The Manta Ray, Part 3

In this series of episodes from Stuff to Blow Your Mind, Robert and Joe discuss the majestic manta ray. In this episode, learn all about their parasites, brains and cleaning stations.

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Episode Transcript

Speaker 1 (00:03):
Welcome to Stuff to Blow Your Mind production of iHeartRadio.

Speaker 2 (00:12):
Hey you welcome to Stuff to Blow Your Mind. My
name is Robert Lamb.

Speaker 3 (00:16):
And I am Joe McCormick, and we're back with part
three in our series on the genus mobula, the manta rays,
and the devil rays. In part one of the series,
we talked about the original inspiration for covering this topic,
which was that Rob you and your family got to
see reef manta rays in person while snorkeling in Indonesia

(00:37):
this summer, which sounds like an amazing experience.

Speaker 2 (00:41):
Yeah. Again, it almost is too much to describe, but yeah,
we jumped out of the boat. This is after an
initial snorkeling in another coral rich area, and then they
took us out to a manta ray cleaning station, which
we're going to get into in this episode. If you
don't know what a cleaning station is, you're about you're
going to find out. It is not like a service station.

(01:02):
It is not an artificial, human made thing. When I
don't remember when this was, but the very first time
I heard about cleaning stations in the water for organisms,
it made me think, oh, well, they installed a big
rotating brush in the water and it draws in the
fish because cleaning stations. Again, we'll get into all the
details of this. It is a place where if you

(01:22):
know where the cleaning stations are, then you as divers
or snorkelers can go there and you have an increased
chance of seeing the various organisms that make use of it.

Speaker 3 (01:31):
Unfortunately, I had a much bloodier picture in my mind,
but I think fish and cleaning station. I think of
like a gutting station where the guys there like ripping
the guts out of the fishy.

Speaker 2 (01:40):
Cot Well, you know, there's a little bit of that
sprinkled in. We'll get into it, but yeah, basically, we
second stop on this snorkeling this morning snorkeling trip that
we did, and they took us out to a cleaning
station and we jumped in the water and it was,
you know, this just reef environment was but it was
much deeper than we'd been in, a little darker than

(02:01):
we'd been in. And I sometimes get a little nervous
when we're talking about like deeper water and bigger things
in the water. But seeing these large reef mantis going
about their business doing some loops here and there, even
it was magical. You just felt absolutely at peace with them.

Speaker 3 (02:19):
So after that. In the first episode, we also talked
a bit about the history of human interactions with manter
rays and devil rays. We got into old misconceptions that
manter rays are threatening to human boats and divers that's
not true, and relatively new misconceptions that their body parts
have medicinal value. Of course, both of these false beliefs

(02:42):
leading to harm to manta and devil ray populations by humans,
and we also talked about ongoing conservation efforts to protect
the world's remaining rays. We discussed some basics of manter
ray biology, including their body design, feeding habits, and their
tendency to breach the water's surface leaping up in the air.
In part two of this series, we followed up on

(03:04):
stories from an older marine biology article that told of
mantas and devil rays taking hold of the anchor lines
and mooring lines of a boat and dragging the boats
out to sea, and we discussed how it seems this
can happen and sometimes does actually happen, but it's clearly
not intentional on the part of the manta, and we

(03:25):
got into some biological reasons that mobulid rays are prone
to getting tangled in loose lines in the water. We
also talked about some recommended methods for making mooring lines
safer for rays. After that we got into mobulid reproduction,
which is really fascinating the way they engage in internal
fertilization and viviparity, meaning sort of full body contact, sexual intercourse,

(03:48):
and live birth respectively, so making them, as in so
many other ways, kind of superficially resembling of mammals, even
though they are fish not mammals. And we also got
into the elaborate fitness displays that males go through in
these sort of mass chain races before the female finally
chooses her mate. And today we're here again to talk about.

Speaker 2 (04:09):
More that's right, and the place I'd like to pick
up is discussing manta rays and their parasites, And there's
some bleed over here into other mobulate parasite loads as well.
Some of the information you know applies to devil rays
and so forth, and a lot and as we've been discussing, like,

(04:30):
there's a lot more known about the ins and outs
of reef manta rays as opposed to the oceanic manta rays,
which are the largest. So you might remember back to
our episode about the gray whale, and like the basic
observation that large marine animals often have to deal with
sizeable parasite loads, or if not actual parasites, then creatures

(04:51):
engaged in some degree of mutualism either way you slice it,
large marine organisms tend to attract a fair number of
hangers on and they become mobile environments for these various organisms.

Speaker 3 (05:04):
In the case of gray whales, am I remembering right,
that barnacles would tend to attach to the outside of
the gray whale, Like the gray whale becomes a substrate
that is useful for the barnacle because they need something
solid to attach the bottom of their body to. And
then also by moving through the water, the whale you know,
brings food to them, essentially allowing water to flow past them.

Speaker 2 (05:25):
Right, And as we discussed in those episodes like there's
there was on one hand a strong case to be
made that oh, well, these these the poor whales are
just covered with these barnacles, like a ship with barnacles
gaining no benefit from it. But then we also explored
a hypothesis that proposed that well, actually there are some
potential benefits to having these barnacles on your body.

Speaker 3 (05:44):
Yeah, the question was do the barnacles form a kind
of armor of sorts That was not known for sure.
To be clear, that was like a possibility, but I
think it was more likely assumed that it is sort
of a net negative to the whale to have all
the particles on it.

Speaker 2 (06:01):
Yeah, but this similar conversation often occurs around these discussions
of symbiosis and mutualism and parasitism, questions about who's getting
the most out of this relationship, is it unbalanced? To
what degree is it unbalanced? And you see it go
various directions where arguments end up being made that what
is thought of as a parasite might actually have some benefits,

(06:23):
and you and the opposite something that seems like there's
a beneficial give and take, and maybe it's a little
less beneficial than we used to think it was. At
any rate, it's definitely the case with the manta ray
that they have a lot of hangers on and they
vary greatly. Mantas have to contend, for instance, with tiny

(06:43):
copa pod parasites that get literally everywhere on them. Meanwhile,
you also have things like harmless juvenile golden travelerfish which
just ride the pressure wave and alongside the creature, and
in the same way that sometimes dolphins are seen to
ride along side ships. But as far as I'm to understand,
they don't pose any risk or damage to the manta rays.

