An international team of researchers led by evolutionary biologist Walter Salzburger from the University of Basel (Switzerland) has discovered that there are some species of deep-sea fish that can detect various wavelengths of light in almost total darkness. Unlike other vertebrates, they have several genes for light-sensitive photopigmentary rhodopsin, which probably enables these fish to detect bioluminescent signals from light-emitting organs. This finding has been published in the journal Science .
Color vision in vertebrates is generally achieved through the interaction of various photopigments in the cells of the retinal cone. Each of these photopigments reacts to a certain wavelength of light. In humans, for example, these wavelengths are the red, green, and blue range of the light spectrum. However, color vision is only possible in daylight. However, in the dark, photoreceptors called rods that make it possible to see in low light only allow vertebrates to see in black and white.
Distinguish the world at 1,500 meters deep
In 99% of all vertebrates, the rods express only one type of light-sensitive opsin, which means that the vast majority of vertebrates are color blind in low light conditions. Vision in most deep-sea fish follows this same pattern, but the new research revealed some notable exceptions.
The scientists analyzed more than 100 fish genomes , including those of fish that live in deep-sea habitats. Zoologists discovered that certain deep-sea fish have expanded their repertoire of genes for rhodopsin – the protein in the rod discs of the retina. In the case of the silver spiny fin ( Diretmus argenteus ), they found no fewer than 38 copies of the rhodopsin gene, plus two other opsins of a different type. They are more opsins than the researchers found in the cones of any other fish and the largest number of opsins found in any known vertebrate. “This makes the silver spiny fin that lives in the dark the vertebrate with the most photopigment genes, ” explains Salzburger.
According to experts, the different copies of the rhodopsin gene in deep ocean fish have been adapted to detect a certain wavelength of light. They demonstrated this through computer simulations and functional experiments with regenerated rhodopsin proteins in the laboratory. Genes cover exactly the wavelength range of light “produced” by the light-emitting organs of deep-sea organisms. It is what we know as bioluminescence, the ability of an organism to produce light on its own or with the help of other organisms.
Detecting signals in the dark
The deep sea is the largest habitat on Earth and yet one of the least explored due to its inaccessibility. Many organisms have adapted to life in the near total darkness of this inhospitable environment. For example, many fish have developed highly sensitive telescope eyes that allow them to detect the small amount of residual light that reaches the depths of the ocean.
“It appears that deep-sea fish have developed this vision based on multiple rhodopsin or multi-rod opsins – several times independently, and that this is used specifically to detect bioluminescent signals,” clarifies Walter Salzburger, leader of the work. This circumstance can give deep-sea fish an evolutionary advantage by allowing them to see much better prey or potential predators, the authors argue.
“In any case, our findings help redefine the current paradigm of vertebrate vision in terms of the role of rod photoreceptors,” the zoologists write. This is another case in which the analysis of whole genomes has led to new biological discoveries.
“This is the first paper to examine a diverse set of fish and discover how versatile and variable their visual systems can be,” says Karen Carleton, a professor of biology at the University of Maryland and a co-author of the study. “The genes that determine the spectrum of light in our eyes are sensitive to becoming a much more variable set of genes, causing further evolution of the visual system much faster than we anticipated.”
It is important to note that the four species of fish that they found with more than three opsins are unrelated species . This suggests that deep-sea color vision evolved independently several times and may confer some survival benefit.
The researchers say their next steps are to expand the study to other deep-sea fish.
Referencia: Zuzana Musilova, Fabio Cortesi, Michael Matschiner, Wayne I. L. Davies, Jagdish Suresh Patel, Sara M. Stieb, Fanny de Busserolles, Martin Malmstrøm, Ole K. Tørresen, Celeste J. Brown, Jessica K. Mountford, Reinhold Hanel, Deborah L. Stenkamp, Kjetill S. Jakobsen, Karen L. Carleton, Sissel Jentoft, Justin Marshall, Walter Salzburger. Vision using multiple distinct rod opsins in deep-sea fishes. Science, 2019; 364 (6440): 588-592 DOI: 10.1126/science.aav4632 science.sciencemag.org/cgi/doi … 1126/science.aav4632
Crédito imagen: Pavel Riha, Univestiry of South Bohemia, Ceske Budejovice / Alexandra Viertler, University of Basel
