Animal Sexual Fluidity

Why do some species change sex and how to they carry out this remarkable transformation? This episode of the STBYM podcast takes you into a world of hermaphrodites, clownfish and the high-stakes game of reproduction in the animal kingdom.

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Episode Transcript

Speaker 1 (00:03):
Welcome to Stuff to Blow Your Mind from how Stuff
Works dot com. Hey, welcome the Stuff to Blow your Mind.
My name is Robert Lamb and I'm Julie Douglas. We
live in a UH we have in a curious biological world.
We've profiled a lot of interesting UH specimens on this

(00:24):
show over the years, and UH today we want to
talk about animal sexual fluidity and general the general fluidity
of of of sex and gender itself in the animal kingdom. Yeah,
because we can't help but sort of take our human
nous and just projected onto other organisms out there. So

(00:46):
when we talk about gender bending, so to speak, in
the animal world, what are we talking about. We're not
just talking about sharing parental duties. So I'm talking about
the sea horse. It's not enough to carry up to
fifteen hundred eggs in your marine animal version of a
baby Bjorn to be considered someone who is gender switching.

(01:07):
So we are going to talk specifically about animals that
change their sex and why they do it. And while
we're talking about this, why not talking about the sex
change chicken? Oh yes, you're talking about Gertie the hen
who later became Bertie B. E R T. I e
Bertie instead of Gertie. H. This was the rooster. Yes two.

(01:30):
This is in two thousand eleven where you had a
pair of British chicken farmers and they observed a spontaneous
gender change in their previously egg laying hen Gertie. So
she began to walk around like a rooster, put on weight,
developed wattles under her chin, and she also grew dark
brown plumage and a scarlet cockscomb on top of her head. Yeah,

(01:50):
and she began to crow. Um. The British couple said
that at first the crow was terrible, but with practice
is she actually sounded like a rooster. And according to
Remy Molina, writing for Live Science, um, what happens with
birds is that you have to sex organs present during
the embryonic stages, but once a chicken's female jeans kick in,

(02:14):
it typically develops only the left ovary. The right go nad,
which is yet to be defined as an ovary or
testies or both. It's called the OVI testis remains dormant.
So the idea here is that something like an ovarian
cyste tumor, or maybe even a diseased adrenal gland caused
the ovary to shut down and Gertie and then the

(02:36):
dormant ov testis kicked in and produced androgens, which are
hormones that are associated with male characteristics, which would have
led to Gurtie's but then Bertie's physical and behavioral changes.
And this is more of an example of a loophole
in sexual dimorphism. Um. But we're really going to talk

(02:57):
more about organisms that are intentionally switching this up as
a survival tactic or even a response to environmental conditions,
situations where sex switching, yeah, is about the long game
of survival. Now, there are a couple of types of
sex switching um. The first is simultaneous hermaphrodites, and they

(03:17):
have both female and male reproductive parts for their entire life,
and they can mate with any other member of their
species they should find we're talking about more like fish
and gastropods slugs to call back to our our slug
sex episode. Yes, that make up the bulk of this type.
And then you have a sequential hermaphrodites. And sequential hemaphrodites

(03:41):
are born as one sex but change completely into the
other sex during the course of their lives. So this
is definitely the more engaging for humanized example of sex
changing because it's one where an animalist is actually transitioning
from one gender into another and sometimes back again. So
the question is why doesn't it occur more especially if

(04:03):
you consider that this kind of strategy would double your
chances for a Saturday night, so to speak, because you'd have,
you know, from these strategies a large number of offspring.
So Suzanne Alonso, Assistant professor of ecology and evolutionary biology
at Yale University, says, quote, an intuitive yet rarely studied

(04:26):
explanation is that the considerable time or energy it takes
to change sex make hermaphroditeism unfeasible for most animals. That
was the idea that she went into when she and
her team created this theoretical model of hermaphrodite and separate
sex life histories and in their their game that are

(04:47):
rather the model sex change players I put players in
quotes vary the age of their sex change, while the
separate sex strategy responds by altering the number of male
and female offspring it produced. And they found that a
hermaphrodite could spend thirty percent of its lifetime in the
process of changing sex and yet still persistent a population.

