The oxygen-carrying molecules in the blood of woolly mammoths was adapted to survive extreme cold.Corbis
- Woolly mammoth hemoglobin has been brought to life in the laboratory.
- Mammoth blood contained special cold adaptations that helped them survive in the Arctic.
- The discovery shows a great example of what's called "convergent evolution."
The woolly mammoth lives! At least the hemoglobin in its blood lives, now that researchers have recreated it using a bacteria reprogrammed with 43,000-year-old mammoth DNA.
What the extinct pachyderm's oxygen-carrying blood molecule has revealed are some unique adaptations to cold which allowed mammoths to survive the most brutal Arctic ice age winters without their limbs falling off. The discovery might also lead to medical applications for humans.
Because hemoglobin doesn't usually do its oxygen-delivering job very well when cold, researchers looked specifically for specialized adaptations in the mammoth hemoglobin that made it better at this task than modern elephants. Sure enough, they found very specific changes to the hemoglobin molecule that helped it operate at lower temperatures.
"The mammoth we wanted to see because elephants evolved in Africa," said Kevin Campbell of the University of Manitoba in Winnipeg. So unlike some other cold-adapted mammals, mammoths were a relatively recent immigrant to the Arctic. Reindeer and musk oxen have special blood adaptations too, but they evolved separately.
"What I was most amazed by is they use a mechanism not used by any other animal," said Campbell. "That, to me is, fantastic."
It's also a great example of what's called convergent evolution, he said. That's when the same adaptation evolves separately in different animals -- like wings, which evolved separately in birds, insects and mammals.
The mammoth hemoglobin cold adaptation mechanism is actually two mechanisms, as Campbell and his colleagues report in the May 2 edition of the journal Nature Genetics. Both adaptations have to do with making sure there is enough energy available to allow the hemoglobin to release oxygen. Under cold conditions, Campbell explained, hemoglobin's grip on oxygen is a lot tighter and there is less energy available to break it free and give it to cells.
"The hemoglobin can't release oxygen," Campbell said. "So these tissues would starve of oxygen and die."
The mammoth hemoglobin gets around this by lowering the amount of energy required to offload the oxygen. Specifically, it uses tiny amounts of heat given off by a couple of reactions that are also underway on the hemoglobin molecule. These other reactions relate to the binding of hemoglobin to other compounds like chloride and protons inside the red blood cells. The result is a far more energy efficient hemoglobin molecule.
"They are really testing an important question about physiological evolution," said Jay Storz of the University of Nebraska in Lincoln. "It's really exciting work."
Next, Campbell would like to look at the hemoglobin of the Steller's Sea Cow of the Arctic, which is believed to have gone extinct in 1768. Then there's the extinct woolly rhinoceros.
As for how this might be of use to humans, Campbell points to the use of cold to treat victims of heart attacks and other maladies. The use of specially designed cold-efficient hemoglobin in these situations could save lives.