- [Matt] Clams usually have one line of defense
against a predator, their tough shells,
but this researcher,
- My name is Dr. Lindsey Dougherty.
- [Matt] just discovered that this clam, the disco clam,
may have a unique defense mechanism,
[disco music]
a mesmerizing light show.
- [Lindsey] The fact that this clam was opening
in the middle of an attack
to flash at the predator made no sense to us.
- [Matt] Especially given that the predator
is the fearsome manta shrimp,
known for its incredibly powerful punch.
- I got hit once and was bruised for a month.
- [Matt] But when the disco clam meets a manta shrimp,
Dougherty discovered something bizarre.
- [Lindsey] The manta shrimp itself, they actually went
into a catatonic state for up to 15 minutes.
- I think this is one of the greatest match-ups
in the animal kingdom.
Can you talk about the combatants we have on both sides?
- They're two very popular and very unique creatures.
Manta shrimp are not technically shrimp,
their taxonomic group is stomatopods,
so there are two main types.
There are smashers, which smash things,
so they usually feed on hard-bodied prey,
things like clams, snails.
And then there are spearers,
which look like the Edward Scissorshands, I suppose,
of the underwater world.
In this case, because we're dealing with a clam,
or a hard-bodied predator,
we studied the smashing manta shrimp,
which can actually hit at the speed of a six-caliber bullet
and cause cavitation under water,
so it's a quite unique strike.
- It does strike with such force
that it causes these cavitation bubbles.
Can you walk us through what those are,
and what happens when they explode?
- The easiest way to explain it is
that they essentially boil the water.
It's actually creating an area of low volume
that creates this boiling,
and when that bubble collapses it actually can create
a shockwave that can stun their prey items.
They can actually break aquarium glass.
We had this happen.
It's a very interesting evolutionary adaptation
to feed on things that are traditionally hard to get at,
like a clam that has a thick, calcium carbonate shell.
- Switching to the clams, what is a disco clam,
and why is it called such?
- A disco clam is a type of file clam.
Disco is a colloquial term.
People also call them flame scallops
or electric scallops.
They are technically a clam, not a scallop,
but they live in the Indo-Pacific on coral reefs,
and what they typically do is they find
a small hole that they can get inside,
and they'll use bissell threads to attach themselves
inside that hole, and then they'll stick out their tentacles
and they'll be flashing any time there's ambient light.
One side of the issue is reflective.
It actually has tiny silicon nanospheres,
which if you think about it,
are essentially like teeny tiny disco balls
inside their tissue that are really effective
at reflecting light.
And then on the other side, it's absorbent.
They basically show the reflective side and then hide it,
almost like an audience doing a wave at a football game.
And that's why, to our eyes, when it happens very quickly,
it looks as though they're flashing.
They speed up when you scare them or give them food,
so anything that excites them will speed up
that flashing display.
- This is fundamentally different
from how most other critters in the sea
that produce light are going about it.
How is this different from bioluminescence?
- A lot of people actually thought
it was bioluminescence initially.
The difference is you can see it during the day,
and usually bioluminescence isn't bright enough
to be seen during the day.
This is based fully on structure within the tissue,
whereas bioluminescence is a chemical reaction
that actually produces light instead of heat.
Yeah, it's quite different, it's quite unique.
- And you did a study recently that looked at this match-up
between the manta shrimp and the disco clam.
What did you find in this study?
- The most interesting interaction was the disco clam
opening mid-attack.
When you think about a clam,
usually their best line of defense is their shell, right?
They can close very tightly, as anyone who's ever tried
to open one knows.
The fact that this clam was opening
in the middle of an attack to flash at the predator
made no sense to us.
That's your best line of defense when you're being attacked
by this voracious predator.
The manta shrimp itself also has a very strange reaction
to that red, external tissue.
They actually went into a catatonic state
for up to 15 minutes.
- Given that the manta shrimp
goes into this catatonic state, might that open it up
to its own predation?
That's this weird symptom of the disco clam
doing its thing, and then the predator itself gets eaten.
- There's clearly something going on
that the manta shrimp is very unsure of
when they encounter this tissue, so that's why
we wanted to look at the tissue further
and see if we could figure out what was going on
that made it so unique and unpalatable.
