The deep sea is home to fish species that can detect various wavelengths in near-total darkness, discovered researchers.
The deep sea is the largest habitat on Earth and yet one of the least explored due to its inaccessibility.
According to the study published in the Journal of Science, 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 tiny amount of residual light that makes it to the depths of the ocean.
A team of researchers led by Professor Walter Salzburger from the University of Basel recently analysed fish living in deep-sea habitat and discovered that certain deep-sea fish have expanded their rhodopsin genes.
Researchers found not less than 38 copies of the gene, in addition to two other opsins of a different type. "This makes the darkness-dwelling silver spiny fin the vertebrate with the most photopigment genes by far," explained Salzburger.
The deep-sea fish have adapted to detect a certain wavelength of light, the researchers further reported.
They demonstrated this through computer simulations and functional experiments on rhodopsin proteins regenerated in the lab.
The genes cover exactly the wavelength range of light "produced" by light-emitting organs of deep-sea organisms. This is known as bioluminescence, which is the ability of an organism to produce light on its own or with the help of other organisms. For example, anglerfish attract prey with their bioluminescent organs.
"It appears that deep-sea fish have developed this multiple rhodopsin-based vision several times independently of each other and that this is specifically used to detect bioluminescent signals. This may give deep-sea fish an evolutionary advantage by allowing them to see much better potential prey or predators," said Salzburger.
"In any case, our findings help redefine the current paradigm of vertebrate vision in terms of the role of rod photoreceptors. This presents yet another instance in which analyzing whole genomes led to new biological discoveries," the zoologists wrote.
Colour vision in vertebrates is usually achieved through the interaction of various photopigments in the cone cells found in the retina. Each of these photopigments react to a certain wavelength of light.
In humans, for example, these wavelengths are the red, green and blue range of the light spectrum. Colour vision is only possible in daylight, however.
In the darkness, vertebrates detect the few available light particles with their light-sensitive rod cells, which contain only a single type of the photopigment rhodopsin, explaining why nearly all vertebrates are colour-blind at night.
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