Andean Leaf-Eared Mouse Thrives Where Humans Cannot Survive

High on the icy peaks of South American volcanoes, a small mouse is doing something no other mammal on Earth can match. The Andean leaf-eared mouse lives at extreme heights — up to about 22,000 feet above sea level — where the air has less than half the oxygen found at sea level and temperatures almost never rise above freezing. Scientists studied these tough little rodents to find out how they manage to survive in such a harsh place. Their findings were published in the journal Science.

Researchers collected and studied 167 of these mice from many different heights along the Andes, the long mountain range running down the west coast of South America. By looking at the full DNA of each mouse, scientists were able to spot important differences between mice living at high elevations and those living lower down. The study was led by Jay Storz, an evolutionary biologist at the University of Nebraska. He said that even the most experienced mountain climbers can only survive at those heights for a short time, but these mice live there year-round.

One of the biggest challenges at high altitude is staying warm without much oxygen. When it is very cold, mammals burn energy to make body heat — but that process needs oxygen to work. Because there is so little oxygen high up in the mountains, these mice have developed special ways to use oxygen more carefully. The highland mice were better at keeping their bodies warm than mice from lower areas, which scientists call maintaining thermogenic capacity.

The muscles of high-altitude mice were also different in important ways. Their skeletal muscles — the ones used for moving around — were better at producing energy inside tiny structures called mitochondria, which work like power plants inside cells. The mice also had brown fat that was better at burning fat for warmth. These changes together help the mice stay alive in cold, oxygen-poor air that would be deadly for most other animals.

Scientists were surprised to find another key adaptation hiding in the mice's diet. The plants that grow at extreme heights are loaded with natural toxins, or poisons, that most animals cannot handle. The researchers found signs in the mice's DNA that they had evolved the ability to break down these plant toxins. In other words, these mice have figured out how to safely eat food that would harm other creatures.

Scientist Guillermo D'Elía, from the Universidad Austral de Chile, helped with the study. He said the team found genes in the mice that are linked to breaking down toxins and to protecting cells from damage. However, researchers still don't know exactly which plants or which specific toxins the mice have adapted to handle. There is still a lot to learn about how these animals manage their extreme lifestyle, including what they eat, how long they live, and whether they raise their young on the mountain summits.

The research could one day help humans, too. Scientists think that studying how these mice deal with low oxygen could offer clues for treating people who have heart or lung diseases. Those diseases often stop the body from getting enough oxygen, even at sea level. By understanding the mouse's natural solutions, doctors might find new ways to help patients with these conditions. Even the most barren mountain landscapes, researchers say, are home to unique life still waiting to be discovered.