- The manta shrimp is famous for being a voracious predator,
it's eating a lot of different things in the sea.
Are there any indications that it's off-put
by any other potential prey items other than the disco clam?
- They're not what I would call picky eaters.
I know my PhD P.I. fed one a blue ring octopus,
which has enough tetrodotoxin to kill eight adult humans,
so not something most people would willfully eat.
The fact that we saw this strange interaction
with the disco clam fascinated us
from a behavioral point of view
because there's just not much that will throw off
the manta shrimp, especially to the point
of going into a catatonic state
and cleaning their mouth parts and just clearly
being very annoyed at what they were encountering.
- I think it's also interesting
because these are intelligent, as we can define it,
creatures that I've seen them actually blow limbs
off of crabs and things like that.
They're crafty animals, and it's just interesting
to see them fall to pieces when they come across
a disco clam.
- Yeah, so they can be very manipulative
with the morphology of any creature that they encounter.
I think they have to be in order to get various things open,
and avoid getting hurt themselves
while they're predating upon something.
To see them not only go catatonic, but just seem
to be completely lost, I don't know how to deal
with this bright red clam that's flashing at me,
I don't know what to do with this.
It's a pretty fascinating behavior to encounter.
In general, animals usually don't do something
unless there's some sort of benefit to them, right?
You don't want to expend too much energy
unless it benefits you in some manner.
And it's not always the case, but most of the time
that's true, so it could be that this flashing
is just a really catchy evolutionary thing
to show predators, don't eat me, you'll regret it.
- I was actually gonna ask about the evolutionary side
of things.
Could it be that the disco clam has evolved this defense
specifically for something like a manta shrimp,
to be able to confuse it?
- One thing that's really important in animal behavior
is to remember to consider the visual capability
of the predator you're assuming is attacking.
All of these different groups that could potentially eat
disco clams all have different visual capacity.
Manta shrimp in particular have up to 16 photo receptors,
which we as humans have three,
so they've got us a little bit beat there.
This is an Indo-Pacific species that has evolved
this display, and Indo-Pacific reefs are incredibly colorful
and you have to do a lot to stand out.
If you're trying to advertise that you're poisonous
or distasteful, you have to be creative in order to do it.
- Given the uniqueness of the structure in the disco clam
that's producing this light,
might there be some inspiration here for human designs
for disco balls or otherwise?
[Lindsey laughs]
- A disco clam disco ball.
Yes, I like to say that anything we can do,
nature does better.
There's a lot that we can learn about structural coloration
from things like morpho-butterflies that use
a very specific interaction between tissue and light
in order to create really amazing displays of color.
There's actually a qualcomm display
that's based on movable mirrors that can create
more light when there's a bright light outside.
If you think about using a tablet,
if you're trying to read a book on your tablet,
and you go outside and there's too much light,
you suddenly can't see the screen.
If we learn from nature and how animals
use structural coloration, given more ambient light,
the screen can actually get brighter
if that screen itself can interact with the light
that's coming in.
With disco clams, we initially studied the size
of the silicon nanospheres,
their spacing against one another.
All of that showed us essentially that they're optimized
for a blue light environment, and that they're reflection
is really quite impressive for a natural animal.
In spectrometry we look at something
called a white standard, which essentially should reflect
every color of the visible spectrum, which gives you white.
The disco clam was quite close to that ideal standard,
and it's pretty amazing to have a reflector
that is that powerful, especially under water
where your light environment is quite limited.
In the ocean, being able to reflect
the entire visible spectrum is particularly impressive
because red light attenuates so quickly,
as do other wavelengths as you go little bit deeper.
The thing that I was most interested in
is the actual flashing display,
and unfortunately, the disco clam is the only bi-valve
I know of that has anything like that.
In a perfect world, I would love
to look at different potential predators
and see how they measure up against the disco clam,
but yeah, it's something we can potentially do
in the future.
- Generally speaking, the disco clam is staying alive?
[Lindsey laughs]
I'm sorry, I'll show myself out now.
[Lindsey laughs]
Thanks for being here with us.
- Thanks for having me.
[disco music]