Speaker 1: Hey, welcome to Stuff to Blow your Mind. It is
Speaker 1: another Vault day here for you. So we have the
Speaker 1: Parrotfish Part two. It originally published five three, twenty twenty four.
Speaker 1: I hope you enjoy.
Speaker 2: 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 Lamb.
Speaker 3: And I am Joe McCormick, and we're back with Part
Speaker 3: two in our series on parrotfish, a group of related
Speaker 3: fishes containing about ninety to one hundred species worldwide, notable
Speaker 3: for their powerful beak like mouths made out of rows
Speaker 3: of fused teeth. In the previous episode, we talked about
Speaker 3: some basics about the biology and taxonomy of parrotfish species.
Speaker 3: We talked about their diet and feeding behavior. Parrot Fish
Speaker 3: are usually considered herbivores or something equivalent to herbivores. They
Speaker 3: survive by grazing for algae, microorganisms, to trite us, and
Speaker 3: sometimes invertebrate animals like coral polyps along the surfaces of
Speaker 3: rocks and coral skeletons within coral reef environments. We talked
Speaker 3: about the fact that some parrotfish species end up biting
Speaker 3: or scraping off significant chunks of hard matter from the
Speaker 3: rocks and coral that they scour for food, and then
Speaker 3: grinding up these coral skeletons and minerals in their phryngial mills.
Speaker 3: It's kind of like horror movie machinery in the back
Speaker 3: of their throats. I think we compared it to like
Speaker 3: a bone transmission gear and then defecating what's left in
Speaker 3: the form of sand. And so as a result, parrotfish
Speaker 3: are major figures in the erosion of coral reefs and
Speaker 3: in the production of sand. So if you walk across
Speaker 3: a white sandy beach in the tropics where there are
Speaker 3: coral reefs nearby, there is a good chance that most
Speaker 3: of the sand under your feet was at one point
Speaker 3: parrotfish poop. This is true of reef islands built entirely
Speaker 3: out of reef sediment, like the Maldives, but also true
Speaker 3: of some white sandy beaches in places like Hawaii and
Speaker 3: the Caribbean. We talked also about writings on parrotfish from
Speaker 3: the ancient world, how the Romans prized certain parrotfishes as
Speaker 3: food items, and why they thought they were in first
Speaker 3: place among the culinary uses of fish. How they developed
Speaker 3: a range of beliefs about these fish, some of which
Speaker 3: were fairly biologically accurate, such as the belief that these
Speaker 3: fish are herbivorous grazers they sort of are, and that
Speaker 3: they produce audible sounds underwater as they scrape the rocks
Speaker 3: and coral for food, also true. Other beliefs not quite
Speaker 3: so accurate. For example, Rob, didn't you talk about this
Speaker 3: idea that they like cooperate altruistically to save one another
Speaker 3: from traps?
Speaker 1: Yes, and in this became an enduring and long lasting
Speaker 1: symbol of free which doesn't really hold up to how
Speaker 1: they actually behave.
Speaker 3: But we also talked last time about some interesting beliefs
Speaker 3: about parrotfishes in Hawaiian mythology, where the parrotfish is sort
Speaker 3: of a progenitor of other sea life and enters into
Speaker 3: a pact with a Hawaiian mythical hero who can sort
Speaker 3: of call upon his friendship with the parrotfish in order
Speaker 3: to produce an abundance of fish catch for the people.
Speaker 3: And then finally, we also talked about research on parrotfish teeth,
Speaker 3: which are made out of some of the hardest, stiffest,
Speaker 3: and most resilient biominerals known even to the extent that
Speaker 3: they are being investigated as a model for high durability
Speaker 3: synthetic materials in the lab. So that was part one,
Speaker 3: and today we're back to talk some more about parrotfish.
Speaker 1: Yeah, and I just want to drive home that if
Speaker 1: you haven't had the opportunity to observe parrotfish in the wild,
Speaker 1: and you find yourself traveling to or in an area
Speaker 1: where there are reef environments and there is some manner
Speaker 1: of snorkeling going on, go check it out. Oftentimes, you
Speaker 1: know there are various snorkeling companies and and you know
Speaker 1: small businesses that are that are very approachable. You don't
Speaker 1: have to have a lot of experience to try these out. Again,
Speaker 1: these are often we're talking like shallow water environments, and
Speaker 1: in these environments there's almost always some sort of parrotfish
Speaker 1: to observe. And if that's not your cup of tea,
Speaker 1: I want to add that for anyone who would like
Speaker 1: to see various parrotfish in action as well as other fish,
Speaker 1: I highly recommend checking out Coral City Camera. It's that's
Speaker 1: just Coralcitycamera dot com, or you can look it up
Speaker 1: and search it's an underwater camera streaming live from an
Speaker 1: urban coral reef in Miami, Florida. Uh, it's it's pretty cool,
Speaker 1: and if you watch long enough, you will see some parrotfish.
Speaker 3: In action, pursuing their new career as streamers.
Speaker 1: Yes. Yes, so we're going to get into parrotfish reproduction
Speaker 1: here in a bit. But first up, we have this
Speaker 1: other delightful area to look at something that I wasn't
Speaker 1: familiar with at all concerning parrotfish. Joe, do you want
Speaker 1: to get into their mucus?
Speaker 3: Oh? Do? I? I feel like I'm already into their mucus.
Speaker 3: I've been in it all day. So I mentioned in
Speaker 3: the previous episode that the topic of parrotfish was one
Speaker 3: that I initially got interested in just by looking at pictures.
Speaker 2: You know.
