At the peak of a 6,739-meter Andean volcano, where the air is thin and temperatures remain below freezing, a small leaf-eared mouse thrives by consuming toxic plants. Researchers at McMaster University in Hamilton, Ont., as part of an international team, have revealed some of the biological adaptations behind this astonishing capability. Their study, which was recently published in the journal Science, demonstrates that high-altitude Andean leaf-eared mice have evolved to produce heat more efficiently in low-oxygen environments. Additionally, genetic evidence suggests that they have developed mechanisms to process harmful compounds found in their food.
The species, known as Phyllotis vaccarum, has been identified on the summit of Volcán Llullaillaco, located on the border between Chile and Argentina. At such extreme elevations, each breath contains only about 44% as much oxygen as at sea level. Grant McClelland, a biology professor at McMaster and one of the study’s authors, expressed awe at the mice’s ability to not only survive but thrive in such harsh conditions.
These mice have the widest known elevation range of any mammal, inhabiting areas from sea level along Chile’s northern coast to peaks surpassing 6,700 meters. Researchers conducted comparisons of mice from various elevations, analyzed their genomes, and subjected both highland and lowland specimens to identical laboratory settings. Heat production was measured at oxygen levels equivalent to sea level, 4,300 meters, and 7,000 meters. Despite a decrease in heat production as oxygen levels dropped, highland mice exhibited a superior ability to retain heat compared to their lowland counterparts and a related lowland species, a crucial advantage in freezing temperatures.
The unique muscle metabolism of highland mice seems to contribute significantly to their survival at extreme altitudes. These mice have adapted to efficiently produce and utilize energy in their muscles, particularly for shivering to maintain body warmth in the cold environment. Mitochondria in their hind-leg muscles exhibit enhanced oxygen and nutrient conversion into usable energy compared to lowland mice, providing a heightened capacity for energy production. This advantage is crucial as lipids, or fats, serve as a lasting energy source for shivering.
One of the study’s remarkable findings pertains to the mice’s diet. Due to the scarcity of vegetation on the highest slopes, the mice are limited in their food choices. Genetic analysis unveiled evidence of genetic selection in genes responsible for detoxifying harmful plant compounds. The mice have adapted to consuming plants with toxic properties, a necessity at such elevations.
The success of these small mammals living near 7,000 meters serves as a testament to the resilience of life in extreme environments. Grant McClelland emphasized the endless surprises of evolution, highlighting how life can adapt and thrive even in seemingly inhospitable conditions on Earth.
