Wednesday, January 29, 2014

Radically different color vision

When we snorkel in a tropical coral reef we are amazed at the colorful displays of the marine fauna and flora. Then we wonder why some of the fish are so flashy, making them conspicuous to predators.

As we wrote in our post on Why are animals colourful? Sex and violence, seeing and signals, Justin Marshall first showed a video snorkeling in a coral reef with a camcorder with spectral sensitivities close to ours, then he showed the same scene using a camcorder with spectral sensitivities close those of coral fish and all the sudden the fish could no longer be distinguished from the background.

In his presentation, Justin Marshall also described how stomatopods like the mantis shrimp are masters of color vision because on top of multiple spectral channels they have sensors for both linear and circular polarization. Shortly thereafter we reported in Nature's almost perfect quarter-wave retarder on Justin Marshall's new paper revealing how the mantis shrimp detects polarization.

How color vision works in the mantis shrimp had remained a mystery, at least until now. Justin Marshall and his collaborators have just published the paper A Different Form of Color Vision in Mantis Shrimp in Science 24 January 2014: Vol. 343 pp. 411-413 (membership required, or check in your local library). It turns out that unlike other animals, mantis shrimp do not have a color-opponent coding system based on a processing system of multiple dichromatic comparisons.

Instead, it appears that their color vision system is based on temporal signaling combined with scanning eye movements, enabling a type of color recognition rather than color discrimination. This would enable the mantis shrimp to make quick and reliable determinations of color, without the processing delay required for a multidimensional color space. This fits their rapid-fire lifestyle of combat and territoriality.

The next step could be to unveil the details of the neural processing from the receptors.