Speaker 3: I was looking at like a photo of a parrotfish mouth,
Speaker 3: and I started thinking, what is going on with this
Speaker 3: awesome palisade of fused together teeth? And so there is
Speaker 3: another parrotfish subtopic that I think one could come to
Speaker 3: in exactly the same manner, and that is their mucus cocoons.
Speaker 3: If you look for photos of parrotfish sleeping, you will
Speaker 3: find images of these animals nestled down into cozy little
Speaker 3: niches in the seafloor or within the reef structure, sometimes
Speaker 3: kind of in a recess or a little heidi hole
Speaker 3: in the reef, surrounded by what looks like some kind
Speaker 3: of of film. Sometimes it looks like the parrotfish is
Speaker 3: enclosed within a gauzy, transparent orb covered like sometimes covered
Speaker 3: in glitter. If you see these in motion and rob
Speaker 3: below the photos here, I did attach a link to
Speaker 3: a video in the outline that you can look at
Speaker 3: so you can see it moving. If you see these
Speaker 3: in motion, they will they will appear to undulate in
Speaker 3: the water, so they're kind of jelly like in movement
Speaker 3: and substance. In other cases, this film looks like the
Speaker 3: fish is wrapped up inside a huge funnel spider web
Speaker 3: that's just covered in sand. Which funny thing about that
Speaker 3: the sand may of course be the parrotfish's own excretion
Speaker 3: from earlier.
Speaker 1: MM. Yeah, I'm looking at the video footage right now.
Speaker 1: It's it's slimy but beautiful.
Speaker 3: So what is this gossamer bubble around a slumbering fish.
Speaker 3: This is what's known as the parrotfish's mucous cocoon. Or
Speaker 3: sometimes in the scientific literature, it's mucus envelope, described by
Speaker 3: an author named H. E. Win in a scientific article
Speaker 3: in nineteen fifty five as a quote thin, transparent and
Speaker 3: gelatinous mucoid substance which starts as a fold at the
Speaker 3: mouth and progresses backwards in folds to surround the body.
Speaker 3: So parrotfish are daytime animals. They sleep during the night,
Speaker 3: they wake and feed during the day, and some species
Speaker 3: have been observed to spend roughly an hour before sleep
Speaker 3: generating this jelly like sleeping bag out of mucus from
Speaker 3: their mouths before actually getting to sleep, so it's like
Speaker 3: a bedtime routine. As night is falling, they start spitting
Speaker 3: out the mucus and it starts to envelop their body
Speaker 3: from front to back. So the fish are making themselves
Speaker 3: bedtime slime sacks. But why now? First, this is a
Speaker 3: side note. I just wanted to say it is normal
Speaker 3: for all kinds of fish species, not just parrotfish or
Speaker 3: the other related fish. Like some rasses that make these
Speaker 3: slime sacks. It is normal for all kinds of fish
Speaker 3: to be covered in a thin layer of mucus on
Speaker 3: the outside of their skin. This omnipresent slime barrier can
Speaker 3: provide a number of benefits, one of which is OSMO regulation,
Speaker 3: and that's maintaining the balance of internal water and solutes
Speaker 3: such as electrolytes, so for example, and OSMO regulation function
Speaker 3: within our bodies human bodies is maintaining the right level
Speaker 3: of salt in our body fluids. Mucous coverings on all
Speaker 3: kinds of fish help with OSMO regulation. But these mucous
Speaker 3: coverings on the skin also cut down on friction. So
Speaker 3: the slippery layer of mucus on the fish's skin makes
Speaker 3: it easier for the fish to swim along. It's like
Speaker 3: a lubricant for the interface with the surrounding water. It's
Speaker 3: also just physical protection of the skin from contact trauma
Speaker 3: such as cuts and scrapes. It in some cases provides
Speaker 3: UV radiation protection. In some cases might protect the fish
Speaker 3: from noxious chemicals or pollutants in the water, and provides
Speaker 3: the fish protection against drying out.
Speaker 1: So this is of course one of the potential issues.
Speaker 1: And just handling fish such as then like ketch and
Speaker 1: release and so forth. The slime isn't just something that's
Speaker 1: on the fish. It's an active barrier.
Speaker 3: Yeah, but that's all just the normal mucous coating common
Speaker 3: to many many fish. What we're talking about here is
Speaker 3: specifically this baggy mucous hyper sleep pod that forms around
Speaker 3: some parrotfish and rasses through the night. So I started
Speaker 3: looking at scientific papers about this to see what I
Speaker 3: could find out. So first I was looking at a
Speaker 3: marine zoology paper from the year nineteen seventy that investigated
Speaker 3: a few species of parrotfish to see how and under
Speaker 3: what conditions the fish would make these cocoons. So this
Speaker 3: is by John E. Byrne, who was a professor of
Speaker 3: zoology at the University of Hawaii. The paper is called
Speaker 3: Mucus envelope formation in two species of Hawaiian parrotfishes, and
Speaker 3: the paper begins by citing previous research by Win and
Speaker 3: co authors on parrotfish from the coral reefs of Bermuda,
Speaker 3: which were observed to make mucus envelopes at night. So
Speaker 3: when and a co author named Bardak argued that the
Speaker 3: purpose of the mucus cocoon of the slimesack was to
Speaker 3: protect the parrotfish from predators while it was sleeping. And
Speaker 3: this is a hypothesis that I've seen repeated in a
Speaker 3: number of sources that maybe somehow the mucus covering will
Speaker 3: help alert the fish more quickly if a predator gets
Speaker 3: close to it, or may in some way help mask
Speaker 3: the fish, maybe mask the fish is sent from predators,
Speaker 3: or provide some kind of benefit along these lines.
