Download Lethal from day one, the tentacled snake uses surprisingly sly tactics

Lethal from day one, the tentacled snake uses surprisingly sly tactics to capture fish
WE HUMANS ARE PRETTY SMUG ABOUT OUR LARGE brains and sophisticated ways. But if there is one thing I
have learned as a biologist, it is to never underestimate the abilities of animals that most people consider primitive and
simple-minded. Usually mammals teach me this lesson. But recently the complexity of the behaviors I observed in a
peculiar reptile known as the tentacled snake made my jaw drop in amazement.
The tentacled snake, Erpeton tentaculatus, is a fully aquatic serpent native to Thailand, Cambodia and South Vietnam. A
relatively small snake (adults are about two feet long), it gives birth to live young and feeds exclusively on fish. The
animal's name refers to its most distinctive trait: the pair of tentacles that project from the sides of the snout. I first
became interested in these creatures around a decade ago on a nostalgic visit to the National Zoo in Washington, D.C.,
where I had worked summers as an undergraduate. Walking through the reptile house, I came across an aquarium thick
with vegetation where a tentacled snake was lying in wait. It hung motionless in the water trying hard to look like a stick,
its body curved into the characteristic J shape that the snakes adopt when hunting.
As I watched the snake, I wondered what the tentacles were for. No other snake has anything quite like them. Because
these animals feed on fish, it stood to reason that the tentacles might be fish detectors of some kind. But when I returned
to my lab at Vanderbilt University and searched the scientific literature, I found that although tentacle theories, including
this one, had been proposed, no one had tested them experimentally. So I set out to solve the mystery of the snake's
bizarre appendages once and for all.
In my quest to discern the true purpose of the tentacles, I discovered that this animal was even more interesting than I
had realized. It turns out that the tentacled snake uses an array of remarkably advanced attack strategies to capture prey.
Furthermore, even newborns of this species possess these skills, revealing a dramatic example of nature, rather than
nurture, molding behavior.
IN THE BLINK OF AN EYE
BEFORE I COULD TEST THE THEORY that the tentacles function as fish detectors, I first had to carefully observe
the snake's hunting behavior. But watching snakes hunt is not as simple as it might sound. Tentacled snakes strike with
incredible speed, and fish are equally fast. The entire contest between snake and fish plays out in about 40 milliseconds,
or 1/25th of a second. To see these events, I recorded strike after strike for a number of snakes using a high-speed camera
shooting at 500 to 2,000 frames per second and then played the video back in slow motion. As I watched the attacks, I
noticed something very strange: seemingly suicidal fish.
In many instances, fish turned toward the approaching jaws of the striking snake, sometimes swimming straight into the
snake's mouth. This made no sense. Fish are a top menu item for many predators, and as a consequence, they are expert
escape artists, having evolved rapid neural circuits and correspondingly swift behaviors to sense and evade enemies.
When they detect the sounds and water motion generated by a predator, they can begin their flight to safety in just six to
seven milliseconds--less than l/150th of a second. This escape response, called a C-start because it starts with a C-shaped
bend of the fish's body, is supposed to propel the fish away from a predator on the hunt. Why, then, were fish moving
toward the tentacled snake's mouth?
The answer, I found, has to do with the unusual J-shaped hunting posture of the snakes, which forms a trap of sorts. These
reptiles prefer to go after fish that have entered the concave area of the J-shaped region formed by their head and upper
body. Careful examination of the slow-motion video revealed that just before attacking, the snake moved a portion of its
body on the side of the fish farthest from the snake's head, startling the fish toward the predator's open mouth. When I
filmed the strikes at 2,000 frames per second and simultaneously recorded sounds in the aquarium with an underwater
microphone, I determined that the movement of the snake's body just before the strike creates a propagating pressure
wave strong enough to startle a fish.
The snake's feint strategy is particularly insidious, because it taps into the neural circuitry that usually works in favor of
fish. Fish have a pair of giant cells in their brain, one on each side, called Mauthner neurons. The neurons' signal-carrying
extensions, called axons, cross over to the opposite side of the body. A race between these two fast-conducting neurons
determines the direction of the escape response. When a sound originates on the left side, for example, the ears excite the
left Mauthner neuron first, which in turn carries a signal down its axon and stimulates motor neurons on the right side
of the body, causing a massive muscle contraction that turns the fish to the right. At the same time, inhibitory neurons
that cross back over to the left side prevent the muscles on the left from contracting, thus ensuring that nothing interferes
with the all-important right turn. The result is an incredibly fast escape--unless the fish swims too close to a tentacled
snake. In that case, the snake's body feint usually sets in motion the cascade of neural events that leads to a turn in the
wrong direction. And unfortunately for the fish, the simultaneous activation of the inhibitory circuitry that usually
functions as a safety means there is no turning back.
