The summit of the Puna de Atacama volcanoes in Chile and Argentina is the closest thing on Earth to the surface of Mars. At more than 6,000 meters above sea level, the temperature is freezing, the atmosphere is thin, the oxygen is reduced by half and hurricane-force winds whip the rocks. Expeditions in the 1970s and 1980s discovered some rat carcasses on those inhospitable peaks, but archaeologists concluded that the rats arrived there hidden in firewood or other supplies brought by the Incas, who traveled more than 1,600 kilometers to what they considered Sacred places. . The peaks of the Andes serve as altars for Capacocha, the ritual offering of children to some of their gods.
The reduction of archaeologists is logical, because in such conditions the life of mammals seems impossible. However, in 2020, Jay Storz, a professor of biological sciences at the University of Nebraska-Lincoln, got a live eared mouse on top of Llullaillaco Peak, a volcano at 6,700 meters on both sides of the border between Chile and Argentina. No mammal has ever been found living at such extreme altitudes.
In addition to capturing more living specimens, Storz and his colleagues reported in the journal ‘Current Biology’ the discovery of 13 mummified rats at the summit of three nearby volcanoes (SalÃn, Púlar and Copiacó), each of which reaches approximately 6.4 km above sea level. “They’re basically mummified, freeze-dried rats,” Stortz said. Researchers believe that they climbed these harsh environments alone, without help from the Incas, because no one was old enough to accompany them. If so, the search will expand the physiological limits of vertebrate life on Earth.
Physiological tolerance
“The most surprising thing about our discovery is that mammals could live on the tops of volcanoes in such an inhospitable environment, similar to that of Mars,” Storz said. »Well-trained mountain climbers can withstand such extreme elevations during a one-day summit attempt, but the fact that rats live at such altitudes shows that we underestimate the physiological allowing small mammals.«
Storz and his colleagues discovered the first mummified rat corpse by chance at the top of the SalÃn volcano on the edge of a rock pile. Soon they saw others. “When my climbing partner and I started searching among the remaining rocks, we found seven more mummies on the same summit,” the researcher recalled.
Then they systematically searched for the summit of all the Andean volcanoes. So far, they have tracked 21 summits, including 18 with elevations of over 6,000 meters. In total, they found 13 mummified rats on the summit of several volcanoes with an altitude of more than 6,000 meters. In some cases, the mummies were accompanied by the skeletons of several other rodents.
Radiocarbon dating shows that the mummified rats found at the summit of the two volcanoes are several decades old. Those at the third site are older, 350 years old at most. Genetic analysis of the summit mummies shows that they represent a species of leaf-eared mouse called Phyllotis cowswhich are known to be found at lower elevations in the region.
“The discovery of rat mummies on the tops of these icy, windy volcanoes was a big surprise,” Storz said. “Coupled with our records of live capture of rats on the summits and flanks of other high-elevation Andean volcanoes, we have gathered further evidence that long-term populations of resident rats are in extreme elevation.”
Today’s find raises important questions, including how mammals can survive in a hellish world of rock, ice and snow. It’s not clear why rats climb so high. Now, researchers want to know if the long rats have special physiological characteristics that allow them to live and function in low-oxygen conditions. To find out, they conducted physiological experiments on captive rats collected at high levels. They also continued their mountaineering studies of small mammals on the high Andean peaks of Argentina, Bolivia and Chile.
