Mantis shrimp eyes outclass DVD players, inspire new technology

The most incredible eyes in the animal world can be found under the sea, on the head of the mantis shrimps. Each eye can move independently and can focus on object with three different areas, giving the mantis shrimp "trinocular vision". While we see in three colours, they see in twelve, and they can tune individual light-sensitive cells depending on local light levels. They can even see a special type of light - 'circularly polarised light' - that no other animal can.

But Nicholas Roberts from the University of Bristol has found a new twist to the mantis shrimp's eye. It contains a technology that's very similar to that found in CD and DVD players, but it completely outclasses our man-made efforts. If this biological design can be synthesised, it could form the basis of tomorrow's multimedia players and hard drives.

Previous studies have found that mantis shrimps can detect polarised light - light that vibrates in a single plane as it travels. Think of attaching a piece of string to a wall and shaking it up and down, and you'll get the idea. Last year, scientists discovered that they can also see circularly polarised light, which travels in the shape of a helix. To date, they are still the only animal that can see these spiralling beams of light.

Its secret lies at a microscopic level. Each eye is packed with light-sensitive cells called rhabdoms that are arranged in groups of eight. Seven sit in a cylinder and each has a tiny slit that polarised light can pass through if it's vibrating in the right plane. The eighth cell sits on top and its slit is angled at 45 degrees to the seven below it. It's this cell that converts circularly polarised light into its linear version. 


In technical terms, the eighth cell is a "quarter-wave plate", because it rotates the plane in which light vibrates. Similar devices are also found in camera filters, CD players and DVD players but these man-made versions are far inferior to the mantis shrimp's biological tech.

Synthetic wave plates only work well for one colour of light. If you change the wavelength slightly, they become ineffective, so designing a wave plate that works for many colours is exceptionally difficult. But the mantis shrimp has already done it. Its eyes work across the entire visible spectrum, from ultraviolet to infrared, achieving a level of performance that our technology can't compete with.

What's more, the same eighth cell not only manipulates circularly polarised light, but it can sense ultraviolet light too. It's a detector and a converter - a two-for-one deal that nothing man-made shares.

Why the mantis shrimp needs such a sophisticated eye is unclear. It could help them to see their prey more clearly in water, which is rife with circularly polarised reflections. It needs good eyesight to be able to hit its prey accurately. Like a crustacean Thor, mantis shrimps shatter their victims with devastating hammer blows inflicted by the fastest arms on the planet. Their forearms, which end in clubs or spears, can travel through water at 10,000 times the acceleration of gravity and hit with the force of a rifle bullet.

Another option is that their super-eyes allow them to send and receive secret messages. A mantis shrimp's shell reflects circularly polarised light, and males and females produce these reflections from different body parts. Their ability to see this type of light could give them a hidden channel of communication that only they can see, for use in courtship or combat.

Whatever the reason for it, Roberts thinks that the eye's structure is "beautifully simple". It's all in the shapes of the cells, their size, and the amount of fat in their membranes. For all its outstanding performance, the eye's abilities were probably easy to evolve, requiring only small tweaks to the basic blueprint of the light-detecting cells.

Now that we know about the microscopic structures behind the mantis shrimp's amazing eye, Roberts is hopeful that engineers can mimic it using liquid crystals. "The cool thing is I think it's actually something you could make and it would improve the workings of current technologies such as Blu-Ray, which uses multiple wavelengths of light, and of future data storage devices," he said. It wouldn't be the first time that crustaceans have inspired technology. A new type of X-ray telescope, for example, was based on the eye of the lobster. 

Reference: Nature Photonics DOI: 10.1038/NPHOTON.2009.189

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As I understand it, we all can see circularly polarized light, just fine. We just can't distinguish it from vertically, horizontally, or randomly polarized light. It's all just photons, to us.

You can experiment with seeing polarized light as a different color by getting some round-lensed hipster polarizing sunglasses, and rotating one of the lenses 90 degrees in its frame. (For different results, rotate one left 45 degrees, the other right.) Experimenting with seeing circularly polarized light takes more specialized equipment. At least we know that you don't need new brain wiring to be able to use the extra information.

By Nathan Myers (not verified) on 25 Oct 2009 #permalink

If Chuck Norris and the mantis shrimp ever entered a death match, the mantis shrimp would certainly be the one to leave the ring alive. That's how badass they are.

If Chuck Norris and the mantis shrimp ever entered a death match, the mantis shrimp would certainly be the one to leave the ring alive. That's how badass they are.

This article and the previous article on mantis shrimp give an explanation of circular polarization so poor and profoundly misleading that I would encourage Mr Yong to remove the articles from this site until articles with decent explanations can be written.