Speaker 1: Okay, So either to some degree a cloaking system, a
Speaker 1: cloaking device, if you will, or perhaps some sort of
Speaker 1: like added security trip wire made out of mucus.
Speaker 3: There you go. Now we'll get to another explanation in
Speaker 3: just a bit here, but we're not there quite yet.
Speaker 3: First we're gonna look at like how and how and
Speaker 3: when these things form. So the author of the study,
Speaker 3: John Burn, begins by investigating envelope formation in a couple
Speaker 3: of different species of parrotfish. There's scare Us dubious, commonly
Speaker 3: known as the regal parrotfish, and scaus parsp pair. Oh wow,
Speaker 3: here's a word, pers bisilatis. There you go, which is
Speaker 3: commonly called the spectacled parrotfish. Both are found in the
Speaker 3: reefs around Hawaii, and I think the spectacled parrotfish may
Speaker 3: be one of the keyfish referred to as oohu and
Speaker 3: some of the Hawaiian legends that we talked about in
Speaker 3: the last episode.
Speaker 1: Yeah. Yeah, So burn.
Speaker 3: Did some experiments on these two species in his laboratory,
Speaker 3: varying conditions of light and darkness within their aquaria, making
Speaker 3: observations of behavior, and then examining the mucus producing organs.
Speaker 3: So Previous field observations had found that as daylight intensities decrease.
Speaker 3: As daylight goes down, fewer parrotfishes can be found swimming
Speaker 3: around the reefs for the night time, these fish will
Speaker 3: disperse their schools and go into recesses within the reef
Speaker 3: to hide and sleep, and that's where they generate these cocoons.
Speaker 3: Within the lab environment, Burne found that if you shine
Speaker 3: a constant light on these fish for twenty four hours straight,
Speaker 3: they will actually never make a mucus cocoon. You just
Speaker 3: keep shining the light on them, at least for twenty
Speaker 3: four hours. He didn't push the experiment to go that
Speaker 3: much longer, because you know, it might just end up
Speaker 3: harming them overall. But for twenty four hours straight, you
Speaker 3: shine a light on them and it, you know, nothing happens.
Speaker 1: Yeah, corp, of course, I mean, there are a lot
Speaker 1: of things I'm not going to do of some sort
Speaker 1: of an intelligent being from highly advanced species shines artificial
Speaker 1: light on me for twenty four hours.
Speaker 3: That's right, So the constant light means you never make
Speaker 3: a pod. However, when darkness was introduced, you turned the
Speaker 3: lights off. This triggered twenty two of the thirty parrot
Speaker 3: fish tested to build mucous envelopes, and it was the
Speaker 3: same frequency in the two different species. The fish took
Speaker 3: different amounts of time to finish building their envelopes after
Speaker 3: the light was turned off. The minimum was like thirty minutes,
Speaker 3: maximum was two hundred and forty minutes. Average building time
Speaker 3: was about seventy minutes. However, if you kept the fish
Speaker 3: the parrot fish in the dark after it made its cocoon,
Speaker 3: it did not stay in the cocoon forever. Eventually it
Speaker 3: would emerge on its own. So what did they do
Speaker 3: when they made these things? They would typically rest their
Speaker 3: bodies on the floor of the tank and the seafloor
Speaker 3: in the wild in an upright position, almost always with
Speaker 3: one side of the body resting against a vertical surface
Speaker 3: like a rock or a coral wall, or, in the
Speaker 3: case of the lab experiments, the aquarium wall, and then
Speaker 3: the cocoon begins. It begins formation at the front of
Speaker 3: the fish around its mouth, and folds of mucus slowly
Speaker 3: move back along the length of the body toward the tail.
Speaker 3: Though interestingly, the mucus never completely closes over the body.
Speaker 3: There is always at least a one to two centimeter
Speaker 3: gap at the back end of the bubble, and Burn
Speaker 3: believes this hole is to evacuate respiratory water that's forced
Speaker 3: out of the buckle cavity, so sort of a breathing hole. Now,
Speaker 3: I mentioned that in a lot of these photos, the
Speaker 3: mucus coccoon seems to sparkle as if it is covered
Speaker 3: in glitter. Burn writes that quote fine debris adhered to
Speaker 3: the envelope's exterior and the outline was thus more clearly defined. However,
Speaker 3: he says this coating of sediment and debris makes the
Speaker 3: bubble appear thin and delicate. This is how Wind described
Speaker 3: it in that article from the fifties. But Burn did
Speaker 3: an experiment by injecting pigmented particles into the cocoon and
Speaker 3: revealed that actually appearances can be deceiving here because the
Speaker 3: cocoon often does look very thin. It's like a you know,
Speaker 3: wispy spider web or this very very thin kind of
Speaker 3: gossamer like material. But in fact he found when he
Speaker 3: injected the pigmented particles in there, the mucus structure was
Speaker 3: up to six centimeters thick in some places. So it's
Speaker 3: not as wispy as it looks.
Speaker 1: Okay, This would just be the case of there being
Speaker 1: like a thin layer of particles on top of this
Speaker 1: otherwise translucent or semi translucent mucus shielding. They would give
Speaker 1: it the appearance of being super thin when in fact
Speaker 1: it is probably thicker.
