Mycologist Explains How a Slime Mold Can Solve Mazes

Maybe you've seen the pictures.

It's a yellow organism that looks a bit like a fern,

or maybe a coral, or maybe a moss.

But really it's something called a slime mold,

and when the Paris Zoological Park

put one on display recently, calling it the Blob,

the internet got itself in a tizzy.

It may look simple, but this brainless organism

can actually make decisions and solve mazes.

To learn more, we sat down with mycologist Anne Pringle

at the University of Wisconsin.

What is this, quote unquote, Blob?

The Blob is a species of slime mold.

People are calling Physarum polycephalum the Blob,

and it's a species.

It's not a plant, it's not an animal.

It's not a fungus.

Outside of those three kingdoms

that we're really familiar with,

there are all these other kids of organisms,

a lot of different groups,

that we're just less familiar with

but they're really diverse.

They play important roles in our environment,

and Physarum is characterized by this

part of its life cycle called the plasmodium,

which is basically a giant, enormous cell.

I like this idea of a slime mold

as completely defying human expectations,

and I guess by extension, befuddling the internet of late.

Was that surprising?

All of a sudden, the Paris Zoo put this on display

and it just blew up.

For me, it's exciting.

It gives lots of people lots of opportunities

to talk about a subject that, you know.

Gosh, when I go to a cocktail party,

I'm not sure a lot of people really wanna hear

about Physarum, or at least it takes a while to get into it.

And having the Paris Zoo,

and I don't know who made that decision or how they made it,

but it feels brilliant to me,

to be able to put something so different out there

and say gosh, look at it.

What is it?

How do we think about it?

How do we talk about it?

And no, I'm not surprised.

I think when I teach my class in biology the fungi,

there are a few comments that I consistently get.

One comment is, I see them all the time now.

In a way that you can't see it

unless you're taught to see it.

And so if you're taught to see it,

then all of a sudden, everywhere you go,

there's a fungus, which is true.

Everywhere you go, there is a fungus.

And then a strong reaction I get is amazement.

How did I not know this before?

How come no-one told me about this before?

So I'm not surprised by that reaction,

and it's also pretty fun to watch it play out.

Is it particularly rare?

And where do you find it?

There are lots of species of Physarum, more than 100.

And if you went to your local woods

and it was the right time of year and a moist habitat,

you'd absolutely find it yourself.

Most people think of a cell as

this really tiny thing you can't see,

but this is one giant cell.

Can you walk us through how it operates

as one big cell with many, many nuclei within?

We understand some answers to that question.

There are other things that we don't know.

So, we do know that there are no cross-walls.

No septa, no barriers of any kind

inside that giant cell.

So fluids can flow across the body very easily,

and that's obviously really different from us.

This is a very, very tiny plasmodium,

and a drop of water just got put on the right hand side,

and now can you see this rhythmic contraction?

Yes. And then there's

another drop, but that's food.

Can you see the tips swelling?

And then just watch, and you'll see waves

pulsing across the body.

So, those waves are caused by peristolsis,

which is basically rhythmic contraction.

Expansion, contraction, expansion, contraction, expansion,

that moves fluids, and we think information,

across the body.

How Physarum communicates across itself,

how it integrates information,

and coordinates behavior, has to do with

some kind of signaling molecule

that's propagated in a very particular way.

What that signaling molecule is, it might be calcium.

It might be something else. Can we talk about

how the organism is, in a sense,

exploring its environment in the way that

it's almost pathfinding in an environment?

It is pathfinding.

And I think that's part of the buzz around it, right?

People hear about it, and they hear things

like it has so many sexes, and it forages,

and that comes across as a really remarkable behavior.

And I think that's because we tend

to associate a word like behavior

with something like a dog or an animal.

But here, clearly, there's an organism

that's moving around and it's foraging.

It's sensing in its environment,

for example, where there are resource-rich patches.

It doesn't have eyes.

It doesn't have the kind of sensory apparatus

that we're used to, and so in some sense

its foraging has to do with sending out tendrils,

if you will, or parts of itself,

to explore the surrounding habitat.

