Spiders Song is a story about a quest to hear the greatest symphony on Earth: the music of evolution. Along the way, we get to know some of nature’s most surprising musicians — the paradise jumping spiders.

Part 1 is the Spiders

Part 2 is the Song

Headphones advised.

— — —

For credits and much more, visit futureecologies.net/listen/fe-5-1-spiders-song

You can listen to Part 2 right now — find it wherever you get your podcasts, or at futureecologies.net

— — —

Funding for this series was provided by the Canada Council for the Arts.

But ongoing support for this podcast comes from listeners just like you. To keep this show going and growing, join our community at patreon.com/futureecologies

Our patrons get early episode releases, exclusive bonus audio content, access to a fantastic discord server, 50% discounts on all merch, and more

You are listening to season five of

Future Ecologies

Are we are we going? We're rolling?

We're back.

This is the second windowless room I've been

trapped in today.

The things we sacrifice for sound.

It's true. What's up Mendel? Why are we what are

we doing here?

Well, Adam, I want to tell you a story that's

really special to me. It's something I've been working on

quietly since mid 2019. Basically, right after season

one.

Okay, so this is, this is a long gestational

process here, even by our standards, which are slow.

Yeah. I, so I don't know if you actually

remember this, but right after we put out season one, we got an

email. It was a criticism of our third episode, The Loneliest

Plants, basically saying that we'd oversimplified the concept

of biodiversity.

How does one not oversimplify the concept of

biodiversity? But I do remember that email actually, didn't I

respond to them?

Yeah, you went back and forth about genetic

diversity versus species diversity. But for me, things

didn't end in that email thread. Because I got the chance to sit

down with the scientist who wrote to us.

I think that who I think I am is not quite who

people know me as, or at least a lot of people know me as.

So this is Wayne Madison. And people tend to know

him as an evolutionary biologist.

The work that I've done in evolutionary

biology that's had the broadest reach is actually the

computational side. It's the analytical tools that computer

programs that help people analyze their data, because, of

course, tools that help them do that really get a lot of

traction in the field. And so a lot of people know me for that.

So Wayne, along with his brother, David, they

developed software which is now widely used to understand the

tree of life, or Phylogenetics.

Phylogenetics being... like the science of how

a group of organisms is related to one another.

Exactly.

Their evolutionary branching patterns... that

connect them — that connect us all.

Yeah.

I'm not an evolutionary biologist. But I do

know that

So you probably have never had to create a Nexus

file or used a program called Mesquite.

No Nexus is for crossing the border, and

Mesquite is a tree from the southwest. As far as I know,

In this context, Nexus and Mesquite are to

phylogenetics kind of what the mp3 and iTunes are to music.

Yeah, that's a good way to think about it.

And Wayne is the co author of both.

Oh wow.

But that's not actually the work he's most

proud of,

The one thing that I'm the most proud of — and

that I think will last the longest, as in hundreds of years

— is actually my work as a taxonomist

Taxonomy. Okay, so we've started with phylogeny,

now we're to taxonomy. But it's the taxonomists who put together

phylogenies, right? They're the ones who figure it out and name

all the things. And then sometimes very frustratingly,

also changed the names of things that you got used to knowing as

one name, and now they're something else... and then

sometimes they change it back.

Yeah, right. Taxonomists are the people who

literally make up the names. And more importantly, they describe

and illustrate exactly what makes one species different from

another.

And I'd never be able to identify all of these

obscure grasses without them.

So way back then, I heard a story from

Wayne, and it kind of changed my life. You know, looking back, I

can say that it made me the person who I am today.

And who is that person, Mendel?

In a word, I am now a musician.

You are. It's awesome. I'm so excited that we

can make music together for this podcast.

Yeah.

And yeah, I guess I hadn't thought too much about

how or why you got there. It just sort of happened

organically, from my perspective. Is this like your

alter ego origin story? Is this the the genesis of Thumbug that

we're talking about here?

You might call it the hatching.

The hatching... that... that sounds very

organic.

Yeah. But you know that that's really just a

tiny part of it. Because to tell that story, first, I need to

tell you Wayne's. And it starts with the moment that put him on

his path.

It's a story of divergence and convergence; melody and rhythm;

pattern and endless variation.

From Future Ecologies, this is Spiders Song, Part One.

