How did the woolly mammoth stay warm?
To keep warm, the woolly mammoth did more than just be woolly, new research has found.
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Other Arctic animals today, such as reindeer and musk-ox, have a "counter-current" blood system. Essentially the blood vessels taking the warm, oxygen-laden arterial blood down into the legs and feet pass very close to the veins carrying colder, venous blood back to be re-oxygenated. The close contact between the two types of vessels allows the arterial blood to pass its warmth on to the venous blood headed back to the heart and lungs. This evolutionary system keeps the warmth in the core of the animal's body and reduces heat loss due to the cold climate, while still allowing the arterial blood to take its oxygen to the extremities.Skip to next paragraph
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"It allows their feet and extremities to get really cold," Campbell said.
This is in contrast to humans, where blood flow simply shuts down in extreme cold to keep warmth in the core – that's why people get frostbite but reindeer don't.
But this counter-current system isn't enough by itself to keep Arctic animals functioning in the cold. The key involves hemoglobin, the blood protein that grabs oxygen in the lungs and delivers it to the other organs of the body. The blood protein essentially needs a certain amount of heat energy to power its release of the oxygen molecules it carries into the tissues and organs that need it.
When blood is cold "it's very unlikely that that threshold is going to be met," Campbell said.
To get around this problem, reindeer and many other Arctic mammals evolved a slightly tweaked form of hemoglobin that requires less energy input to deliver its oxygen.
Resurrecting an ancient molecule
Campbell wanted to see if mammoths were also able to evolve a specialized form of hemoglobin that would keep working at cold temperatures and allow them to conserve body heat.
There was just one problem: mammoths are extinct.
"We can't take a frozen blood sample," Campbell explained.
Instead, Campbell and his colleagues used genes extracted from mammoth remains to recreate and examine mammoth hemoglobin.
"We had to bring it back to life," Campbell said.
The team extracted DNA from a 43,000 year-old Siberian mammoth specimen and had the portion of it that holds the instructions for hemoglobin sequenced.
When Campbell saw the results he said could tell that "there were some changes that were very suggestive of physiological processes" that meant the mammoths did indeed evolve a specialized cold-adapted form of hemoglobin.
The changes amounted to just 1 percent of gene region that contained the instructions for hemoglobin, "but one of those changes is profound," Campbell said. That change "is going to make them adapted to cold."
To find out if these gene changes actually produced a different type of hemoglobin, the team used a method that has been used to make human hemoglobin. The method involves putting the specific genes into E. coli, which will read the human, or mammoth, DNA like its own DNA and produce the substance in question.
But mammoth DNA samples retrieved from frozen specimens are very damaged, so Campbell and his team first turned to the mammoth's closest living cousin. They got the DNA and RNA (the stuff that holds the instructions for proteins in cells) from a living Asian elephant and put them into E. coli.