Speaker 3: That's right. So dissection of the fish revealed that the
Speaker 3: presence of gland tissue in the buckle cavity correlated with
Speaker 3: whether or not the fish would make a cocoon. It
Speaker 3: was found that fish that did not have this gland
Speaker 3: tissue in the mouth cavity, they did not form the
Speaker 3: mucus cocoons. So that's how they're made and win. But
Speaker 3: what are they for? Well, again, the burn paper mentions
Speaker 3: this hypothesis that the mucus sleeping bag somehow protects the
Speaker 3: fish from large predators. A commonly mentioned predator in the
Speaker 3: reef environment would be the more eel. You know, and
Speaker 3: it can get down there in the recesses and attack.
Speaker 3: But apparently there's some doubt about this because, for example,
Speaker 3: when faced with reef dwelling predators such as more eels,
Speaker 3: there is some evidence that sleeping fish within within a
Speaker 3: cocoon are still vulnerable, like they still get eaten. But
Speaker 3: actually I came across an interesting twenty eleven paper that
Speaker 3: looked directly into the function of the mucus cocoon and
Speaker 3: came to a different conclusion. So this was published in
Speaker 3: the journal Biology Letters by Grutterer at All and the
Speaker 3: title is this will give some of the findings away
Speaker 3: fish mucus cocoons the mosquito nets of the sea. This
Speaker 3: was in the year twenty eleven. So in this paper
Speaker 3: the authors look at another hypothesis, which is the idea
Speaker 3: that mucus envelopes actually protect the fish inside from parasites
Speaker 3: such as ectoparasitic nathid isopods. These are these little bloodsucking
Speaker 3: parasites that live throughout the ocean, often compared to terrestrial
Speaker 3: mosquitoes and ticks. Raw I attached to a little photo
Speaker 3: of these things for you to look at. They're kind
Speaker 3: of shrimp like in appearance maybe look like a cross
Speaker 3: between a shrimp and a tick. Yeah yeah, And the
Speaker 3: authors point out that during the daytime, when parrotfish are
Speaker 3: swimming around, they actually get some help. They get some
Speaker 3: protection against blood drinking isopods from cleaner fish. You know,
Speaker 3: this is a relationship where a smaller fish that wants
Speaker 3: to eat these parasites will come along and help pick
Speaker 3: them off to sort of groom the outside of the
Speaker 3: larger fish. But how do the fish protect themselves at night.
Speaker 3: The idea behind this experiment was that maybe the mucus
Speaker 3: cocoon functions like a mosquito net to protect the sleeping
Speaker 3: fish from these heimatophagous parasites. So they tested this hypothesis
Speaker 3: on the coral reef parrotfish Chlorurus sordid us. And the
Speaker 3: way they tested it was they got some of these fish,
Speaker 3: they separated them into groups that would sleep with and
Speaker 3: without the benefit of cocoons in the presence of these
Speaker 3: isopod parasites. And actually, the way they did it was
Speaker 3: they took a subset of cocoon fish and found a
Speaker 3: way to sort of gently push them out of their
Speaker 3: envelopes without waking them up. So what do they find Yes, indeed,
Speaker 3: the fish without the mucus bag experienced way more attacks
Speaker 3: by parasites. How much more well, about ninety five percent
Speaker 3: of the fish without cocoons were attacked by isopods and
Speaker 3: only about ten percent of the fish with cocoons were attacked.
Speaker 1: So huge difference, all right, Right, so yeah, coming back
Speaker 1: to the mosquito net comparisons, Like, initially we looked at
Speaker 1: it and we're like, this mosquito net must protect the
Speaker 1: sleeper from bears, but in reality it protects them from
Speaker 1: mosquitoes and similar insects that sort of thing.
Speaker 3: Or maybe even something downstream from mosquitoes in the analogy here,
Speaker 3: because the authors also investigated the question of how energetically
Speaker 3: costly it is for the fish to make these mucous orbs,
Speaker 3: and they calculated that it takes about two point five
Speaker 3: percent of a fish's daily energy budget to make the
Speaker 3: mucus bag. Now, when I first saw that figure, I
Speaker 3: kind of thought, oh, hey, that seems fairly cheap, only
Speaker 3: two point five percent. But actually I was reading some
Speaker 3: news reporting on this that quoted the lead author, Alexandra Grutterer,
Speaker 3: and she framed it a different way. She said, quote
Speaker 3: the amount of effort that goes into building these cocoons,
Speaker 3: which requires fish to have developed very large glands about
Speaker 3: the size of a quarter to produce the cocoons, is extraordinary.
Speaker 3: Parasites must exert an enormous pressure on these fish in
Speaker 3: order for the fish to have evolved such a specific
Speaker 3: way of avoiding the parasites. So what could be so pressing?
Speaker 3: Is it really just that you don't want to get
Speaker 3: bitten by these isopods and have them drink some of
Speaker 3: your blood? Well, Grutterer mentions the possibility that the blood
Speaker 3: directly lost to the parasite might not be the only cost.
Speaker 3: These isopods may also transmit a secondary endo parasite which
Speaker 3: lives in the fish's blood, much like how mosquitoes transmit
Speaker 3: malaria in humans. So the mosquitoes themselves are annoying and
Speaker 3: you don't like the mosquitoes, but the malaria is much
Speaker 3: more concerning than the mosquito. Malaria can be deadly in
Speaker 3: a similar way. It's possible that it's worth it for
Speaker 3: these fish to build these slimy bionets to protect themselves
Speaker 3: from blood disease. Wow, so it seems like a good trade.
Speaker 3: You spend a little energy to weave a slime tube
Speaker 3: before bed. Every night, you sleep without these tiny shrimp
Speaker 3: monsters drinking your blood, possibly giving you diseases of the blood.