Broadcasting from the uceded, shared and asserted

territories of the Musqueam, Squamish, and Tsleil-Waututh,

this is Future Ecologies:

exploring the shape of our world

this is Future Ecologies:

through ecology, design, and sound.

Our story begins in 1970, when Wayne was 12 years

old.

Burned into my memory is this one day. We were

in the Rocky Mountains, my family, my brother and I.

They were on a trip through Kicking Horse pass

Not too far from the border between Alberta and

British Columbia, just traveling through the mountains.

While they were there, Wayne found himself at

the headwaters of a small mountain stream

That has a really peculiar thing happening

to it, or at least it was really peculiar to me as a 12 year old.

You follow the little creek along, it's going downstream.

And at one point, there's this pile of rocks there, and the

stream splits in two.

One side flowing to the west, the other to the

east.

It's not like a normal stream that you think

about where you have tributaries that come together. This was a

case where it split. And there's a little plaque there, and the

plaque explained

That this stream was positioned precisely on top

of the great continental divide. From this point of divergence,

the two halves of this creek would end in different oceans.

The left half of the split continues, eventually

joining other creeks becoming rivers and going to the Pacific

Ocean. The right half continued down the other side, into

Alberta, and eventually going to the Arctic Ocean. And I remember

looking at that, and thinking, "Whoa, just imagine the water is

coming, and two little bits of water that are just a millimeter

apart, strike this pile of rocks, and the one little bit

happens to bounce to the Pacific. And the other little

bit happens to bounce to the right and ends up in the Arctic

Ocean. And these two little bits of water from being right next

to each other, suddenly find that they have such different

destinies."

So this place was called Divide Creek.

And, of course, I realized that life is full of

Divide Creek moments. Every one of us has these moments when

some little different decision that you could have thought of,

or some little different bit of chance that might have

encountered you could have led you on a completely different

path in your life.

One such moment would come for Wayne the very

next year, on the shores of Lake Ontario.

And as we were there on the shore, a mat of

grass floated by — presumably some nearby house or something

had mowed their lawn and thrown it onto the lake. We we didn't

compost back in those days. And on that mat of grass floating by

was a spider. She was a fairly small spider as spiders go. But

she looked up at me. And it was the fact that she looked up at

me that was I think the thing that I noticed so much, because

I'm not used to little things in the world paying attention to

me. I imagine now that my eyes twinkled when she looked up at

me. I don't think her eyes twinkled, but it was a real

special moment.

She was about as cute as a spider can be. Tiny in

almost every way, except for a big pair of eyes.

So of course, not only did she look up at me,

but she was looking around at things in general. Like when I

had her on my hand she looked around.

She would tilt her whole body to look at

different things. Clearly paying attention to the world around

her

With how she looked around, with obviously

her really good vision, she felt more like a little cat than like

a spider.

You know, at that moment I felt connected to her as individuals.

It was a connection about a common way of seeing the world.

But as I became a biologist, and I learned more about evolution,

I came to understand that we were connected, of course, by

more than that — because we're all part of the same

evolutionary tree. We are relatives. And so there must

have been a moment, which we now think is maybe about 600 million

years ago, where there was an ancestor common to both of us.

That is to say that once upon a time, the

ancestor of Wayne and the ancestor of this tiny spider

were siblings — both part of a population of ancient animals,

probably small, bilaterally, symmetrical wormy things living

in the ocean, when something happened, that caused that one

population to split into two.

That was a Divide Creek moment. So that for

whatever reason, one of the subpopulations became isolated,

and it evolved and changed. And eventually it diversified into

many, many thousands, and in fact millions of different

species, including snails, and insects, and spiders, and so

forth, and including, therefore, the spider that was on my hand

then. And going back to that ancestral worm, the other

population that split off from it, starting at the beginning,

looking almost exactly the same ended up evolving and

diversifying into many thousands of things, including humans,

including me.

And so he kept this spider as a pet, and fell

in love. And of course, as a budding taxonomist, the first

order of business was to give her a name.

So I had to first of all figure out what she

was, in terms of human names, what species. So I went, and I

looked in a bookstore. They had the little golden nature guides,

and there she was Phidippus audax. That was her species. But

because her name was Phidippus audax, her species name, I

called her Phiddy. So she was Phiddy.

Audax, a species in the genus Phidippus, in the

family Salticidae — a family of tiny arachnids, also known as

jumping spiders.

