Deep-sea snailfish repairs its DNA to survive 7 km below the surface
With pressure pushing down on it, a deep-sea fish has evolved a catalogue of adaptations to help it survive in the crushing depths of the Pacific Ocean. The fish has extra genes for repairing its DNA for making a chemical that stabilises essential proteins. It has also lost many of the genes that underpin the sense of smell, perhaps because it has a limited diet.
The fish was collected in 2017, when the Chinese submersible Jiaolong descended into the Yap Trench in the western Pacific Ocean. At a depth of 6903 metres, a deep-sea lander caught two fish belonging to a previously unknown species.
They were snailfish, a little-studied group of fish whose members live at a huge range of depths. Snailfish look a bit like tadpoles, don’t have scales: their bodies are jelly-like.
Because the new species was found in the hadal zone, which begins at 6000 metres below sea level, it has been tentatively called Yap hadal snailfish. At such depths, there is no sunlight, the water is cold, food is scarce the pressure is intense.
To find out how the Yap hadal snailfish survives, researchers led by Xinhua Chen at Fujian Agriculture Forestry University in Fuzhou, China, have now sequenced its genome.
They found that the snailfish genome has extra copies of genes involved in DNA repair, including eight copies of a gene called rad51. Some DNA repair genes also contained mutations that would alter the proteins they coded for – although it is unclear at the moment if or how this is a helpful adaptation for life at depth.
The snailfish also had five copies of a gene called fmo3, which is crucial for the production of trimethylamine N-oxide (TMAO): a chemical that stabilises proteins may protect them from becoming damaged by the intense pressure. In line with this, the snailfish’s muscle tissue had elevated levels of TMAO, compared with zebrafish that live in shallower waters.
The Yap hadal snailfish had lost many olfactory receptor genes, suggesting a limited sense of smell. Chen says this may be because it has a repetitive diet – the snailfish’s stomach was filled with just one species of crustacean. Curiously, it has extra genes for sour taste receptors, it isn’t clear why.
Chen his team also explored the origins of the Yap hadal snailfish. They compared its genome to that of the Mariana hadal snailfish, which lives in the Mariana Trench hundreds of kilometres to the north-east, was sequenced in 2019.
The two snailfish species turned out to be closely related. Chen says the two trenches they live in formed 8 to 10 million years ago, so it may be that the ancestral snailfish found their way into the two trenches subsequently evolved independently. “These two trenches are isolated, they have different depths environmental conditions,” says Chen.
Journal reference: PLoS Genetics, DOI: 10.1371/journal.pgen.1009530
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Article amended on
17 May 2021
We updated the story to clarify how the two fish were caught
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