"The coelacanth isn't called a "living fossil" for nothing. The 2-meter-long, 90 kg fish was thought to have gone extinct 70 million years ago—until a fisherman caught one in 1938—and the animal looks a lot like its fossil ancestors dating back 300 million years. Now, the first analysis of the coelacanth's genome reveals why the fish may have changed so little over the ages. It also may help explain how fish like it moved onto land long ago…
In order to sequence a coelacanth's (Latimeria chalumnae) genome, scientists required fresh tissue and blood. That's no easy task: These fish dwell in deep-sea caves and are exceedingly rare. Only 309 have been spotted in the past 75 years, off the east coast of sub-Saharan Africa and Indonesia. Moreover, caught coelacanths die immediately because of the change in pressure and temperature, and under the hot tropical sun, their DNA quickly degrades.
One of the 91 members of the coelacanth genome team, cell biologist Rosemary Dorrington of Rhodes University in Grahamstown, South Africa, showed fishermen in the Comoros archipelago off South Africa's coast how to collect coelacanth tissue in case they accidentally caught one again. She handed out kits including scalpels and glass vials filled with a solution to preserve the genetic material for a few days until it could be shipped to a laboratory and refrigerated.
Dorrington helped convince the fishermen that the genome project was worth their effort. "For these fishermen, fossils and evolution don't have significance," she says, "but they understand that this creature makes the world a richer place." Her efforts paid off: Fishermen collected samples for the project in 2003. The genome sequencing didn't begin until 2011, however, when the research team had the funds and technological power to do it."
It took about 6 months to sequence the coelacanth's genome at the Broad Institute in Cambridge, Massachusetts, and a year to analyze the data. Lead author Chris Amemiya, an evolutionary biologist at the University of Washington, Seattle, and his colleagues looked at genes that encoded a few hundred proteins. Then they calculated the number of estimated changes that occurred in the genes over the time since the coelacanth branched off from other vertebrates on the animal family tree. Finally, they compared those data with the corresponding rates of genetic change in various mammals, lizards, birds, and fish…"
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Amicalement
Armand
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