At the peak of a 6,739-meter Andean volcano, where the air is thin, temperatures remain below freezing, and survival is challenging for humans, a small leaf-eared mouse has established its habitat by consuming toxic plants.
An international research team, which included scientists from McMaster University in Hamilton, Ont., has revealed some of the biological adaptations enabling this phenomenon. The study, released in the journal Science, demonstrates that high-altitude Andean leaf-eared mice possess the ability to generate heat more efficiently in low-oxygen environments. Genetic analysis also indicates their capacity to process harmful compounds present in their diet.
The species, known as Phyllotis vaccarum, has been identified on the summit of Volcán Llullaillaco on the Chile-Argentina border. At this elevation, each breath supplies only about 44% as much oxygen as at sea level.
Grant McClelland, a co-author of the study and a biology professor at McMaster University, expressed his astonishment at the mice’s ability to survive in such extreme conditions. The leaf-eared mice exhibit the widest known elevation range among mammals, inhabiting regions from sea level along Chile’s northern coast to Andean peaks exceeding 6,700 meters.
Researchers collected mice from various altitudes, conducted genome comparisons, and subjected highland and lowland specimens to identical laboratory conditions. Heat production was measured at simulated oxygen levels equivalent to sea level, 4,300 meters, and 7,000 meters. Highland mice displayed lower heat production reduction compared to lowland mice of the same species and a related lowland species, offering a potential survival advantage in freezing temperatures.
The efficiency of muscle energy production and utilization appears to benefit the highland mice. Graham Scott, a co-author and biology professor at McMaster University, highlighted the crucial role of muscle metabolism in sustaining body temperature in cold environments through shivering. Mitochondria in the hind-leg muscles of highland mice exhibited a higher capacity to convert oxygen and nutrients into energy than those of lowland mice.
The study also uncovered the mice’s genetic adaptations for coping with limited food sources on the barren high slopes. The mice, constrained by scarce vegetation, have evolved genes that aid in detoxifying harmful plant compounds found in their diet.
Surviving at nearly 7,000 meters is a remarkable achievement for a creature as small as the leaf-eared mouse, underscoring the resilience of life in seemingly inhospitable environments. McClelland emphasized that evolution continues to surprise biologists by showcasing life forms thriving in diverse conditions worldwide.