The snake's astonishing trick explains some previously puzzling observations. In 1999 John C. Murphy of the Field
Museum of Natural History in Chicago reported that fish were eaten very quickly and sometimes disappeared completely
during the snake's strike, within one frame of his 30-frames-per-second video--much faster than expected. My high-speed
videos reveal that even when the fish do not oblige the snake by swimming straight into its mouth, the turn they make
toward the snake usually allows it to capture them headfirst, which is the quickest way for a snake to swallow fish. This
fast eating not only allows the snake to eat more often, but it also helps to keep the predator's identity under wraps (it is
hard to look like a harmless stick if other fish have seen you devour their comrade). Furthermore, the snakes have their
own predators and are most likely to be seen themselves when swallowing a fish, so rapid dining may reduce the hunter's
chances of becoming the hunted.
MAKING PREDICTIONS
PSYCHOLOGIST B. F. SKINNER once said, "When you run into something interesting, drop everything else and study
it." In that spirit, I decided to put my interest in the tentacles aside temporarily and focus on the snake's predatory
behavior--a shift that turned up more tricks in the creature's repertoire.
Although startling fish toward a strike is impressive, it works only when the fish is situated in the "sweet spot" between
the snake's head and neck and parallel to its jaws. What about fish in other orientations? Because the fish's escape
response propels it either to the left or the right, the snake cannot startle a fish toward its mouth if the fish is already
facing its jaws. In this case, the tentacled snake employs another, even more impressive strategy: it predicts fish behavior.
First it uses a body feint to startle the fish away from its body, sending the fish on a path parallel to the snake's jaws.
Then, before the fish even moves, the snake strikes toward the future location of the fish's head, such that its jaws reach
the spot just as the ill-fated fish arrives. The events occur far too quickly for the snake to use visual feedback to track the
moving fish during the strike--it must plan ahead. In some experimental trials, the fish did not turn away from the body
feint (the tactic is not foolproof), yet the snake still struck in the direction the fish should have moved in had it reacted in
the usual way. This behavior confirmed that the snake strikes based on prediction, rather than tracking the fish as it
moves.
Sometimes snakes simply struck at a fish even if they were unable to startle it in a particular direction. But for the most
part, snakes patiently waited for fish to enter the trap formed by their J-shaped hunting posture. To my surprise, I observed
yet more kinds of predictive strikes for fish in this zone, depending on the position of the fish. In one contortionistic
variant, snakes curled their head under their own body to meet an escaping fish head-on. It seems tentacled snakes can
choose from a range of attack strategies in their arsenal, depending on the situation at hand. These predictive strikes
raised an interesting question: Do tentacled snakes learn to predict the movements of a C-starting fish from a lifetime of
striking, or are they born with this ability? As luck would have it, several of our snakes gave birth. When we tested the
newborns with live fish, they clearly struck for the future location of escaping fish (when fish were in the appropriate
position), thus showing they were born knowing how a fish moves and how best to outsmart it.
Reporting our findings last year in PLoS ONE, we observed that this innate ability testifies to the long evolutionary
history of tentacled snakes preying on fish and bears on one of the most fundamental questions in biology--namely, the
relative roles of nature and nurture in the development of behavior. Tentacled snakes sit at the extreme nature end of this
continuum, at least when it comes to strikes by newborns. The very reliable response of fish to a sudden water disturbance
provided a framework for the evolution of one innate behavior (predictive strikes) that takes advantage of another innate
behavior (fish-escape responses).
That the fish have not evolved a counterstrategy suggests that tentacled snakes are acting as what Stephen Jay Gould
termed "rare enemies," exploiting a behavior that is normally adaptive. Fish have many predators, and most of the time
their best bet on detecting a sudden water disturbance is to flee in the opposite direction. It is the unlucky fish that
encounters this snake and is tricked into turning toward its enemy rather than away from it.
