“Are you a man or a mouse?” the proverbial expression rings. Turns out, mice deserve more credit than we have given them so far. A towering 6700-meter volcano on the border between Chile and Argentina houses the most unexpected inhabitant – the leaf-eared mouse.
High and Dry
At Llullaillaco’s summit, relentless winds and a barren, plantless landscape create a harsh environment. Daytime temperatures stay below freezing and drop even further at night, while oxygen levels are only 40% of those at sea level, making the area nearly uninhabitable for mammals. Surprisingly, researchers found a live leaf-eared mouse (Phyllotis vaccarum) thriving at this extreme altitude. Since the discovery, five other mouse species have been discovered living above 5000 meters in the Central Andes, challenging our understanding of mammalian adaptation to high altitudes.
The Previous Record-Holder; The Pika
For decades, the cold temperatures and thin air associated with high-altitude environments have been perceived as barriers for animals. Previously, the record-holder for high-altitude mammal habitation was the pika, a distant relative of rabbits. The discovery was made nearly a century ago at an elevation of almost 6200 meters on Mount Everest.
High Flying Rodents
The first hints that some rodents could survive at even higher altitudes emerged 50 years ago when archaeologists exploring Inca religious sites on Andean summits stumbled upon naturally mummified mice. However, it was only recently, with the collaboration of climbers and researchers, that the secrets of these high-altitude mouse populations began to unravel.
Discovering This Mighty Mouse
It was Jay Storz, an evolutionary biologist at the University of Nebraska—Lincoln, specializing in high-altitude adaptations, who took the leap to investigate further. This pursuit led to the discovery of these record-breaking mouse species and a quest to understand how they manage to survive in such extreme conditions.
Demystifying the Mice’s Survival
One of the many mysteries surrounding these high-altitude mice is their diet. Living at least 650 meters above the vegetation line on volcanoes, and sometimes thousands of meters higher, what sustains them? Preliminary DNA analysis of their stomach contents hints at lichens being a significant part of their diet, shedding light on their remarkable survival strategies.
Interesting Adaptions Of These Mice
Another enigma is how these mice stay warm in the brutal cold. Surprisingly, initial data suggests that these Andes mice do not possess the same genetic adaptations observed in deer mice living at 4350 meters in the Rocky Mountains. This enables them to withstand the cold. With the mission to unlock the secrets of their physiology, Storz and his colleagues have established a lab colony of the Llullaillaco rodents and other high-altitude mice in Chile for further study.
What’s the Next Discovery?
Discoveries like these are exciting to the curious mind; it sparks the question “What else is there to discover?” What beliefs do we hold and assume to be general knowledge, that would be disproven in the near future? One can only wonder. In the meantime, I believe the leaf-eared mice will definitely enjoy their view.
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