Speaker 1: Welcome to Stuff to Blow Your Mind production of iHeartRadio.
Speaker 2: Hey, welcome to Stuff to Blow Your Mind. My name
Speaker 2: 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. Parrotfish are
Speaker 3: usually considered herbivores or something equivalent to herbivores. They survived
Speaker 3: by grazing for algae, microorganisms, to trite us, and sometimes
Speaker 3: invertebrate animals like coral polyps, along the surfaces of rocks
Speaker 3: and coral skeletons within coral reef environments. We talked about
Speaker 3: the fact that some parrotfish species end up biting or
Speaker 3: scraping off significant chunks of hard matter from the rocks
Speaker 3: and coral that they scour for food, and then grinding
Speaker 3: up these coral skeletons and minerals in their phyryngial 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 cooperate altruistically to save one another from traps?
Speaker 2: Yes, and in this became an enduring and long lasting
Speaker 2: symbol of friendship, which doesn't really hold up to how
Speaker 2: 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 2: Yeah, And I just want to drive home that if
Speaker 2: you haven't had the opportunity to observe parrotfish in the wild,
Speaker 2: and you find yourself traveling to or in an area
Speaker 2: where there are reef environments and there is some manner
Speaker 2: of snorkeling going on, go check it out. Oftentimes, you know,
Speaker 2: there are various snorkeling companies and small businesses that are
Speaker 2: very approachable. You don't have to have a lot of
Speaker 2: experience to try these out. Again. These are often we're
Speaker 2: talking like shallow water environments, and in these environments there's
Speaker 2: almost always some sort of parrotfish to observe. And if
Speaker 2: that's not your cup of tea, I want to add
Speaker 2: that for anyone who would like to see various parrotfish
Speaker 2: in action as well as other fish, I highly recommend
Speaker 2: checking out Coral City Camera. That's just Coralcitycamera dot com
Speaker 2: or you can look it up and search. It's an
Speaker 2: underwater camera streaming live from an urban coral reef in Miami, Florida.
Speaker 2: It's pretty cool and if you watch long enough, you
Speaker 2: will see some parrotfish.
Speaker 3: In action pursuing their new career as streamers.
Speaker 2: Yes, yes, so We're going to get into parrotfish reproduction
Speaker 2: here in a bit, But first up, we have this
Speaker 2: other delightful area to look at something that I wasn't
Speaker 2: familiar with at all concerning parrotfish. Joe, do you want
Speaker 2: to get into their mucus?
Speaker 3: Oh?
Speaker 2: Do? I?
Speaker 3: I feel like I'm already into their mucus. I've been
Speaker 3: in it all day. So I mentioned in the previous
Speaker 3: episode that the topic parrotfish was one that I initially
Speaker 3: got interested in just by looking at pictures, 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 mucous 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 film. Sometimes it looks like the parrotfish is enclosed
Speaker 3: within a gauzy, transparent orb covered like sometimes covered in glitter.
Speaker 3: If you see these in motion and rob below the
Speaker 3: photos here, I did attach a link to a video
Speaker 3: in the outline that you can look at so you
Speaker 3: can see it moving. If you see these in motion,
Speaker 3: they will appear to undulate in the water, so they're
Speaker 3: kind of jelly like in movement and substance. In other cases,
Speaker 3: this film looks like the fish is wrapped up inside
Speaker 3: a huge funnel spider web that's just covered in sand.
Speaker 3: Which funny thing about that the sand may of course
Speaker 3: be the parrotfish's own excretion from earlier.
