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Some fish living in a deep, dark sea can see their world in more than shades of gray.
A study of 101 fish species found that four deep-sea species had a surprising number of genes for light-sensitive ophthalmic proteins called Rod Opsins, researchers said on May 10. Science. Depending on how animals use these light sensors, the discovery may challenge the widely held view that deep-sea fish do not see color, says co-author Zuzana Musilová, an evolution biologist. Charles University of Prague.
To see, many fish, humans, and most vertebrates use two types of cells that detect light in the eye, called rods and cones. Cone cells use two or more types of ops and need a decent amount of light to function. Stems usually use a single opsin called RH1, which works in low light. This variety of opsins in cones, but not in sticks, allows vertebrates to see a well lit range of colors, but to be color – blind in the dark.
In the new study, Musilová and Fabio Cortesi from the University of Queensland in Brisbane, Australia, sailed aboard research vessels equipped to reach the ocean depths. L & # 39; abyss–the specimens of the sea came from the "twilight" zone 200 to 1,000 meters below the surface, where the sunlight only becomes a subtle diminution of the darkness. The most colorful things to watch would be the bioluminescent stains on the bodies of animals.
The four special-eyed deep-sea fish came from three different lineages that had independently grown genes of more than one type of opsin RH1 rod, report Musilová, Cortesi and their colleagues. Glacier lantern fish (Icy benthosema) had genes for five different forms of RH1 and an ocular tube (Stylephorus chordatus) had six. Two species of spines still have more genes, 18 genes for spruceDiretmoides pauciradiatus) and a superb 38 for silver spruce (Diretmus argenteus).
It would have been remarkable to find only two opsine canes, but the count of silver spinach is "staggering," says evolution biologist Megan Porter of the University of Hawaii at Manoa, who has not participated in the new research. But she and others warn against abandoning conclusions about how fish use all these varieties, as there is no test for fish behavior.
According to Musilová, these tests may not even be possible given the place of residence of these fish. When they came to the surface, "most of them die simply because of pressure changes," she says. "Even bringing them to the surface alive does not guarantee that they would behave in the same way as they do in the depths. "
The fish caught by the researchers allowed them to check which opsin genes were actually activated in the animal's retina. This work has confirmed that silver silver spine uses at least 14 of its 38 RH1 genes to make proteins.
The researchers also introduced the different RHI genes of the silver spine spine into a bacterium that made fish opsins. Tests on the function of these opsines have shown that they have the potential to capture both a very dim light and a wide range of blue and green lights from living bioluminescent creatures, the scientists discovered.
Overall, the authors are rightly "cautious" in not claiming that deep-sea fish can see colors, explains Almut Kelber of Lund University in Sweden, who has studied color vision by low light in frogs.
The new fish findings, for example, do not specify whether different RHI opsines cluster in individual rod cells or are dispersed with different rod cells bearing different opsins. To differentiate the colors, the opsins of the sticks should be in different cells. But if the proteins clump together in each stick, the fish will likely have increased sensitivity to light and will be able to distinguish lighter objects in black and white tones.
Even with the uncertainties, finding all these unexpected problems "is always exciting," says Kelber.
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