Whale sharks can see clearly in the dark due to a genetic mutation. Yes, their sense of sight works even 656 feet deep where the sunlight does not penetrate.

Why Whale Sharks Can See in the Dark

A new study has learned that whale sharks' eyes should strain in dealing with the contrast of light in their vertical range. However, an unusual genetic mutation helps the gentle giant see in the deep of the ocean, Forbes.

They reportedly have a pigment in their retina that is more sensitive to temperature changes. By activating certain sections of their eyesight in the frigid deep sea and deactivating them when they surface on the warmer surface, sharks can prioritize different areas of their vision at various depths (where they can see a spectrum of colors instead of only blue).

Genetic mutation may be familiar to those with medical backgrounds because it is similar to the one that causes night blindness by destroying retinal pigments.

The inability to see properly at night or in poorly lit environments, such as a movie theater or restaurant, is a symptom of night blindness (nyctalopia), a disorder that affects humans.

Rhodopsin, a light-sensing pigment in whale sharks' retinas, allows them to navigate in the dark waters of our ocean. These pigments are less useful in bright surroundings, but they aid many vertebrates in detecting light in low-light conditions. The only hue that can travel to these depths in the deep sea is blue, and the rhodopsin pigments inside whale sharks' eyes have been specifically tuned to sense this color.

Other studies have shown that cloudy catsharks (Scyliorhinus torazame) and whale sharks exhibit similar pigments in their eyes.

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More About the Research Study

Professors Mitsumasa Koyanagi and Akihisa Terakita of the Osaka Metropolitan University Graduate School of Science investigated the genetic information and structure of the photoreceptor rhodopsin, which helps whale sharks see in the dark, EurekAlert! reported.

According to Koyanagi, the research achieved astounding outcomes by utilizing genetic data and molecular biological approaches without endangering whale sharks or their biology. The goal of the study strategy is to employ these methods to offer hints about the mysteries of how these species live.

They are amazed that it even applies to species about which little is known, such as huge or wild creatures that are challenging to see or track in their native environment.

The study showed that two amino acid modifications changed the light spectrum that rhodopsin detects, making it sensitive to blue wavelengths. This made rhodopsin more sensitive to blue light, the most prevalent wavelength in the deep sea.

Contrary to popular belief, one of the amino acid alterations corresponds to a mutation at a location known to result in congenital stationary night blindness in humans.

The whale shark rhodopsin is less thermally stable due to the amino acid substitutions; compared to human or other shark rhodopsin that does not have the substitution, it degrades quickly at 37 ºC. Yet, the whale shark rhodopsin can still operate at temperatures below 37 °C, indicating that this unusual adaption developed for living in the low-temperature low-light deep sea.

The study was published in the Proceedings of the National Academy of Sciences. 

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