Speaker 2: Yeah, I'm looking at the video footage right now. It's
Speaker 2: 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 mucous envelope, described by
Speaker 3: an author named H. E. Wynn 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 full the mouth
Speaker 3: and progresses backwards in folds to surround the body. So
Speaker 3: parrotfish are daytime animals. They sleep during the night, they
Speaker 3: wake and feed during the day, and some species have
Speaker 3: been observed to spend roughly an hour before sleep generating
Speaker 3: this jelly like sleeping bag out of mucus from their
Speaker 3: mouths before actually getting to sleep, so it's like a
Speaker 3: bedtime routine. As night is falling, they start spitting out
Speaker 3: the mucus and it starts to envelop their body from
Speaker 3: front to back. So the fish are making themselves bedtime
Speaker 3: slime sacks. But why now? First, as a side note,
Speaker 3: I just wanted to say it is normal for all
Speaker 3: kinds of fish species, not just parrotfish or the other
Speaker 3: related fish. Like some rasses that make these slime sacks.
Speaker 3: It is normal for all kinds of fish to be
Speaker 3: covered in a thin layer of mucus on the outside
Speaker 3: of their skin. This omnipresent slime barrier can provide a
Speaker 3: number of benefits, one of which is osmo regulation, and
Speaker 3: that's maintaining the balance of internal water and solutes such
Speaker 3: as electrolytes. So for example, and osmo regulation function within
Speaker 3: our bodies. Human bodies is maintaining the right level of
Speaker 3: salt in our body fluids. Mucous coverings on all kinds
Speaker 3: of fish help with OSMO regulation. But these mucous coverings
Speaker 3: on the skin also cut down on friction. So the
Speaker 3: slippery layer of mucus on the fish's skin makes it
Speaker 3: easier for the fish to swim along. It's like a
Speaker 3: lubricant for the interface with the surrounding water. It's also
Speaker 3: just physical protection of the skin from contact trauma such
Speaker 3: as cuts and scrapes. It in some cases provides UV
Speaker 3: radiation protection, in some cases might protect the fish from
Speaker 3: noxious chemicals or pollutants in the water, and provides the
Speaker 3: fish protection against drying out.
Speaker 2: So this is of course one of the potential issues.
Speaker 2: And just handling fish such as then like catch and
Speaker 2: release and so forth. The slime isn't just something that's
Speaker 2: on the fish. It's an active barrier.
Speaker 3: Yeah, But that's all just the normal mucus coating common
Speaker 3: to many many fish. What we're talking about here is
Speaker 3: specifically this baggy mucus 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 those lines.
Speaker 2: Okay, So, either to some degree a cloaking system, a
Speaker 2: cloaking device, if you will, or perhaps some sort of
Speaker 2: 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 and how and when
Speaker 3: the things form. So the author of the study, John Burn,
Speaker 3: begins by investigating envelope formation in a couple of different
Speaker 3: species of parrotfish. There's scas dubious, commonly known as the
Speaker 3: regal parrotfish, and scas per pair. Oh wow, here's a word,
Speaker 3: pers bisilattis there you go, which is commonly called the
Speaker 3: spectacled parrotfish. Both are found in the reefs around Hawaii,
Speaker 3: and I think the spectacled parrotfish may be one of
Speaker 3: the keyfish referred to as oohu and some of the
Speaker 3: Hawaiian legends that we talked about in the last episode.
Speaker 2: 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 founding around
Speaker 3: the reefs. For the night time, these fish will disperse
Speaker 3: their schools and go into recesses within the reef to
Speaker 3: 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't 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 2: Yeah, corp, of course, I mean there are a lot
Speaker 2: of things I'm not going to do of some sort
Speaker 2: of an intelligent being from a highly advanced species shines
Speaker 2: artificial light on me for twenty four hours.