All animals can "see circularly polarized light", just as all animals can "see linearly polarized light"; due to decomposition of arbitrary unpolarized light, I don't see how saying otherwise could even make any sense. The important distinction here is that some species of mantis shrimp can distinguish between different circular polarizations which, to humans, would look the same without external factors.

It's important to note, too, that this is only the case with some species. There are around 400 species of mantis shrimp. I've only read papers on circular polarization detection involving Odontodactylus scyllarus; in fact, Chiou et al (Curr Biol 18, 429) go so far as to suggest that detection of circular polarization, and use of specific-circular-polarization reflective surfaces that also exist on the species, may have arisen to give advantages over competing species of mantis shrimp that can detect linear polarization and use it for complex social signalling, and also predators that can distinguish between linear polarizations.

By the way, Nature's doi-finding system doesn't seem to work well for new articles, so it would probably be best to actually link to the article online Roberts, Chiou et al, A biological quarter-wave retarder with excellent achromaticity in the visible wavelength region. I suspect this may be due to the fact that the article hasn't appeared in print yet.

By Philosophus (not verified) on 25 Oct 2009 #permalink

How do you know it was easy to evolve?

What on earth does "can travel through water at 10,000 times the acceleration of gravity" mean?

In reply to Philosophus

Ed has done a great job of writing up our paper. Philosophus seems to forgot that we also commonly talk about seeing colour. Well of course, just like polarized light, we don't see a colour, it's a representation of comparative processing of several photoreceptor inputs. But no one is going to attack you for saying "I see a colour"

It's perfectly fine to talk about seeing polarized light, seeing the polarization of light or discriminating between different polarizations (linear or circular).

The important part of the above discovery, and that Philosophus seems to have missed entirely, is that this is a completely new optical structure to convert between linearly and circularly polarized light. Even in our world of remarkable technology, evolution has refined some fantastic optics that still continue to make us go Wow.

Nick Roberts

PS Why do people hide behind weird names?

By Nicholas Roberts (not verified) on 26 Oct 2009 #permalink

The conflict between Nick and "Philosophus" is common between people deep in a field and outsiders. People deep in a field develop a shorthand, and don't even consider interpretations of their words that don't make sense in terms of what else they know. For outsiders the shorthand may be actively misleading. Some insiders are better at avoiding dependence on shorthand than others.

If Ed said "cats can't see red light", he would be speaking the same way as in the article, and would be equally misleading: they can see red light, they just can't distinguish it from green. By contrast, they, and we, can't see infrared light at all.

By Nathan Myers (not verified) on 26 Oct 2009 #permalink

Why do people hide behind weird names?

Lots of www denizens tend to use screen names instead of real names, usually out of habit. They don't "hide" behind them (it's not like seeing a random comment by "Joe Blow" would help you much in identifying the person would it?). It's just that they identify differently.

That's pretty neat. It sort of reminds me of the "Dark Visor" in Metroid Prime 2, a visor that you wear to see matter hidden by dark energy. The rest of the world looks kind of greyed-out, but the dark matter looks bright red. I wonder if the mantis shrimp is doing something similar: since the circularly polarized light is invisible to everyone else, these shrimp may be seeing things that, to the rest of us, aren't even there!

Sometimes I wonder if there are organisms that might only be seen on the spectrums we cannot see. I doubt it, but that would be so cool!

See, Zach's confusion results from the misleading wording in the article. If the placement of circularly-polarizing markings on male and female shrimp are the only thing that visibly distinguishes them, then the shrimp are seeing something (sex dimorphism) that to us isn't there. But of course the shrimp are visibly there, and those markings are reflecting/refracting/iridescing light we see just fine; it just looks the same to us.

"Matter hidden by dark energy", by the way, also doesn't make sense, but probably for different reasons.

By Nathan Myers (not verified) on 26 Oct 2009 #permalink

I'm not aware of anyone who uses "see polarization" as a shorthand for being able to distinguish polarization of light: "detect polarization" or "distinguish polarization" would be better, and are in fact used. Seeing is generally a poor term to use for many things. The meaning is far too ambiguous: I'd even be against using "see color".

There's a reason for jargon to exist, and unfortunately, when you try to remove it, you can easily make things unintentionally misleading.

masklinn: interestingly enough, this screen name was devised, years ago, to hide behind. I prefer that my discussions about science online not be connected with my actual research, and not be construed as official statements. When I constructed it, I was primarily working to combat outright crackpottery on Wikipedia, where my identity being known would have resulted in complaints to my institute and harassment of my colleagues; the name eventually became, however, what I use for almost all non-official discussions I have about science.

By Philosophus (not verified) on 27 Oct 2009 #permalink