(05:10):
And so would that suggests is that UM only huge
changes or cost rather UM can disfavor sex change SOT
is not really enough to be of concern to limit
that species lifespan. They can still exist while doing this.

(05:30):
If it were more up to a fifty of their time,
so many percent of their their time and energy changing
into another sex, then it might become an issue. And
so Alonso and the researchers say that just taken a loan,
that this cannot be the only reason why it's rare
in nature. And maybe it's more about the environmental conditions

(05:51):
which are generally more balanced, so you don't have to
worry so much about there being too many females are
too many males, Okay, So it's when the environment is
out of balance that's when something has to change. Yeah,
And she also said for some species, parental duties might
affect this as well, so it might be more advantageous
just to have a separate sex system in place. Okay. Alright,

(06:17):
so this leads us to the area of gender performance. Now,
this is an obviously a situation where a male is
not changing into a female, female is not changing into
a male, but sometimes there is an advantage in pretending
that you are a member of the opposite gender. One
wonderful example of this, UH is the occurs with cuttlefish.

(06:38):
So you have to you have a two tiered system
of males with cuttlefish. You have a big brash brawlers
and then you have smaller, stealthy lotharios. And the footage
of of these encounters between the males, particularly in the
larger cuttlefish species, not the cute, small ones, the little
iridescent ones that you see um at so many aquariums

(06:58):
that I'm talking about, the big cthulu esq ones. They
get into these big carrying fights with each other, like
ripping tentacles apart, just really brawling all over the rights
to the female cuttle fish that are that are sort
of waiting in the wings there. So on the surface
of things, this might seem like it would just really

(07:19):
favor the big, brash brawlers while the stealthy gal gutarios
would be on the outskirts, right, what are the how
are they going to get in there? Well, so what
they do is they use uh the cuttlefish powers of
shape changing and color changing, particularly by use of their chromatophores, uh,
to look like a female to sort of draw in, uh,
change their color a bit, and then they can move in.

(07:39):
They move in closer to the female. And then the
big the big brawler guy that's over here hanging out,
he looks over and he's like, oh, that's just another
female getting close to the female that I want. Maybe
all made with both of them, So I'm not gonna
do anything, right, But meanwhile that the little guy is
getting closer and closer so that he can breed and
often does successfully breed with the female cuttlefish. And so

(08:02):
just clever is this disguise and so so perfect the
use of their chromatophores. Two thousand twelve study out of
McQuire University in Sydney, Australia found that males can actually
split themselves down the middle, appearing to be a male
on one side of their body and a female on
the other. So he's floating here between the big brawler

(08:25):
and the female and the big brawler it looks like
a lady cuttlefish just floating there harmless. But on the
other side he's flirting and uh and and gaming to
mate with the female. I like that. It's kind of
like having your own split billboard. Yeah, indeed, all right, Now,
the female market squid does a similar thing. What she

(08:47):
does is she flashes a pair of fake testies. And
this is really interesting because the life of a female
market squid is not an easy one. You have hundreds
of thousands of market squids gathering to reproduce with really
aggressive behavior from the males, which often causes injuries. And

(09:08):
female squids they will lay tubes of their eggs on
the seafloor and that's all good and well, except that
a lot of times above them will be a big
ball of um, sort of breeding ball in the ocean
going on, and so it's really easy for them to
kind of get sucked back into that breeding ball. And

(09:29):
again it's very violent. It takes up a lot of
their energy and their resources. And they have just laid
these tubes of eggs on the floor. So what do
they do to try to counteract this, Well, they use
a little subterfuge. They control the appearance of this white
stripe down the part of their body that mimics the
approximate size, color, and position of testies on a male squid.