The rest of that summer, I started noticing

jumping spiders on houses, on bushes, on fences on trees, and

I realized that there were lots of different species.

They were all recognizably related.

They all shared these great big eyes, they all

reacted to the world like a cat. And yet,

They were also radically different from each

other. With all sorts of spectacularly weird shapes and

colors.

Some of them were small and striped, some of

them had metallic pink rear ends, some of them had green

bits, some of them are longer and thinner, and so forth. It

was an incredible diversity, all of them being jumping spiders,

all of them having this behavior.

So you you said that they come in all different

shapes and colors, but um, do they also come in all different

sizes?

No, basically, as a rule, no jumping spider is

very big. And they're all harmless to humans. You know,

most wouldn't even be half as wide as your pinky nail.

Got it. Okay, these are not not huge spiders.

Yeah, they're teeny tiny.

One of the things that I learned that

summer was that you don't have to go to exotic tropical places

to find absolutely gorgeous, spectacularly beautiful

biodiversity. Here in Vancouver on the beaches, There's this one

species, Habronattus americanus, that the males have these bright

red pom poms. And the face is this metallic mauve color.

Absolutely spectacular. They're so beautiful. And yet no one

knows that they're there because they're only half a centimeter

long. If they were birds, Vancouver would be famous for

them.

In a way, a lot of my career has been driven by this fascination

by biodiversity, and wanting to see all of the ways there are

for a jumping spider to be.

And as it turns out, jumping spiders — of which

Phidippus and Habronattus are just two subgroup — this is the

most diverse family of spiders on the planet at around 6000

described species that accounts for nearly 15% of all spiders.

Oh, wow. That's a lot of spiders. Good thing

they're small.

Yeah. And this is the group that Wayne focuses

on as a taxonomist, so we're going to spend the rest of this

episode talking about biodiversity in general by

talking about jumping spiders in detail, because they're just an

amazingly illustrative microcosm of evolution itself.

Okay, okay, we have these colorful, beautiful

charismatic divers, but very small spiders that make up a

fairly significant proportion of all spiders. But just backing up

for a sec, jumping spiders...?

They are called jumping spiders because they

jump. So I tend to think of their eyes as being their most

distinctive feature. But their jumping is used in combination

with their eyes for their prey capture behavior. They don't

build a web to catch prey.

Wait, what is a spider if it doesn't build a

web? Do they still spin silk?

So they use their silk for little cocoons

that they sleep in. They use silk to wrap their egg masses.

They use silk as these little draglines that they carry behind

them, sort of like a rock climber, in case they fall. So

they see very well, they sneak up on things, and then they

pounce using a really well executed jump.

Oh, they really are like little cats, aren't

they?

Yeah, you know, in in a number of ways,

actually. For example, those two big front facing eyes — thanks

to those jumping spider vision is even sharper than a cat's.

Which is pretty incredible for something that

small, because they're running against the physical limits of

how small the pixels can be, so to speak, and still get enough

light to detect the signal.

But there's at least one major distinction

between cats and spiders.

Like... like besides the number of legs?

Yeah. And that's how they jump. Cats basically

jump in the same way that we do with muscles moving bone and

joints to push off of the ground. But jumping spiders

don't have big muscley legs.

Right? How does it... how does it work?

It turns out that the power for the jumping

doesn't come from the legs themselves. The power from the

jumping comes from blood pressure rising quickly and

squirting into the legs and propelling the leg straight.

The powerful muscles that allow these spiders

to jump aren't in their legs, but in their heads.

And so it's actually a hydraulic jumping

mechanism that they use.

So in order to jump, they clench the muscles in

their head, push a bunch of blood into their legs, and off

they go,

They can jump quite precisely. They are known

to be able to jump and nab flies flying by. So they can nab flies

out of the out of the air.

But remember, these guys are teeny tiny.

The furthest they can jump that I've ever

seen is maybe about 25 centimeters. And that's an

Olympic jumping spider jump.

Usually their jumps are just a few

centimeters.

Little hops.

But that precise control also allows them to do

more than just jump. They sing, and they dance.

You're joking.

This amazing vision is not just used by the

spiders in catching prey, but it's also an opportunity for

them to communicate with one another.

