Shrimps see beyond the rainbow(lue sky with polarising sunglasses. But ...)

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

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

Any changes to the amount of polarisation 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 polarisation from their bodies, and hypothesized that circular polarisation vision is used for sexual signalling. Professor White smiles and says, I think of that as the 'prawnographic' hypothesis.

He continues, 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 polarised markings on their bodies. Each eye measures the six polarisation components that are precisely required for optimal polarisation 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 polarisation simultaneously which presents a completely new concept of polarisation vision, Dr Kleinlogel continues. There wouldn't be much point in only being able to see circular polarisation as it is extremely rare in nature. Even the polarized light reflected from some shrimps bodies is only weakly circular polarised and often contains more linear polarisation.