[ad_1]
Is there animal more intimidating to study than the great white shark? Just try to fix a radio transmitter or take a tube of blood on a six-ton razor-tooth missile. But the scientific understanding of these iconic top predators has been limited by technical challenges as much as by human bias to study species that reside on branches closer to the taxonomic tree. Sharks evolved from the rest of the animal kingdom 400 million years ago, before the first adventurous amphibians left the oceans for dry land. What could the Great White teach humans in the 21st century?
Many in fact, according to scientists who have spent years painfully decoding his DNA. Today, they reported on their efforts to map the first large white shark genome in the latest issue of Proceedings of the National Academy of Sciences.
The main scientific step is a boon for conservation biologists seeking to better understand the population dynamics of large white sharks and other shark species, almost all of which are in sharp decline. And the massive genome – the great whites, in this case, have 41 pairs of chromosomes compared to our 23 – also contains clues as to how these ancient animals have so long ruled the oceans of the Earth. These clues may one day help our own infant-evolving species to live longer and less exposed to the disease. (Provided of course we do not burn the planet first.)
"Getting money for shark genomics is very difficult," says Michael Stanhope, an evolution biologist at Cornell University, who led the genome mapping project with his conservation friend, Mahmood Shivji, a conservation biologist. Guy Harvey Research Institute, Nova Southeastern University. Despite the decreasing cost of DNA sequencing, it was still a gigantic enterprise, costing hundreds of thousands of dollars, most of which was funded by the Save Our Seas Shark Research Center. "Historically, sequencing of other vertebrates, such as cattle and primates, has attracted much more interest," says Stanhope. "But sharks have a fascinating biology that really requires more investigation."
On the one hand, sharks are super healers. Fishermen and marine biologists have for decades exchanged stories of sharks bitten and skinned recovering completely from these serious external wounds a few months later. A recent study of black-headed reef sharks showed that they were remarkably resistant to physical trauma: they recovered from injury in a few weeks or even days.
The new genome map reveals how the Great White achieves this legendary health benefit inspired by red potions. Millions of years of competition in the dangerous waters of the world's oceans have refined a set of genes involved in several key processes of wound healing. These include DNA sequences encoding supercharged blood coagulation agents and scaffold proteins responsible for determining the fundamental units of the new flesh. In addition to having specially adapted versions of these genes, great white sharks also seem to have more than any other vertebrate. "They have dedicated a large part of their genome to healing wounds," says Stanhope, suggesting that the reign of the species at the top of the food chain is only a relatively recent development, in times of evolution.
In the absence of natural predators, great white sharks live regularly up to 75 years. Given their massive size and long lifespan (two recipes for accumulating many mutations), they should be mathematically more likely to develop cancer. But more and more researchers are realizing that large, long-lived, long-lived species, including elephants and whales, have no more cancer than humans. (Biologists call this the Peto paradox.) Sequencing studies suggest that these superior cancer control capabilities come from clusters of genes that serve to protect the integrity of the genetic code itself, a trait known as stability of the genome.
The new map of Stanhope and Shivji reveals that great white sharks also have huge pieces of code for these DNA repair mechanisms that stabilize the genome and suppress the tumors. Sharks having evolved so long ago and so far from the man on the tree of life, it is possible that these genes represent totally new cancer defenses. The incidence of cancer in wild sharks being poorly understood, scientists plan to test this hypothesis in the laboratory. By splicing genome-stabilizing shark genes into transgenic mice, and then exposing rodents to well-known carcinogens, they hope to measure the protection powers of shark DNA.
"Understanding how these genes could inoculate these animals against cancer could be a huge benefit for humans," says Stanhope. But he points out that it will take years of work to translate these findings into potential anticancer drugs or new methods of treating human wounds. Consuming shark products will not confer any of their super powers. "When you eat shark, you're no more likely to be protected from cancer than to develop the ability to swim faster," says Stanhope.
But people peddling this false belief support an illegal fishing industry that would clog around 100 million sharks each year, cut off their fins and send them back to the sea to prevent them from dying under the waves. Stanhope and Shivji hope that their work will help shed light on how remarkable these creatures are, to encourage people to conserve rather than consume them. Of the more than 500 species of sharks swimming in the waters of the Earth, the big white is only the second to have its genome sequenced. Who knows how many mysteries are hidden under the surface, in DNA chains just waiting to be decoded.
More great cable stories
[ad_2]
Source link