Speaker 3: That's right. So the constant light means he 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 mucus 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 parrotfish 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 cocoon 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 A Wind
Speaker 3: described it in that article from the fifties. But Burn
Speaker 3: did an experiment by injecting pigmented particles into the cocoon
Speaker 3: and revealed that actually appearances can be deceiving here because
Speaker 3: the cocoon often does look very thin, it's like a
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 2: Okay, this would just be the case of there being
Speaker 2: like a thin layer of particles on top of this
Speaker 2: otherwise translucent or semi translucent mucous shielding. They would give
Speaker 2: it the appearance of being super thin when in fact
Speaker 2: 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 fish,
Speaker 3: mucus cocoons the mosquito nets of the sea. This was
Speaker 3: in the year twenty eleven. So in this paper the
Speaker 3: authors look at another hypothesis, which is the idea that
Speaker 3: mucus envelopes actually protect the fish inside from parasites such
Speaker 3: as ectoparasitic nathid isopods. These are these little bloodsucking parasites
Speaker 3: that live throughout the ocean, often compared to terrestrial mosquitoes
Speaker 3: and ticks. Raw I attached to a little photo of
Speaker 3: these things for you to look at. They're kind of
Speaker 3: shrimp like in appearance. Maybe look like a cross between
Speaker 3: a shrimp and a ticky. Yeah, And the authors point
Speaker 3: out that during the daytime when parrotfish are swimming around,
Speaker 3: they actually get some help, they get some protection against
Speaker 3: blood drinking isopods from cleaner fish. You know, this is
Speaker 3: a relationship where a smaller fish that wants to eat.
Speaker 3: These parasites will come along and help pick them off
Speaker 3: to sort of groom the outside of the larger fish.
Speaker 3: But how do the fish protect themselves at night? The
Speaker 3: idea behind this experiment was that maybe the mucous cocoon
Speaker 3: functions like a mosquito net to protect the sleeping fish
Speaker 3: from these heimatophagous parasites. So they tested this hypothesis on
Speaker 3: the coral reef parrotfish Chlorurus sortied us. And the way
Speaker 3: 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 3: So huge difference.
Speaker 2: All right, Right, So Yeah, coming back to the mosquito
Speaker 2: net comparison, it's like, initially we looked at it and
Speaker 2: we're like, this mosquito net must protect the sleeper from bears,
Speaker 2: but in reality it protects them from mosquitos and similar
Speaker 2: insects that sort.
Speaker 3: Of thing, or maybe even something downstream from mosquitoes in
Speaker 3: the analogy here, because the author is also investigated the
Speaker 3: question of how energetically costly it is for the fish
Speaker 3: to make these mucus orbs, and they calculated that it
Speaker 3: takes about two point five percent of a fish's daily
Speaker 3: energy budget to make the mucus bag. Now, when I
Speaker 3: first saw that figure, I kind of thought, oh, hey,
Speaker 3: that seems fairly cheap, only two point five percent. But
Speaker 3: actually I was reading some news reporting on this that
Speaker 3: quoted the lead author, Alexandra Grutter, and she framed it
Speaker 3: a different way. She said, quote, the amount of effort
Speaker 3: that goes into building these cocoons, which requires fish to
Speaker 3: have developed very large glands about the size of a
Speaker 3: quarter to produce the cocoons, is extraordinary. Parasites must exert
Speaker 3: an enormous pressure on these fish in order for the
Speaker 3: fish to have evolved such a specific way. Of avoiding
Speaker 3: the parasites. So what could be so pressing? Is it
Speaker 3: really just that you don't want to get bitten by
Speaker 3: these isopods and have them drink some of your blood. Well,
Speaker 3: Grutterer mentions the possibility that the blood directly lost to
Speaker 3: the parasite might not be the only cost. These isopods
Speaker 3: may also transmit a secondary endo parasite which lives in
Speaker 3: the fish's blood, much like how mosquitoes transmit malaria in humans.
Speaker 3: So the mosquitoes themselves are annoying and you don't like
Speaker 3: the mosquitoes, but the malaria is much more concerning than
Speaker 3: the mosquito. Malaria can be deadly. So in a similar way,
Speaker 3: it's possible that it's worth it for these fish to
Speaker 3: build these slimy bionets to protect themselves from blood disease. Wow,
Speaker 3: so it seems like a good trade. You spend a
Speaker 3: little energy to weave a slime tube before bed every
Speaker 3: night without these tiny shrimp monsters drinking your blood possibly
Speaker 3: giving you diseases of the blood, and it all works out.