Speaker 3: And it all works out. And in fact, there was
Speaker 3: one more observation from grutter speaking to the media that
Speaker 3: kind of maybe there's a strategy to recoop some of
Speaker 3: that nightly cost. So Grutterer says, quote, I have observed
Speaker 3: on occasion a fish at dawn with what appeared to
Speaker 3: be mucus stuffed in its mouth. And then she goes
Speaker 3: on to say she has seen other fish, not parrotfish,
Speaker 3: but related fish that also produce mucus cocoons pecking it
Speaker 3: at its old cocoons in the morning. So like recooping
Speaker 3: some of that nightly cost by eating the mucus that
Speaker 3: you created before.
Speaker 1: I mean, that's just it's economically sound. It's like if
Speaker 1: humans produce, say an ectoplasm defense shield at night, you
Speaker 1: would want to to recoup that cost, and that might
Speaker 1: mean consuming all that actoplasm again and getting all that
Speaker 1: liquid back into your body. You know, it reminds us
Speaker 1: of other examples we've looked at in biology, such as
Speaker 1: various reptiles that will eat their own shed skin because
Speaker 1: you know, why waste that, you know.
Speaker 3: Yeah, so may still provide some kind of benefit against
Speaker 3: larger macroscopic predators too. Not certain about that, but it
Speaker 3: does seem like there's a very good case that these
Speaker 3: mucous bags help prevent against parasite attacks.
Speaker 1: Very fascinating, all right, And so for the rest of
Speaker 1: the episode, we're going to turn to the world of
Speaker 1: parrot fish reproduction and pair fish sex. So, as we
Speaker 1: teach out in the first episode, one of the other
Speaker 1: amazing aspects of parrotfish biology broadly is that they change
Speaker 1: sex during the course of a normal lifetime. That's to say,
Speaker 1: this is not something that occurs, you know, only when
Speaker 1: certain environmental conditions are right. It occurs as part of
Speaker 1: a normal life cycle.
Speaker 3: And within a fairly predictable pattern, right.
Speaker 1: That's right. Yeah, And they're going to be a couple
Speaker 1: of exceptions. Again, as we've been distressing, there are a
Speaker 1: number of different species of parrotfish, but still the vast
Speaker 1: majority of them do follow this example that we're going
Speaker 1: to be discussing. So they are proto gynos that means
Speaker 1: female first, hermaphrodites that always turn into males if they
Speaker 1: live long enough, so they're born female and then at
Speaker 1: a certain point during their development they become male and
Speaker 1: live out the rest of their life as a male.
Speaker 3: And this would feedback into something we talked about in
Speaker 3: the first episode, which is sometimes difficulty in identifying parrotfish
Speaker 3: species because they undergo these changes, and these changes come
Speaker 3: with changes to their outer appearance.
Speaker 1: That's right along the way, multiple changes in colorization take place,
Speaker 1: some of which have to do with just aging, some
Speaker 1: of which have to do with changing their sex, and
Speaker 1: others that have to do with diet and other factors.
Speaker 1: This pointed out by the National Marine Sanctuary Foundation as
Speaker 1: resources about the parrotfish. I also want to point out though,
Speaker 1: that according to NAA fishery biologist Ronald J. Saals, gonecharism
Speaker 1: has been reported for I think three species within the
Speaker 1: parrotfish family, which is to say, there are at least
Speaker 1: three species of parrotfish where we have the more typical
Speaker 1: scenario of male female division as opposed to what we
Speaker 1: predominantly see in parrotfish, which again is this this sequential
Speaker 1: hermaphroditism in which the fish are born female and then
Speaker 1: if they live long enough, become male, live out the
Speaker 1: rest of their life as males. And so the basic
Speaker 1: scenario is most parrotfish are born females, continue to grow
Speaker 1: to reproduce externally as females, generally in the harem of
Speaker 1: a larger protective male who also tends to a grazing territory,
Speaker 1: and in time, if that female lives long enough and
Speaker 1: grows large enough, she transitions into a larger terminal, reproductive male.
Speaker 3: Interesting.
Speaker 1: Now, in general, parrotfish experience what I've seen referred to
Speaker 1: as moderate longevity. It's going to vary depending on the
Speaker 1: particular specimen, and I think it even the general generalities
Speaker 1: about how long they live is going to vary. I've
Speaker 1: seen in general parrotfish life span sited seven to ten years.
Speaker 1: I've seen it cited as less than twenty. I've also
Speaker 1: seen it sighted as five to six. Again, we have
Speaker 1: a number of different species we're talking about here, and
Speaker 1: I'll throw out additional numbers for a specific species here
Speaker 1: in a bit. We also have to remind ourselves that
Speaker 1: these are creatures living in the ocean, and so there
Speaker 1: are a whole number of factors from blood diseases to
Speaker 1: parasites to eels trying to eat them. To human fishermen
Speaker 1: and so forth.
Speaker 3: It's just hard to imagine like ten straight years of
Speaker 3: biting and scraping on rocks with your teeth.
Speaker 1: Yeah, we're literally scraping by right now. Parrotfish display what
Speaker 1: is referred to as indeterminate growth, which means that there's
Speaker 1: not a full sized growth limit. They just keep growing
Speaker 1: as long as they're alive. And so parrotfish just continue
Speaker 1: to grow at a consistent rate. And this is important
Speaker 1: to consider in making sense of their sex changes because
Speaker 1: one of, if not the primary hypotheses for why they
Speaker 1: do this, why they evolve to do this, does relate
Speaker 1: to their size. Maximum size again, it's going to depend
Speaker 1: on the species. I see ranges like one to four feet.
