They had been the summits of 20,000-foot volcanoes. Amid the driest desert on Earth. The place temperatures by no means breached freezing, the place lower than half of sea-level oxygen quenched lungs, the place gale-force winds scoured the hardscrabble rocks littering the peaks.
So when archaeologists first reported stumbling throughout a couple of mouse cadavers throughout expeditions to a number of Andean peaks within the Seventies and ’80s, they figured, naturally, that the rodents should have hitched a experience with the Incas who as soon as pilgrimaged a thousand-plus miles to what they thought-about sacred websites.
These apexes served as altars for Capacocha, the ritual sacrifice of kids to a number of Incan gods. Perhaps, the considering went, the mice had scurried into firewood or different provides hauled up the slopes by the Incas. Or they had been among the many animal sacrifices that generally accompanied the human.
“You possibly can’t fault the archaeologists for considering this fashion, as a result of what different clarification is there?” stated Jay Storz, a Willa Cather Professor of organic sciences on the College of Nebraska–Lincoln. “Nothing may very well be dwelling up there, so that they needed to have been introduced there.”
However Storz would inadvertently solid doubt on the speculation in early 2020. Alongside good friend and fellow mountaineer Mario Pérez Mamani, he captured a dwell specimen of leaf-eared mouse atop the 22,000-foot peak of Llullaillaco (zhoo-zhuh-ZHEYE’-koh), a volcano straddling the Chile-Argentina border. No mammal had ever been discovered dwelling at such excessive altitude.
Alongside the seize of extra dwell specimens, Storz and his colleagues have now reported the invention of 13 leaf-eared mouse cadavers throughout the summits of three neighboring volcanoes — Salín, Púlar and Copiapó — that every stretch almost 4 miles above sea stage.
“These are principally freeze-dried, mummified mice,” Storz stated.
Analyzing the baker’s dozen of mummies has solely strengthened the staff’s conviction that the seemingly modest mice ascended the volcanoes with out Incan help. By measuring concentrations of carbon-14, an atom that decays at a identified price, the staff decided that the eight mummies atop Salín and one on Copiapó died no quite a lot of a long time in the past, possible after 1955. The 4 mummies on Púlar perished, at most, 350 years in the past — a full century after the final of the Incan empire fell to Spanish invaders.
“It now appears increasingly clear,” Storz stated, “that the mice received there of their very own accord.”
The mummified state of the mice additionally helped protect their DNA, permitting Storz’s collaborators from the College of Montana to match genetic variation amongst leaf-eared mice collected within the lowlands, midlands and highlands of Atacama Desert. Analyzing that variation throughout members of a species will help hint the evolutionary historical past of populations separated by distance, obstacles or, on this case, altitude.
Storz and his colleagues questioned whether or not the genomes of the skyscraping, mummified mice may signify a definite subpopulation of the leaf-eared rodent — one with a colonization historical past completely different from that of their lower-dwelling friends.
“Our genomic information point out no: that the mice from the summits, and people from the flanks or the bottom of the volcanoes within the surrounding desert terrain, are all one huge joyful household,” Storz stated, citing it as extra proof that the mummies weren’t hitchhikers however mountaineers.
In reality, the staff discovered that two pairs of the leaf-eared mummies on Salín had been carefully associated, probably siblings or mother and father and offspring. And it famous one other telltale: the equal ratio of males to females among the many mummies. Mixed with the current discovery of different dwell specimens and mouse burrows within the heights of the Puna de Atacama, or Atacama Plateau, Storz stated it appears that evidently the leaf-eared mouse is not only touring the volcanic summits, however by some means dwelling on them.
“It’s precisely what you’d count on,” he stated, “in case you had been to seize a set of mice from some localized space in an surroundings that’s liveable.”
Which is bewildering, Storz stated, on condition that the Puna de Atacama ranks among the many most inhospitable locales on the planet — one so arid, chilly and oxygen-poor that NASA has visited the Atacama to follow looking for life on Mars.
“Even on the base of the volcanoes, the mice reside in an excessive, Martian surroundings,” he stated. “After which, on the summits of the volcanoes, it’s much more so. It seems like outer area.
“It simply boggles the thoughts that any sort of animal, not to mention a warm-blooded mammal, may very well be surviving and functioning in that surroundings. Whenever you expertise all of it firsthand, it even additional impresses upon you: How in God’s title is something dwelling up there?”
It’s one of some questions that the researchers are persevering with to pursue. Members of Storz’s lab and colleagues in Santiago, Chile, have since established colonies of leaf-eared mice collected from numerous altitudes. By acclimating every group to situations that simulate the Puna de Atacama at 20,000 ft, the researchers hope to pinpoint no matter physiological variations are serving to the rodents cope.
Much more basic is the query of what would drive the mice to such heights within the first place. Like most small rodents, the leaf-eared mouse — which grows to about 2 ounces — spends a good quantity of its time, vitality and a spotlight avoiding predators. And even within the Puna de Atacama, these predators are quite a few: foxes, mountain lions, smaller cats, birds of prey.
May the risks imposed by the Atacama summits — the near-absence of water, the seeming lack of meals, the specter of freezing to demise — actually be definitely worth the promise of escaping predation all collectively?
“Actually, in case you’re hunkering down on prime of a 6,000-meter volcano, you’re at the very least protected from that,” Storz stated. “You simply produce other issues to fret about.
“However why they’re ascending to those excessive elevations continues to be a thriller.”