Sharks could hold genetic secret to long life

The sharks, which live for up to 392 years, are believed to have unique genes which could help explain not only its incredibly long life span, but life expectancy in other vertebrates, including humans.

In a lecture at the University of Exeter, as part of the Fisheries Society of the British Isles symposium, Professor Praebel, of UiT the Arctic University of Norway, described the sequencing of the DNA from Greenland sharks, some of which were alive in the Georgian era.

Professor Praebel and his collaborators are now searching for the ‘unique genes’ which could hold the secret to the shark’s longevity. The scientists have obtained the Greenland shark’s DNA from tiny clippings from the fin of the shark which are caught on a line live and tagged and released.

The geneticist, with his team of scientists from the Old and Cold project, has sequenced the full mitochondrial genome (the complete mitochondrial DNA information of an organism) of almost 100 Greenland sharks, which includes individuals born in the 1750s. The genetic sequences has helped them understand whether the Greenland shark has evolved specific metabolic adaptations towards extreme longevity.

They are now attempting to find the genes that hold the secret to why the sharks live so long. The geneticist believes the Greenland shark’s extreme life span makes it so unique that there is a case for giving it a special conservation status.

“This is the longest living vertebrate on the planet. Together with colleagues in Denmark, Greenland, USA, and China, we are currently sequencing its whole nuclear genome which will help us discover why the Greenland shark not only lives longer than other shark species but other vertebrates,” he said. “The results we presented here in Exeter will help us understand more about the biology of this elusive species.”

When found, the ‘long-life’ genes could shed light on why all vertebrates have a limited life span, and what dictates the life expectancy of different species including humans.

Little is known about the biology and genetics of the Greenland shark which is found in deep water in the Atlantic ocean from Canada to Norway including the deep oceans around the North of Britain.

The Greenland shark is widely distributed in the north Atlantic ocean. The Greenland shark is part of the sleeper shark family which has existed for around 110 million years.

The oldest and largest (502 cm female) Greenland shark analysed by the scientists were 392 years, plus or minus 120 years: in other words they were at least 272 years old.

The study of the shark’s DNA has shed new light on its behaviour, and how it is related to other members of its species living thousands of kilometres away, he told an audience of marine scientists at Exeter University this week.

“Since the Greenland shark lives for hundreds of years, they also have enough time to migrate over long distances and our genetic results showed exactly that. Most of the individuals in our study were genetically similar to individuals caught 1000s of kilometres away,”, Professor Praebel said. “We still do not know where and how the Greenland shark reproduce, but the results we presented here in Exeter showed that the shark may prefer to mate in deep hidden fjords of the Arctic.”

But Professor Praebel also said that we are still far from understanding how and why the elusive type of shark, which feeds on seals and fish, lives so much longer than other sharks and vertebrate species.

Many living Greenland sharks are so old that they pre-date the industrial revolution and the introduction of commercial fishing by mankind on a grand scale.

Professor Praebel said the sharks are living time-capsules that could help uncover the impact of man on the oceans over time.

Tissues, bones, and genetic data from the shark help measure the impact of climate change on the population, when and how contaminants and chemical pollution from industry began to affect the oceans, and the extent to which commercial fishing over hundreds of years has affected the shark population.

“The longest living vertebrate species on the planet has formed several populations in the Atlantic Ocean. This is important to know, so we can develop appropriate conservation actions for this important species,” he said.