(09:52):
So the male sees this and thanks, oh, not female
leave alone. She gets off scott free. And according to
Daniel Dumar teeny, one of the co authors of us
study on female market fish, So we've seen the chromatov force, right,
the chromatov force. Um, this those sort of specialized pigment
cells and the ability to change coloring, right, but we

(10:15):
have never seen before, uh, the ability to turn white
on and off. And this is due to a specialized
type of cell called ol lucaphour. So she's essentially it's
like when the taxi sign goes in service out of service,
we m with, you know, just testies as the stumble.
I suppose all right, well that that brings us to

(10:37):
the world of garter snakes. Now I want to everyone
to imagine themselves in Manitoba, Canada for a minute. Alright,
the snow has melted, spring is setting in, and that's
when it pens of thousands of red sided garter snakes
emerge from their limestone dens and begin to engage in
great tangled mating rituals. We're talking Roman orgies of serpentine

(10:59):
sex performed right out in the open, right there on
the limestone. Yeah, and just big, big yeah, caligula, balls
of snakes going at it right there in front of
God and everybody. Afterwards, after all of a sudden done,
now they end up sliding off into the local marshes
for the summer, carry about their life, and then they
return to their dens in early fall. Now, generally speaking,

(11:23):
in each of these big clustered balls of snakes, there's
a female at the center because the males are competing
for the mating rights there, and that's all that. That's
what's going on in this big tangle. But in some
cases the males actually mimic females to wind up at
the center of the heap slide. Yeah. Now you might

(11:44):
wonder why why would a male snake do that? Well,
I think think again about the fact that they're they're
doing this. They're having this big snake orgy out in
the open. So birds of prey are well aware that
this occurs, because this isn't all you can eat snake buffet.
Just just come down to you know, talents and beaks,

(12:04):
blazeon and just eat as much as you want. So
there is a survival advantage in being at the center
of that heap, because you're gonna be far harder to
get to there's far less possibility that these birds of
prey are going to feed on you. So maybe this
male snake, he doesn't have an actual shot at reproductive
success in in a tangle, but he pretends to be
a female, he can at least get a survival advantage

(12:27):
and and and get to snake off into the marshes.
So all plots in nature lead back to boozing buddies.
So you're saying, yeah, okay, so we're talking about females
imitating males imitating females. Yeah, I'm pretty sure this was
in one of Shakespeare's Traumatis, but I don't remember which one.
I'm sure. I'm sure that Shakespeare looked at the African

(12:49):
bat bug, which is a small, reddish brown parasite that
feeds off bat blood. Take that bats, and uh probably
penned a couple of stories based on the um. These
bat bugs practice something called traumatic insemination. We've talked about
this before. It's when males stab females in the abdomen
with needle like penises and the inject spurned directly into

(13:12):
the bloodstream. And uh, yeah right, it's it's pretty it's
pretty violent. It's hard on the females, and it's also
hard on other males because sometimes males do it to
other males and so this may be more of a
combat thing. So to protect themselves, the female bat bug
developed something called para genitals. We're talking about a funnel

(13:32):
like genital opening on their body that tricks the male
bat bug into sticking that, you know, the needle like
penis into this area that is filled with immune cells.
So it's it's really a smart strategy by the female
batbugs because what it does is it reduces the site

(13:54):
of injury to this one location and it's guiding the
pro straight and straight into a bucket of immune cells,
and that helps to reduce the impact of injury. Now,
male bat bugs took notice of this, and this is
where the males who are imitating females comes in and

(14:17):
created a similar paragenital to redirect attacks on their bodies.
Except that the para genitals made them look more like females,
so right, oops. So they adopted a differently shaped funnel
which is more open and exposed, and that greatly reduced

(14:38):
to texts. So now you have females noticing that the
males have done this and made this adaptation, and they
also adopt the differently shaped funnel and clause. Rerhinehart of
the University of Sheffled UK, who led us study on
this um says that both of these female and male

