Stomatopods, or mantis shrimps, have the most amazing eyes of any animal. They are pugilistic relatives of crabs and prawns and are known for throwing very fast and powerful punches. Their eyes sit on stalks and move independently of one another. It’s called “trinocular vision,” and each eye can tell the difference between depth and distance on its own by focusing on things with three different areas. They can see a special spiralling type of light called circularly polarised light that no other animal can. And the structure in their eyes is like the technology in CD and DVD players, but it works a lot better.
Hanne Thoen from the University of Queensland has found that mantis shrimp see color very differently from all other animals.
Most people have three types of light-detecting cells, or photoreceptors, in their retinas. These are sensitive to red, green and blue light, respectively. Birds, reptiles and many fish have a fourth photoreceptor that detects ultraviolet light. Four is plenty. Our math models tell us that you only need four or five receptors to effectively store the colors in that range.
They cover eight parts of the spectrum that we can see and four parts that are ultraviolet. That seems like a ludicrous excess. “Why on earth do stomatopods need 12 channels?” asks Justin Marshall, who led the new study. Four or five receptors are all an animal needs.
The obvious answer is that they’re very good at discriminating between different colours. That would be a handy skill: mantis shrimps live in coral reefs, which are bursting with colours. Many of them are brightly coloured themselves, and use their lurid body parts to communicate with one another. “With 12 receptors, you’d think that they can detect colours much better than any other animal,” says Marshall.
Mantis shrimp are marine crustaceans that have fascinated humans for decades due to their incredibly complex eyes. Specifically, the mantis shrimp visual system has 12 different photoreceptor types compared to only 3 in human eyes. This led to speculation that mantis shrimp can see a kaleidoscope of colors beyond human comprehension. However, recent research shows their color vision is more limited than previously thought.
In this article, I’ll walk through the science to answer the question – how many colors do mantis shrimp actually see?
Mantis Shrimp Have 12 Photoreceptor Types
Mantis shrimp eyes contain 12 types of photoreceptors, which are light-sensitive cells in the eye.
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Humans have photoreceptors for detecting red green and blue light.
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Mantis shrimp photoreceptors pick up different wavelengths across the visible and ultraviolet spectrum.
Early researchers hypothesized that having 12 photoreceptor types meant mantis shrimp had dodecahemavision – the ability to perceive 12 primary colors and corresponding combinations This idea of mantis shrimp seeing a “kaleidoscope” of colors took hold in pop culture
However, the latest research indicates mantis shrimp color vision is more simplistic than scientists first predicted.
Testing Mantis Shrimp Color Discrimination
A 2014 study published in Science debunked the idea that mantis shrimp see a vast number of colors.
Researchers trained mantis shrimp to discriminate between 2 colors by rewarding them when they correctly identified a colored light stimulus. This tested the limit of their color discrimination ability.
Key findings:
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Mantis shrimp could only discriminate between colors 25-100 nanometers apart.
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They failed to distinguish between colors 12-25 nanometers apart.
This indicates mantis shrimp likely see a limited number of fairly broad color categories, rather than millions of shades. Their 12 photoreceptor types appear to operate independently rather than combining signals to generate new color perceptions like human vision.
Estimating the Number of Colors Mantis Shrimp Can See
While we don’t know the exact number, mantis shrimp probably see somewhere around 8-12 basic colors based on their photoreceptor sensitivity ranges.
Their color vision system is:
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More complex than many marine species with 1-3 photoreceptor types.
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But more simplistic than the combinatorial color mixing of human trichromatic vision.
So mantis shrimp don’t see a “kaleidoscope” of colors. However, they can still detect a broader spectral range than humans since we lack dedicated ultraviolet receptors.
The Evolutionary Advantage of Mantis Shrimp Vision
Seeing additional ultraviolet colors helps mantis shrimp spot prey and mates that reflect UV wavelengths. Their independent photoreceptor channels provide fast color recognition to support their rapid hunting strikes.
So while not as spectacularly colorful as once imagined, mantis shrimp vision is well-adapted to their aquatic environment and predatory lifestyle. Their visual system is yet another fascinating example of natural selection in action.
Early speculation about mantis shrimp perceiving millions of colors was disproven by behavioral experiments. Instead of kaleidoscopic vision, current evidence indicates they likely see between 8-12 basic colors. Their 12 photoreceptor types operate independently to allow quick color discrimination. Though not as flashy as hypothesized, mantis shrimp vision is still incredibly complex and gives them an advantage in underwater habitats.
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“Actually, they’re much worse!”
