Glowing Sharks can see Complex Light Patterns: PLOS ONE
Researchers have found how the eyes of mysterious glowing sharks are able to see complex light patterns in the gloomy waters. Numbers of light-sensitive retinal cells, known as rods, are higher in bioluminescent sharks than their non-glowing shark relatives.
Also, the glowing sharks evolved to have adaptations in their vision to signal each other and capture their prey in the mesopelagic twilight zone, where the light is very dim, said the study published in the open-access journal PLOS ONE.
The zone is located from 650 feet down to 3,200 feet and bioluminescent light is only available there. Belgian researchers have found that light is produced by about 50 different shark species.
Julien Claes, a biologist at the Catholic University of Louvain and the study's lead author, said bioluminescent sharks are able to adjust their illumination as camouflage because of a translucent region of the eye's upper orbit.
Moreover, a gap between the iris and lens of the eye makes it possible for the retina to get more light. The resolution capability in detecting dim lights is significantly improved by the higher density of rod cells in the eyes, which is very good for receiving bioluminescent signals used in social interactions.
"Every bioluminescent signal needs to reach a target photoreceptor to be ecologically efficient. Here, we clearly found evidence that the visual system of bioluminescent sharks has co-evolved with their light-producing capability, even though more work is needed to understand the full story", said Claes.
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