 2: and of course this is the most vulnerable time for
Speaker 2: a Galapagos tortoise when they're a hatchling, but the ones
Speaker 2: that survived make it out. They find food, they avoid predators,
Speaker 2: and they eventually grow up, though apparently the growing up
Speaker 2: also takes a good bit of time. The tortoises do
Speaker 2: everything pretty slow, including reaching maturity. I've read that they
Speaker 2: don't reach sexual maturity until several decades later.
Speaker 1: The mating itself is also kind of interesting because they
Speaker 1: basically consists of the males chasing the females around until
Speaker 1: they can corner them. But then there's also, given these
Speaker 1: are large shelled creatures, the male's shell has like an
Speaker 1: indention on the bottom that allows for it to mount
Speaker 1: the female, because otherwise, unless there was some arrangement of
Speaker 1: the shells in this capacity, that they would not be compatible.
Speaker 2: Right, And there was also a fact I came across
Speaker 2: that I thought was funny. In this book, they talk
Speaker 2: about how the larger size of the Glopagos tortoise can
Speaker 2: make the physical active mating sometimes kind of cumbersome and laborious,
Speaker 2: and the authors note that quote, males often slide off,
Speaker 2: even inadvertently, landing upside down, at which point they must
Speaker 2: right themselves and try again, which I don't know if
Speaker 2: it's juvenile that I found that funny, but I did.
Speaker 2: The authors also note that the male tortoises sometimes get confused.
Speaker 2: For example, they try to mate with large rocks.
Speaker 1: Well, that's just, in and of itself funny. We can't
Speaker 1: help but laugh at that.
Speaker 2: But there's also surprising. For these very slow moving animals,
Speaker 2: there is some surprisingly fierce competition between males for access
Speaker 2: to mates, and Darwin notes this. He says, during breeding season,
Speaker 2: you can hear the males emit what he calls a
Speaker 2: horse roar. And I think this roar is probably indicative
Speaker 2: of male on male competition, which sometimes leads to these
Speaker 2: mock fights where they will raise their necks up at
Speaker 2: each other. Rob, I think you actually maybe saw one
Speaker 2: of these going on.
Speaker 1: Yes, I got to see this happen, and I actually
Speaker 1: got to film it. I was able to my wife
Speaker 1: was like, quick, get your camera out, make sure you're
Speaker 1: getting this. So I did. Yeah, it's amazing to watch
Speaker 1: because you'll have these two lumbering giants that are kind
Speaker 1: of on a collision course with each other, and you're like,
Speaker 1: what's going to happen, what's going to happen? And then
Speaker 1: as they get closer, they'll both rear their heads up
Speaker 1: and they'll have this showdown that doesn't it does not
Speaker 1: come to blows or bites or anything like that, but
Speaker 1: it is a competition to see who to determine who
Speaker 1: is the tallest and the tallest tortoise, who had the
Speaker 1: one that can raise its head up the highest, he's
Speaker 1: the winner, and the other one accepts defeat and carries on.
Speaker 1: And that's as violent as it seems to get. But
Speaker 1: it's spectacular to watch. And this was the finest nature
Speaker 1: footage I have ever captured or will ever capture.
Speaker 2: Now, one last thing I wanted to read from Darwin
Speaker 2: here where he's talking about the tortoise's reaction to humans.
Speaker 2: This is another infamous section from the Voyage of the
Speaker 2: Beagle chapter. Darwin says, I was always amused when overtaking
Speaker 2: one of these great monsters as it was quietly pacing along,
Speaker 2: to see how suddenly the instant I passed it would
Speaker 2: draw in its head and legs and uttering a deep hiss,
Speaker 2: fall to the ground with a heavy sound, as if
Speaker 2: struck dead. I frequently got on their backs and then
Speaker 2: giving a few wraps on the hinder part of the shells,
Speaker 2: they would rise up and walk away, but I found
Speaker 2: it very difficult to keep my balance.
