Greenland sharks, the longest-lived vertebrates in the world, show no signs of physical deterioration in their retinas even after living for hundreds of years. The finding is especially surprising as some scientists suspected the animals were functionally blind since they live in such deep, dark waters.
at the University of Basel, Switzerland, and her colleagues conducted physical studies of the eyes of eight dead Greenland sharks (Somniosus microcephalus) and sequenced their DNA.
In humans and most other animals, the light-detecting cells on the retina at the back of the eye degenerate over time, resulting in blurred vision. But even though the sharks in the study were estimated to be centuries old when they died, the team found no signs of retinal degeneration.
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Most vertebrates have two types of light-detecting cells: cones, which can differentiate colours, and rods, which don鈥檛 allow colour vision but work much better at low light levels. The researchers found that genes involved in cone function were largely inactive, suggesting that Greenland sharks rely mostly on their rods for vision.
The team attributes the extreme longevity of Greenland shark vision to a gene involved in DNA repair called ercc1, which seems to be more active in Greenland sharks than other sharks.
They also found that the gene for melanopsin, a light-sensitive protein that mediates the circadian rhythm in vertebrates, has become non-functional in Greenland sharks.
鈥淚t thus appears that Greenland sharks may not rely on light to regulate [their] circadian rhythm or may use alternative mechanisms to mediate this process,鈥� Fogg and her colleagues write in a paper submitted to a journal. They declined to speak to 快猫短视频 about the study.
at the University of Manchester, UK, says in the absence of melanopsin, it is possible that the sharks use other cues to regulate their life cycle and biological processes, such as temperature or the need to feed.
It is intriguing that the Greenland sharks seem so adapted to maintaining their eyesight when previous research suggested they may not be reliant on their vision, he says.
鈥淎s someone who studies ageing, it鈥檚 great to see some research showing the Greenland sharks鈥� range of adaptations, which make it so suited to its extreme longevity.鈥�
bioRxiv