The beautiful colors of these males and the complex ornaments

are used in these courtship dances — where the males display

in front of the females and the females use their excellent

vision to watch the males. In some species of jumping spiders,

like the one that Phiddy belongs to, the courtship behavior is

pretty simple. The males just stick the front legs out and

wiggle them around and sort of dance side to side a little bit.

And it's not much more than that. But in other species, it's

incredibly complicated! So complicated as to almost defy

description.

So just for a couple of examples, jumping

spiders have dance moves like the tick-rev and the foreleg

wave.

Oh, these have been named.

Yeah. Well, Wayne and his colleagues named

them.

Oh, got it.

Do you want to try them with me?

I would love to try them with you.

Okay, so we're going to do the tick-rev. So

bring both your front legs forward, up and over your head.

You mean my... you're talking about my arms?

Yeah.

Okay.

Okay. Now bring your wrists down, so your hands

point forward.

Yes.

Now, pop your hands up. That's the tick. Tick!

Tick!

Now, flap them forward, up and down as fast as

you can. That's the rev.

Revvvvvvvvv

Revvvvvv

I think I've done this in aerobics class before.

All right. All right. One more time. Tick!

Tick!

Revvvvvvv

Revvvvvvvvvvv

Tick!

Tick!

Revvvv

Revvvvvvv. Aaaaa I love it.

I'm glad. So let's keep it going and we're

going to do the foreleg wave. Bring your arms down a little.

Okay.

Keeping your hands pointing forward.

Okay.

But instead of ticking and revving, wave your

hands in circles from the wrist.

Which... which direction do I wave my hands in

here? Do I wave them together or opposite directions?

Well, different spiders have different dances.

So whatever feels right.

There's almost as much variation among jumping

spider species in their dances as there is among their

appearances. Of course, they've got eight legs, they've got

these palpae up front, and they've got an abdomen. And so

there are lots of things that they can wiggle and move. So

they'll rotate their little pelvis in little circles.

They'll flick the front legs, they'll shuffle the third legs,

they'll be moving the abdomen up and down. And so all these

different body parts can be moving in different times and

different sequences in different ways. And if you think you get

confused, when you try to do the Macarena, just be thankful

you're not trying to do these jumping spider dances because

it's much, much more complicated.

And these tiny, intricate dances are taking

place all around us all the time.

This is happening in people's backyards

all across North America. Like they're just these little birds

of paradise that are hopping around people's backyards.

Okay, so they dance. And you also said that...

that they sing?

In a manner of speaking, they vibrate.

It almost sounds like a cat purring

Yeah, or a motorcycle.

If a cat was a motorcycle!

That clicking is not actually being done by the

first legs, even though it looks like it might be. The first leg

simply are synchronized with the part of the body that is making

a noise, which is the abdomen. The way that his abdomen is

making that noise is a combination of stridulation — so

he's rubbing the front of the abdomen against the back of the

carapace — but a lot of the noise is coming just from the

inertia of the flicks of the abdomen, being transmitted

through the body, through the legs and so that it's he's

basically making his feet pulse up and down against the

substrate. So these displays are better thought of as not as

acoustic, but seismic.

And because of that, you can't really hear

these songs with your naked ears, which also makes them

really hard to document. Instead of a microphone, these

recordings were made with a laser that measures changes in

the surface deflection of whatever the spider is standing

on.

So jumping spiders don't really have great

ears in terms of anything that would hear through the air. And

primarily, they sense vibrations through the ground, so that

they're feeling the ground shaking by how it affects their

legs.

And despite accounting for nearly 1/6 of all

spider species, jumping spider songs are almost completely

undocumented. When people have heard about jumping spiders,

they usually know about the dances, but almost never about

the songs. Both the songs and the dances are part of the same

courtship performance. Each dance motif is paired with a

pattern of vibrations. And it would be really easy to assume

that they were making the sound directly by moving their legs,

but they're really just amazingly well synchronized.

That's so wild.

And you could say the songs are

pre-programmed. The structure of them is pretty consistent

between performances. And they're similar between closely

related species. But there's evidence that female jumping

spiders prefer... novelty! They respond better to a song and a

dance that they haven't seen a million times before.

Yeah they're just like us.

In some ways. One thing I think it's

particularly amazing is that in the most complex performances,

there are certain sections where individual spiders will

apparently improvise — almost as if they're covering a jazz

standard.

