Bowhead whales are the longest-lived mammals known, with one male estimated to have been about 211 years old when it was killed by hunters. Now it has been found they have a gene duplication that appears to slow the division of cells, allowing the whales to live longer 鈥� but at the cost of reduced male fertility.
The long life of bowheads is probably a result of many genetic changes, but this one may be especially important, says of the University at Buffalo in New York, whose team discovered the duplication.
鈥淭he effect of this particular gene being duplicated is probably pretty significant,鈥� he says.
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One of the greatest obstacles to a long life is cancer, because the longer you live, the more time there is to acquire cancer-causing mutations. Yet large, long-lived animals such as elephants and whales seem to have very low rates of cancer, a phenomenon known as Peto鈥檚 paradox.
This must be because these animals have evolved mechanisms for preventing tumours forming. Lynch and others have shown that even low levels of DNA damage trigger programmed cell death in elephants, eliminating cells before they can turn cancerous.
But it seems that bowhead whales have another strategy. 鈥淭he alternative is to keep the cell from dividing, and give the cell time to fix the damage,鈥� says Lynch.
This is what he thinks happens in bowhead whales as a result of the duplication of a gene called CDKN2C. At some point not long after bowhead whales and right whales split from a common ancestor some 5 million years ago, an RNA copy of CDKN2C got turned back into DNA and inserted into the genome at a site that ensures the gene is highly active 鈥� that is, lots of the CDKN2C protein gets made.
Studies of human and mouse cells have shown that high levels of the CDKN2C protein halt cell division and also prevent programmed cell death. It seems to have the same kind of effect in bowhead whales 鈥� Lynch found that it takes about 15 hours longer on average for various types of bowhead whale cells to double in number than it does for cells from other whales.
Other studies have also shown that higher levels of this protein affect male fertility. CDKN2C helps determine how many cells are involved in generating sperm and the size of the testes, says Lynch.
The testes of bowhead whales are relatively small, weighing about 200 kilograms compared with 1000 kilograms for the closely related right whale, the team notes. Several apparently female bowhead whales have turned out to be males with underdeveloped testicles.
While the findings help explain how bowhead whales live so long, it doesn鈥檛 explain why they are the only whale species to have evolved this trait, says Lynch. 鈥淭hat鈥檚 still a mystery.鈥�
Other whale species are thought to live for just 50 to 70 years. But it is possible that their lifespans have been underestimated, says at the University of California, San Diego, who developed the technique used to estimate the ages of bowhead whales and other animals.
鈥淥ther whales were so badly over-harvested during the time of extensive whaling that their ages are only now starting to show,鈥� says Bada.
There may be other long-lived animals with quite different ways of resisting cancer, says Lynch. One of the many issues with the loss of biodiversity is that these animals could go extinct before we have a chance to discover and study these mechanisms, he says.
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