Scientists find weird shrimp has astounding vision / Scientific Frontline Communication Center

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Scientists find weird shrimp has astounding vision

Wednesday, May 14, 2008

A Swiss marine biologist and an Australian quantum physicist have found that a species of shrimp from the Great Barrier Reef, Australia, can see a world invisible to all other animals.

Dr Sonja Kleinlogel and Professor Andrew White have shown that mantis shrimp not only have the ability to see colors from the ultraviolet through to the infrared, but have optimal polarization vision — a first for any animal and a capability that humanity has only achieved in the last decade using fast computer technology.

"The mantis shrimp is a delightfully weird beastie," said Professor White, who is an ARC Federation Fellow in the Schol of Physical Sciences at The University of Queensland.

"They're multi-colored, their genus and species names mean `mouth-feet' and `genital-fingers'; they can move each eye independently, they see the world in 11 or 12 primary colors as opposed to our humble three, and now we find that this species can see a world invisible to the rest of us."

Dr Kleinlogel is based at the Max Planck Institute for Biophysics in Frankfurt, and collected the shrimp from the reef.

"Scuba divers know them as 'thumb-splitters', they've got wickedly strong claws and are very aggressive," she said.

Most animals can tell how fast the electric field in a light wave is oscillating, which is perceived as color. (Blue light oscillates faster than green, which is faster than red).

The direction of the oscillation is known as polarization: many animals, from budgerigars to ants have some form of polarization vision.

Since the 1950s animals have been shown to use linear polarization vision for navigation, for finding food, for evading hunters, and for sex, or as Professor White says "...for the four eff's: feeding, fighting, fleeing and ... flirting".

Commonly polarization vision is quite restricted: in its simplest form different directions of polarization show up as lighter or darker patches — you can see this yourself by looking at clear blue sky with polarizing sunglasses. But polarization is more subtle than this: the electric field of the light can oscillate back and forth in a line or around and around in a circle, or anywhere in between.

The two scientists have shown that shrimp of the species Gonodactylus smithii have eyes that simultaneously measure four linear and two circular polarizations, enabling them to determine both the direction of the oscillation, as well as how polarized the light is.

"This is very useful because natural light can vary from strongly polarized, like the glare off snow or water, to unpolarized, like the sun," Professor White said.

"Any changes to the amount of polarization instantly tells the animal that something is going on."

Colleagues at The University of Queensland have recently found a related species where the males reflect circular polarization from their bodies, and hypothesized that circular polarization vision is used for sexual signaling.

"I think of that as the `prawnographic' hypothesis," Professor White said.

"It can't be the whole story in our case, though. We found the same structures in the eyes of both boy and girl mantis shrimps, and yet neither have circularly polarized markings on their bodies.

"Each eye measures the six polarization components that are precisely required for optimal polarization vision.

"In fact, the physics we used to understand what was going on is the same physics that we use in quantum computing for optimal storage of information."

“It is this unique talent — to measure linear and circular polarization simultaneously — which presents a completely new concept of polarization vision,” Dr Kleinlogel said.

"There wouldn't be much point in only being able to see circular polarization as it is extremely rare in nature. Even the polarized light reflected from some shrimp's bodies is only weakly circular polarized and often contains more linear polarization."

"We doubt that circular polarization is used exclusively as a secret shrimp sex signal. It makes more sense that mantis shrimp evolved both circular and linear polarization receptors to work together so they can detect tiniest changes in any polarization."

Professor White said some of the animals they liked to eat were transparent, and quite hard to see in sea-water — except they were packed full of polarizing sugars.

"I suspect they light up like Christmas trees as far as these shrimp are concerned," he said.

"And of course, they can still flirt with each other using fancy polarization cues," Dr Kleinlogel said.