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The Andes are home to some of the highest peaks in the world. Lots of volcanoes. Where temperatures never exceed 0°C. Cold and dry environments. deserts. Where the oxygen levels are a little over half of what we experience on the floor of cow cows. When archaeologists found the corpses of mice there, they initially thought that the poor animals had been carried along in the luggage of some Incas on the way to a sacred site. Because no mammal can survive under these conditions. That’s what researchers thought in the 1970s and 1980s. And that was until recently.
Until 2020. At that time, a biology professor at the University of Nebraska (USA) reported that he had also observed mice in the region. It was located on the summit of Llullaillaco, the second highest active volcano in the world. At over 6,700 meters above sea level, on the border between Chile and Argentina. Jay Storz has come across some amazing mice. Patagonian mice, but especially mice… alive!
These mice survive in an extreme environment
Since then, researchers have found other equally live mice, as well as some mouse mummies. And this on at least three peaks in the Andes, each of which is more than 6,000 meters above sea level. They present their work today in the journal Current Biology.
Carbon-14 analysis shows that several of the mouse mummies found on Andean peaks date from after 1955. The others died no more than 350 years ago. Long after the fall of the last Inca Empire. The latter therefore had nothing to do with their presence at these heights. DNADNA analysis, in turn, shows that the mice found there come from the same family as those that live on the flanks or base of volcanoes. So mountain mice? Maybe still not. The researchers observed just as many female mice as male mice. And a few caves too. Enough to imagine that these mice have managed to settle on these peaks and live in conditions that are neither more nor less similar to those that exist on the planet Mars!
“It is simply mind-boggling that any type of animal, let alone a warm-blooded mammal, can survive and function in this environment,” the researchers emphasize. Now the question arises: How can these mice, which weigh just over 50 grams, live under such extreme conditions? To find out, researchers are currently conducting acclimatization experiments at different altitudes. They hope to identify physiological adaptations that help rodents cope.
It is amazing! Scientists also wonder what drives these mice to climb high in this way. Perhaps a desire to escape their predators. Because under such conditions, predators naturally become rarer. But the other risks – lack of water, lack of food and the threat of cold – are becoming so great that the question of the actual benefits ultimately remains unanswered.
World altitude record for a mammal
Despite its weight of 55 grams and its fearsome appearance, the yellow borer seems to adapt perfectly to extreme temperatures and lack of oxygen: scientists have just caught a specimen living at an altitude of 6,739 meters on the summit of the Llullaillaco volcano in the Andes. We still don’t understand how it feeds.
Article by Céline DeluzarcheCéline Deluzarche published on March 28, 2020
How far will she go? After being spotted at 6,200 meters above sea level in 2013 (see article below), the little yellow-eared mouse (also called Patagonian fur-eared mouse, Phyllotis xanthopygus) was captured in February 2020 at 6,739 meters above sea level at the summit of Llullaillaco Volcano, a volcano in the Andes, on the border between Argentina and Chile. University of Nebraska biologist Jay Storz and his mountaineer friend Mario Perez Mamani followed the rodent’s trail for many years and managed to film and capture the mouse as it sought refuge under a rock.
Cold, lack of oxygen and food: extreme living conditions
Even in the Himalayas, no one has ever seen a mammal venture so high. And for good reason: the environment there is particularly hostile to life, with extreme temperatures, very low oxygen levels and a complete lack of food. Some birds and mammals have adapted their physiology to life at altitude, but cannot live permanently without vegetation or insects. What does the little mouse that can be found more than 2,000 meters above the last blade of grass feed on?
The question remains unanswered. Regardless, “this new discovery shows that we underestimate the physiological limits of small mammals,” writes Jay Storz in his report, published online on the scientific platform bioRxiv. Since biologists rarely venture to the world’s highest peaks, it is possible that other creatures have found refuge there out of sight.
What is gray or light beige, weighs 55 grams, has large tufted ears and occurs at an altitude of 6,000 meters? Answer: the yellow-eared mouse, also called the Patagonian fur-eared mouse. This animal lives in the Andes, in places where there is no trace of vegetation left.
Article by Céline Deluzarche published on August 1st, 2019
In 2013, American emergency doctor Matt Farson couldn’t believe his eyes when he encountered a small rodent running under his nose at 6,200 meters as he attempted to climb Llullaillaco, a 6,739m peak in the Andes mountains on the border between Argentina and Chile. The volcano’s still active slopes are considered one of the most inhospitable places on the planet, with oxygen levels half that of sea level, a lunar landscape swept by gusts of wind, and temperatures that can plummet to -50°C in winter and rise to 32°C on the rocks in summer.
A habitat that extends from 0 to 6,200 meters
Matt Farson barely had time to photograph the animal and shared his find with Scott Steppan, a mouse specialist at the University of South Florida. The latter suspects that it is a yellow-eared mouse, a species that is known to live at altitude but is also found in fields at sea level. “This means that it is also the animal that is able to live with the greatest difference in altitude,” enthuses the scientist. It is simply extraordinary.” A second expedition, organized in 2016, confirms this assumption. The researchers managed to find another specimen and took soil samples from around the burrow, whose DNA analysis matched exactly that of Phyllotis xanthopygus.
The previous record holder, the big-eared pika (Ochotona macrotis), was already observed at 6,120 meters above sea level, i.e. 80 meters lower. The difference is that the yellow boreal mouse appears to live permanently at these altitudes. The small size of the observed specimen suggests that it is a young mouse from a colony and not a loner that happened to venture here.
A specially adapted physiology
But how can such a small animal survive the extreme conditions that exist at these altitudes? Jay Storz, a biologist at the University of Nebraska, has closely studied the white-footed mouse, the North American equivalent of the yellow-bored mouse, which lives up to 13,000 feet (4,000 m). “These animals survive thanks to a number of physiological adaptations, such as slowed muscle metabolism and a specialized cardiovascular system,” he explains to National Geographic. The yellow-eared mouse also has a lot of brown fatty tissue, which ensures thermogenesis, especially in hibernating animals.
However, there are still unanswered questions. What can the rodent eat at an altitude where the only vegetation is rare patches of lichen on the rocks? Scott Steppan suspects that the small animal could benefit from wind-blown food scraps, but that seems insufficient. In any case, this little mouse is further proof that living creatures have unimagined adaptive abilities.