(07:07):
And then they split when they're old enough to fin
for themselves, and then you have these sucker plate headed
remorras to continue with. And there's sometimes a little harder to.

Speaker 3 (07:15):
Figure out sort of gray area here.

Speaker 2 (07:18):
Yeah, sometimes, I mean again, this is often the case
the deeper you look into any of these relationships. But basically,
if you're not familiar with the remorra, ramorra's dorsal fin
has evolved into an oval slatted sucker organ, so like
by flexing the little slats on there, they can suction
onto a surface such as the side of a whale

(07:42):
or a shark or you know, a turtle or a
ship or a human diver. I think it occurs occasionally.
They're free swimming fish, but they like to hitch a ride,
and there are many different species, and yeah, they attach
to all sorts of organisms, including manta rays, and indeed
they've been known to take up more or less permanent residents,

(08:04):
sometimes inside a manta's mouth or hide in other body
openings such as gills or the cloeca. They typically feed
on the ectoparasites and loose skin flakes and other leavings
of an organism. And yeah, it seems to be what's
happening with manta rays. Not every variety of remora that
latches onto a manta can keep up with it, can

(08:26):
remain with the host, especially as it ventures into deeper waters.
Some get displaced, And in general, it seems like the
longer a manta hangs out in a shallow reef environment,
the more it's liable to attract ramoras. So that's the
case I've read with certainly the reef manta over the
oceanic manta. And then it's also the case with mantas

(08:48):
hanging out closer to shallow waters due to some particular
state of their own life cycle. Now, the book that
I keep referring to in these episodes Guide to the
Manta and Devil Rays of the World by Stevens, Fernando Dando,
and Discaria. In this they point out that scientists often
cleanly label this relationship between the remoras and the manta

(09:10):
rays as parasitic are arguing there's no real benefit for
the mantis here. For instance, the gill activity going in
and out of the gills can result in heavy scarring
for example, essentially like mutilating the gills over time. Now,
others argue, well, the remorras does seem to do some
level of cleaning though they're eating up parasites, you know,

(09:32):
dead skin flakes, and this, they would point they point out,
would be helpful, especially to the oceanic manta, as it
frequents cleaning stations far less as we'll be discussing. Cleaning
stations tend to be you know, in reef environments, and
if you're out there in the middle of it, there
are fewer of these around. So perhaps the assistance in
these cases would balance out the harm at least to

(09:54):
some degree. Maybe it's not. I mean, I don't know
how often you really see a fifty to fifty split
with these relationships in nature, Like you know, there's there's
gonna be you know, all the factors of evolution and
behavior or in play here, and it's this is ever
the question when we're pondering relationships like this.

Speaker 3 (10:14):
So for a very rough analogy, It's kind of like
if you had a squirrel that lived on your body
and it climbed all over you, eating the fleas that
you also have eating the fleas and mosquitoes that swarm
your skin. So that's good, you don't want the fleas
and mosquitos. But also the squirrel's claws are like scratching
you up, and it's probably causing problems while you're trying
to move around. So you get a plus an a minus.

Speaker 2 (10:37):
Yeah, I mean it always reminds me of the Doctor
Seuss book Thidwick the Big Hearted Moose. This is it's
not a situation where Fidwick's dealing with parasites and creatures
eating the parasites, but he's he has a big heart,
and he keeps letting animals ride in his antlers until
it gets out of hand.

Speaker 3 (10:53):
I feel like it's got to be one of the
less big hearted Doctor Seuss books.

Speaker 2 (10:57):
Yeah, the message there is maybe a little less less rosy,
but I don't know. I do come back to it
and think about it from time to time. Though you
know that in the Sleep book, I guess really really home.
But at any rate, this is the case with large
organisms like this, there's just much more space for ectoparasites

(11:19):
to get everywhere, and parasites have their own parasites. Filter
feeders also swim around with their mouths wide open while feeding.
You know, they're bringing organisms into their mouth and that
can bring in extra creatures as well, So you know,
what is a manta to do. Breaching may help, as
we discussed, as it may help with other marine organisms. Again,

(11:43):
as we just mentioned, they can shake some of their
hangers on via their deeper dives. But at the end
of the day, they're going to need some help. They
can't turn to each other. They don't really have much
in the way of you know, limbs. They can't groom
each other in the way that say primates do. So
they're going to have to head to the cleaning stations.

Speaker 3 (12:13):
All right, So we're finally here. Tell me about the
cleaning stations, all.

Speaker 2 (12:16):
Right now, I want to add a caveat I am
very likely to accidentally call a cleaning station a feeding station.
I've been doing this in casual conversation over and over
again over the past several weeks, perhaps in part because
for the fish working and some I'm shrimp working at
these cleaning stations. It is a feeding station because that's
what they're doing. They're feeding, that's what they're getting out

(12:38):
of it. Ultimately, were talking about a cleaning symbiosis situation
that benefits all of the organisms involved, and it's not
unique to mantus. You'll find the scenario throughout the aquatic environment,
both in fresh water and saltwater. Fish deal with their
individual parasite loads in a variety of ways, but it's
often useful to get some help. These relationships have developed

(13:00):
over time in which fish will seek out areas populated
by various other organisms that generally we're talking and certainly
in marine environments about small reef fishes. Also sometimes some
shrimp are involved in this, and there are various examples
of this outside of the water as well. For instance,
on land, examples such as the crocodile and the Egyptian

(13:23):
plover or crocodile bird have been observed since ancient times.
You can find like Herodotus writing.

Speaker 3 (13:29):
About this and still cute to see today.