Speaker 1: Oh, Charles, no doing, Why are you riding a tortoise?
Speaker 1: I mean it is kind of I mean it based
Speaker 1: on this account, the tortoise is doing exactly what you
Speaker 1: know I observed, and all these sources say they do
Speaker 1: if someone gets too close or something gets too close.
Speaker 1: But it is kind of interesting this added detail that
Speaker 1: apparently eventually the tortoise is like, Okay, I guess this
Speaker 1: weird British man is not going away. I have things
Speaker 1: to do in places to be I'm just going to
Speaker 1: start walking around with him on there and maybe I
Speaker 1: can sort of shake him off.
Speaker 2: Yeah, and this is actually not an isolated report. Again,
Speaker 2: we are not recommending riding the tortoises, and other other
Speaker 2: people talk about how well you can get on their
Speaker 2: backs and ride them and they'll just go about their business.
Speaker 2: And this is apparently a common occurrence. There was a
Speaker 2: common occurrence.
Speaker 4: Back in the day.
Speaker 2: Sometimes they say, you can get two people on one
Speaker 2: of these tortoise shells and just ride them and they'll
Speaker 2: do their thing, like you know, they don't seem they
Speaker 2: don't seem bothered. Now, I'm sure that puts extra strain
Speaker 2: on their muscles and their energy requirements and all that.
Speaker 2: So it's not like okay to do. But just showing
Speaker 2: the strength of the tortoise and how powerful and huge
Speaker 2: this animal is that it could just continue on its
Speaker 2: way trying to graze with like multiple humans riding on
Speaker 2: its back.
Speaker 1: Oh, poor creatures. Yeah, again, do not attempt to don't
Speaker 1: do not get close to the tortoises, and do not
Speaker 1: ride them. Now, we have a fair amount of variety
Speaker 1: with the Glapygos tortoises that they're all of the genus Chellinitis,
Speaker 1: and you get into some discussion about the different varieties
Speaker 1: like the exact variety count. And then we have two
Speaker 1: that are definitely extinct. There's the Floriana Island subspecies that's
Speaker 1: thought to have been hunted to extinction by I think
Speaker 1: eighteen fifty when Darwin visited. This is I believe the
Speaker 1: one where he only describes seeing their bones. The Pina
Speaker 1: Island species is extinct as of twenty twelve, with the
Speaker 1: death of Lonesome George, who was of course famous for
Speaker 1: being the last of his variety. He died and that
Speaker 1: was seemingly it for this variety of tortoise.
Speaker 4: Yeah.
Speaker 2: I've read that there are either twelve or thirteen extant species.
Speaker 1: Yeah. So, coming back to the challenges that tortoises faced
Speaker 1: during the age of humans, we've thoroughly discussed. I think
Speaker 1: the human hunting and human harvesting of tortoises, at least
Speaker 1: for our purpose, is here. But of course there are
Speaker 1: all these invasive species that humans introduced, and while we
Speaker 1: are dealing with cases in some cases where you'll have
Speaker 1: animals directly going after young tortoises, there are also other
Speaker 1: ways that these creatures were harmful and are and can
Speaker 1: still be harmful to the native Galapagos tortoises.
Speaker 2: Right, And in fact, one example of this came up
Speaker 2: in some episodes we did back in October on goats, right,
Speaker 2: the issue of goats competing for resources with tortoises.
Speaker 1: That's right again. Goats, as we discussed, are amazing at
Speaker 1: what they do at roaming around finding odd bits of
Speaker 1: vegetation to consume, and yeah, they're they're ultimately better at
Speaker 1: it than tortoises. They're more thorough than the tortoises, and
Speaker 1: ultimately so thorough that they can be even more disruptive
Speaker 1: to like the to the ground itself, like you know,
Speaker 1: getting in there and actually making it unstable. So that's
Speaker 1: that's one thing to consider. Also when you're dealing with
Speaker 1: any creature that lays its eggs in the ground. Not
Speaker 1: only do you have to worry with certain species, like
Speaker 1: especially pigs and rats going after those eggs and then
Speaker 1: going after the young. Potentially, you also have to deal
Speaker 1: with cattle because there are still cattle on the islands,
Speaker 1: and cattle were brought to the islands, and cattle aren't
Speaker 1: interested in really eating those tortoise eggs, but they will
Speaker 1: definitely step on those tortoise eggs if they happen to
Speaker 1: be ranging in the same area.
