Mummified mice are discovered on the summits of the Andes volcanoes, the place on Earth most similar to Mars

2023-10-23 17:00:07

The summits of the Puna de Atacama volcanoes in Chile and Argentina are the closest thing on Earth to the surface of Mars. At more than 6,000 meters above sea level, temperatures are freezing, the atmosphere is thin, oxygen is reduced by half and hurricane-force winds whip the rocks. Expeditions in the 1970s and 1980s discovered some mouse corpses on those inhospitable peaks, but archaeologists concluded that the rodents had arrived there hidden in firewood or other supplies carried by the Incas, who made a pilgrimage of more than 1,600 km to what they considered Sacred places. The peaks of the Andes served as altars for Capacocha, the ritual sacrifice of children to several of their gods.

The archaeologists’ deduction was logical, since in those conditions the life of mammals did not seem possible. However, in 2020, Jay Storz, a professor of biological sciences at the University of Nebraska-Lincoln, captured a live leaf-eared mouse atop Llullaillaco Peak, a volcano at 6,700 meters on both sides of the border. between Chile and Argentina. No mammal had ever been found living at such an extreme altitude.

In addition to capturing more live specimens, Storz and his colleagues have reported in the journal ‘Current Biology’ of the discovery of 13 mummified mice on the summits of three neighboring volcanoes (Salín, Púlar and Copiacó), each of which extends almost 6.4 km above sea level. “They’re basically mummified, freeze-dried mice,” Stortz says. Researchers believe that they ascended to these harsh environments alone, without help from the Incas, since none are old enough to have coexisted with them. If so, the finding would expand the physiological limits of vertebrate life on Earth.

Physiological tolerance

“The most surprising thing about our discovery is that mammals could be living on the summits of volcanoes in such an inhospitable environment, similar to that of Mars,” says Storz. »Well-trained mountaineers can tolerate such extreme elevations during a one-day summit attempt, but the fact that mice live at such elevations demonstrates that we have underestimated the physiological tolerances of small mammals.«

Storz and his colleagues discovered the first mummified mouse corpse by chance at the top of the Salín volcano at the edge of a rock pile. They soon found others. “When my climbing partner and I started searching among the rest of the rocks, we found seven more mummies on the same summit,” recalls the researcher.

They then systematically searched the summits of all the Andean volcanoes. So far, they have tracked 21 summits, including 18 with elevations over 6,000 meters. In total, they have found 13 mummified mice on the summits of multiple volcanoes with an elevation of more than 6,000 meters. In some cases, the mummies were accompanied by the skeletal remains of many other mice.

A member of the research team at the summit of Ojos del Salado, 6,893 m (Puna de Atacama, Chile-Argentina) Mario Pérez Maman

Radiocarbon dating showed that mummified mice found on the summits of two volcanoes were at most a few decades old. Those at a third site were older, 350 years at most. Genetic analysis of the summit mummies showed that they represent a species of leaf-eared mouse called Phyllotis cowswhich is known to be found at lower elevations in the region.

“The discovery of mouse mummies on the tops of these icy, windswept volcanoes was a big surprise,” says Storz. “Combined with our records of live capture of mice on the summits and flanks of other high-elevation Andean volcanoes, we are accumulating more and more evidence that long-term resident mouse populations exist at extreme elevations.”

The find now raises important questions, including how mammals can live in a hellish world of rock, ice and snow. It is not clear why the mice would have climbed to such heights. Now, researchers want to know if high-altitude mice have special physiological traits that allow them to survive and function in low-oxygen conditions. To find out, they are conducting physiological experiments on captive mice that were collected at high elevations. They also continue their mountaineering studies of small mammals in the high Andean peaks of Argentina, Bolivia and Chile.