SEEING IN DARKNESS
AS FOR THE TENTACLES, my graduate student Duncan B. Leitch and my research assistant Danielle Gauthier and I
conducted a series of investigations to determine their function. We published our results in 2010 in the Journal of
Experimental Biology. By examining the anatomy of the nerve endings in these appendages, their responses to various
stimuli and how they map into the brain, we were able to show that the tentacles are exceptionally sensitive touch organs
that detect water movements generated by nearby moving objects. That is, the tentacles function exactly as would be
expected for a fish-detecting organ in an ambush predator. We also filmed snakes under infrared illumination, which they
cannot see, and demonstrated their ability to catch fish without using eyesight. Apparently the tentacles allow snakes to
detect and capture fish at night or in murky water. Armed with a world-class motion detector and the ability to scare a
target to its death, a tentacled snake is a fish's worst nightmare.
Pretest A
Read the following statements, and fill in your best guess for the word or phrase (up to 3 words) that
completes the sentence in the blank. You must write some answer in each blank, and the answer must
make grammatical sense.
1. The prey's attempt to escape is called a ____________________ because of the way it bends to get
out of the way.
2. The way newborn snakes behave tells us that their hunting behavior is at the extreme
________________ end of the spectrum.
3. One theory was that the snake's unique trait might helpful in catching its main diet,
____________________.
4. The way the prey turn toward the snake allow the snake to eat them ____________________, which
is the fastest way for snakes to dine.
5. This species of snake is unique because of the ____________________ on its snout.
6. When the snake moves its body as it prepares to strike, it creates a propagating
____________________ that startles the prey into motion.
Pretest B
Read the following statements, and fill in your best guess for the word or phrase (up to 3 words) that
completes the sentence in the blank. You must write some answer in each blank, and the answer must
make grammatical sense.
1. The snake can catch its prey in as little as ____________________.
2. The ____________________ neurons stimulate muscles so the prey will twitch in the opposite
direction of a sound.
3. The prey fall for this trick because the snakes are ________________, and for all other predators the
prey's actions would have allowed it to survive.
4. T2hey snake only succeeds in startling the prey into suicide when they are in the
___________________ between the head and neck.
5. The purpose of the snake's distinctive feature is to let it catch its prey ________________.
6. The prey move so quickly that the snake cannot possibly use ________________ to track them, and
must be anticipating their movements.
Posttest
Read the following statements, and fill in your best guess for the word or phrase (up to 3 words) that
completes the sentence in the blank. You must write some answer in each blank, and the answer must
make grammatical sense.
1. This species of snake is unique because of the ______________on its snout.
2. The snake can catch its prey in as little as ______________
3. When the snake moves its body as it prepares to strike, it creates a propagating ______________that
startles the prey into motion.
4. The way the prey turn toward the snake allow the snake to eat them ______________which is the
fastest way for snakes to dine.
5. One theory was that the snake's unique trait might helpful in catching its main diet,
______________
6. The prey's attempt to escape is called a ______________because of the way it bends to get out of the
way.
7. The prey move so quickly that the snake cannot possibly use ______________to track them, and
must be anticipating their movements.
8. The way newborn snakes behave tells us that their hunting behavior is at the extreme
______________end of the spectrum.
9. They snake only succeeds in startling the prey into suicide when they are in the
______________between the head and neck.
10. The ______________ neurons stimulate muscles so the prey will twitch in the opposite direction of
a sound.
11. The purpose of the snake's distinctive feature is to let it catch its prey ______________.
12. The prey fall for this trick because the snakes are ______________, and for all other predators the
prey's actions would have allowed it to survive.
Posttest Answer Key
Read the following statements, and fill in your best guess for the word or phrase (up to 3 words) that
completes the sentence in the blank. You must write some answer in each blank, and the answer must
make grammatical sense.
1. This species of snake is unique because of the _tentacles___ on its snout.
2. The snake can catch its prey in as little as ___40 milliseconds (1/25th second)___________
3. When the snake moves its body as it prepares to strike, it creates a propagating _______pressure
wave_______ that startles the prey into motion.
4. The way the prey turn toward the snake allow the snake to eat them __headfirst____________ which
is the fastest way for snakes to dine.
5. One theory was that the snake's unique trait might helpful in catching its main diet, __fish__.
6. The prey's attempt to escape is called a ___C-start___________ because of the way it bends to get
out of the way.
7. The prey move so quickly that the snake cannot possibly use __________visual feedback____ to
track them, and must be anticipating their movements.
8. The way newborn snakes behave tells us that their hunting behavior is at the extreme
__innate____________ end of the spectrum.
9. They snake only succeeds in startling the prey into suicide when they are in the ____sweet
spot__________ between the head and neck.
