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Mice Found To Thrive At Extreme Altitudes

“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

The harsh environment at Llullaillaco’s summit is characterized by relentless winds and a barren landscape devoid of plant life. Daytime temperatures never rise above freezing and plummet even further during the bone-chilling nights. Oxygen levels are a mere 40% of what you’d find at sea level, making it virtually uninhabitable for mammals.

Andean leaf-eared mice, Phyllotis vaccarum. Photo: Jay Storz

Intriguingly, just three years ago, a research team captured a live leaf-eared mouse (Phyllotis vaccarum) at the summit of Llullaillaco. Studies of these summit-dwelling mice and their counterparts provided evidence that they thrive nearly 7000 meters above sea level.

The research team has since encountered five other mouse species, each making their homes above 5000 meters on various mountains throughout the Central Andes. These findings have forced us to rethink the limits of mammalian adaptation to high altitudes.

What led to the discovery

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. Speaking of rabbits, read about the poor fellow that was swallowed whole by a seagull!

Previous high-altitude record-holder, the pika

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.

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.

Summit of Volcán Salín where researchers found mummified leaf-eared mice. Photo: Jay Storz

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.

In conclusion

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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