Speaker 1: But let's go ahead and just talk about the biggest
Speaker 1: parrotfish just to give us like a nice frame of reference,
Speaker 1: because also the largest parrotfish is also pretty gnarly.
Speaker 3: Is this the bumphead we talked about last time?
Speaker 1: It is the bumphead, So we have a little more
Speaker 1: on the bump head here. The bump head, according to
Speaker 1: the NOAA, reaches size as a four point two feet
Speaker 1: long and up to one hundred pounds, So one hundred
Speaker 1: and thirty centimeters forty six kilograms, And not only are
Speaker 1: they the largest parrotfish, but they're among the largest reef
Speaker 1: fish period. Reef environments are generally shallow and tight, so
Speaker 1: you know, they're not inviting places for larger fish. And
Speaker 1: their namesake bump is used like a rams horns in
Speaker 1: male to male competitions, though females also have smaller bumps, which,
Speaker 1: of course, if the parrotfish lives long enough, is going
Speaker 1: to grow in size once they have changed sect.
Speaker 3: Okay, so these are fish that just keep growing, even
Speaker 3: though that's not necessarily the best for them in all ways,
Speaker 3: like it might limit what coral surfaces they can access
Speaker 3: and so forth.
Speaker 1: Well, these guys are just bigger anyway. This is just
Speaker 1: But this would I guess, seem to be like the
Speaker 1: maximum size that seems to fit into the evolutionary economy
Speaker 1: of living around the reef. Okay, like I guess it
Speaker 1: would be. It would be hard to argue that parrotfish
Speaker 1: should get larger than this, because we have no living
Speaker 1: parrotfish that get larger than this. I see, the market
Speaker 1: won't allow it. You know, Now, bump head parrotfish can
Speaker 1: live to be forty years old. I've read they don't
Speaker 1: reach sexual maturity until five to eight years old, and
Speaker 1: sadly their numbers are down except in protected reef environments.
Speaker 3: So I believe based on what I've read, these are
Speaker 3: the ones that are classic. When we talked about the
Speaker 3: different classifications of parrotfish feed behaviors based on like sort
Speaker 3: of how hard they gouge the rock or the coral,
Speaker 3: and these would be like the excavators, right, like they
Speaker 3: are plowing into that stuff.
Speaker 1: Yeah, these guys take the big bites. I was reading
Speaker 1: a little bit more about this on the NOAA website
Speaker 1: and they said that, yeah, they take out those big
Speaker 1: bites that also end up taking out a little bit
Speaker 1: of live coral. But they stress that this is still
Speaker 1: very healthy for the coral in all the ways we
Speaker 1: already mentioned. I don't remember if we mentioned this. I
Speaker 1: don't remember if we mentioned this or not. But there's
Speaker 1: also the idea that they'll break down dead reef and
Speaker 1: of course turn that into sand, dead bits and branches
Speaker 1: that might otherwise break off in storms and damage other
Speaker 1: parts of the reef.
Speaker 3: Oh yeah, I see, So it's better for it to
Speaker 3: better for this chunk to get ground up in a
Speaker 3: parrotfish's pharyngial mill and pooped out as sand rather than
Speaker 3: knocked off in the storm and hit some other healthy
Speaker 3: part of the reef.
Speaker 1: Yeah, because it's one of the interesting things about about
Speaker 1: reef environments, and this is something you're def only instructed
Speaker 1: about anytime you go out and snorkel or scuba dive.
Speaker 1: Certainly I imagine around these these is that there is
Speaker 1: like a hardness to them. Certainly they can also be
Speaker 1: very like you certainly don't want to stand on them
Speaker 1: or walk on them or touch them for a number
Speaker 1: of reasons, because a lot of times they can be
Speaker 1: quite harmful and scrape you out, they can cut you.
Speaker 1: You don't want any of that. But on top of that,
Speaker 1: they can be actually quite delicate, and they can be
Speaker 1: easily broken. And so this would be another case of
Speaker 1: where if the parrotfish are doing their thing, that limits
Speaker 1: the amount of damage that they're going to sustain via
Speaker 1: their own dead parts.
Speaker 3: I see.
Speaker 1: But anyway back to sex changes in parrotfish in general. So,
Speaker 1: according to Jennifer Hodge, a postdoctoral researcher in the Department
Speaker 1: of Evolution and Ecology in the UC Davis College of
Speaker 1: Biological Sciences in twenty twenty. The indeterminate growth factor may
Speaker 1: in fact be key. I was reading a couple of
Speaker 1: from a couple of sources. Here. One is a UC
Speaker 1: Davis article by Andy Fell covering her work titled male
Speaker 1: size advantage drives evolution and sex change of sex change
Speaker 1: in Refish. And then also there is a full paper
Speaker 1: I was looking at, and this is by Hodge at
Speaker 1: All titled Correlated Evolution of sex allocation and Mating system
Speaker 1: in Rasses and Parrotfishes, published in The American Naturalist the
Speaker 1: same year.
Speaker 3: Okay, so how would this indeterminate growth factor affect how
Speaker 3: sex is distributed and developed in a fish species.
Speaker 1: It basically comes down to the fact the observation that
Speaker 1: reproduction among parrotfish and also some of these other fish,
Speaker 1: but for our interests here, the parrotfish is often dominated
Speaker 1: by large males.
Speaker 3: Meaning that like, a larger male has a better chance
Speaker 3: of mating more.