10. The ___Mauther___________ neurons stimulate muscles so the prey will twitch in the opposite
direction of a sound.
11. The purpose of the snake's distinctive feature is to let it catch its prey __in the dark________.
12. The prey fall for this trick because the snakes are _rare enemies_____________, and for all other
predators the prey's actions would have allowed it to survive.
The grand scheme, a stepping-stone to string theory, is still high on physicists' wish lists. But if no
solid evidence surfaces soon, it could begin to have a serious PR problem
For decades now physicists have contemplated the idea of an entire shadow world of elementary particles,
called supersymmetry. It would elegantly solve mysteries that the current Standard Model of
particle physics leaves unexplained, such as what cosmic dark matter is. Now some are starting to wonder.
The most powerful collider in history, the Large Hadron Collider (LHC), has yet to see any new
phenomena that would betray an unseen level of reality. Although the search has only just begun, it has
made some theorists ask what physics might be like if supersymmetry is not true after all.
"Wherever we look, we see nothing -- that is, we see no deviations from the Standard Model," says
Giacomo Polesello of Italy's National Institute of Nuclear Physics in Pavia. Polesello is a leading member
of the 3,000-strong international collaboration that built and operates ATLAS, one of two cathedral-size
general-purpose detectors on the LHC ring. The other such detector, CMS, has seen nothing, either,
according to an update presented at a conference in the Italian Alps in March.
Theorists introduced supersymmetry in the 1960s to connect the two basic types of particles seen in nature,
called fermions and bosons. Roughly speaking, fermions are the constituents of matter (the electron being
the quintessential example), whereas bosons are the carriers of the fundamental forces (the photon in the
case of electromagnetism). Supersymmetry would give every known boson a heavy "superpartner" that is
a fermion and every known fermion a heavy partner that is a boson. "it is the next step up toward the
ultimate view of the world, where we make everything symmetric and beautiful," says Michael Peskin, a
theorist at SLAC National Accelerator Laboratory.
The monumental collider at CERN near Geneva should have the oomph to produce those super-particles.
Currently the LHC is smashing protons with an energy of four trillion electron volts (TeV) apiece, up from
3.5 TeV last year. This energy is divided among the quarks and gluons that make up the protons, so the
collision can generate new particles with the equivalent of about 1 TeV of mass. But despite the high
expectations (and energies), so far nature has not cooperated. LHC physicists have been searching for
signs of particles new to science and have seen none. If super-particles exist, they must be even heavier
than many physicists had hoped. "To put it bluntly," Polesello says, "the situation is that we have ruled
out a number of 'easy' models that should have showed up right away." His colleague Ian Hinchliffe of
Lawrence Berkeley National Laboratory echoes him: "If you look at the range of masses and particles that
have been excluded, it's quite impressive."
Many are still hopeful. "There are still very viable ways of building supersymmetry models," Peskin says.
Expecting to see new physics after just a year of data taking was unrealistic, says Joseph Lykken, a theorist
on the CMS team.
What has theorists on edge, however, is that for supersymmetry to solve the problems for which it was
invented in the first place, at least a few of the superparticles should not be too heavy. To constitute dark
matter, for example, they need to weigh no more than a few tenths of 1 TeV.
Another reason most physicists want some superparticles to be light lies in the Higgs boson, another major
target of the LHC. All elementary particles that have mass are supposed to get it through their interaction
with this boson and, secondarily, with a halo of fleeting "virtual particles." In most cases, the symmetries
of the Standard Model ensure that these virtual particles cancel one another out, so they contribute only
modestly to mass. The exception, ironically, is the Higgs itself. Calculations based on the Standard Model
yield the paradoxical result that the boson's mass should be infinite. Superpartners would solve this
mystery by providing greater scope for cancellations. A Higgs mass of around 0.125 TeV, as suggested
by preliminary results announced in December 2011, would be right in the range where supersymmetry
predicts it should be. But in that case, the superparticles would need to have a fairly low mass.
If that proves not to be the case, one explanation is that heretofore underappreciated symmetries of the
Standard Model keep the Higgs mass finite, as Bryan Lynn of University College London suggested last
year. Others say Lynn's idea would provide at best a partial explanation, leaving a vital role
for physics beyond the Standard Model -- if not super-symmetry, then one of the other strategies that
theorists have devised. A popular plan B is that the Higgs boson is not an elementary particle but a
composite of other particles, just as protons are composites of quarks. Unfortunately, the LHC simply
does not have enough data to say much about that idea yet, says CERN's Christophe Grojean. More exotic
options, such as extra dimensions of space beyond the usual three, may forever lie beyond the LHC's
reach. "Right now," points out Gian Francesco Giudice, another theorist at CERN, "every single theory
has its own problems."