And that's really what it's doing

in all of these experiments

that have to do with getting Physarum

to grow in particular ways, mimic the optimal network

that would connect the rail stations of Tokyo

or state capitals of the United States, or et cetera.

It's really growing across a lot of space,

and then it's reorganizing itself

into a configuration that allows it to optimally eat,

and eventually optimally reproduce.

Anne, it's hard to talk about intelligence

with an animal like this, 'cos we have so many

concepts around intelligence.

We base it so much on humans and other animals.

But this isn't like it knows it's in a maze,

it's gonna solve the maze.

It's doing what it would typically do

in a natural environment.

It absolutely is doing what it would typically do

in a natural environment.

When people think about Physarum solving a maze,

what a lot of people think Physarum is doing

is solving the maze the way you or I would solve a maze.

It starts at point A,

it finds the shortest route through the maze,

and it reaches point B.

That's not what Physarum is doing.

Physarum grows through the entire maze.

It searches all that space.

Then it retracts its body just to the shortest path.

So, that's a really different way

of quote unquote solving a maze

than what we tend to think about.

And I think that's a really important distinction.

I find the world intelligence really problematic

like the word sex, just because both words

are so loaded with meaning,

and with meaning that has nothing to do

with the biology of fungi or fungal life organisms.

When we talk about sex in Physarum,

first of all, Physarum has a really complex life cycle,

or more complex than we're used to as humans,

and in a different part of the life cycle

there are single cells called swarm cells.

Those are the cells that,

when mating happens, they fuse.

And they fuse to become one body.

So, I love my husband very much,

but when we got married,

we did not fuse into a single body.

My body is here, his body is over in his office.

So it's a really different kind of process

when we're talking about mating for Physarum.

And basically, whether or not two cells

can fuse and form one body has to do with three genes.

And one of the genes there are 16 loci, at least 16.

And another there are 15, and another there are three.

So, if you multiply 16 times 15 times three,

you get 720 possible combinations,

and that's the start of this idea

that it has more than 700 sexes.

And then the giant plasmodium, when it reproduces,

the whole body turns into spores

that then disperse on the wind.

It's just a very different path.

So outside of a maze in a natural environment,

what are these organisms actually eating?

So, in the lab we feed it Quaker Oats,

and it seems to like the oats very much,

and it actually seems to eat the oats,

and digest them down into little bits

and discard bits of it out of its body.

In nature, we think that it's hoovering up

bacteria and fungal spores and other

really small creatures that are on the substrates,

the rock, or the woods, or the mulch that it's growing on,

and engulfing them.

Where exactly in the tree of life

do these organisms fit?

Imagine that you were back in a time

where you were just looking at organisms.

Grouping organisms according to what they looked like.

Then you would quite reasonably

look at a Physarum, look at a slime mold,

and say, gosh, it looks a lot like a fungus.

And then something comes along called a PCR machine,

and we can start sequencing DNA,

and when you start sequencing DNA,

there's a massive rearrangement in our understanding of

how things are related to each other.

So we begin to understand that

slime molds are not the true fungi, as we call them,

even though they're fungal-like organisms,

but they're something really apart.

And so at this point I would say

it's one of the most exciting areas of biology,

is we know what plants are, more or less.

We understand what animals are, more or less.

Fungi, maybe less than more, but

we think we know what fungi are.

But then there are all these groups of organisms

that aren't any of those three,

and even more interestingly,

we don't have a sense of their biodiversity.

There're very few people who study

the biodiversity of slime molds.

It's genuinely fun to talk about this stuff.

Also because, I think, the language around

intelligence and maze-solving

is fantastic in its own way, but for me

it also just becomes a tool to talk about

some much larger issues about biodiversity

and what do we know about this earth that we're living on,

and what do we not know?

And to me, it seems like we don't know quite a lot.

And it would be fantastic to have

more people involved and thinking about

how many slime molds are there in my woods?

Gosh, is it a local Physarum?

Et cetera.

So, it seems a real opportunity.

Thank you for being here and

bringing up all these crazy philosophical questions

about a seemingly simple organism.

My pleasure! [chime ringing]