Andean leaf-eared mice living at high altitudes produce more heat than those living at sea level
It’s not easy living the high life. Take it from the Andean leaf-eared mouse, Earth’s tallest mammal.
To tolerate the freezing temperatures atop dormant volcanoes, these mice generate more body heat than members of species that live lower down, researchers report in July 9 Science. Their mitochondria, the cells’ energy producers, have also adapted to stimulate oxygen-dependent processes in low-oxygen conditions.
Andean leaf-eared mouse (Phyllotis cows) extends from the sea to the summitliving anywhere from the desert coast of Chile to the peaks of the Andes. Those living at altitudes above 6,700 meters face freezing temperatures as low as –60°C and oxygen levels about 44% of those at sea level. How the rodents cope with the harsh conditions is unclear.
Evolutionary biologist Jay Storz of the University of Nebraska-Lincoln and his colleagues have climbed many Andean peaks looking for small mammalsincluding on a 2020 excursion that discovered the Andean leaf-eared mouse as the world record holder. The excursions last several weeks so the team can acclimatize to the altitude and conduct wildlife surveys during the climb, Storz says. But unlike human mountain climbers, “mice can’t wear Gore-Tex jackets.”
Storz and his colleagues compared how Andean leaf-eared mice captured at different altitudes behaved in small chambers that simulated the frigid, oxygen-poor environment of mountaintops. Mice living at high altitudes consumed more oxygen than animals living at lower altitudes, suggesting that mice living at high altitudes would be more active in cold weather.
Metabolic and genetic analyzes suggest that muscle tremors help mice living at high altitudes produce extra heat. Additionally, animals’ blood cells could store more carbon dioxide, reducing the risk of hyperventilation from rapid breathing at high altitudes, where air is thin.
“They basically engage all of their metabolic machinery in an effort to maintain a constant body temperature,” says Storz.
Genetic analysis also revealed that lowland and upland mice can detoxify compounds from a toxic diet. Desert animals, limited by what is available, often feed on toxic plants. It’s unclear how adaptations to a harsh environment and a toxic diet may be related, but it might be more complicated to manage both at the same time.
For these mice, Storz says, “things are really difficult everywhere.”