Speaker 2 (13:32):
Yeah, this is the bird that goes inside the crocodile's mouth,
holds the mouth open, goes in there and starts doing
some dental cleanup. The Egyptian plover by the way, not
to be confused with Egyptian lever. That's a that's a
musical artist, a legendary musical artist that I've referenced on
the show before. Look it up, kids. The oxpecker is

(13:54):
a great example from the surface world as well, a
bird that feeds exclusively on the bodies of large mammals,
though this one is also much discussed in scientific circles
because it's definitely a case where there are strong arguments
to be made that the oxpecker might not ultimately help
the organism that it's landing on all that much, and
might be as much of a nuisance in and of

(14:15):
itself in the ocean. To return to the waters, however,
you see various fish take advantage of these services, including
the parrotfish, which were previously discussed on the show. So
you don't have to be a behemoth to benefit from
a visit to the various organisms that want to eat
your parasites, as well as perhaps some loose, dry skin
or rancid flesh around your wounds. In fact, some cleaners

(14:37):
are specialized wound cleaners. But naturally, when you're a large
fish riddled with parasites, you know you can't scratch those
itches again, so manta rays have to head to these stations,
and it seems again, it seems to work for everyone.
Small Fish and shrimp can't swim as far or do
so safely in search of food, so they'll, you know,

(14:57):
they set up at a cleaning station. Generally this is
like a rocky outcropping the edge of a reef or
you know, something like that, and here they can just
hang out and their meals will be delivered to them
because the customers will show up. They will go where
the cleaner organisms.

Speaker 3 (15:14):
Are right, So by being easy to locate and offering
a service, they can have this dependable influx of resources
from abroad. It almost makes me think about like the
economies of I don't know, freeway exits where there will
be you know, gas stations and restaurants built up around
a freeway exit, like you know the traffic's coming in.

Speaker 2 (15:33):
Yeah, yeah, exactly. I mean that you often see this
compared to like a trip to the barber, the dentist,
and so forth, all wrapped into one. Because yeah, they'll
they'll get inside the mouth to clean out the teeth,
they'll clean out gills, they'll eat away algae. Growths, dead
and molting skin, bacterial fungal growths, you know, getting food

(15:56):
particles out of the mouth. It's really quiet extensive. And
then these are generally small organisms that are doing this,
so they can target those tiny acto parasites and seek
them out all over the host's body in every every
crevice yum yum. And so the mantas actually the kind
of queue up for this. If one of the bits

(16:16):
of advice that the the the Snorkel guides had for
us was was, you know, among all the reasons not
to get too close is you also don't want to
essentially enter the cleaning station, not because the fish are
going to clean you, but because the mantas are going
to be like, oh, it's occupied, I can't go in there,
Like you're taking up room. It's like you've pulled into

(16:37):
the car wash ahead of people who want their car cleaned.
What would they do?

Speaker 3 (16:41):
Would they patiently wait their turn?

Speaker 2 (16:43):
Maybe? Or potentially clear? I mean also the humans being
where they need to be. I think they're a number
of reasons that they might sort of scare them off.
You know, yeah, like you're too loud with your flippers,
you're coming out of the water too much. I think
in general they might just decide well, another time enough
to bring it back to Fidwick, the big hearted moose.
I you know, I don't think he ever considered visiting

(17:05):
a wolf cleaning station or something for all of those
various mammals and birds living on his antlers. Now. As
discussed before, again, symbiosis is a spectrum and it can
shift with either party reaping more of the benefits and
in some cases perhaps taking a bit of advantage, at
least from the human perspective. So some cleaner species do

(17:26):
seem to agage engage. This is in general in occasional
acts that feel more parasitic, like maybe they're you know,
they're eating parasites, but maybe they're eating a little body
mucus off of the surface of a fish or aquatic
creature as well. You know, maybe they're grabbing a little
flesh that's less on the rancid side, but you know,
just because they can. So, you know, I guess to

(17:49):
answerpomorphize the scenario, there are always going to be some
bad actors, maybe some folks who take advantage of the
trust in a given scenario. But I think still on
the whole, even with the cases, cleaning stations seem to
benefit everyone, even if sometimes there's a little advantage taken. Yeah.

Speaker 3 (18:05):
Well, and all kinds of organisms have symbiotic relationships that
are sort of balanced on a knife's edge like this.
I mean, I would say it's true of us with
our own microbiota. You know, of course, human beings rely on,
for example, our gut flora in order to do all
kinds of things you know, to be healthy, to help

(18:26):
with digestion. So we're definitely worse off without it. We
need it, but at the same time, it can turn
opportunistic and it can harm us if you know, there's
something wrong with the immune system or other kinds of
conditions come online.

Speaker 2 (18:38):
Now, there are some additional levers that the manta ray
can pull and stevens that I'll get into this in
the guide book. These are things that the manta will
also do it feeding stations, which it makes sense. The
manta knows that it is at a location where the
local population is heavily invested in in the manta's parasites,

(19:00):
its previous meals, and so forth. So first of all,
they frequently defecate at these cleaning stations, makes sense, I mean,
with all creatures, and stuff that's defecated is going to
include things that are still of interest to various scavenging creatures.
They will also cough or vomit, blasting particles like food

(19:20):
particles out of their mouth, which cleaners are also going
to be interested in. And Steven said all right that
sometimes they blast out massive clumps of undigested zooplankton exoskeletons.
I don't have a photograph to refer to, but I
just have like a mental image of what this might
look like. And then back to their defication. They'll also

(19:40):
invert their intestines up to thirty centimeters or twelve inches
out of their cloaca while they're doing it, just to
better clean everything out that's feces, but also parasites, presumably
indo and ectoparasites, And interestingly enough, their feces i've read
is basical dark red due to all the plankton. So

(20:02):
when they do this, if you're in the water with them,
and you know, they don't care if you're in the
water when they when they do this, they're gonna they're
they're gonna let loose as needed. This process has often
been misinterpreted by divers as like they don't know what
they're looking at. It looks like it might be blood
or something. Maybe they're injured, or in some cases they
might think they're about to view a berth, which makes

(20:24):
sense when you look at We talked about this video
footage in the last episode from an aquarium in Okinawa, Japan,
where we see one of the very few recordings of
a manta giving birth, and it does like like this
initial discharge of particles in the water. I can see

(20:44):
where you might confuse the two acts.

Speaker 3 (20:46):
A burrito in the middle of a cloud, and then
the burida unfolds.

Speaker 2 (20:50):
Yeah, so that might be a case where someone's like, oh,
I think it's giving birth, but then you realize, oh,
there's no baby. It's it's just a cloud of red
manta fecal matter.

Speaker 3 (20:59):
They're just out part of their own intestines to get
it all cleaned out.

Speaker 2 (21:03):
Yeah, that's right. Yeah, all right, Joe, I believe there's
at least one more organ we want to talk about
inside the manta's body, right, that's right.