(15:00):
bat bugs who made these for their adoptions adaptations, uh,
they suffered fewer mating scars than those with standard closed forms.
So we see just this arms race between the genders
in these African bat bugs. Right, So then the question becomes,
so cool, do they just keep creating these these uh

(15:22):
iterations of para genitalia until they become ridiculous looking? Yeah,
until it becomes I mean, I guess there has to
be a point where the like the wave kind of
breaks and falls back, right, because at some point, um
it would it would not be sustainable. So there'd be
like a level of complexity that it couldn't go beyond. Right,
So yeah, that brings up the question about what form

(15:44):
will they ultimately take? Now, another wonderful example of this
time of pseudo gender is the female spotted heighteninga. And
this is this is pretty remarkable because female spotted hyenas
are the socially dominant, larger and more aggressive of their species,
and they have a pseudo penis. Now, to be clear,

(16:05):
what they have here is an enlarged delatorus that can
actually achieve a seven insurrection, as well as a structure
that looks like a scrotum, a pseudoscurotum that's formed from
the labbya and uh. This makes them the only female
mammalian species devoid of an external vaginal opening. And that's
why we used to we used to think that that

(16:26):
they might be hemaphrodites, that they're these were either hemaphrodite
individuals in the species or or that the species itself
featured hemaphrodites um. Now, on a there are a lot
of mysteries that remain about like what purpose this actually
serves for the for the spotted hyenas. But on a
biological basis, it's all due to higher levels of the

(16:47):
hormone androgen in the females, particularly the pack dominant females,
So it gives them their greater sizes, the greater strength,
but it also makes reproduction difficult. So this uh, they're
basically three areas where where where the where we see
the wages of this first of all creates an awkward
mounting situation for males and females, but sure that clariss

(17:09):
is getting in the way. Yeah. In fact, it's the
point they say that the males like really have to
learn how to do it. Like there are some species
they just you know, take to it like a horse
to water. But with the spotted hyena, the male is
going to have to get in a little practice before
we can actually connect um. Also, there's a there's some
difficult plumbing here when it comes to to the birth

(17:31):
of the pups because they have to give birth through
this pseudo penis. So on one level, you're talking about
a narrow birth canal. It's an inch in diameter and
the tissue often caress a two pound pup squeezes through,
and that rip can actually prove fatal, So that means
there's a higher mortality rate for a first time spotted
hyena mothers. Additionally, the umbilical cord is a bit on

(17:55):
the short side compared to the length of the birth tube,
so the cord often breaks before the cub and merges,
and this can this can lead to uh to death
for the for the young cub. In fact, of hyena
cubs die of suffocation inside the pseudo penis. So another
example of this that we we've had on this show

(18:15):
many times, I feel like I need to say and
come out to the stage again once again and join us.
Brazilian cave insects um because in the May two thou
and fourteen edition of Current Biology Yoshizawa Casauro at All,
they documented their findings from when they dissected four species

(18:36):
of cave dwelling winged insects from Brazil called Neo Trogola,
and they realized when they dissected them that the females
had an internal penis like structure that they likely only
extended during mating, and the males had a pouch like vagina,
and so, okay, what are the mechanisms of this well mating,

(19:01):
the female spiny penis gets tightly anchored to the males
male vaginas sperm duct, allowing the female to receive the semens. So,
in other words, the penis function is more like a
straw than a spout, and if the male tries to
break away, the abdomen would well rip open and he
would lose his genitals there um. The female insects also

(19:24):
mate with multiple males, and they can store two batches
of sperm in the body, all right. What they think,
the researchers think is that it could be the environmental
conditions that have created this sort of penis like structure
in the female cave insects. That's because there is a
lot of competition among males for fertile females, and in

(19:47):
the cave environment, food is scarce, and so it turns
out the female sperm is seen as a nuptial gift
because not only um can the female cave sy fighter
transfer this to her eggs, but before she does so,
she can actually eat some of it and it has
nutritional value. So you see here that that's why the