Speaker 1: Right, and that and that male large males and this
Speaker 1: would be the terminal mail in parrotfish fishes. They are
Speaker 1: the ones dominating like all of the mating. So if
Speaker 1: you are not a large male, you are just not
Speaker 1: going to be effective at reproduction. If you are a
Speaker 1: small parrotfish male, your chances of passing on your genes
Speaker 1: is rather slim. And remember the genetic mission is to
Speaker 1: pass on your genes. Now, as a small parrotfish female, however,
Speaker 1: it's less of an issue. The bigger males, they have
Speaker 1: the advantage. They're going to form these harems. If you
Speaker 1: are a small female, you can be part of that
Speaker 1: harem and you are doing your reproductive part as a parrotfish.
Speaker 1: And so that's according to this hypothesis, this is where
Speaker 1: the evolution of sequential hermaphrotitism evolves as a strategy by
Speaker 1: which all individuals have a better shot at participating in reproduction.
Speaker 1: So start off small and female, you definitely get to reproduce.
Speaker 1: And then if you live long enough and you grow
Speaker 1: big enough, you shift to the male set, and then
Speaker 1: you have the size to prove effective. You're better at
Speaker 1: controlling territory resources, harems, etc.
Speaker 3: That's interesting, Okay, So it gives more individuals of the
Speaker 3: species a chance to mate more often.
Speaker 1: Yes, yeah, that's the way I understand it. And I
Speaker 1: was looking again at the writings of in Oa's fishery
Speaker 1: biologist Ronald J. Salce and Salce points out that, yeah,
Speaker 1: the largest parrotfish are always terminal males, and he points
Speaker 1: out that the species, the various species in the genus
Speaker 1: Skeras typically exhibit the following reproductive characteristics. So we see this.
Speaker 1: First of all, there is this proto Guynus female first hermaphrotitism,
Speaker 1: There are breeding territories, there are harems, and there is
Speaker 1: external fertilization.
Speaker 3: Oh yeah, the external fertilization is a good point, because
Speaker 3: I don't want to give the wrong idea when I
Speaker 3: was mentioning mating that it's like, you know, the kind
Speaker 3: of active you might be picturing that. Instead, there's a
Speaker 3: there's an external meeting of the game meats of these animals.
Speaker 1: Right, And I think, I don't know humans, maybe we
Speaker 1: have a problem imagining fish sex in general. But somehow
Speaker 1: this makes it a little easier to sort of picture
Speaker 1: how all this is happening. I think it's all out
Speaker 1: in the open. So SAAL's points out though that in
Speaker 1: the past, and really maybe not in the two distant past,
Speaker 1: we've had these other hypotheses that there might be a
Speaker 1: social trigger for the change in sex. But apparently, based
Speaker 1: on what he wrote, this hasn't necessarily been observed, or
Speaker 1: at least not in all cases or in a broad
Speaker 1: array of cases, because we have scenarios where large terminal
Speaker 1: males are removed from a population, such as by fishing,
Speaker 1: and the females don't just switch over at an earlier age,
Speaker 1: but rather have more difficulty finding a mate.
Speaker 3: Oh okay, so it might be kind of baked in
Speaker 3: that they need to reach a certain size.
Speaker 1: Seems to be the case now, I don't, But again,
Speaker 1: we're dealing with hypotheses here. I don't think that there
Speaker 1: that anything is like one hundred percent proven out here.
Speaker 1: There's still a lot of work that needs to be
Speaker 1: done because a lot of it comes down to, Okay,
Speaker 1: you can have this general idea that this practice evolved
Speaker 1: because large males dominate reproduction and and it makes more
Speaker 1: sense from a reproductive standpoint to start off as female
Speaker 1: and then become male. But then what is the trigger
Speaker 1: is it? Is it purely based on how big you grow?
Speaker 1: Or are there environmental or social triggers? And Uh, ultimately
Speaker 1: the size advantage explanation is just one hypothesis. Uh, there's
Speaker 1: an you know, other hypotheses put more emphasis on possible
Speaker 1: social or in mental environmental triggers such as changes and
Speaker 1: in population density, that sort of thing, in the same
Speaker 1: way that we see examples and say the world of salamanders,
Speaker 1: where uh, you know something they're too many, or you know,
Speaker 1: something goes on demographically in a collect in a certain group,
Speaker 1: then you may have biological changes that result. But I
Speaker 1: guess broadly if there are, if there are social or
Speaker 1: environmental triggers that are involved in theory, we would be
Speaker 1: able to observe them, you know, such as response to
Speaker 1: overfishing of large males in response to changes in the
Speaker 1: environment and so forth. Now there are individual species of
Speaker 1: parrotfish where we might see some of those, like social triggers.
Speaker 1: Perhaps I've seen discussion of the stop light parrotfish in
Speaker 1: particular as perhaps being influenced by population density, growth and
Speaker 1: mortality rates. So if terminal the idea here being that
Speaker 1: it may be the case that terminal males in stop
Speaker 1: light parrotfish populations, if they experience higher mortality rates so
Speaker 1: more of them are dying, or if they are just
Speaker 1: smaller overall sizes in the terminal males, then this change
Speaker 1: may trigger earlier onset of the sex change in the
Speaker 1: female parrotfish in that population. So, like I say, it's
Speaker 1: still would line up with this idea that this evolved
Speaker 1: because male parrotfish, large male parrotfish dominate reproduction. But it
Speaker 1: would maybe be a slightly different case of like what
Speaker 1: is actually causing it based on my understanding looking at
Speaker 1: this documentation. But I like to say there's still I
Speaker 1: think a lot of work going on here. Two thanks.