Speaker 3 (21:11):
We wanted to come back to the subject of manta
brains and intelligence, so we already talked in previous parts
of this series about how when people have close encounters
with manta rays they often report similar feelings. You'll read
about this in people describing their dives with them. The
manta is a fish, but it does not feel like

(21:33):
a fish when you're in its presence. It has a
kind of palpable intelligence and emotionality, a sense of curiosity
that we generally only associate with social mammals and maybe
sometimes with other strange intelligences like that of an octopus,
but certainly not with fish. You'll read about this over

(21:55):
and over with these manta experiences. Now, of course, that
feeling of being in communion with a higher intelligence, it's
just a subjective impression people have. Could be an illusion.
Maybe it's based in some kind of esthetic charisma, something
about the way the manta looks, or something about the
way it moves. The question would be, is there any

(22:16):
objective scientific reason for thinking there's actually something special about
the intelligence of the genus mobula compared to other fish.
I think the answer is pretty clearly yes.

Speaker 2 (22:29):
Yeah, that's my indication as well, because you know, to
your point, people have this feeling about their dogs and
cats all the time. Not to discount the intelligence of
dogs and cats, which is with each of which are unique.
But like we have this of course amazing human ability
to anthropomorphize, to personify, and imbue just about anything with

(22:49):
a remarkable level of intelligence and free will.

Speaker 3 (22:52):
Well, yes, that is certainly true. I mean I have
the beholder quality to this whole thing. But I would
also say that, even just somewhat objectively, I think dogs
and cats, as somewhat social mammals do have a higher
level of cognitive complexity than most fish. You could argue, yes, yeah,
absolutely so, there are definitely I of the beholder elements.

(23:16):
These are mammals that need to navigate a somewhat socially
complex world. That they've got something going on up there.

Speaker 2 (23:23):
Well, let's dig into the old mantamelon what are they
working with up there?

Speaker 3 (23:26):
Okay, First of all, I think we should address the
question of raw hardware. What kind of neural equipment do
manta rays and devil rays have to work with? And
to get into this question, I wanted to look at
a paper by a name you'll see popping up a
whole lot in manterray research. This was by a researcher
named scilla Ari that's spelled CSI L. L. A and

(23:51):
then the last name is Ari If you want to
look her up. Her research is all over the place.
She studies manterray neurobiology and the paper is called in
Cephalization and Brain organization of mobulid rays myleobataforms Elasmo Bronchi
with ecological perspectives. This was published in the Open Anatomy
Journal in twenty eleven. And so this paper set out

(24:16):
to measure the brain size of three different species in
the genus Mobula. It looked at Mobula japanica or the
spinetiale devil ray also known as the Japanese devil ray,
Mobula Thurstoni or the bent fin devil ray, and Mobula birostras,
known at the time this paper was published as Manta birostras.
Manta was once treated as a separate genus, but now

(24:39):
the mantas are grouped with the rest of the Mobula genus.
But anyway, this is the giant oceanic manta ray. This
is the big one, the biggest of them all. So
to run through a selection of some of the main findings.
First of all, the giant oceanic mantray Biostras has the
largest brain of any known fish species. It's just in

(25:00):
absolute terms, biggest brain of all the fish. Also, mantas
and devil rays not only have large brains in absolute terms,
but they have very high brain to body mass ratios.
This is known in anatomy as the encephalization quotion. So
a larger brain is not always a sign of greater intelligence,

(25:25):
at least when measured along the dimensions of intelligence that
we find interesting. Often a large brain in an animal
is necessary, especially when the animal is itself large, simply
to control movement and nerve feedback for that massive body.
So if you have a huge body, you need to
control a lot of big muscles all over the place.

(25:45):
You need to get sensory feedback from all over the body,
so you need a big brain just to handle all that.
It might not necessarily be for the kinds of things
we think of when we say the word intelligence, things
like problem solving, memory learning, social cognition, that sort of thing.
What tends to correlate more often with those kinds of

(26:06):
intelligence is having a bigger brain relative to the size
of your body. And even then, the relationship between in civilization,
quotient and observed intelligence is not completely linear, but it's
a fairly strong relationship in terms of the structure of
the brain and the characteristics of the brain tissue. These

(26:26):
rays showed first of all, an enlarged telencephalon. The telencephalon
is the four brain, the front part of the brain
corresponding to the cerebrum in mammals, and also what the
author calls a highly foliated cerebellum, and this means that
the cerebellum has a more folded texture, which increases the

(26:48):
surface area of the cerebellum and that in turn increases
the number of neurons and the density of neurons on
the cerebellum, allowing more connections and thus greater information processing power.
And these anatomical features, the larger teleencephalon and the more
highly foliated cerebellum are correlated with more complex behavior and

(27:10):
cognition in other species. So just looking at their brains
and brain tissue, it definitely does look like something special
is going on with the mobula rays. Compared to other fish.
You're seeing patterns that you see more with smarter animals
across different types of lineages.

Speaker 2 (27:29):
There's a great illustration in the Manta and Devil Rays
of the World book where they show on one hand,
the brain of a spinetailed devil ray mobula mobular, and
then they compare it to the brain of a similarly
sized common skate. You know, so this is a not

(27:50):
unrelated creature, similar size, and you can see like drastic
difference between the two. The ray's brain just looks absolutely
bloated and in gorge, you know, and then the skate's
brain is streamlined and by comparison, so you know, even
not knowing exactly what sorts of neural tissues you're looking at,

(28:10):
you can see like, oh, this thing looks super charge.
This one looks oversized compared to a similarly sized organism. Yeah.

Speaker 3 (28:18):
This paper also has some very juicy illustrations and some
fiend without a face kind of stuff.

Speaker 2 (28:24):
Yeah, yeah, definitely.