Within a group of say 5, 10, 20 species,

they're all playing basically the same genre — they're all

playing jazz, basically, right in a particular genre of jazz.

But they'll use the elements with different numbers of

repetitions, or maybe a little extra note in there or something

like that. But it's the same basic thing. Whereas the next

group over will be big band.

And when jumping spiders evolve to be showy, they

really go all out.

So the most complicated colors and ornaments

are held by the species that have the most complicated

movements, and the most complicated songs.

The ones with the most complex songs can

perform for over an hour! And again, we're talking about a

spider that might just be the size of a pea. So while we don't

see a huge amount of creativity across individual spiders,

the creativity comes at the evolutionary level,

as natural selection generates new variants of the displays.

And so there is creativity in the system, but it's more at the

broad level across millions of years among species, and not at

the actual individual spiders inventing new little songs.

But when we step back to observe the group of

species...

The fact that the lineages that are doing

this, that are holding these patterns are also beautiful,

each in their own way, that each has this amazing set of

structures and colors, and behaviors and noises and

everything,

You might say, nature's creativity,

It's just stunning.

Pretty early on, as I was getting into jumping spiders, I

started drawing them. And for me, it was not only just an

expression of an artistic side that I've always had, but it was

also a way for me to celebrate these organisms that I just

thought were so cool. Eventually, that turned into

biological illustrations for the sake of documenting the

differences among all these species. And I, of course, I

built up a bigger and bigger library of all these drawings.

And I remember at some point, as I was putting these together

into a single big illustration representing the diversity for a

publication, that I could see all these little parts of the

spiders that I had drawn, and they were all arrayed like that.

And it suddenly struck me that the spider bits had sort of

patterns to them, there was a sense to them.

That is, although they were very

different, there was something in those differences that was

recognizable.

You know, maybe it's easier to think about it

was something that people know, like an orchid or something like

that, like you look at an ark and you say, oh, that's an

orchid, right? And you can look at a different species of

orchid. And it's like, oh, it's clearly an orchid, but it's

different, right? And you get to see what you can compare. Oh,

that's that bit. That's that bit. But you can see how those

bits differ. And so you start to notice that this is variations

on a theme. And that variation, as you look across species

starts to feel like a little bit like a dance. It's obviously a

very different dance from the dance at the spiders do in their

lifetime.

But this evolutionary dance is more than

just endless variation. Because sometimes creeks divide, and

then later reunite. That's after the break.

You know, these Divide Creek moments in

evolution where a lineage splits in two, and then each

diversifies. You look at one of the points, of jumping spiders,

and another point, humans — we're so different in so many

ways. You might think, "Oh my gosh, evolution is just all this

chaotic diversification." And then you look within jumping

spiders and how much diversity there is in jumping spider

dances "Oh my gosh, it's just constantly diverging,

everything's different from everything else." And yet at the

same time, as you're getting this divergence, many of them

are also finding common solutions.

So understanding the dance of evolution isn't

just about appreciating variation. Sometimes organisms

will each take different evolutionary journeys, and still

end up in a remarkably similar place. In a word, they converge.

Right. Convergent evolution.

Right, yeah. And maybe you've heard that there's

kind of a meme about how all sorts of animals keep evolving

into crabs.

It has been brought to my attention, Mendel,

that we are all heading inevitably towards crab.

Crabs have happened at least five separate

times now. So to kind of build on our metaphor of Divide Creek,

we've got these two blobs of water, they hit a rock in a

stream, go their separate ways and find themselves in different

oceans on opposite sides of the planet. Then maybe eons later,

subject to the wind and the whims of the currents. They are

eventually reunited.

And eventually, both of them will be crabs.

Yeah, maybe.

Am I following?

Yeah, yeah, but, but in jumping spiders, you can

see a whole set of really vivid convergences. For example,

depending on where certain species live, you know, either

mostly on tree trunks or in vegetation. They'll take on

certain typical body forms.

Sure.

But there's also apparently a really strong

pressure for a jumping spider to pretend to be an ant! 14

different genera of jumping spiders from all around the

world, separately evolved into near perfect ant mimics. Their

bodies become long and skinny. And sometimes they grow whole

fake heads and eyes, or they'll wave their forelegs around like

antenna.

You're saying that while the rest of us may be on

an inexorable trend towards crab, jumping spiders are headed

towards ant.