Thoen discovered their surprising ineptitude by studying a small species called Haptosquilla trispinosa. She presented the animals with two optic fibres, each displaying a different colour. If they attacked the right one, they earned a tasty snack. Thoen then changed the colour of the off-target fibre to the point when the mantis shrimp could no longer tell the difference between the two.
We could tell the difference between colors whose wavelengths are 5 nanometers apart if someone did this test. Look at the left and middle columns below to see what we mean. A mantis shrimp would struggle with that. The can only discriminate between colours with a 15-25 nanometre difference—compare the middle and right columns.
Despite their 12 photoreceptors, mantis shrimps are worse at telling apart different colours than humans, honeybees and butterflies.
“Thoen is a very careful scientist, so the data are completely convincing, if quite surprising,” says Tom Cronin from the University of Maryland, Baltimore County, who studies mantis shrimp vision. “We certainly would have predicted a much more competent sense of color discrimination than this! However, behaviour is the ultimate test of what an animal can do, so this is what the animals say that they are capable of.“
They must be using the information from those receptors in a very strange way.
We see colours by making comparisons between our three receptors. By comparing the outputs of the red and green receptors, we can tell the difference between reds and greens. And by comparing their combined output against that of the blue receptors, we can discriminate between blues and yellows. This is called the “colour opponent process” and it’s what every colour-sighted animal does.
Every animal… except the mantis shrimps. Given their poor performance in Thoen’s tests, they cannot possibly be making these comparisons. What are they doing instead?.
“The simple answer is: Dunno,” says Marshall. “I’ll admit right up front we don’t fully understand.”
Their main idea is that the mantis shrimps look at the signals from all 12 of their receptors at the same time. They don’t compare those receptors; instead, they send the whole pattern of outputs to the brain without any processing. “One could imagine that they have a look-up table in their brain,” says Marshall. So rather than discriminating between colours like we do, their eyes are adapted for recognising colours.
“Oddly enough, the closest device to stomatopods would be a satellite,” says Marshall. “Remote sensing algorithms have look-up tables of colour to fill in the that the satellite forms. ”.
Marshall says that this way of dealing with color should be much faster than the way we do it now, since the signals from the photoreceptors don’t have to go through any extra neurons. And speed matters for mantis shrimps. These sneaky hunters attack their prey with arms that quickly spread out and end in either spears or clubs that hit hard. Smashers are the species that have clubs. They can hit their targets with the force of a rifle bullet and throw the fastest punches in the animal kingdom. They need fast eyes to complement their fast arms.
And they only have a small brain. “A mantis shrimp only has a fraction of our cortical processing power, yet it handles 4 times more input,” says Nicholas Roberts from the University of Bristol. “The non-comparative processing system they have evolved represents a novel solution for increasing data acquisition while minimising any downstream processing overhead.”
Of course, this is still conjecture. That mantis shrimps don’t see colors the same way humans do has been shown by Thoen and Marshall. But what they do is still unknown. They are now trying to figure out what happens to signals after they leave photoreceptors and how these cells connect to the brain.
Also, Cronin wants to know “if these animals use their color receptor signals in different ways for different tasks.” Perhaps analysis of mate displays or colour signals demands a more thorough discrimination than food recognition. ”.
He also says that the mystery has something to do with one of the most important questions in neuroscience: how does the nervous system process information from the outside world? “This is clearly a very different way of computing that information,” he says. “It’s not just about weird shrimp biology. It touches on a number of neuroscience questions. ”.
Reference: Thoen, How, Choiu & Marshall. 2013. A Different Form of Color Vision in Mantis Shrimp. Science http://dx.doi.org/10.1126/science.1245824
What does the mantis shrimp see?
How many colors can mantis shrimp see?
Mantis shrimp can also see a wider range of the spectrum—from ultraviolet to infrared—and in more colors than humans can. Where we see three colors (red, yellow, and blue, combining them in different proportions to see green, orange, purple, and the rest), mantis shrimp can see between 12 and 16 colors, depending on the species.
Why do mantis shrimp have different colours?
The brain compares the information from each type of receptor to come up with yellow. Using this system, the human eye can distinguish between millions of different colours. Mantis shrimp are fierce predators.
How many color receptors does a mantis shrimp eye have?
These claws measure only a few inches long, but can deliver blows that accelerate as fast as a .22-caliber bullet. Researchers have long known that the mantis shrimp eye contains 12 color receptors, but they had no idea why. Humans and most other animals use three color-receptors to see the spectrum of light.
Can mantis shrimp see?
Mantis shrimp vision puts everything else to shame. These marine crustaceans may be well-known for their record breaking punch (the same acceleration as a .22 calibre bullet), but they also hold the world record for the most complex visual system. They have up to 16 photoreceptors and can see UV, visible and polarised light.