Speaker 3 (28:25):
But anyway, so the question would be, what is all
of this high powered neural equipment for. What would they
need these powerful and highly foliated brains for. One possible
explanation that Ari gets into in this paper is complex
social behaviors. As we already discussed in the previous episodes,

(28:49):
mobular rays show these interesting, complicated group behavior patterns. Examples
of this would include forming schools that engage in coordinat
and organized feeding behaviors. So remember that chain feeding where
they'll go in a line feeding together, or cyclone feeding
where they go in a circle. They organize into these

(29:11):
patterns to take better advantage of food sources. Also, another
example of group coordinated group behavior patterns are when they
get into these large mate fitness competitions with potentially dozens
of rays chasing around in these athletic courtship displays. Broadly,
the management of complex social relationships and social behaviors is

(29:37):
thought to be one of the key drivers of brain
evolution in other species. So when you need to navigate
a complex social landscape full of other members of your
species and you need to maybe work together and manage
relationships like recognizing specific individuals of your species and remembering

(29:58):
interactions with them you've had in the past, that is
often when evolution starts really putting pressure on you to
wise up. That is thought to be a big driver
of brain evolution in other lineages. We've already talked about
evidence of mantas working together and engaging in these complex
group behaviors, but is there any evidence that they do

(30:21):
what I was just saying that they recognize and remember
each other as individuals. In effect, do they have time
stable social relationships. I went looking for an answer here
and I found it seems to be yes, there is
some evidence of that. So I came across a paper
by Perryman at All published in the journal Behavioral Ecology

(30:42):
and Sociobiology in the year twenty nineteen called Social Preferences
and Network Structure and a Population of reef manta rays.
Rob very interesting connection for you. In this paper to
study the social networks of mobular rays, the authors here
collected data on more than five hundred groups of reef

(31:02):
manta rays this is the species Mobula alfredi over five
years in raja Ampat in Indonesia. So this may have
been in some of the same locations or around some
of the same locations you visited.

Speaker 2 (31:14):
Yeah, I mean, I'm looking at the maps in the
paper now and like, yep, yep, I was in that square.

Speaker 3 (31:20):
And so in observing the mantas in these locations, the
authors did indeed observe what they call social preferences in
mobular rays, especially between females. And social preferences here would
mean that individual rays seem to show either an increased
tendency to affiliate with or a desire to avoid specific

(31:43):
other individual rays to anthropomorphize a bit, So this might
kind of give the wrong idea, but roughly they had
something analogous to friends and enemies.

Speaker 2 (31:55):
Room for frenemies in that equation or is that more
of a human thing unclear.

Speaker 3 (32:00):
Yeah, we'll see what we think. So the authors found
pretty strong evidence for female mantas having these relationships on
both long and short time scales, so in the scale
of weeks and months, they might have a consistent preference
for or against certain other female individual rays. They also
found pretty strong evidence for mixed sex social preferences kind

(32:23):
of friendships or enemy ships between males and females. Between males,
they only found kind of weak evidence for short term relationships,
so perhaps males are less social with each other on average.
The overall social networks were categorized as what they call
a dynamic fission fusion society, with differentiated relationships linked to

(32:48):
strong fidelity to cleaning station sites. So this idea of
a fission fusion society is one whether it's not like
a fixed group that stays together for you know, the
duration of these animals lives. They're kind of like these
groups that come together for some period of time and
then split apart and then can dissolve, and then different

(33:09):
groups can kind of reform. It's a more more freeform
kind of social network formation and division. And then in
their discussion section, the authors say, quote, our results show
that stable, differentiated social relationships lasting over several weeks or
months are an important driver of group structures in reef
manta rays, which suggests that both familiarity and long term

(33:33):
social relationships are important in structuring their societies. In complex
social systems, such capabilities can be essential too, identify partners
in reciprocal altruism, to maintain social hierarchies, and to avoid inbreeding.
So those three things are strong biological reasons why it

(33:53):
might be useful to remember who another individual of your
species is and remember past interactions with them, be able
to repay favors back and forth, you know, reciprocal altruism,
or remember if they did something mean to you in
the past. To avoid inbreeding, of course, and to maintain
kind of dominance relationships. So anyway, it seems yes, the

(34:26):
answer is modular rays do seem to be especially social
relative to most fish, and social cognition pressures are thought
to be a big driver of brain evolution in other
vertebrate lineages, so that could be a big factor at
play here. We don't know for sure, but that seems
like a very plausible explanation for why these animals would

(34:46):
need to have more powerful brains. Any other reasons they
might need to have extra brain power, yes, or He
gets into some other ideas as well. One is the
need to understand their spatial firement. So mobulids are pelagic fish,
and they often inhabit coastal waters, including places like reefs

(35:08):
and seamounts and so forth, and Ari says that there
may be an evolutionary pressure for them to learn the
quote complex spatial organization of these habitats, which I think
that would include like creating mental maps of not only
the underwater topography of like a reef or a seamount,
but I think it would also include dynamic elements across

(35:29):
these maps, like water currents and the presence of other
organisms such as prey or predators or especially cleaning mutualists.
Another possible explanation for their neurobiology is what Ari calls
their active and maneuverable lifestyles. She points out that in
other species, high cerebellar foliation, which remember that's the folding

(35:50):
of the cerebellum that allows more neuron density there. That
is associated with, among other things, maneuverability and strong locomotor abilities,
which Mobula rays absolutely do possess. You know, they're very acrobatic.
They can move around a lot, and so their brain
structures here could have something to do with their tendency
toward acrobatics. Another thing, she points out, I thought this

(36:13):
was kind of interesting. It could have something to do
with their wide heads. Some aspects of the large brain
and the powerful telencephalon of the manta ray could be
related to the fact that they have a broad head
similar to the hammerhead shark, which our rites could help
with organizing and integrating different kinds of sensory feedback. Now

(36:39):
I was confused about that at first. I was like,
that doesn't come together for me, Like what's the deal.
So I had to look this up to understand it better.
But the idea is like in hammerhead sharks, the wide
head and the hammerhead sharks also have an enlarged telencephalon
the wide head and the enlarged telencephalon in the brain
seem to help give the shark enhanced sensory abilities like

(37:01):
electrosensory abilities, vision, and even maybe a more stereoscopic sense
of smell, so they can determine the direction that smells
are coming from more easily. So like by spacing out
the sensory organs across a wider head, you can sort
of increase the resolution you get across multiple different sensory modalities.

(37:24):
It's again this is a loose analogy, but it's like,
you know, having a bigger camera lens kind of like
you're increasing the resolution you can get on things. And
so the wide spacing there for chemical sensing or electrosensing
and the hammer heads especially or vision and all that
it can help you in a way. And then the
strong tellencephalon the big four brain can help you gather

(37:45):
and make sense of all that information. That does seem
to be the case in hammerhead sharks, and Broadly already
says it's possible that similar sensory management could be at
play within mobula heads and brains. They also have these big,
wide heads that are put the different sensors far apart.