Speaker 3: And in fact, there was one more observation from grutter
Speaker 3: speaking to the media that kind of maybe there's a
Speaker 3: strategy to recoop some of that nightly cost. So Grutterer says, quote,
Speaker 3: I have observed on occasion a fish at dawn with
Speaker 3: what appeared to be mucus stuffed in its mouth. And
Speaker 3: then she goes on to say she has seen other fish,
Speaker 3: not parrotfish, but related fish that also produce mucous cocoons
Speaker 3: pecking it at its old cocoons in the morning. So
Speaker 3: like recooping some of that nightly cost by eating the
Speaker 3: mucus that you created before bed.
Speaker 2: I mean, that's just it's economically sound. It's like if
Speaker 2: humans produce, say an ectoplasm defense shield at night, you
Speaker 2: would want to to recoop that cost, and that might
Speaker 2: mean consuming all that ectoplasm again and getting all that
Speaker 2: liquid back into your body. You know. It reminds us
Speaker 2: of other examples we've looked at in biology, such as
Speaker 2: various reptiles that will eat their own shed skin because
Speaker 2: you know, why waste that, you know.
Speaker 3: YEA, 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: mucus bags help prevent against parasite attacks.
Speaker 2: Very fascinating, all right, and so for the rest of
Speaker 2: the episode, we're going to turn to the world of
Speaker 2: parrotfish reproduction and parrotfish sex. So, as we teach out
Speaker 2: in the first episode, one of the other amazing aspects
Speaker 2: of parrotfish biology broadly is that they change sex during
Speaker 2: the course of a normal lifetime. That's to say, this
Speaker 2: is not something that occurs, you know, only when certain
Speaker 2: environments conditions are right. It occurs as part of a
Speaker 2: normal life cycle.
Speaker 3: And within a fairly predictable pattern, right.
Speaker 2: That's right. Yeah, And they're going to be a couple
Speaker 2: of exceptions. Again, as we've been distressing, there are a
Speaker 2: number of different species of parrotfish, but still the vast
Speaker 2: majority of them do follow this example that we're going
Speaker 2: to be discussing. So they are proto gynos that means
Speaker 2: female first, hermaphrodites that always turn into males if they
Speaker 2: live long enough. So they're born female, and then at
Speaker 2: a certain point during their development they become male and
Speaker 2: live out the rest of their life as a male.
Speaker 3: And this would feed back into something we talked about
Speaker 3: in the first episode, which is sometimes difficulty in identifying
Speaker 3: parrotfish species because they undergo these changes, and these changes
Speaker 3: come with changes to their outer appearance.
Speaker 2: That's right. Along the way, multiple changes in colorization take place,
Speaker 2: some of which have to do with just aging, some
Speaker 2: of which have to do with changing their sex, and
Speaker 2: others that have to do with diet and other factors.
Speaker 2: This pointed out by the National Marine Sanctuary Foundation as
Speaker 2: some resources about the parrotfish. I also want to point
Speaker 2: out though, that according to NAA fishery biologist Ronald J. Saals,
Speaker 2: gonecharism has been reported for I think three species within
Speaker 2: the parrotfish family, which is to say, there are at
Speaker 2: least three species of parrotfish where we have the more
Speaker 2: typical scenario of male female division as opposed to what
Speaker 2: we predominantly see in parrotfish, which again is sequential hermaphroditism,
Speaker 2: in which the fish are born female and then if
Speaker 2: they live long enough, become male, live out the rest
Speaker 2: of their life as males. And so the basic scenario
Speaker 2: is most parrotfish are born females, continue to grow to
Speaker 2: reproduce externally as females, generally in the harem of a
Speaker 2: larger protective male who also tends to a grazing territory
Speaker 2: and in time, if that female lives long enough and
Speaker 2: grows large enough, she transitions into a larger, terminal, reproductive male.
Speaker 3: Interesting.
Speaker 2: Now, in general, parrotfish experience what I've seen referred to
Speaker 2: as moderate longevity. It's going to vary depending on the
Speaker 2: particular specimen, and I think it even the general generalities
Speaker 2: about how long they live is going to vary. I've
Speaker 2: seen in general parrotfish life span sited seven to ten years.
