Mantis Shrimps Process Color Better Than Most, Say Researchers

Researchers from the University of Queensland have unraveled the mystery behind why the mantis shrimp have 12 photo receptors in their eyes.

Researcher Hanne Theon says in her study that the mantis shrimp ( Haptosquilla trispinosa) has 12 different  photoreceptors and yet its vision is worse than that of humans who have only three color channels. Previous studies have shown that animals having four to seven photoreceptors are able to see any color under the sun.  "Theoretically, mantis shrimp should be far better at distinguishing colors than we are," Thoen , the lead researcher, said. "Human brains - and all other animals including birds, monkeys, frogs and fish - determine the colors of objects by comparing the relative excitation of inputs. For instance, in humans this is red, green and blue. The critical finding is that mantis shrimp do not do this, and this means their way of encoding color is different to all other animals known."

Tests were done to determine how shrimps differentiated between different colors in the spectrum. They were given a choice of two very distinct colors like red and blue. The shrimps were even trained to choose a certain color with rewards But when they were offered a choice of colors very near in the spectrum like red and yellow or red and orange, they got confused.

"We tested their ability to discriminate between colors that differ a lot - such as red and blue - and then changed to colors that got closer and closer together along the spectrum - red-green, red-yellow, red-orange - and noted when they started to make mistakes," Thoen said.

Professor Justin Marshall , Theon's  Phd supervisor, said that this was the first time they had determined how an animal processed color in a different manner.

"It solves a long-standing problem of why mantis shrimp have 12 color receptors - because they process colors and the contrast they provide in a totally different way to anything we have previously seen in an animal," Professor Marshall said.

Theon said the discovery could also help in innovations  and advancements in visual technology and aid us process more color efficiently.

he project was supported by grants from the Asian Office of Aerospace Research and Development, Air Force Office of Scientific Research, Australian Research Council and Doctoral Fellowship (2013) from Lizard Island Research Station - a facility of the Australian Museum.