Dr. Tom Cronin in Wired Magazine

Fearless Mantis Shrimp: The Eyes Have It

January 23, 2014 11:29 AM

Behind this incredible method of hunting are the animal kingdom’s
most complex eyes, peepers so amazingly evolved that their
sophistication seems damn near unnecessary. (That’s me being hyperbolic.
They’re anything but unnecessary, of course. Animals don’t just waste
energy and resources building worthless features.)

As with bees or flies or crabs, they are compound eyes,
but unlike those creatures, mantis shrimp “have a very unusual
adaptation in that multiple parts of the same eye view the same point in
space,” said biologist Tom Cronin of the University of Maryland,
Baltimore County, “which is sort of like having multiple eyes in one, in
a way.” Whereas we use two eyes to judge distance, mantis shrimp can do
that with a single eye.

Some mantis shrimp species also have the most complex set of color
receptors of any animal on Earth, a total of 16 classes compared to our
measly four (interestingly, though, half of all stomatopods can’t detect
color at all). Their often wild coloration combined with these highly
developed powers of color-detection aren’t accidents — they’re likely
key in species recognition. You’d hate to try to mate with the wrong
species and get a club to the face for your efforts.

On top of that, some mantis shrimp can see a variety of colors in
ultraviolet, so “they’re seeing colors that no other animal can see, in a
sense,” said Cronin. “Basically color is a property of the nervous
system so it’s not really present in the real world, but they can see
aspects of the ultraviolet that nothing else can see.”

That’s right: Colors only exist because your brain thinks they do.
Your noodle is simply assigning a color to a wavelength of light
collected by your retina. Same goes for the mantis shrimp with its
ridiculous variety of photoreceptors. (It’s a polychromatic
philosophical nightmare, really. What if a mantis shrimp had synesthesia,
a human brain disorder in which sounds can produce the experience of
color? They’d be freaking out, man, but not really because their brain
would perceive it as normal reality. It’s … complicated.)

Anyway, in addition to all of these visual superpowers, the mantis shrimp is the only known critter to see circular polarization of light.
Linearly polarized light — the glare off windows and such that’s
neutralized by those expensive polarized sunglasses you lost recently —
is common, but the circular type is quite rare.

“It’s only created under very special circumstances,” said Cronin,
“and the only thing we know about it for sure with the mantis shrimp is
that they use it for signaling, so they themselves produce patterns that
are circularly polarized on their bodies, which is extremely odd.”

It’d be easy to assume that this staggering amount of information
would require an enormous brain to handle, but this is not the case with
a mantis shrimp. Whereas our eyes funnel raw data to the brain, in
stomatopods the bulk of the processing is done in the eye itself.
Indeed, the mantis shrimp’s eye is actually larger than its brain, which
if you think about it would look crazy weird if humans were the same
way.

“By having all of this complexity at the receptor level,” said
Cronin, “you basically are preprocessing everything. So that when it
leaves the receptors it’s already streamed into information channels and
the brain just basically says, How much is there of this, and How much is there of that, and Make a decision based on that.”

All this data and processing power is pivotal when hunting with such
speed and strength, or when defending yourself, for that matter. These
things are seriously ornery, like the honey badgers of the sea, and the
more information they have to work with to push back against large predators like octopuses, the better.

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