Speaker 2: I've seen it cited as less than twenty. I've also
Speaker 2: seen it sited as five to six. Again, we have
Speaker 2: a number of different species we're talking about here, and
Speaker 2: I'll throw out additional numbers for a specific species here
Speaker 2: in a bit. We also have to remind ourselves that
Speaker 2: these are creatures living in the ocean, and so there
Speaker 2: are a whole number of factors, from blood diseases to parasites,
Speaker 2: to eels trying to eat them, to human fishermen and
Speaker 2: 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 2: Yeah, literally scraping by right now. Parrotfish display what is
Speaker 2: referred to as indeterminate growth, which means that there's not
Speaker 2: a full size growth limit. They just keep growing as
Speaker 2: long as they're alive, and so parrotfish just continue to
Speaker 2: grow at a consistent rate. And this is important to
Speaker 2: consider in making sense of their sex changes because one of,
Speaker 2: if not the primary hypotheses for why they do this,
Speaker 2: why they evolve to do this, does relate to their size.
Speaker 2: Maximum size Again, it's going to depend on the species.
Speaker 2: I see ranges like one to four feet. But let's
Speaker 2: go ahead and just talk about the biggest parrotfish just
Speaker 2: to give us like a nice frame of reference, because
Speaker 2: also the largest parrotfish is also pretty gnarly.
Speaker 3: Is this the bumphead we talked about last time?
Speaker 2: It is the bumphead, So we have a little more
Speaker 2: on the bump edd here. The bump head, according to
Speaker 2: the NOAA, reaches size as a four point two feet
Speaker 2: long and up to one hundred pounds, so one hundred
Speaker 2: and thirty centimeters forty six kilograms. And not only are
Speaker 2: they the largest parrotfish, but they're among the largest reef fish.
Speaker 2: Period reef environments are generally shallow and tight, so you know,
Speaker 2: they're not inviting places for larger fish. And their namesake
Speaker 2: bump is used like a rams horns in male to
Speaker 2: male competitions, though females also have smaller bumps, which, of course,
Speaker 2: if the parrotfish lives long enough, is going to grow
Speaker 2: in size once they have changed sexes.
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 2: Well, these guys are just bigger anyway. This is just.
Speaker 2: But this would I guess, seem to be like the
Speaker 2: maximum size that seems to fit into the evolutionary economy
Speaker 2: of living around the reef. Okay, like I guess it
Speaker 2: would be. It would be hard to argue that parrotfish
Speaker 2: should get larger than this, because we have no living
Speaker 2: parrotfish that get larger than this.
Speaker 3: I see.
Speaker 2: The market won't allow it, you know. Now, bumphead parrotfish
Speaker 2: can live to be forty years old. I've read they
Speaker 2: don't reach sexual maturity until five to eight years old,
Speaker 2: and 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. We talked about the different
Speaker 3: classifications of parrotfish feeding behaviors based on like sort of
Speaker 3: how hard they gouge the rock or the coral, and
Speaker 3: these would be like the excavators, right, like they are
Speaker 3: plowing into that stuff.
Speaker 2: Yeah, these guys take the big bites. I was reading
Speaker 2: a little bit more about this on the NOAA website
Speaker 2: and they said that, yeah, they take out those big
Speaker 2: bites that that also end up taking out a little
Speaker 2: bit of live coral. But they stress that this is
Speaker 2: still very healthy for the coral in all the ways
Speaker 2: we already mentioned. I don't remember if we mentioned this.