Yeah, some of them, at least. And this ant

mimicry has happened over and over across jumping spider

evolution. But it doesn't stop there. Some jumping spiders have

independently evolved color vision.

Jumping spiders can see color, but in a limited

way for most species.

So most spiders can only see green and

ultraviolet light

Sort of the equivalent of a human being

colorblind. There are though some jumping spiders that have

evolved a color vision probably as rich as ours.

What's really incredible is that they've

accomplished this in different ways.

But only in a few groups. One of them is

Habronattus, a group that I've looked at a lot.

Habronattus is a mostly North American genus,

also known as the paradise jumping spiders, many species of

which have red ornaments on their legs or their faces,

despite the fact that they have exactly zero photoreceptors

sensitive to the color red.

But instead, they've sort of hacked their

green photoreceptors in a way to be able to see red by putting a

red filter over some subset of those green photoreceptors. On

the other hand, some other groups of jumping spiders have a

different solution to a richer color vision. And so the peacock

spiders, genus Maratus have instead done it in sort of the

more traditional way to add colors, which is to add extra

sensitive photoreceptors.

Incredible.

And remember how you asked which way to wave your

hands while we were doing the spider dances?

Yeah?

There there are actually convergences there as

well. Several different lineages of spiders have independently

evolved asymmetrical dance moves, despite theories that

sexual selection favors symmetry.

Are the ones like in the southern hemisphere, like

they go one way and the ones in the northern hemisphere go the

other way?

I don't think so.

Has anyone checked?

Probably not? That's a PhD right there. But

speaking of sexual selection, it could be that many of these

other evolutionary patterns, especially the ones that seem to

be important for these courtship rituals, are connected to

another convergence. Just one that's a little harder to see...

Their sex chromosomes.

Their sex chromosomes. Stay with me here.

Well, you said the word sex, and then you said the

word chromosomes, so I'm torn. I hate to admit it, but my, my

cellular bio is a little rusty.

Well, if I may?

By all means,

In your body, inside the nucleus of every

cell, you've got a copy of your DNA, and that DNA is tightly

coiled up and split into separate chunks. Those chunks

are your chromosomes.

Okay, yeah, I can keep up with this.

Each chromosome is part of a matched pair, half

your chromosomes are from one parent, half her from the other.

I'm with you.

The overall set of chromosomes is shared by

every member of your species, except for the sex chromosomes,

which occur in two different forms so called X and Y. Without

getting into gender, which is a subjective experience slash

social construction, or the spectrum of genetic exceptions

to this binary, sex chromosomes in mammals, humans included, are

typically an XX pair in females, and typically an XY pair in

males.

Yeah, the X chromosomes, which are the nice

long, fully formed ones, and then the Y one, which is like

the runty little fragment of a chromosome.

Yeah.

Okay. This I understand — humans, XX, XY.

That's us. What about the jumping spiders?

Well, most spiders, you can think of it as

being a little bit the same. I mean, obviously, the the basic

idea of having chromosomes it's the same as with mammals. The

way it works in mammals is that that Y chromosome typically

doesn't do a lot. And so you could almost dispense with it,

right? You could always imagine the few functions it does, they

move somewhere else. And then you've just got the X all by

itself. In which case, if you were to dispense with it, you

could make something where the males have only 1 X, and they

don't have the Y anymore, and the females have their two Xs,

and maybe that system could work.

And in fact, that's what exactly spiders do. And so some of them

have a single X in the male and two Xs in the female, others do

a little duplication thing. So they've got two Xs in the male

and four Xs in the female. But one way or another, it's just

about how many Xs you have.

This arrangement of sex chromosomes, in spiders in

general, and in jumping spiders, in particular, it's actually

generally pretty constant. Most species are like this. But every

so often, you find a group of spiders, where are they suddenly

do something different. And that's the way it is in

Habronattus. In Habronattus, it's clear that their ancestors

had this two Xs male, four Xs female system, but a number of

them have evolved something else where they have either two or

three Xs and a Y chromosome! This Y chromosome has evolved in

Habronattus at least eight times in different lineages, possibly

as many as 15 times.

Within just this one genus of Habronattus, there

are four different versions of male sex chromosomes — from a

single X up to three X and a Y.

Okay, I get it sex chromosomes are weird. But

what's the relationship between this and all the other

convergences we were talking about?