Speaker 2 (38:02):
That's interesting. That makes me think about some of the
hypotheses concerning breaching in mantas that like the slap of
their bodies hitting the water again, could be a signal
in some cases to other rays to come and start
engaging in these social feeding configurations with them.

Speaker 3 (38:19):
Mmm. Yeah, okay, so you got.

Speaker 2 (38:22):
To receive that signal and then know what to do
with it.

Speaker 3 (38:25):
And then finally there was an issue brought up in
this paper that was a lot more interesting than I
first realized once I started looking into it, and that
was a little bit less directly related to intelligence, but
very worth mentioning. And that's the idea of thermal issues.
So I'm going to start with a quote from the
paper here, Ari Write's quote endothermy as. The elevation of

(38:47):
body temperature by metabolic heat production represents one of the
most significant developments during vertebrate evolution that might be connected
to enlarged brain size. Sharks in general are poikilothermic, meaning
cold blooded. Their body temperature varies with the environment, but
some shark species like Eshuris and Lamna, are homeothermic, and

(39:12):
that in this case it means regionally warm blooded. They
can keep blood in certain parts of their body elevated
warm as they are able to maintain body temperatures well
above ambient temperature of the environment by countercurrent flow of
blood at certain places of their body. So countercurrent blood
flow is another interesting phenomenon. It works essentially by positioning

(39:36):
the hot pipes right next to the cold pipes. So generally,
the blood that is returning to an animal's heart from
its extremities through the veins is going to be cold.
It goes out there to the edges of the body,
it loses heat, and then it has to come back
to the heart, so it gets cold and it's coming
back cold. Meanwhile, arterial blood leaving the heart and headed

(40:00):
for the extremities is comparatively warm. It just came from
the warmest part of the body right there in the core.
Countercurrent blood flow places long stretches of arteries right next
to long stretches of veins, so that the warm blood
coming from the core can warm up the cold blood

(40:20):
in the veins before it gets back to the core.
And even human bodies actually take advantage of this. In
our arms and legs, the veins and arteries tend to
be close to each other, sort of next to each
other to help warm the cold blood returning from the
fingers and toes, and this adaptation helps animals maintain higher

(40:40):
body temperatures in cold environments. But sometimes it's not just
positioning major vein and artery pathways next to each other.
Sometimes there are dedicated structures in an animal's body that
really maximize this artery to vein heat exchange. And one
example of a structure like this would be what's called

(41:03):
a red mirabulae chronica, which comes from the reading mirabilae
comes from the Latin for wonderful net, and then the
cranica would be of the skull, the wonderful net of
the skull. This is a sort of dense web of
veins and arteries inside the cranial cavity around the brain,

(41:23):
which helps regulate the temperature of blood flow around the brain.
Ari writes quote among mobulid rays in Mobula terrapacina and
Manta birostras. Again, that's now Mobula birostras, a ret mirabulae
cranica as a countercurrent heat exchanger has been described around
their brain. Interestingly, the same families are also characterized as

(41:48):
large brained elasmo bronchs, in which these unique adaptations might
serve to enhance their ability to exploit cooler environments, either
deeper water or at higher latitudes, with greater efficiency by
slowing the rate of metabolic heat loss to the environment
or allowing them a higher activity level. And I thought

(42:09):
this was interesting. So I was reading a little bit
more about this in a paper called Cranial endothermy in
Mobulid rays Evolutionary and ecological Implications of a thermogenic brain
by mc Arostigui in the Journal of Animal Ecology, twenty
twenty four. And here the author makes a very interesting

(42:29):
kind of comparison. So Arostigwi writes, quote, whereas early hominids
in hot terrestrial environments may have experienced a thermal constraint
to evolving larger brain size, cetaceans and mobulids, so like
whales and rays here in cold marine waters may have

(42:49):
experienced a thermal driver for enlargement of a thermogenic brain.
So does that converse relationship make sense to like for
human evolution, we want to have a bigger brain, right,
bigger brain's great, you can get real smart. But heat
concerns place among other things. Of course, you know, heat
concerns place upper limits on our ability to grow bigger brains.

(43:12):
Those brains can easily get too hot, which is dangerous
to us. For mantas and devil rays, there could be
an opposite direction thermal influence on brain evolution. The cold
waters that you want to live in and dive down
to make it pay thermally to have a bigger brain
with this big mesh of blood vessels and so erostig

(43:34):
Wei writes in the abstract quote the potential for brain
enlargement to yield the dual outcomes of cranial endothermy and
enhanced cognition in mobulids suggests one may be an evolutionary
byproduct of selection for the mechanisms underlying the other, and
highlights the need to account for non cognitive functions when

(43:55):
translating brain size into cognitive capacity. So I thought that
was a fascinating and this is not proven, but it's
raising the possibility. What if mantas evolved greater intelligence as
an accidental byproduct of growing bigger brains, which and the
growing of the bigger brains was mainly driven in the

(44:16):
first place by thermal pressure. You want to keep the
brain warm when you're going into these cold waters.

Speaker 2 (44:23):
That's fascinating. So yeah, it would be the environmental reasons
to have a big brain are like the main driving
force here. But then the idea is that if this
were true, they would also then of course use those
cognitive powers to sort of flesh out their behavior as
well well.

Speaker 3 (44:43):
Right, so, yeah, if you accidentally evolve a more powerful
brain just because you're trying to keep a warmer brain
in cold waters, that brings new capacities online which could
further just arise as a contingency, but then could further
shape your revolution if you lean into them.

Speaker 2 (44:59):
Ah. So it's like think of the There's a Marvel
super villain called the Leader, and he has enlarged brain
and he uses that brain power you know, you know
for supervillain things to try and take over the world.
But you could make an argument though the Leader didn't
evolve or developed this massive brain to take over the world.
He did it for thermal reasons. But then of course

(45:20):
he's going to try and take over the world with
it because he's got a big brain. As a result
of these these thermal conditions.