Speaker 2: I don't remember if we mentioned this or not. But
Speaker 2: there's also the idea that they'll break down dead reef
Speaker 2: and of course turn that into sand, dead bits and
Speaker 2: branches that might otherwise break off in storms and damage
Speaker 2: other 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 2: Yeah, because it's one of the interesting things at about
Speaker 2: reef environments, and this is something you're definitely instructed about
Speaker 2: anytime you go out and snorkel or scuba dive. Certainly
Speaker 2: I imagine around these is that there is like a
Speaker 2: hardness to them. Certainly they can also be very like
Speaker 2: You certainly don't want to stand on them or walk
Speaker 2: on them or touch them for a number reasons, because
Speaker 2: a lot of times they can be quite harmful. You
Speaker 2: can scrape you out, they can cut you. You don't
Speaker 2: want any of that. But on top of that, they
Speaker 2: can be actually quite delicate, and they can be easily broken.
Speaker 2: And so this would be another case of where if
Speaker 2: the parrotfish are doing their thing, that limits the amount
Speaker 2: of damage that they're going to sustain via their own
Speaker 2: dead parts. I see. But anyway, back to sex changes
Speaker 2: in parrotfish in general. So, according to Jennifer Hodge, a
Speaker 2: postdoctoral researcher in the Department of Evolution and Ecology in
Speaker 2: the UC Davis College of Biological Sciences in twenty twenty,
Speaker 2: the indeterminate growth factor may in fact be key. I
Speaker 2: was reading a couple from a couple of sources. Here.
Speaker 2: One is a UC Davis article by Andy Fell covering
Speaker 2: her work titled male size advantage drives evolution and sex
Speaker 2: change of sex change in refish. And then also there
Speaker 2: is a full paper I was looking at, and this
Speaker 2: is by Hodge at All titled Correlated Evolution of Sex
Speaker 2: Allocation and Mating System in Rasses and Parrotfishes, published in
Speaker 2: the American Naturalist the 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 2: It basically comes down to the fact the observation that
Speaker 2: reproduction among parrotfish and also some of these other fish,
Speaker 2: but for our interests here, the parrotfish is often dominated
Speaker 2: by large males.
Speaker 3: Meaning that like, a larger male has a better chance
Speaker 3: of mating more.
Speaker 2: Right, and that and that that male large males and
Speaker 2: this would be the terminal males in parrotfish fishes. They
Speaker 2: are the ones dominating like all of the mating. So
Speaker 2: if you are not a large male, you are just
Speaker 2: not going to be effective at reproduction. If you are
Speaker 2: a small parrotfish male, your chances of passing on your
Speaker 2: genes is rather slim. And remember the genetic mission is
Speaker 2: to pass on your genes. Now, as a small parrotfish female, however,
Speaker 2: it's less of an issue. You know, the bigger males
Speaker 2: they have the advantage. They're going to form these harems.
Speaker 2: If you are a small female, you can be part
Speaker 2: of that harem and you are doing your reproductive part
Speaker 2: as a parrotfish. And so that's according to this hypothesis,
Speaker 2: this is where the evolution of sequential hermaphrotitism evolves as
Speaker 2: a strategy by which all individuals have a better shot
Speaker 2: at participating in reproduction. So start off small and female,
Speaker 2: you definitely get to reproduce. And then if you live
Speaker 2: long enough and you grow big enough, you shift to
Speaker 2: the male sex, and then you have the size to
Speaker 2: prove effective. You're better at 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 2: Yes, yeah, that's the way I understand it. And I
Speaker 2: was looking again at the writings of in Oa's fishery
Speaker 2: biologist Ronald J. Salce, and Salce points out that, yeah,
Speaker 2: the largest parrotfish are always terminal males. And he points
Speaker 2: out that the species, the various species in the genus
Speaker 2: Scaas typically exhibit the following reproductive characteristics. So we see this,
Speaker 2: first of all, there is this proto Guynus female. First hermaphrotitism.
Speaker 2: There's there are breeding territories, there are harems, and there
Speaker 2: is 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 activity you might be picturing that Instead, there's a
Speaker 3: there's an external meeting of the game meats of these animals.
