Whale Shark Sight: How Rhodopsin Evolved for Them To See Through the Years?

A team of researchers discovered that whale sharks' rhodopsin (a protein in the eye that detects light) has evolved to detect blue light, which can easily penetrate deep sea water.

The amino acid substitutions, one of which has been linked to congenital stationary night blindness in humans, aid in detecting low levels of light in the deep sea.

Despite the fact that these changes make whale shark rhodopsin less thermally stable, the deep-sea temperature allows their rhodopsin to continue working.

This implies that the one-of-a-kind adaptation evolved to function in the low-light, low-temperature environment in which whale sharks live.

How Whale Shark Rhodopsin Evolved To See, In The Deep Blue Sea

(Photo : Koichi Kamoshida/Getty Images)

Professors Mitsumasa Koyanagi and Akihisa Terakita of the Osaka Metropolitan University Graduate School of Science led a study into the genetic information and structure of whale sharks' photoreceptor rhodopsin, which detects dim light, to better understand how they can see at extreme depths, as per ScienceDaily.

The whale sharks were compared to zebra sharks, their closest relatives, and brown-banded bamboo sharks, both of which belong to the same order: the orectolobiformes, also known as carpet sharks.

This study used genetic data and molecular biological techniques to achieve stunning results while causing no harm to whale sharks or their biology.

Koyonagi's research strategy is to use these techniques to uncover mysteries about how these organisms live.

The best part is that it works for species with limited information, such as large or wild animals that are difficult to observe or track in their natural habitat.

The whale shark's rhodopsin can detect blue light, the most common wavelength of light in the deep sea, thanks to two amino acid substitutions that shifted the light spectra that rhodopsin detects, making it sensitive to blue wavelengths.

One of the amino acid substitutions, however, defies conventional wisdom because it corresponds to a mutation known to cause congenital stationary night blindness in humans.

Also Read: Satellite Tracking Shows Migratory and Feeding Behavior of Whale Sharks

Rhodopsin

Rhodopsin is a G-protein coupled receptor and the most abundant protein in the retina's rod cells.

It is the primary photoreceptor molecule of vision and is composed of two components: an opsin molecule linked to a chromophore, 11-cis-retinal, as per Frontiers.

Opsin is made up of 348 amino acids and has seven transmembrane domains.

Rhodopsin is produced in the rough endoplasmic reticulum of photoreceptor inner segments and then undergoes posttranslational modifications in the Golgi before becoming functional.

Phototransduction occurs when light activates rhodopsin, initiating the exchange of GDP for GTP on the G-protein, transducing (Gt), and thus increasing cGMP (or cG) hydrolysis via the PDE complex.

When the concentration of cGMP falls, the cGMP-gated channels close, preventing depolarization caused by the influx of Na+ and Ca2+.

As a result, photon-induced rhodopsin activation is followed by a small, graded hyperpolarization in membrane potential.

Rhodopsin's photoreceptor function allows it to participate in the circadian rhythm. Degeneration of these photoreceptors can be characterized by a gradual thinning of the outer nuclear layer, a decrease in electroretinogram amplitudes, and vision loss.

According to a recent study, rhodopsin receptors in drosophila act as a circadian pacemaker in neurons.

Other studies have found that disruptions in normal circadian rhythms can have a significant impact on health, and potential mechanisms linking circadian dysfunction and neurodegenerative diseases have been proposed.