Speaker 3 (45:25):
World domination plots an unfortunate side effect of keeping a
nice and toasty up there. So that's an interesting possibility
fascinating question. I'd never considered anything like that. So that's

(45:48):
all I've got from that original paper by sila Ari
on the neurobiology of the mantas and the devil rays here.
But there was one more thing I wanted to mention
about mobular ray brains and intelligence, and that is there
is there's one famous experiment which showed that manta rays may,
depending on your interpretation, pass a well known animal cognition

(46:10):
milestone known as the mirror self recognition test. So we've
talked about this test on the show before, but if
you never heard of it, the most common version goes
like this. You place a mark somewhere on an animal's body,
somewhere that they wouldn't be able to see it just
by looking directly at themselves, but somewhere they could see

(46:31):
with the aid of a mirror. So for a human example,
you could imagine putting a spot of dye on the skin,
maybe on the front of your throat. So you look
in a mirror, you'll see it, but you can't see
it by looking down. Yeah, then you give that animal
a mirror and you watch what they do. Most animals
do not seem to recognize their reflections as themselves. A

(46:54):
lot of animals will just kind of ignore a mirror.
Sometimes they react as if it were another an in
their space, So they react, you know, maybe they puff
up and get aggressive, or they try to interact with
it somehow, or they just act confused. A small number
of animals, including some of the great apes, some marine
mammals like bottlenosed dolphins, I think, maybe orcas, some corvids,

(47:18):
and know the magpie. I believe elephants may have passed
the mirror test. They do something different. They will touch
their own bodies on the spot with the mark and
try to rub it off if they can. Sometimes, because
of different animal body plans, you have to organize different
sort of equivalents here. But they will see the mark

(47:41):
and they will try to mess with it, indicating that
they understand the animal they're looking at in the mirror
is the self and not another. That's my own body,
and I react by touching the part of my body
that I see as modified in the mirror.

Speaker 2 (47:55):
Yeah, it's something we take for granted because we do
it every day, but if calibrated just right, it can
arguably give us some insight into what might be happening.
Inside the brain the mind of a non human.

Speaker 3 (48:08):
Animal, right, and so this is taken as evidence of
rare self awareness, though we should strongly caveat this because
that phrase can bring a lot of associations or baggage
that are not necessarily proven by these experiments. There is
debate over exactly what the mirror test shows, but even
with that big asterisk there, I do think the results

(48:29):
of these experiments are fascinating. Like most animals don't recognize
that the mirror reflection is their own body, a few
animals do appear to recognize that. What about mopular rays, well,
there was a paper published in the Journal of Ethology
in the year twenty sixteen by same author as before
sila Ari but also Dominic P. Dagostino, called contingency checking

(48:54):
and self directed behaviors in giant manta rays do elasmo
broncs have self awareness, and so the authors set this
up in their abstract by saying, quote, manta rays have
a high encevilization quotion. As we already talked about it,
Remember large brains compared to their body size, similar to
those species that have passed the mirror self recognition test

(49:17):
and possessed the largest brain of all fish species. Again,
that would be in the mobula of Birostris, the giant
oceanic mantray, biggest fish brain. They write quote in this study,
mirror exposure experiments were conducted on two captive giant manta
rays to document their response to their mirror image. So

(49:40):
this test was different from the standard format than that
I just described a minute ago because the authors were
not able to do the body mark component of the test,
And there are some good reasons for thinking about that.
For one, thing like mantas don't have hands, so they
can't reach out and tut. There's nothing they have that's

(50:00):
prehensile they can use to reach out and touch a
part of their body to mess with it. So it
didn't have that important body mark component of the test.
That places some major limits on how to interpret these
results when compared to the results of many other mirror
test experiments. But the authors did document the manta's behavior

(50:20):
in response to the presence of a mirror, and then
they controlled for that by just putting in a non
reflective white board of the same size in their tank,
and the results were really interesting. The mantas showed a
lot of interest in the mirror like a lot of interest.
They really were attracted to the mirror and they wanted

(50:43):
to hang out around it. They spent a lot of
time moving around in front of it and messing with it.
They did not, on the other hand, attempt to interact
socially with the mirror image. And the authors could measure
this because there are certain kinds of physiological responses that
mantas tend to show when in the presence of another

(51:03):
another manta, like they might show like a kind of
widening of spots, or like something kind of like changes
on their coloration patterns, and they didn't observe anything like that.
They did not see the behaviors you would normally see
when a manta sees another of its species, so there
were no signs that they thought of this as another animal.
The author is right quote frequent, unusual and repetitive movements

(51:28):
in front of the mirror suggested contingency checking. In addition,
unusual self directed behaviors could be identified when the manta
rays were exposed to the mirror. So what exactly do
they mean by contingency checking. This seems to mean testing
to see if the mirror image does the same things
you do so you know, you might think of making

(51:50):
faces in a mirror or like wiggling repetitively in front
of a mirror, and they the arch yes, yeah, exactly, yeah,
they were doing that. So exam they observed were things
like positioning the body to stare into the mirror and
then repeatedly wiggling the cephalic fins, like opening and closing
the cephalic fins over and over, blowing bubbles into the mirror.

(52:13):
And then also what about these unusual quote self directed behaviors.
This is what look to the researchers like the manta
trying to investigate parts of its own body that it
can't normally see, like orienting so that it could look
at the reflection of its ventral surface of its belly

(52:34):
or part of its back for example. They note that
quote body turns into a vertical direction, exposing the ventral
side of the body to the mirror while visually oriented
to it was something that they only ever saw the
mantas do when the mirror was in the tank. So
they take the mirror out. They don't see the mantas
doing like orienting vertically like this and look, so it's

(52:57):
like it looked to them like they were trying to
see parts of their body that were not ever visible
to them otherwise. So at the end of their abstract,
they say, quote, the present study shows evidence for behavioral
responses to a mirror that are prerequisite for a prerequisite
of self awareness, and which has been used to confirm
self recognition in apes. But again the authors do acknowledge

(53:20):
the limitations. You know, this doesn't necessarily prove self awareness
this version of the test. Of course, it did not
include the mark checking component, and there are multiple ways
you could interpret their behavior in front of the mirror.
It's possible they didn't recognize it as themselves and we're
just reacting with curiosity to something visually unusual. Though, the

(53:42):
behaviors that look like, you know, checking out your belly
flesh only when the mirror is around, that does sound
pretty interesting to me.

Speaker 2 (53:49):
Yeah. Absolutely, Oh man, Yeah, I have a couple of
thoughts on all of this. Like, on one level, I
have to say that, you know, so like the hard
science side, I do like the idea of leaning into
interpretations of animals as being more conscious and having you know,
if there's a case to be made, I'm like, let's

(54:11):
go ahead and consider it, because if it helps protect
a species like this, then all the better. On the
other hand, like just the idea of let's go ahead
and assume for the sake of argument that the manta
does recognize the reflection as itself. What is that like
for a cret Now granted, this is an aquarium scenario,
so with the glass involved, there may be some other scenarios.

