At an altitude of 6,739 meters on an Andean volcano, where the air is thin, temperatures remain below freezing, and survival is challenging for humans, a small leaf-eared mouse thrives by consuming toxic plants. An international team, including researchers from McMaster University in Hamilton, Ontario, has unveiled the biological mechanisms behind this remarkable feat. The study, recently published in the journal Science, reveals that high-altitude Andean leaf-eared mice possess the ability to produce heat more efficiently in low-oxygen conditions. Furthermore, genetic evidence indicates their adaptation to process harmful substances found in their food.
The species, known as Phyllotis vaccarum, has been discovered on the summit of Volcán Llullaillaco, situated on the border of Chile and Argentina. At this elevation, each breath contains only about 44% as much oxygen as at sea level. Grant McClelland, a co-author of the study and a biology professor at McMaster, expressed astonishment at the mice’s ability to live and thrive in such extreme conditions.
These highland mice have the widest known elevation range among mammals, spanning from sea level along Chile’s northern coast to Andean peaks exceeding 6,700 meters. Researchers conducted genome comparisons of mice from different elevations and tested both highland and lowland mice under controlled laboratory conditions simulating various oxygen levels. The highland mice exhibited a reduced loss of heat production compared to lowland mice of the same species and a related lowland species, providing a potential survival advantage in freezing environments.
According to McClelland, the capacity to generate body heat is crucial as it requires oxygen to fuel energy-demanding muscles. The highland mice seem to benefit from their muscles’ energy production and utilization mechanisms. Graham Scott, a biology professor at McMaster and co-author of the study, highlighted the importance of the mice’s ability to shiver to maintain body warmth in cold environments.
In the hind-leg muscles responsible for shivering, the mitochondria of highland mice showed a higher capability to convert oxygen and nutrients into usable energy compared to those of lowland mice. Mitochondria, the cell structures that combine oxygen and nutrients to produce energy, were found to be more abundant in highland mice and had a heightened capacity to utilize lipid fuels, providing a sustained energy source for shivering.
The study’s noteworthy discoveries also revolved around the mice’s diet. Limited vegetation at higher altitudes forces the mice to consume whatever is available, often including toxic plants. Genetic analysis uncovered genetic adaptations in the mice that aid in detoxifying harmful plant compounds, enabling them to cope with their diet challenges.
The exceptional survival of these small mammals near 7,000 meters serves as a powerful reminder that life can thrive in unexpected places. McClelland emphasized the continuous surprises of evolution, stating that life finds ways to flourish even in seemingly inhospitable environments on Earth.
