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Thursday, September 20

Sharks are color blind, confirms a new molecular study

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Sharks are one of the most dreaded organisms under water. The killer label has made them a nightmare for divers all along the globe. However, a recent study reveals crucial information about the vision of sharks which can help avert fatal encounters with sharks under water.

Ornate Wobbegong, Orectolobus ornatus, colour blind shark
Ornate Wobbegong ( Orectolobus ornatus)
Image Courtesy: 
Peter Halasz
In the study which was published in the Biology Letters, a team of researchers explains the peculiar vision system in sharks. Existing knowledge about sharks’ way of looking at things reveals that they are most likely to be color bind. However, the new study confirms this understanding and exposes the reason behind.

The single con cell aka looking at a grey world
The study has analyzed the cone monochromy in two species of carpet sharks (the spotted wobbegong Orectolobus maculatus and the ornate wobbegong O. ornatus) at molecular level. Cones are special type of light sensitive cells inside the retina of the eye of the organism. The cone cells are used for distinguishing fine details and different colors. They often work well under brighter light conditions. However, the cone cells in the eye of sharks can detect light rays from a single spectrum which makes them color blind.

The researchers have isolated the visual opsin genes of the two genuses of carpet sharks to search for an answer for the monochromy at molecular level. During the analysis, the researchers have found that only two opsin genes were present in the carpet sharks – RH1 and LWS. Among these, RH1 is related to rod cells while LWS is related to cone cells. This analysis confirms the fact that sharks has only a single cone cell type on their retina, which in turn explains why sharks may be looking at a grey world.  

Rudimentary color vision
Since their color vision is not functional, researchers consider a possibility of sharks comparing the signals from the rods and con cells in their retina at intermediate light levels. Whales actually have similar vision mechanism. If the sharks also do so, they will have a rudimental color vision. But researchers were unable to detect any behavioral evidence to support this theory.

The study is a crucial one about the evolution of color vision among vertebrates. There are very less studies on color vision in organisms like sharks, skates and rays. It also points to the trend of convergent evolution - a phenomenon in which unrelated groups of organisms develop similar traits (here color blindness among sharks and whales). 

Better understanding, less conflicts
The study may help develop invisible fishing nets in the future which will reduce the rate of shark death due to accidental by-catch. This is presently is the major threat to the shark population in the world. It will also help make less attractive wetsuits for divers which will reduce fatal encounters with sharks.

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