Shrimp Gives Insight Into Color Vision

Researchers have uncovered new insights into color vision by studying the mantis shrimp.

Asian Scientist (Feb. 4, 2014) – A new study of color vision on a tropical reef shrimp has dispelled the illusion that complex eyes with more color channels mean better color vision.

In the study, University of Queensland researcher Hanne Thoen found that the mantis shrimp (Haptosquilla trispinosa), which has 12 color channels in its eyes, has worse color vision than humans who have only three color channels.

This finding contradicts the theory that more color channels mean better color vision since the mantis shrimp should be far better at distinguishing colors than humans if the theory is correct.

According to Thoen, human brains – and all other animals including birds, monkeys, frogs and fish – determine the colors of objects by comparing the relative excitation of inputs, whether they are red, green or 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,” said Thoen.

A number of tests were conducted, including training the shrimps to respond to certain colors and using a two-way choice test with food as a reward. By receiving food when choosing one particular color and not any other, the shrimp quickly learned which choice to make and also revealed how they encode color.

“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.

Other than humans, the researchers also found that the mantis shrimp has far worse color vision than a number of other animals which have fewer color channels, including bees, fish and butterflies.

According to the researchers, the findings also solves a long-standing mystery of why mantis shrimp have 12 color receptors.

“They process colors and the contrast they provide in a totally different way to anything we have previously seen in an animal,” said Professor Justin Marshall who led the study.

“This is the first time since the original descriptions of color vision in the 1800s that we are able to say that there is another way of color processing out there.”

“The findings demonstrate how evolution pushed the design of nervous systems towards a simple arrangement, rather than trying to fully interpret all the information from a very complex color vision at the retinal level.


Source: University of Queensland; Photo: Jayvee F./Flickr/CC.
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