As ATLAS and CMS continue to accumulate data, they will either discover superparticles or exclude
wider ranges of possible masses. Although they may never be able to strictly disprove super-symmetry, if
the collider fails to find it, the theory's usefulness may fade away, and even its most hardcore supporters
may lose interest. That would be a blow not just to supersymmetry but also to even more ambitious unified
theories of physics that presume it, which include string theory and other approaches [see "Loops, Trees
and the Search for New Physics," by Zvi Bern, Lance J. Dixon and David A. Kosower, on page 34]. LHC
physicists take this uncertainty in stride and expect the collider to find some new and exciting physics -not just the physics theorists had expected. Hinchliffe says, "The most interesting thing we will see is
something that nobody thought of."
Pretest A
Read the following statements, and fill in your best guess for the word or phrase (up to 3 words) that
completes the sentence in the blank. You must write some answer in each blank, and the answer must
make grammatical sense.
1. A "plan B" some theorists are considering is that the main target is actually a
____________________.
2. The investigations into particles work by ____________________protons together.
3. The world of elementary particles is called ____________________.
4. The theorist who said that expecting to see results in just a year was named
____________________.
5. The particles called ___________________are involved in forces like electromagnetism.
6. Some physicists are worried because some particles, like the ones that would make up
____________________must weigh only a fraction of a TeV.
Pretest B
Read the following statements, and fill in your best guess for the word or phrase (up to 3 words) that
completes the sentence in the blank. You must write some answer in each blank, and the answer must
make grammatical sense.
1. Failure to support this theory would also hurt other theories such as ____________________.
2. The fact that these investigations haven't worked yet tells us the particles must be
____________________than anyone thought.
3. The machine scientists are using to investigate these particles is called the ____________________.
4. The theorist who said that the search show far has shown no deviations from the usual physics was
named ____________________.
5. The particles called ____________________are the building blocks of matter.
6. The main target of these investigations so far has been on a particle called the
____________________.
Posttest
Read the following statements, and fill in your best guess for the word or phrase (up to 3 words) that
completes the sentence in the blank. You must write some answer in each blank, and the answer must
make grammatical sense.
1. The investigations into particles work by ____________________ protons together.
2. The theorist who said that the search show far has shown no deviations from the usual physics was
named ____________________
3. The particles called ____________________are involved in forces like electromagnetism.
4. The fact that these investigations haven't worked yet tells us the particles must be
____________________than anyone thought.
5. The machine scientists are using to investigate these particles is called the ____________________.
6. The main target of these investigations so far has been on a particle called the
____________________
7. A "plan B" some theorists are considering is that the main target is actually a
____________________
8. The theorist who said that expecting to see results in just a year was named ____________________
9. Some physicists are worried because some particles, like the ones that would make up
____________________must weigh only a fraction of a TeV.
10. Failure to support this theory would also hurt other theories such as ____________________
11. The particles called ____________________are the building blocks of matter.
12. The world of elementary particles is called ____________________
Posttest Answer Key
Read the following statements, and fill in your best guess for the word or phrase (up to 3 words) that
completes the sentence in the blank. You must write some answer in each blank, and the answer must
make grammatical sense.
1. The investigations into particles work by ___smashing_______ protons together.
2. The theorist who said that the search show far has shown no deviations from the usual physics was
named __ Giacomo Polsello __________________
3. The particles called ___bosons_______ are involved in forces like electromagnetism.
4. The fact that these investigations haven't worked yet tells us the particles must be
____heavier______ than anyone thought.
5. The machine scientists are using to investigate these particles is called the ____Large Hadron
Collider______.
6. The main target of these investigations so far has been on a particle called the ___Higgs
Boson_______.
7. A "plan B" some theorists are considering is that the main target is actually a ____composite______.
8. The theorist who said that expecting to see results in just a year was named ____ Joseph Lykken
________________
9. Some physicists are worried because some particles, like the ones that would make up __dark
matter________ must weigh only a fraction of a TeV.
10. Failure to support this theory would also hurt other theories such as ___string theory______.
11. The particles called _____fermions_______________ are the building blocks of matter.
12. The world of elementary particles is called _supersymmetry_________.