Speaker 2: Now, in the previous episode, we talked about some hypotheses
Speaker 2: about how marine iguanas first arrived on the Galapagos Islands,
Speaker 2: probably via some kind of rafting from the mainland. Is
Speaker 2: that also the idea of what likely happened with the
Speaker 2: ancestral tortoises.
Speaker 1: That's my understanding based on the sources I was looking at,
Speaker 1: and based on conversations with some of the naturalist and
Speaker 1: guides in the Galapagos Islands. The idea is that it
Speaker 1: would have been much the same tortoises in South America,
Speaker 1: swept up in river floods, washed out with vegetation which
Speaker 1: they were able to raft on, and reaching these far
Speaker 1: flung islands.
Speaker 2: So it's amazing to imagine these extremely unlikely, kind of
Speaker 2: one off events that allowed the population of each island,
Speaker 2: because it's not something you see happening every day. But
Speaker 2: you know, all it takes is a is a small
Speaker 2: seed population to get there and then wow, what's this.
Speaker 2: You know, there's all these food resources and no predators
Speaker 2: and you can really boom once you arrive.
Speaker 1: Yeah. And I'm not sure if the numbers on this
Speaker 1: are you know, certified as it were, but it seems
Speaker 1: like the first Glapacos tortoises probably reached the islands two
Speaker 1: to three million years ago via rafting. They would have
Speaker 1: probably arrived on the eastern islands of Espanola and San
Speaker 1: Cristobile first and then spread west from there. So it's yeah,
Speaker 1: it's interesting to think about. Now. The other question that
Speaker 1: I guess came up for me, and this was like,
Speaker 1: how big were these tortoises when they first arrived, because
Speaker 1: at least some sources out there make the case that
Speaker 1: they were already big, that they were already quote unquote gigantic,
Speaker 1: while plenty of other sources also discuss Glapago's tortoises as
Speaker 1: a case of island gigantism.
Speaker 2: Yeah, so island gigantism is something that often occurs. There's
Speaker 2: known as island dwarfism and island gigantism. These kind of
Speaker 2: runaway pressures on the size of animals that can really
Speaker 2: bulk them up or shrink them down when they're in
Speaker 2: a contained ecosystem like an island. And I don't think
Speaker 2: we know exactly what all the pressures would be, but
Speaker 2: you could imagine something like, well, maybe there is always
Speaker 2: sexual selection on, say the size of adult male tortoises,
Speaker 2: to make them bigger and bigger, because the bigger you are,
Speaker 2: the more likely a female is to be receptive to mating.
Speaker 2: So there's a sexual selection driving them to be bigger.
Speaker 2: But then there's naturally some kind of other pressure that
Speaker 2: wants to keep their size smaller. You know, like you
Speaker 2: there's that advantage in being bigger. But once you're bigger,
Speaker 2: maybe you're more at risk of predation, or it's harder
Speaker 2: to thermoregulate or something like that. And you can imagine
Speaker 2: cases where you get on an island and suddenly those
Speaker 2: other pressures are relieved and so you can just keep
Speaker 2: getting bigger and bigger than you would have been allowed
Speaker 2: to on the mainland.
Speaker 3: Yeah.
Speaker 1: Yeah, I guess on the like supporting the idea that
Speaker 1: they were already big there is. There is, of course,
Speaker 1: fossil evidence of gigantic tortoises existing on I think every
Speaker 1: continent except Australia and Antarctica at some point in the past,
Speaker 1: so it's not like these forms only emerged on various
Speaker 1: islands island environments. But I don't know. On the other hand,
Speaker 1: it seems like plenty of sources are discussing this as gigantism.