Speaker 1: Keep in mind, though there is no evidence that any
Speaker 1: species of parrotfish can undergo a sex change, reversal, or
Speaker 1: a second sex change. Like it is, it is sequential,
Speaker 1: sequential hermaphroditism. So it's female, then male. There are no
Speaker 1: known cases where a male can then change back to
Speaker 1: female do to you do to any kind of you know,
Speaker 1: social pressure, environmental or what have you. It is female
Speaker 1: and then male and again sequential hermaphroditism of one form
Speaker 1: or another can be found in other fish. As I
Speaker 1: mentioned the ras is. Apparently you see some version of
Speaker 1: this in some molluscs and crustaceans. The size reproduction hypothesis
Speaker 1: is widely e employed across the board, but I've also
Speaker 1: seen I think the prevention of inbreeding being brought in
Speaker 1: as another possible reason though I'm not sure if that
Speaker 1: really pans out, particularly with the parrotfish. That may just
Speaker 1: really have more to do with hermaphroditism as an evolutionary
Speaker 1: trait in general.
Speaker 3: But the sequential version you're saying, it seems that there's
Speaker 3: a similar evolutionary explanation given across these different classes of animals,
Speaker 3: which is that it likely has to do with a
Speaker 3: relationship between the animal's size and its likelihood of successful reproduction, yes, exactly,
Speaker 3: or specifically the size of males and successful reproduction, and
Speaker 3: the fact that the animals just keep growing.
Speaker 1: Yeah, So it's fascinating. Yeah, this is like a factoid
Speaker 1: about parrotfish that I'd long heard, but I'd never really
Speaker 1: looked into it. I guess one of the problems is
Speaker 1: when you're in the water, it's it's really hard to
Speaker 1: research stuff. You're just like, oh, I'm gonna take your
Speaker 1: word for it, and I'm I'm gonna look at it
Speaker 1: and then I'll try to remember to read about it later.
Speaker 3: Man, you would never guess that there is so much
Speaker 3: interesting stuff about these fish just watching them scrape the rocks.
Speaker 1: Yeah, yeah, I mean just observing them, and I've observed
Speaker 1: in plenty of times in the past. You know, it's
Speaker 1: like you look at them and you're like, well, they're
Speaker 1: a little bit goofy looking, they're beautifully colored, and then
Speaker 1: you learn a little bit more about them, but there's still,
Speaker 1: you know, greater depths of interest there. I guess that's
Speaker 1: the that's the nature of most fish in the sea.
Speaker 1: Never take them for granted.
Speaker 3: In between recording these two episode parts, did you end
Speaker 3: up googling more human parrot fish bites?
Speaker 1: I did.
Speaker 3: I don't know why I did. I shouldn't have.
Speaker 1: Why would you do that?
Speaker 3: I don't know. I regret it. I wish I hadn't
Speaker 3: done it. I just did.
Speaker 1: The only thing of that nature that I did run
Speaker 1: across is when I was looking up pictures and looking
Speaker 1: at articles about the big boys, the bumphead parrotfish is
Speaker 1: there was an image of some coral with some big,
Speaker 1: chunky bites taken out of it, and that was pretty impressive,
Speaker 1: and it did cross my mind. It's like that I
Speaker 1: would not want those bites taken out of my own flesh.
Speaker 3: Yeah, I would not want that to be my bones.
Speaker 1: Yeah.
Speaker 3: But to emphasize yet again, as we did last time, parrotfisher.
Speaker 3: There's no indication that they're very aggressive or looking to
Speaker 3: bite humans that like, these stories come from people who
Speaker 3: were getting up in the parrotfish's business.
Speaker 1: Right, Yeah. I think I saw one account and this
Speaker 1: is like, you know, this is I guess inherently unverified
Speaker 1: of snorkelers or divers where someone was just sort of
Speaker 1: casually bitten by a parrotfish. But in that thread, like
Speaker 1: everyone was like, wow, that's weird. It's never happened to me.
Speaker 1: So I don't know, you know, in the wild one
Speaker 1: officer certainly possible. Who knows what that that parrotfish was
Speaker 1: going through that day?
Speaker 3: Yeah. I guess any species of any fish could in
Speaker 3: some case be aggressive, but it's not like generally thought like,
Speaker 3: oh wow, you gotta be careful, like they're they're coming for.
Speaker 1: You, right, Yeah, I don't think they're they're coming for you.
Speaker 3: Yeah, I'm just because I'm imagining so like, you know,
Speaker 3: the James Bond villain has a pool of piranhas that
Speaker 3: he drops his henchman into when they make a mistake,
Speaker 3: And I'm just thinking like, could they have gone with
Speaker 3: a pool of parrotfish? How would that work out differently?
Speaker 1: We have cotajo bodhi, mister bond with a fine layer
Speaker 1: of algae in coral dust, you will now drop you
Speaker 1: into that of parrotfish.
Speaker 3: M No, not the bump edge. Okay, does that do
Speaker 3: it for parrotfish?
Speaker 1: I think it does. You know, they may have more
Speaker 1: mysteries that we didn't explore, but I think we hit
Speaker 1: all the really interesting stuff here. But hey, if you
Speaker 1: know of other dimensions to the parrot fish or various
Speaker 1: parrotfish species that we didn't talk about, write in because
Speaker 1: we would love to hear from you. Just a reminder
Speaker 1: that's Stuff to Blow your Mind Here is primarily a
Speaker 1: science and culture podcast, with core episodes on Tuesdays and Thursdays,
Speaker 1: listener mail on Mondays, short form episode on Wednesdays, and
Speaker 1: on Fridays. We set aside most serious concerns to just
Speaker 1: talk about a weird film on Weird House Cinema.
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