(20:09):
female is taking the role here as the aggressor in
the reproductive relationship and essentially scooping out that sperm with
this penis like structure. All right. That brings us to
the area of gender change outright, ginger change. And we
see this particularly in three different fish species, which serves
as wonderful examples, the first of which is the anonymy

(20:32):
fish a k a. The clown fish, and if you're
a parent a k a. The nemo fish. Um. These
are some of the most prominent examples of sequential hermaphrodites.
UH they live in a mutualistic relationship with a single
an enemy for most of their lives. Since this, of
course the uh you know, the small aquatic organism with

(20:52):
the with the stinging tendrils, right, but the the anemone
fish are have an immunity to that sting. So it's
wonderful safe place to live. But they're also kind of
isolationalist here. Okay, So in this anonymy neighborhood, you have
a sole female UH and the and the largest male,
and those are the ones doing all the mating. But

(21:13):
when the female dies, the largest fish in the ananymy
neighborhood becomes a female, and then she begins mating with
the next male. So you have a huge advantage to reproduction.
In this UH. You get additional genetic diversity because every
fish in the immediate environment is a potential mate. But
it's also particularly good since again as we're talking about
a secluded little neighborhood, a secluded environment, they don't stray

(21:36):
from far from home. So if you need that that diversity,
if you need a new female, you just make one
from the population. Another example of this is the parrot fish,
which is common around around tropical reefs. Throughout the world,
and one of the adaptations that makes them unique and
really interesting is that they have pharyngeel teeth which you

(22:00):
can use to grind up corals, or they used to
grind up corals. Another thing is that at night they
surround themselves in this mucus like cocoon to protect them
while they sleep in The idea is that the cocoon
could mask their scent in making them harder for nocturnal
predators like more eels to find. But of course the
super interesting thing about them um is that they can

(22:24):
change sex in response to fluctuations in population density. So
they have two strategies when it comes to this. In
the first strategy, they're all born female and then later
they can change sex into males and they can also
begin life as males. Second strategy known as primary males,

(22:45):
and it's thought again that this sex change is in
response to low population density in in one or the
other of the genders. So in parrot fish populations, the
large superman males these are large males that were once female,
are dominant and they claim most of the females and

(23:07):
the primary males often spawning groups with one female, So
starting out as a female and then changing sex later
would be really advantageous. Females don't have any trouble finding
mates no matter how large they are, while the males
are much more reproductively successful as larger individuals, so they
can reproduce as females when they're younger, and then when

(23:28):
they grow to a large enough size to compete as males,
they change sex and reproduce as super males. And they
see a similar situation with hawk fish now hawk fisher
another tropical corald dwelling fish um and in the while,
they have been been observed to participate in what we
call bidirectional sex change. Uh so they're going from female

(23:51):
to male but then also back again. So it's a
similar situation with the parrot fish. You know, functional females
changing into males. If a don and it's super mail dies,
but they can change back. Ah. So they are multidirectional
when it comes to that. Yeah, multidirectional. You can think
of it in terms of, you know, they there's a
there's an opening on the staff, this individual can transition

(24:12):
into that road for into that role for a little bit,
but then when they're no longer needed there back into
their previous role. And this kind of this reminds me
of that whole concept of survival as a whole, as
a species, right, because it's not just about the individual
fish here, it's looking at the whole population and responding
accordingly and making sure that yes, we can respond to
that and change and and um you know, offspring and

(24:36):
it's corresponding genetic packages can be furthered into the future. Yeah,
it's like we need a mail to survive. We need
a female to survive who's going to step up and
change and then you you have you have a fish
that comes up and does the job, and then the
genetic lineage can continue. Now, we wanted to leave off
this episode with this really cool butter fly that was

(25:01):
discovered at the Natural History Museum of London in two
thousand and eleven. It's a Mormon butterfly. It hatched and
the staff noticed today that the coloring looks a bit
off on this and uh, they looked closer and they
discovered that it was almost black on its male side,

