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TED2014

Ed Yong: Zombie roaches and other parasite tales

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In this fascinating, hilarious and ever-so-slightly creepy talk, science writer Ed Yong tells the story of his favorite parasites -- animals and organisms that live on the bodeis (and brains!) of other organisms, causing them to do their bidding. Do humans have them too? Maybe ...

- Science writer
Ed Yong blogs with a mission: to ignite excitement for science in everyone, regardless of their education or background. Full bio

A herd of wildebeests, a shoal of fish,
00:12
a flock of birds.
00:15
Many animals gather in large groups
00:16
that are among the most wonderful spectacles
00:18
in the natural world.
00:20
But why do these groups form?
00:22
The common answers include things like
00:25
seeking safety in numbers or hunting in packs
00:26
or gathering to mate or breed,
00:29
and all of these explanations,
00:32
while often true,
00:34
make a huge assumption about animal behavior,
00:35
that the animals are in control of their own actions,
00:38
that they are in charge of their bodies.
00:41
And that is often not the case.
00:43
This is Artemia, a brine shrimp.
00:47
You probably know it better as a sea monkey.
00:50
It's small, and it typically lives alone,
00:52
but it can gather in these large red swarms
00:54
that span for meters,
00:57
and these form because of a parasite.
01:00
These shrimp are infected with a tapeworm.
01:03
A tapeworm is effectively a long, living gut
01:06
with genitals at one end and
a hooked mouth at the other.
01:08
As a freelance journalist, I sympathize.
01:11
(Laughter)
01:13
The tapeworm drains nutrients from Artemia's body,
01:15
but it also does other things.
01:18
It castrates them,
01:20
it changes their color from transparent to bright red,
01:22
it makes them live longer,
01:27
and as biologist Nicolas Rode has found,
01:28
it makes them swim in groups.
01:31
Why? Because the tapeworm,
like many other parasites,
01:34
has a complicated life cycle
01:37
involving many different hosts.
01:39
The shrimp are just one step on its journey.
01:41
Its ultimate destination is this,
01:44
the greater flamingo.
01:46
Only in a flamingo can the tapeworm reproduce,
01:48
so to get there, it manipulates its shrimp hosts
01:51
into forming these conspicuous colored swarms
01:54
that are easier for a flamingo to spot
01:58
and to devour,
02:00
and that is the secret of the Artemia swarm.
02:02
They aren't sociable through their own volition,
02:05
but because they are being controlled.
02:07
It's not safety in numbers.
02:09
It's actually the exact opposite.
02:11
The tapeworm hijacks their brains and their bodies,
02:13
turning them into vehicles
02:16
for getting itself into a flamingo.
02:17
And here is another example
02:21
of a parasitic manipulation.
02:22
This is a suicidal cricket.
02:25
This cricket swallowed the
larvae of a Gordian worm,
02:28
or horsehair worm.
02:31
The worm grew to adult size within it,
02:33
but it needs to get into water in order to mate,
02:35
and it does that by releasing proteins
02:38
that addle the cricket's brain,
02:41
causing it to behave erratically.
02:43
When the cricket nears a body of water,
02:45
such as this swimming pool,
02:47
it jumps in and drowns,
02:48
and the worm wriggles out
02:51
of its suicidal corpse.
02:52
Crickets are really roomy. Who knew?
02:56
The tapeworm and the Gordian worm are not alone.
03:00
They are part of an entire cavalcade
03:03
of mind-controlling parasites,
03:05
of fungi, viruses, and worms and insects and more
03:07
that all specialize in subverting and overriding
03:11
the wills of their hosts.
03:13
Now, I first learned about this way of life
03:16
through David Attenborough's "Trials of Life"
03:17
about 20 years ago,
03:20
and then later through a wonderful book called
03:22
"Parasite Rex" by my friend Carl Zimmer.
03:23
And I've been writing about
these creatures ever since.
03:26
Few topics in biology enthrall me more.
03:28
It's like the parasites have subverted my own brain.
03:31
Because after all, they are always compelling
03:35
and they are delightfully macabre.
03:37
When you write about parasites,
03:38
your lexicon swells with phrases like
03:40
"devoured alive" and "bursts out of its body."
03:42
(Laughter)
03:45
But there's more to it than that.
03:46
I'm a writer, and fellow writers in the audience
03:48
will know that we love stories.
03:50
Parasites invite us to resist the allure
03:53
of obvious stories.
03:55
Their world is one of plot twists
03:57
and unexpected explanations.
03:59
Why, for example,
04:03
does this caterpillar
04:04
start violently thrashing about
04:06
when another insect gets close to it
04:08
and those white cocoons that it seems
04:10
to be standing guard over?
04:12
Is it maybe protecting its siblings?
04:14
No.
04:17
This caterpillar was attacked
04:18
by a parasitic wasp which laid eggs inside it.
04:20
The eggs hatched and the young wasps
04:23
devoured the caterpillar alive
04:24
before bursting out of its body.
04:26
See what I mean?