Speaker 2: Right, And I think, I don't know humans, maybe we
Speaker 2: have a problem imagining fish sex in general. But somehow
Speaker 2: this makes it a little easier to sort of picture
Speaker 2: how all this is happening. I think it's all in
Speaker 2: the open. So Suz points out though that in the
Speaker 2: past and and and really maybe not in the two
Speaker 2: distant past, we've had these other hypotheses that there might
Speaker 2: be a social trigger for the change in sex. But apparently,
Speaker 2: based on what he wrote, this hasn't necessarily been observed,
Speaker 2: or at least not in all cases or in a
Speaker 2: broad array of cases, because we have scenarios where large
Speaker 2: terminal males are removed from a population, such as by fishing,
Speaker 2: and the females don't just switch over at an earlier age,
Speaker 2: 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 2: Seems to be the case. Now I don't, But again
Speaker 2: we're dealing with hypotheses here. I don't think that there
Speaker 2: that anything is like one hundred proven out here. There's
Speaker 2: still a lot of work that needs to be done
Speaker 2: because a lot of it comes down to Okay, you
Speaker 2: can have this general idea that this practice evolved because
Speaker 2: large males don't dominate reproduction and and it makes more
Speaker 2: sense from a reproductive standpoint start off as female and
Speaker 2: then become male. But then what is the trigger is it?
Speaker 2: Is it purely based on how big you grow? Or
Speaker 2: are there environmental or social triggers? And ultimately the size
Speaker 2: advantage explanation is just one hypothesis. Uh, there's an you know,
Speaker 2: other hypotheses put more emphasis on possible social or in
Speaker 2: mental environmental triggers, such as changes in population density, that
Speaker 2: sort of thing. In the same way that we see
Speaker 2: examples and say the world of salamanders, where you know
Speaker 2: there are too many, or you know something goes on
Speaker 2: demographically in a collect in a certain group, then you
Speaker 2: may have biological changes that result. But I guess broadly
Speaker 2: if there are very if there are social or environmental
Speaker 2: triggers that are involved in theory, we would be able
Speaker 2: to observe them, you know, such as response to overfishing
Speaker 2: of large males, in response to changes in the environment,
Speaker 2: and so forth. Now there are individual species of parrotfish
Speaker 2: where we might see some of those like social triggers.
Speaker 2: Perhaps I've seen discussion of the stop light parrotfish in
Speaker 2: particular as perhaps being influenced by population density, growth and
Speaker 2: mortality rates. So if terminal the idea here being that
Speaker 2: it may be the case that terminal males in stop
Speaker 2: light parrotfish populations, if they experience higher mortality rates so
Speaker 2: more of them are dying, or if they're just smaller
Speaker 2: overall sizes in the terminal males, then this change may
Speaker 2: trigger earlier onset of the sex change in the female
Speaker 2: parrotfish in that population. So, like I say, it still
Speaker 2: would line up with this idea that this evolved because
Speaker 2: male parrotfish, large male parrotfish dominate reproduction, but it would
Speaker 2: maybe be a slightly different case of like what is
Speaker 2: actually caused it based on my understanding looking at this documentation.
Speaker 2: But I like to say, there's still I think a
Speaker 2: lot of work going on here. Two thanks. Keep in mind,
Speaker 2: though there is no evidence that any species of parrotfish
Speaker 2: can undergo a sex change, reversal or a second sex change.
Speaker 2: Like it is, it is sequential sequential hermaphroditism. So it's female,
Speaker 2: then male. There are no known cases where a male
Speaker 2: can then change back to female. Do to you do
Speaker 2: to any kind of you know, social pressure, environmental or
Speaker 2: what have you. It is female and then male and again.
Speaker 2: Sequential hermaphroditism of one form or another can be found
Speaker 2: in other fish. As I mentioned the ras is. Apparently
Speaker 2: you see some version of this in some molluscs and crustaceans. Uh.
Speaker 2: The size reproduction hypothesis is widely employed employed across the board,
Speaker 2: but I've also seen I think the prevention of inbreeding
Speaker 2: being brought in as another possible reason, though I'm not
Speaker 2: sure if that really pans out, particularly with the parent fish.
Speaker 3: Hmm.