Speaker 1: One paper I was looking at this is from Jaffe
Speaker 1: at All, from a twenty eleven paper in the Royal
Speaker 1: Society Biology Letters, The Evolution of Island gigantism and body
Speaker 1: size variation in Tortoises and turtles. They point out that
Speaker 1: they do point out that quote, the other evolutionary determinants
Speaker 1: of size diversity in Chilonians are poorly understood. But they
Speaker 1: also point out that Chelonians span some four orders of
Speaker 1: magnitude in their sizes, and that there is quote a
Speaker 1: pronounced relationship between habitat and optimal body size. Also worth
Speaker 1: noting that the apparently the closest living relative to the
Speaker 1: Galapagos tortoise is not a direct ancestor of those tortoises,
Speaker 1: but it is itself a relatively small bodied variety of
Speaker 1: tortoise that's found in South America, the Chaco tortoise, I
Speaker 1: believe it is called now. I also mentioned that there
Speaker 1: are other giant tortoises still in the world outside of
Speaker 1: the Galapagos. These would be giant tortoises that survived in
Speaker 1: the Western Indian Ocean in the form of Aldabra giant
Speaker 1: tortoises leave.
Speaker 2: When Darwin arrived, he thought that these were the same species,
Speaker 2: like that the ones on the Galapagos were the same
Speaker 2: as those, or at least the same as some other
Speaker 2: island gigantic tortoise he was aware of. I think it
Speaker 2: would have been those, because those are the only other
Speaker 2: ones I know of, and he was mistaken in that
Speaker 2: in fact that they're just they're different parallel forms of
Speaker 2: gigantic tortoises. But one last thing I wanted to talk
Speaker 2: about with these tortoises before we wrap up today is
Speaker 2: the differences in the shell shapes, because we mentioned earlier
Speaker 2: that some species have more dome shaped shells and some
Speaker 2: have these saddle shaped shells, and there are also intermediate
Speaker 2: species that have sort of somewhere in between. A creature
Speaker 2: and Laughlin have a great section on this in their
Speaker 2: chapter on the tortoises, and I wanted to talk about
Speaker 2: it a bit. So one of the questions is why
Speaker 2: you can observe some things that might lead to these differences.
Speaker 2: The tortoises with the domed shells tend to live more
Speaker 2: in the highlands and around caldera rims, where vegetation is
Speaker 2: much thicker and lush all the time, whereas the ones
Speaker 2: with the saddle backed shells tend to live more or
Speaker 2: even exclusively in the low lands, where conditions are more
Speaker 2: often dry. Of course, the differences in these shells is
Speaker 2: that while as the domed ones are more just kind
Speaker 2: of like an upturned cup over the reptiles back. The
Speaker 2: saddleback tortoises, their shell tends to have like a relief
Speaker 2: area above the head and neck. It's almost like a
Speaker 2: collar that's pulled back. And there are some other differences too.
Speaker 2: The domed tortoises tend to have a larger body size,
Speaker 2: but shorter legs and necks, whereas the saddleback tortoises tend
Speaker 2: to be smaller overall but have longer legs and longer necks.
Speaker 4: Now, remember in the.