04:27
Now, the caterpillar didn't die.
04:30
Some of the wasps seemed to stay behind
04:33
and controlled it into defending their siblings
04:35
which are metamorphosing
04:38
into adults within those cocoons.
04:40
This caterpillar is a head-banging
zombie bodyguard
04:42
defending the offspring
04:46
of the creature that killed it.
04:47
(Applause)
04:49
We have a lot to get through.
I only have 13 minutes. (Laughter)
04:53
Now, some of you are probably just
04:57
desperately clawing for some solace
04:59
in the idea that these things are oddities
05:01
of the natural world, that they are outliers,
05:04
and that point of view is understandable,
05:06
because by their nature, parasites are quite small
05:07
and they spend a lot of their time
05:10
inside the bodies of other things.
05:11
They're easy to overlook,
05:14
but that doesn't mean that they aren't important.
05:16
A few years back, a man called Kevin Lafferty
05:18
took a group of scientists
into three Californian estuaries
05:21
and they pretty much weighed and dissected
05:24
and recorded everything they could find,
05:26
and what they found
05:28
were parasites in extreme abundance.
05:29
Especially common were trematodes,
05:32
tiny worms that specialize in castrating their hosts
05:34
like this unfortunate snail.
05:37
Now, a single trematode is tiny, microscopic,
05:39
but collectively they weighed as much
05:42
as all the fish in the estuaries
05:44
and three to nine times more than all the birds.
05:46
And remember the Gordian worm that I showed you,
05:50
the cricket thing?
05:52
One Japanese scientist called Takuya Sato
05:53
found that in one stream,
05:56
these things drive so many crickets
05:58
and grasshoppers into the water
06:00
that the drowned insects
06:01
make up some 60 percent of the diet of local trout.
06:02
Manipulation is not an oddity.
06:06
It is a critical and common part
06:09
of the world around us,
06:12
and scientists have now found
06:13
hundreds of examples of such manipulators,
06:15
and more excitingly, they're starting to understand
06:17
exactly how these creatures control their hosts.
06:20
And this is one of my favorite examples.
06:24
This is Ampulex compressa,
06:26
the emerald cockroach wasp,
06:29
and it is a truth universally acknowledged
06:31
that an emerald cockroach wasp in possession
06:33
of some fertilized eggs
06:35
must be in want of a cockroach.
06:37
When she finds one,
06:39
she stabs it with a stinger
06:41
that is also a sense organ.
06:43
This discovery came out three weeks ago.
06:44
She stabs it with a stinger that is a sense organ
06:47
equipped with small sensory bumps
06:49
that allow her to feel the distinctive texture
06:51
of a roach's brain.
06:54
So like a person blindly rooting about in a bag,
06:56
she finds the brain, and she injects it with venom
06:59
into two very specific clusters of neurons.
07:01
Israeli scientists Frederic Libersat and Ram Gal
07:05
found that the venom is a
very specific chemical weapon.
07:08
It doesn't kill the roach, nor does it sedate it.
07:12
The roach could walk away
07:15
or fly or run if it chose to,
07:17
but it doesn't choose to,
07:20
because the venom nixes its motivation to walk,
07:22
and only that.
07:25
The wasp basically un-checks
the escape-from-danger box
07:26
in the roach's operating system,
07:30
allowing her to lead her helpless victim
07:32
back to her lair by its antennae
07:35
like a person walking a dog.
07:37
And once there, she lays an egg on it,
07:40
egg hatches, devoured alive, bursts out of body,
07:41
yadda yadda yadda, you know the drill.
07:44
(Laughter) (Applause)
07:46
Now I would argue that, once stung,
07:49
the cockroach isn't a roach anymore.
07:52
It's more of an extension of the wasp,
07:54
just like the cricket was an
extension of the Gordian worm.
07:56
These hosts won't get to survive or reproduce.
07:59
They have as much control over their own fates
08:02
as my car.
08:04
Once the parasites get in,
08:06
the hosts don't get a say.
08:07
Now humans, of course,
08:10
are no stranger to manipulation.
08:11
We take drugs to shift the chemistries of our brains
08:13
and to change our moods,
08:15
and what are arguments or advertising or big ideas
08:17
if not an attempt to influence someone else's mind?
08:21
But our attempts at doing this
08:24
are crude and blundering compared
08:26
to the fine-grained specificity of the parasites.
08:28
Don Draper only wishes he was as elegant
08:31
and precise as the emerald cockroach wasp.
08:33
Now, I think this is part of what makes parasites
08:38
so sinister and so compelling.
08:42
We place such a premium on our free will
08:45
and our independence
08:47
that the prospect of losing those qualities
08:48
to forces unseen
08:50
informs many of our deepest societal fears.
08:51
Orwellian dystopias and shadowy cabals
08:54
and mind-controlling supervillains --
08:57
these are tropes that fill our darkest fiction,
08:59
but in nature, they happen all the time.
09:02
Which leads me to an obvious
09:07
and disquieting question:
09:09
Are there dark, sinister parasites
09:11
that are influencing our behavior
09:13