Speaker 2: That may just really have more to do with hermaphroditism
Speaker 2: as a as an evolutionary trait in general.
Speaker 3: But the sequential version you're saying, it seems that there's
Speaker 3: a there's a similar evolutionary explanation given across these different
Speaker 3: classes of animals, which is that it likely has to
Speaker 3: do with a relationship between the animals size and its
Speaker 3: likelihood of successful reproduction, yes, exactly, or specifically the size
Speaker 3: of males and successful reproduction. Yeah, and the fact that
Speaker 3: the animals just keep growing.
Speaker 2: Yeah. Yeah, So it's fascinating. I yeah, this is like
Speaker 2: a factoid about parrotfish that I'd long heard, but I'd
Speaker 2: never really looked into it. I guess one of the
Speaker 2: problems is when you're in the water, it's it's really
Speaker 2: hard to research stuff. You're just like, oh, I'm going
Speaker 2: to take your word for it, and I'm gonna I'm
Speaker 2: gonna look at it, and then I'll try to remember
Speaker 2: 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 2: Yeah. Yeah, I mean just observing them, and I've observed
Speaker 2: in plenty of times in the past. You know, it's
Speaker 2: like you look at them and you're like, well, they're
Speaker 2: a little bit goofy looking, they're beautifully colored, and then
Speaker 2: you learn a little bit more about them, but there's still,
Speaker 2: you know, greater depths of interest there. I guess that's
Speaker 2: the that's the nature of most fish in the sea.
Speaker 2: Never take them for granted.
Speaker 3: In between recording these two episode parts, did you end
Speaker 3: up googling more human parrotfish bites? I did. I don't
Speaker 3: know why I did. I shouldn't have.
Speaker 2: 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 2: The only thing of that nature that I did run
Speaker 2: across is when I was looking up pictures and looking
Speaker 2: at articles about the big boys, the bumphead parrotfish. Yeah,
Speaker 2: is there was an image of some coral with some big,
Speaker 2: chunky bites taken out of it, and that was pretty impressive,
Speaker 2: and it did cross my mind. It's like that I
Speaker 2: would not want those bites taken out of my own flesh.
Speaker 3: Yeah, I would not want that to be my bones. 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 2: Right, Yeah. I think I saw one account and this
Speaker 2: is like, you know, this is I guess inherently unverified
Speaker 2: of snorkelers or divers where someone was just sort of
Speaker 2: casually bitten by a parrotfish. But in that thread, like
Speaker 2: everyone was like, wow, that's weird. It's never happened to me.
Speaker 2: So I don't know, you know, in the wild one
Speaker 2: officer certainly possible. Who knows what that parrotfish was going
Speaker 2: 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, oh, wow,
Speaker 3: you gotta be careful, like they're they're coming for.
Speaker 2: You, right, Yeah, I don't think they're they're coming.
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 2: We have Cotajo Bodhi missed a bond with a fine
Speaker 2: layer of algae coral dust. You will now drop you
Speaker 2: into that of parrotfish.
Speaker 3: M No, not the bump che Okay does that do
Speaker 3: it for parrotfish?
Speaker 2: I think it does? You know they may have more
Speaker 2: mysteries that we didn't explore, but I think we hit
Speaker 2: all the really interesting stuff here. But hey, if you
Speaker 2: know of other dimensions to the parrotfish or various parrotfish
Speaker 2: species that we didn't talk about right in, because we
Speaker 2: would love to hear from you. Just a reminder that
Speaker 2: Stuff to Blow your Mind here is primarily a science
Speaker 2: and culture podcast, with core episodes on Tuesdays and Thursdays,
Speaker 2: listener mail on Mondays, short form episode on Wednesdays, and
Speaker 2: on Fridays. We set aside mostly concerns to just talk
Speaker 2: about a weird film on Weird House Cinema.
Speaker 3: Huge thanks as always to our excellent audio producer JJ Posway.
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Speaker 3: with feedback on this episode or any other, to suggest
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Speaker 3: you can email us at contact at Stuff to Blow
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