Mantis shrimps are known as aggressive animals. They have a pair of legs at the front used to catch their prey, but 40 times faster than the preying mantis. They can pack a punch like a 0.22 calibre bullet and can break aquarium glass. However, a University of Queensland study of mantis shrimp discovered a new form of light communication employed by the shrimps.
The findings having potential applications in satellite remote sensing, biomedical imaging, cancer detection, and computer data storage.
Dr Yakir Gagnon, Professor Justin Marshall and their colleagues at the Queensland Brain Institute previously found that mantis shrimp (Gonodactylaceus falcatus) can sense and reflect circular polarizing light, an ability extremely rare in nature. Until now, no-one has known what they use it for. The study follows up on that research and shows how shrimp use circular polarization to covertly communicate their presence to aggressive competitors.
Where linear polarized light travels in only one plane, circular polarized light travels in a clockwise or anti-clockwise spiral. The human eye is unable to detect polarized light, but special lenses(often found in sunglasses) make it visible. It’s also invisible to most other animals, and the shrimp use this to their advantage.
The research team determined that mantis shrimp display circular polarised patterns on the body, particularly on the legs, head and heavily armoured tail; these are the regions most visible when when they curl up during conflict.
“These shrimp live in holes in the reef,” said Professor Marshall. “They like to hide away; they’re secretive and don’t like to be in the open.”
Researchers dropped a mantis shrimp into a tank with two burrows to hide in: one reflecting unpolarised light and the other, circular polarised light. The shrimp chose the unpolarised burrow 68% of the time. This suggested the circular polarised burrow was perceived as being occupied by another mantis shrimp.
Crabs use polarised light to communicate too
Fiddler Crabs (uca stenodactylus) also uses polarized light as a form of communication. They live on mudflats, a very reflective environment, and use the the amount of polarisation reflected by objects, to navigate through and react to their environment.
“It appears that fiddler crabs have evolved inbuilt sunglasses, in the same way as we use polarising sunglasses to reduce glare,” Professor Marshall said.
Fiddler crabs react to ground-based objects based on how much polarized light they reflected, moving in either a forward mating stance, or retreating back into their holes, at varying speeds.
Both animals deal with polarisation that is completely invisible to humans.
Secret light communication may help cancer detection
Cameras equipped with circular polarizing sensors, similar to the shrimp’s sensory organs, may detect cancer cells long before the human eye can see them. Cancerous cells do not reflect circular polarised light in the same way as healthy cells.