(25:22):
all black, and on the female side it was paler
and flecked with blue red and tortoiseshell. And of course
at first they didn't realize that this was half female,
half male butterfly, because really you only see that in
circus shows, right, Yeah, I mean there's sex organs were
essentially welded together. You would think this is like a

(25:45):
Fiji mermaid kind of a thing, right, what comes to
you the half half man, half woman butterfly. Right, Yeah,
they had one antenna was actually smaller than the others.
And as you say, the reproductive organs refused together. And
this is actually something called guy Nan Droom Morphy happens
from time to time. Yeah, so it serves as kind
of an interesting symbol. I think of the fluidity of

(26:08):
of sex and gender that in butterflies, but in just
any organism, it's not. It's not so so fixed an issue.
It isn't and it's again it's a response to environmental conditions. Um,
it's somewhat of a question of energy resources, uh, survival.

(26:30):
And we wanted to point out too that we have
an episode called Can Animals Be Gay that explores more
of the behavior of animals. We didn't. We want to
make a distinction between what we're talking about today in
this idea that animals behave in a way that seems gay.
I'm putting that in quotes to us. Yeah, when you

(26:50):
bring in the human baggage of trying to figure out
how animals work. So indeed, check out that episode if
you like. We'll make sure that we linked to that
in on the landing page. At this episode, it's Stuff
to Blow your Mind dot com. You know, we have
a few minutes here. Let's call over the robot and
UH have a little listener mail. All right, This one

(27:11):
comes to us from Porter. Porter writes and it says, Hi,
I'm the digital director at the US Fund for UNI
Stuff and also an average Stuff to Blow your Mind listener.
I've been working all weekend trying to raise funds for
the Nepal earthquake relief effort, and I was listening to
Stuff to Blow Your Mind episodes early Monday, and when
what do I hear? During the Power of Polite episode,
Julie mentioned donating to UNI Stuff is a nice thing

(27:33):
to do while explaining the off record indirect politeness strategy.
I can't tell you how happy that made me. Donated
the unit stuff is a nice thing to do. Hey, Also, restaurants,
maybe there should be a National Pizza Day where you
give ten percent of your profits to UNI SEF. If
you can mention our Nepal donate form on the podcast,
I'd be really grateful. Thanks for all the thanks for

(27:54):
all the great episodes over the years. That's unis f
USA dot org slash Nepal. That's you in and I
c e f u s A dot org slash Nepaul.
Thanks Porter and uh yeah, guys, make sure to check
that out if if that has been on your mind, um,
that would be a great thing to contribute to. We
also have a bit of correspondence here from Caroline. This

(28:18):
was a Facebook message that she sent us. She said,
I just listened to your episode about politeness, and I
thought it was so great When you were leading up
to the most impolite society, I literally shouted Eastern Europeans.
I laugh because I'm a first generation American whose parents
are Polish. I spent much of my life in Poland
and the United States, and I can appreciate the direct

(28:39):
attitude that Polish people have. It can be very abrasive
to anyone from outside the culture. If I go to
Poland for a few weeks at a time, I definitely
begin to miss the friendliness of Americans. But I know
a lot of my American friends perceived me as very
direct and poland it's certainly no big deal for someone
at a bus stop to tell a complete stranger that
their kid is being too loud? Would that would never

(29:01):
happen here? And she's right, it wouldn't. I get the
unique experience of having both personality traits. You did also
make a great point about familiarity in Eastern European culture.
If you're a stranger, you will be looked at with suspicion,
but if you are in the inner circle, you are
among some of the kindest, loving people. We wouldn't greet
a stranger with kisses, but your closest friends and family

(29:22):
definitely get three cheek kisses. I love that you totally
have the nail on the head with this episode. Keep
up the great work, Caroline. All right, So there you
have it. Hey, if you want to check out more episodes,
including that can Animals Be Gay? Episode that we referenced earlier,
I don't know where to stuff to blow your mind
dot com that is the mothership. That's where you find
all of our podcast episodes, videos, blogs, you name it,

(29:43):
and if you have some thoughts on animal sexual fluidity
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