Speaker 2: Last episode when we talked about the marine iguanas and
Speaker 2: we were trying to come up with the biological explanation
Speaker 2: for why the iguana kept returning out of the water
Speaker 2: after Darwin threw it in, even though you know it's
Speaker 2: got to go in the water all the time to eat,
Speaker 2: So why doesn't it just stay in the water to
Speaker 2: stay away from him? And the answer we came up
Speaker 2: with that the Darwin did not land on himself is
Speaker 2: that it's probably for thermoregulation reasons because the water is
Speaker 2: cold and it was removing heat from the iguana's body
Speaker 2: and the iguana needs to get back up on land
Speaker 2: to heat back up. I think a good explanation for
Speaker 2: One of the explanations for the different body plans of
Speaker 2: these different tortoises probably also has to do with reptile
Speaker 2: thermoregulation with the regulation of body temperature, because of course,
Speaker 2: animals with a larger body volume also tend to retain
Speaker 2: more heat because they have less surface area proportional to
Speaker 2: their volume. So if you're living in a cold place
Speaker 2: and you're trying to retain body heat, it's easier to
Speaker 2: do that if you're bigger. You've got there's just more
Speaker 2: body in there and less relatively less surface area, and
Speaker 2: vice versa. It's easier to cool off if you're smaller,
Speaker 2: because a bigger percent of your body is surface area
Speaker 2: that you can lose heat through. This would seem to
Speaker 2: correlate with the observation that the domed tortoises, which live
Speaker 2: up in the highlands where it tends to be a
Speaker 2: little bit cooler, tend to have a larger body size
Speaker 2: but also shorter legs and necks, so less extremities poking
Speaker 2: out that can lose heat, whereas the saddleback tortoises tend
Speaker 2: to be smaller overall, with longer legs and longer necks
Speaker 2: and they live down in the lowlands where things tend
Speaker 2: to be hotter.
Speaker 4: Yeah.
Speaker 1: Yeah, Now, most of the tortoises I got to observe
Speaker 1: were definitely in highland environments, but their relationship with temperature
Speaker 1: is notable as well. In one case, we've got to
Speaker 1: go out and see these tortoises out there in this
Speaker 1: this this this highland area, and it was early enough
Speaker 1: in the day that some of them were essentially sleeping in.
Speaker 1: They were still bedded down in the mud where they
Speaker 1: could they could, you know, keep their temperature relatively stable
Speaker 1: throughout the night. And some were already getting up to
Speaker 1: begin their their day of eating. Others just weren't quite
Speaker 1: ready yet.
Speaker 2: Oh yeah, And I've read that these tortoises just love
Speaker 2: the mud, like they'll love to get in the mud
Speaker 2: puddles and they'll just hang out there for days sometimes.
Speaker 1: Yeah, so you'll see them trooping around and yeah, on
Speaker 1: one level, they kind of look like bulldozers because they're
Speaker 1: just covered with mud, and of course they've been eating too.
Speaker 1: There are lots of pictures you included one here of
Speaker 1: one with just this spectacularly messy's face from all the
Speaker 1: vegetation and or fruits it's been consumed. It's just smeared
Speaker 1: all over.
Speaker 2: It's like one of those gross baby pictures where the
Speaker 2: baby just looks they've been face down in a play
Speaker 2: of spaghetti.
Speaker 1: Yeah, and their face, the face of the Glabgos tortoise
Speaker 1: does kind of look like like old baby, so it
Speaker 1: really matches up with that well.
Speaker 2: But there are other differences in the environments that might
Speaker 2: explain the different body plans of these tortoise species, So
Speaker 2: a lot of it probably has to do with vegetation.
Speaker 4: Right.
Speaker 2: Domed tortoises tend to live in more lush highlands with
Speaker 2: dense undergrowth and a creature in Laughlin right quote. The
Speaker 2: domed shells, smoothly rounded as they are, may prove adaptive.
Speaker 2: Is the tortoises move tank like through dense plant cover,
Speaker 2: which is of course also the animal's food source. On
Speaker 2: the other hand, saddle type shells with a large forward
Speaker 2: notch can actually become snagged in low vegetation, impeding the
Speaker 2: movement of the tortoise. Saddle shells are not very adaptive
Speaker 2: in low dense vegetation, so it's just going to be
Speaker 2: easier to move around with a more rounded shell. In
Speaker 2: all that thick brush in the Upper Highland forest regions,
Speaker 2: whereas if you had the saddle shell with the turned
Speaker 2: sort of collar in the front, Yeah, they'd just be
Speaker 2: getting hooked on stuff all the time.