Okay, so I, I want to preface that that this

part is theoretical, and doesn't necessarily apply to mammals and

humans. But it could boil down to a sexual conflict between the

different versions of certain genes.

What do you mean by that?

So males and females are really different in all these regards.

Of course, when we're talking about these

And as each of these features of males and females were evolving,

courtship features, the dances and the ornaments and songs and

so forth, males and females are different in these — males have

them, females don't. What the females have instead is probably

there's a really good chance that there was a time, a moment

this whole array of invisible preferences that we can't see,

right? So they've got their own things, but they're harder to see.

when the feature that was appropriate for one sex was

coming in, and it might have been a problem for the other

sex.

So you could think of an example, for instance, where a

mutation happens that would generate a red face. If the

little males could think about it, which they don't, they would

say "woohoo! I get to have a red face," right? And the females

would say "oh, my gosh, I don't want a red face, I don't want to

be so visible to predators." So that red face could be

advantageous in males and disadvantageous females.

But if there was then at that point the change in chromosome

organization that generates the Y chromosome, it turns out that

the variant that's good for males could be isolated to the Y

chromosome, and the variant that is good for females could stay

on what will then become the X. And that can allow the males to

have a red face and the females to have a white face. And so it

resolves that conflict. And that means that that chromosome

change can be selected for — it can be advantageous, it can

spread. And thus the species acquires this Y chromosome.

because it was a useful thing to resolve this conflict between

the interests of the males and the interest of the females.

So a Y chromosome could be a way for the spiders

to develop sexual dimorphism. And that would give you colorful

dancing males and less colorful but highly discerning females,

just like you see in many birds.

No, not exactly. There are lots of sexually

dimorphic jumping spiders that don't have a Y chromosome. In

fact, it's actually really interesting here, because it's

the exception, not the rule.

So for what it's worth, it turns out that when

you look at the data for animals, there is only one other

case that seems to have even close to this density of Y

chromosome evolutions. It's some lizard case. But it's like this

is like hugely rare to have this many origins in a small

phylogenetic space.

But this mechanism could play a part in

reinforcing the especially strong dimorphism that we do see

in certain genera, like Habronattus.

One of the hints, even though we don't have

really good data, that this is what's happening in this group —

when you look in Habronattus, those groups of species that

have the most complex courtship dances are in fact those that

seem to have evolved the Y chromosome most often.

And the spectacular thing is when you see convergence, as you

do with jumping spider dances, and chromosomes and so forth, is

that you start to realize that there are certain repeated

patterns. And those repeated patterns show up in one lineage,

they show up in another lineage, they show up in another lineage.

And there might have been a certain sequence in each case.

When you start to think about it like that, and think about these

changes through time, in consistent sequences full of

counterpoint and harmony, you start to feel as if each one of

these lineages is an instrument, and that all of these branching

lineages of evolution, therefore, are just like this

giant orchestra playing this most amazing symphony.

And like a symphony, evolution isn't

completely random. But it also isn't completely predictable.

There are similar evolutionary sequences, motifs and melodies

that come again and again. There's harmony, rhythm,

repetition. And yet, there are surprises everywhere. To Wayne,

this was a shift in perspective not unlike looking up at the

stars at night, and realizing that the Milky Way isn't just a

dusty stripe across the sky, but it's something gigantic, that

we're all inside of.

And after a while of feeling this way — of imagining this

grand symphony — Wayne got to thinking...

What if somehow I could hear it?

That's coming up in part two.

Music in this episode was produced by Elisa Thorne, Curtis

Andrews, West McClean, Patricia Wolf, Sunfish, Moon Light, and

me, Thumbug. All the jumping spider audio recordings you

heard came courtesy of Dr. Damian Elias and his lab at UC

Berkeley. This series of Future Ecologies was produced by me,

Mendel Skulski, with help from my co-host, Adam Huggins and our

guest, Wayne Maddison. Special thanks to Teresa Madidson for

first introducing me to Wayne's story, and for helping us tell

this one. And thanks to Leya Tess for the amazing cover art.

You can hear Part Two right now. Follow Future Ecologies wherever

you get your podcasts, or visit us at futureecologies.net.

Funding for this episode was provided by the Canada Council

for the Arts. But ongoing support for this podcast comes

from listeners just like you. To keep this show going, join us at

patreon.com/futureecologies. And if you like what we're doing,

please just spread the word. It really helps.