without us knowing about it,
09:15
besides the NSA?
09:17
If there are any —
09:20
(Laughter) (Applause)
09:21
I've got a red dot on my forehead now, don't I?
09:25
(Laughter)
09:27
If there are any, this is a good candidate for them.
09:30
This is Toxoplasma gondii, or Toxo, for short,
09:33
because the terrifying creature
09:36
always deserves a cute nickname.
09:37
Toxo infects mammals,
09:40
a wide variety of mammals,
09:42
but it can only sexually reproduce in a cat.
09:43
And scientists like Joanne Webster have shown that
09:47
if Toxo gets into a rat or a mouse,
09:49
it turns the rodent into a cat-seeking missile.
09:52
If the infected rat smells the delightful odor
09:55
of cat piss,
09:58
it runs towards the source of the smell
09:59
rather than the more sensible direction of away.
10:02
The cat eats the rat. Toxo gets to have sex.
10:06
It's a classic tale of Eat, Prey, Love.
10:08
(Laughter) (Applause)
10:11
You're very charitable, generous people.
10:19
Hi, Elizabeth, I loved your talk.
10:22
How does the parasite control its host
10:25
in this way?
10:28
We don't really know.
10:29
We know that Toxo releases an enzyme
10:31
that makes dopamine, a substance involved
10:32
in reward and motivation.
10:34
We know it targets certain parts of a rodent's brain,
10:36
including those involved in sexual arousal.
10:39
But how those puzzle pieces fit together
10:41
is not immediately clear.
10:43
What is clear is that this thing
10:45
is a single cell.
10:47
This has no nervous system.
10:49
It has no consciousness.
10:50
It doesn't even have a body.
10:51
But it's manipulating a mammal?
10:53
We are mammals.
10:55
We are more intelligent than a mere rat, to be sure,
10:57
but our brains have the same basic structure,
10:59
the same types of cells,
11:02
the same chemicals running through them,
11:03
and the same parasites.
11:05
Estimates vary a lot, but some figures suggest
11:07
that one in three people around the world
11:09
have Toxo in their brains.
11:12
Now typically, this doesn't lead to any overt illness.
11:13
The parasite holds up in a dormant state
11:17
for a long period of time.
11:19
But there's some evidence that those people
11:21
who are carriers score slightly differently
11:23
on personality questionnaires than other people,
11:26
that they have a slightly
higher risk of car accidents,
11:29
and there's some evidence
that people with schizophrenia
11:31
are more likely to be infected.
11:34
Now, I think this evidence is still inconclusive,
11:36
and even among Toxo researchers,
11:39
opinion is divided as to whether the parasite
11:40
is truly influencing our behavior.
11:43
But given the widespread
nature of such manipulations,
11:45
it would be completely implausible
11:48
for humans to be the only species
11:50
that weren't similarly affected.
11:51
And I think that this capacity to constantly
11:54
subvert our way of thinking about the world
11:59
makes parasites amazing.
12:02
They're constantly inviting us to
look at the natural world sideways,
12:03
and to ask if the behaviors we're seeing,
12:06
whether they're simple and obvious
12:09
or baffling and puzzling,
12:10
are not the results of individuals
12:12
acting through their own accord
12:14
but because they are being bent
12:15
to the control of something else.
12:17
And while that idea may be disquieting,
12:20
and while parasites' habits may be very grisly,
12:22
I think that ability to surprise us
12:25
makes them as wonderful and as charismatic
12:27
as any panda or butterfly or dolphin.
12:30
At the end of "On the Origin of Species,"
12:33
Charles Darwin writes about the grandeur of life,
12:35
and of endless forms most beautiful
12:38
and most wonderful,
12:41
and I like to think he could easily have been talking
12:43
about a tapeworm that makes shrimp sociable
12:45
or a wasp that takes cockroaches for walks.
12:48
But perhaps, that's just a parasite talking.
12:52
Thank you.
12:55
(Applause)
12:56

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About the Speaker:

Ed Yong - Science writer
Ed Yong blogs with a mission: to ignite excitement for science in everyone, regardless of their education or background.

Why you should listen

Whether he's exploring a possible resurrection for extinct mouth-birthing amphibians or skewering media misunderstandings of hyped hormones like oxytocin, Ed Yong has a gift for illuminating the beauty (or controversy) in difficult and complex topics.

The award-winning blog Not Exactly Rocket Science (hosted by National Geographic) is the epicenter of Yong’s formidable web and social media presence. In its posts, he tackles the hottest and most bizarre topics in science journalism. As he says, “The only one that matters to me, as far as my blog is concerned, is that something interests me. That is, excites or inspires or amuses me.” When not blogging, he also finds time to contribute to Nature, Wired, Scientific American and many other web and print outlets.

He is also the author of the book I Contain Multitudes: The Microbes Within Us and a Grander View of Life

More profile about the speaker
Ed Yong | Speaker | TED.com