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Silver spruce, or small dori, inhabits a deep seabed, where the blue of the Twilight Zone turns black, often half a mile from the surface. There, they can see the world like no other animal known to science.
Scientists have generally understood that color vision is not necessary on the high seas. It is too far for the sun's rays to penetrate, so there is no light that gives way to color. But in a study published Thursday in Science, researchers interested in the evolution of color vision analyzed the genomes of 101 different fish. They discovered that one of them, silver spruce, has more genes to discriminate dull light than any other vertebrate on the planet. These genes can visualize the entire daylight range and the entire spectrum of bioluminescence on the high seas. Other fish can also have this ability to detect color in the deep sea.
"In vertebrate fish, we had never seen anything like it," said Megan Porter, who studied the evolution of vision in Canada. University of Hawaii in Mānoa and has not been involved in the research. "This goes against what we have understood as the way visual systems have evolved in the deep sea, which means that we have to wonder about how visual systems work in low light conditions. . "
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The basics of vision begin when light hits our retinas, which contain photoreceptor cells called rods and cones sensitive to particular wavelengths. Inside these cells, photopigments or proteins called visual opsines help to translate light into signals that our body can understand.
Vertebrates usually have up to four cone photoreceptors and a rod photoreceptor. Most humans, for example, see color entering three cones: red, green, and blue. Cones help us see colors in bright light, but under dim light, we are usually color-blind and we only see the intensity based on the inputs of a single stem.
But some deep water fish seem to see their world in a very different way.
Looking more closely at 101 genomes, they discovered that three different lines of deep-sea fish had additional copies of genes to see in low light. Of these, the spruce money took the cake. He possessed genes for two conical opsines and 38 opsines stems – more abundant and sensitive to more blue than any known vertebrate.
"We are quite surprised, say, by this discovery, because it is very unique," said Dr. Musilová.
But more surprising was that the silver spines still used up to 14 of these rod-producing genes (adults in deeper water expressed more rod genes than their larvae living in shallower waters). And each opsin is tuned to a slightly different wavelength, green or blue.
These fish can use their extra genes to detect subtle differences and see the world in shades of blue and green that we can not even imagine.
It is also possible that these fish do not use all this extra visual power. Scientists have previously studied mantis shrimps, which have complex eyes with over a dozen color-sensitive cones and a visual treatment system unlike any other on the planet. Of course, they can detect more colors, but other research has shown that Mantis shrimps are no better than humans in discerning subtle color differences when paired with treats.
"The shrimp mantis is a case study of how wrong we were to know how they used all their different receptors," Dr. Porter said. It is possible that these fish use canes to see the colors, but what would this world look like? "I'm not even willing to take risks just because it looks like everything we've ever seen," she added.
Most scientists thought that when creatures entered and adapted to the deep sea, they lost expensive and unnecessary functions, such as vision, especially the genes used to visualize colors. So what is the benefit of copying and conserving the genes that make the rod opsins?
Silver spinners, which are not bioluminescent, could better detect the bioluminescent signals of predators and prey that use them at depth. Their vision could also help them see better as they migrate between different depths during development.
"Either there is an ecological difference that is at the root of that, or have we just not looked enough to see the same pattern in other marine species?" Said Dr. Porter. "We still do not know much about the deep sea."
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