Speaker 1: And I mean they are little bulldozers. They can tear
Speaker 1: stuff up. Like for instance, you know there are gonna
Speaker 1: be limits. They could continue, you know, be slowed down
Speaker 1: or I guess stuck in vegetation. But to give one
Speaker 1: example that I was told about, do you have again
Speaker 1: individuals who are still ranching in these in these parts
Speaker 1: of the Highland, they have cows. They need to contain
Speaker 1: those cows. But if they're gonna be tortoises moving through,
Speaker 1: they're gonna they're just gonna take down your barbed wire
Speaker 1: fence or your your whatever kind of fencing you have.
Speaker 1: So in many cases they'll have the fencing, they'll have
Speaker 1: this big gap at the bottom that will allow a
Speaker 1: tortoise to move through, because that way you still get
Speaker 1: to have your fence and the tortoise won't won't tear
Speaker 1: it down when it makes a bee line for whatever
Speaker 1: wherever it's going.
Speaker 2: Yeah, fortunately the cows can't crawl under Yeah.
Speaker 1: I guess not. It did raise some questions like, well, yeah,
Speaker 1: can the cow what about really short cows? I don't know,
Speaker 1: but apparently it works.
Speaker 2: But the final thing with the difference between the domed
Speaker 2: tortoises and the saddlebacks is probably food sources as well,
Speaker 2: because again, the domed ones are going to be munching
Speaker 2: on a lot of you know, lush, low lying vegetation,
Speaker 2: so you know, that's just that's okay to have a
Speaker 2: normal kind of dome dome shaped shell for that. But
Speaker 2: the saddleback tortoises, which live in the more arid lowlands,
Speaker 2: are going to be eating cacti, often tall cacti that
Speaker 2: they need to reach up to get to, and so
Speaker 2: the upturned front of the shell allows more room to
Speaker 2: raise the neck, and of course, of course, as I
Speaker 2: said as well, they've got longer necks and longer legs
Speaker 2: to help reach Robin, I think you said you observe
Speaker 2: stuff about those cactuses sort of reacting to that by
Speaker 2: growing taller and taller to try to escape the munching tortoises.
Speaker 1: Yeah. Yeah, And it's it's remarkable to see because yeah,
Speaker 1: here's this, here's this cac that has evolved to thrive
Speaker 1: alongside the tortoises, and it ends up, Yeah, it ends
Speaker 1: up feeling more like a tree than a cactus, if
Speaker 1: that makes sense. Yeah, it's a remarkable ecosystem.
Speaker 4: All right.
Speaker 1: So there you have it. Hopefully we gave just at
Speaker 1: least a nice snapshot, a nice overview of the Galapagos tortoise. Obviously,
Speaker 1: there's a lot of research out there about these creatures,
Speaker 1: so perhaps there's some details that we managed to leave out.
Speaker 1: If you think that we left out something that is
Speaker 1: particularly exciting, then right in. We'd love to hear about it.
Speaker 1: We'd love to see it for ourselves and to share
Speaker 1: it in a future listener mail. Likewise, as I mentioned
Speaker 1: the first one, if you've traveled with the Glabgos Islands,
Speaker 1: if you live on the Galapagos Islands or are an Ecuadorian,
Speaker 1: we would also love to hear from you. We love
Speaker 1: your thoughts on these fabulous creatures that we've discussed here,
Speaker 1: or any of the other creatures of the Glabgos Islence,
Speaker 1: I'm always excited to hear more. Just a reminder to
Speaker 1: everybody's Stuff to blow your mind. Publishes us it's core
Speaker 1: episodes on Tuesdays and Thursdays. In the Stuff to Blow
Speaker 1: Your Mind podcast feed we have listener mail episodes on Mondays,
Speaker 1: a short form artifact or monster fact episode on Wednesdays,
Speaker 1: and on Fridays we set aside most serious concerns and
Speaker 1: just talk about a weird film.
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