Summary of a Genetics-Related Article from a Magazine
Whale sharks are enormous sharks that travel long distances in search of their food. These white and blue spotted sharks are also known for their long vertical range within the ocean. They can swim from the brightest surface of the ocean to two thousand meters deep. Scientists began to question how these sharks can dive deep into the ocean where no sunlight can penetrate the darkness below. Studies have provided genetic evidence of how a whale shark’s vision is critical and pertinent to its vertical range.
Through their research, scientists have discovered how these whale sharks can see and deal with the contrasting light in their vertical range. An unusual genetic mutation in these gentle giants makes a pigment in their retina more sensitive to temperature changes.1 As a result, whale sharks can utilize different parts of their vision at diverse levels within the sea. This genetic mutation aids the whale sharks in navigating through the deep dark waters of the ocean with rhodopsin, which is a light-sensing pigment in the retinas of their eyes. Research has shown that this pigment within the whale sharks’ eyes has been calibrated to see blue light only. This specific configuration helps these sharks because the only color that can reach the depths of the deep sea is blue.
One evolutionary biologist and his colleagues organized experiments on zebra sharks’ eyes. The scientists compared their findings about the zebra sharks to genetic data that was published earlier on whale sharks to determine the differences in the genetic makeup of the two sharks. There were two spots – known as sites 94 and 178 in their DNA – where the rhodopsin protein was altered due to mutations that altered its amino acid composition.1 The scientists discovered that the rhodopsin mutants from the whale shark contained a blue shift caused by a unique spectral tuning in site 94. This genetic mutation allows whale sharks to alter their vision in order to see the blue light when they are in the lower depths of the ocean.
Another study supports the article in the idea that changes in the identity of the amino acid in one’s DNA sequencing can cause a spectral shift between pigments of one’s visual opsins. Opsins are proteins that can combine with retinal to form a visual pigment or perception. Based on nucleotide and amino acid sequence homology, vertebrate opsins cluster into five major classes: rhodopsin type 1 (RH1), rhodopsin type 2 (RH2), short-wavelength-sensitive type 1 (SWS1), short-wavelength-sensitive type 2 (SWS2), and long-wavelength-sensitive (LWS).2 This research study expresses how the spectral tuning of the long wavelength sensitive opsin clusters within the whale shark is the source of the blue color shift in the shark’s eyes.
Overall, this article relates to genetics through its discussion and explanation of how the whale shark received its ability to see in the deep sea. It described how the RHO mutant within the whale shark uncovered that the tuning of site 94 in its DNA caused a blue shift in its vision to see deep underwater. This genetic mutation has provided the whale shark with the remarkable ability to travel and maneuver its way through different depths of the ocean. This genetic alteration has also permitted this endangered species to filter feed in the shiniest surfaces to the darkest crevices of the ocean.
References
1. Márquez, M. C. Whale sharks can see in the dark thanks to genetic mutation. Forbes; https://www.forbes.com/sites/melissacristinamarquez/2023/04/02/whale-sharks-can-see-in-the-dark-thanks-to-genetic-mutation/?sh=7e5b94242efd (2023).
2. Yamaguchi, K. et al. Whale shark rhodopsin adapted to deep-sea lifestyle by a substitution associated with human disease. PNAS; https://doi.org/10.1073/pnas.2220728120 (2023).