(54:32):
But imagine a purely wild manta that has, as far
as I'm imagining, it never encountered a reflection of itself,
and then it is presented with one. What would that
be like? What would that be like for a human being?
If we managed to make it to adulthood without ever
encountering an unnatural mirror, reflection or something like it, say,

(54:54):
on the surface of water. I mean, I have no
doubt that we'd be able to pass it. I mean,
that's certainly part of the human mental capabilities. But but man,
what would that what would that encounter be like?

Speaker 3 (55:06):
But the human I think, you know, you can see
a lot of your own body, not the whole thing.
You know, you got a lot of back, and you
got a face and head and I guess all that.
But you can see at least like the front of
your body. Yeah, the mantas, I don't know, can they
even see that? Again, it seems like they were very
interested in checking out their their ventral side here, so
they may have very very little visual awareness of themselves

(55:29):
within their space ever, maybe all kind of like only
proprioceptive awareness of their own body. Again, I'm not sure
of that, but that's it seems plausible.

Speaker 2 (55:41):
Yeah, yeah, I think it's fascinating. Now were we kept
talking about their their bellies, their ventral side, So I
want to come back to this as we're we're closing
out here. As we've mentioned, some mantas have distinct appearances
because of significant scarring, you know, scarring from mating, scarring
from predators interactions. And then you have mantas such as

(56:03):
the celebrity manta Baba Ganoosh of the Maldives that apparently
survived a rather horrific boat strike. You can look up
images of this one. So these individuals you tend to
stand out. But as we've discussed, their wounds tend to
heal rapidly, you know, maybe not completely, and certainly in
the case of severe injuries, not completely, but on the whole,

(56:24):
these are changing markers. What doesn't change, however, are the
dark spots on their bellies, on their ventral side. You
can look up, you know, images of this, and if
you've been in the water you might get to observe
this as well. But yeah, you look at the ventral
side of a manta and it is a unique fingerprint,
the array of spots and blotches on their generally white bellies.

(56:48):
It is, It is a fingerprint. It can be used
to i D a particular manta, and scientists are able
to put these into a database and track individuals without
the aid of actual physical tracks or tax And it
gets even cooler because you get into like a citizen
scientist scenario here because you have the global ID the

(57:09):
Manta Photo database, which via this database, anyone who swims
in proximity to mantas. Again, I'm assuming by following all
the rules, but if you manage to get a photos,
particularly of their spots, they can I think other parts
of the manta can also prove useful, but especially their spots.
They can be uploaded into the database and this can

(57:31):
be used to help study their movements and their behavior.
And yeah, you can learn more about this at Manta
Trust dot org. I believe we've referred to the Manta
Trust already, and I'd say, in general, if you've been
moved at all by anything we've discussed in these episodes
about the manta, the plight of the manta, or the
majesty of these creatures, visit Manta Trust dot org. You

(57:54):
can learn more about them, you can sign up for
their newsletter. You can support their work via donations and purchases.
In fact, that book that I've been referring to, Guide
to the Manta and Devil Rays of the World, is
available to purchase there, and even if you don't purchase
it directly from them, royalties from that book go to
the Manta Trust. You can even this is this is

(58:15):
super cool. You can of course adopt a manta. This
is not uncommon. You can, you know, and but you
can also pay to name a specific Maldives manta in
their database. I was looking at this on their website.
I think they had like four up for grabs. So
these are mantas that have you know, like a technical tag,
like you know, string of numbers and letters, but they

(58:36):
don't have a fun name yet. And for a very
reasonable donation, you can provide a name for such a
Manta Ray.

Speaker 3 (58:44):
Do they place any limits on how stupid the name
can be?

Speaker 2 (58:48):
I don't know. I mean, I mean there may be
some reasonable limits there. I mean I would place reasonable
limits if I were running this. But but yeah, I
mean it makes me I kind of want to adopt
a Manta Ray for the show. Could call it, I
don't know, Blowfield, Stuffington or something. I wouldn't want it
to be a complete.

Speaker 3 (59:04):
Advertiser Delia the self Aware.

Speaker 2 (59:09):
There you go at any rate check it out listeners.
If you happen to adopt a Manta Ray or or
name a Manta Ray via this website, let us know
and we will. We will spread the will, spread the word,
and we'll also look this Manta Ray up and see
what they look like.

Speaker 3 (59:24):
Yeah, contact at stuff to Blow your Mind dot com.

Speaker 2 (59:27):
Let us know. All right, we're gonna go ahead and
close these episodes out. I hope you've enjoyed them. Again,
we'd love to hear from everyone out there. You have
any experiences with Manta's, other rays, thoughts and anything that's
discussed here right in. Yeah, send your photos. We'd love
to see photos. We heard from some snorklers already, but
not the sort of snorkelers. I was imagining. We'll get

(59:49):
to that in a future listener mail episode, but we
heard from some bog snortlers. Is that a joke?

Speaker 3 (59:54):
I couldn't tell.

Speaker 2 (59:55):
I could not tell. I haven't had a chance to
research it yet, but I flagged that one to come
back to. If it was a joke, it was elaborate.
Those were I think real photos.

Speaker 3 (01:00:04):
We'll learn more and report.

Speaker 2 (01:00:06):
Just a reminder to everyone that's Stuff to Blow Your
Mind is primarily a science and culture podcast, with core
episodes on Tuesdays and Thursdays, short form episodes on Wednesdays
and on Fridays. We set aside most serious concerns to
just talk about a weird film on Weird House Cinema.

Speaker 3 (01:00:19):
Huge thanks as always to our excellent audio producer JJ Posway.
If you would like to get in touch with us
with feedback on this episode or any other, to suggest
a topic for the future, or just to say hello,
you can email us at contact stuff to Blow your
Mind dot com.

Speaker 1 (01:00:40):
Stuff to Blow Your Mind is production of iHeartRadio. For
more podcasts from my Heart Radio, visit the iHeartRadio app,
Apple Podcasts, or wherever you're listening to your favorite shows

Speaker 2 (01:01:00):
With red Ratt