Woolly mammoths went extinct near the end of the last major ice age, more than 10,000 years ago. Now, genetic analysis reveals how these iconic creatures were able to withstand the bitter cold of that long-gone era.
Investigators on the study examined the genetic code of a pair of mammoths who died 60,000 and 20,000 years ago. To reduce the risk of errors, each letter of the genome was read an average of 20 times.
"I've been trying for a long time to show that ancient genomes can be sequenced as accurately as extant genomes, and the woolly mammoth seemed like an ideal species for demonstrating this capability. The Asian elephant genomes were needed for comparison in the subsequent analyses," Stephan Schuster from Nanyang Technological University said.
The genetic codes of woolly mammoths were compared with those found in modern-day elephants, including those from Asia and Africa. Researchers found the genomes of the ancient creatures directed the growth of hair and skin capable of withstanding a bitterly cold environment. The genes also directed specific patterns of fat metabolism and insulin signaling designed for living conditions in the frigid conditions.
One protein, TRPV3, responsible for temperature sensation, storage of body fat and growth of body hair, was found to have a specific mutation in mammoths. Investigators resurrected this gene in the lab by placing it within a human kidney cell.
In addition to genes coding for physical characteristics design for cold-weather living, researchers also found segments of the genome calling for small ears, short tails and the animal's distinctive mammoth-shaped heads.
"This is by far the most comprehensive study to look at the genetic changes that make a woolly mammoth a woolly mammoth. They are an excellent model to understand how morphological evolution works, because mammoths are so closely related to living elephants, which have none of the traits they had," said Vincent Lynch, a geneticist from the University of Chicago.
Mammoths once roamed North America, Europe and northern Asia. In addition to their thick, distinctive coats, the animals also possessed a layer of fat to keep them warm, including a storehouse at the backs of their necks.
The genetic code of once-living beings decays over a relatively short period of time. Because of this, DNA extracted from the remains of mammoths is incomplete and riddled with errors.
Researchers hope their analysis will help paleontologists and biologists learn more about the long-extinct animals. This study could also help lead to bringing back the extinct animals.
Investigation into the genetic mutations that allowed woolly mammoths to thrive in cold weather was published in the journal Cell Reports.
Photo: Andrew Wilkinson | Flickr