(The Center Square) – Atop the stark, windy and frozen summits of 20,000-foot volcanos, it seems unlikely that anyone would find mice unless someone brought them there. That’s wrong.
The little “mountaineers” climb there on purpose a Nebraska researcher has discovered. Archaeologists first came across a few mouse cadavers during expeditions to several Andean peaks in the 1970s and ’80s.
When discovered, the researchers assumed the rodents made it to those heights while riding with Incas, who made the trek to visit sacred sites.
These apexes were altars where the Incans committed child sacrifice to attempt to appease their gods. Therefore, archaeologists thought the mice got mixed up with firewood and other supplies as the Incas moved up the slopes; some also thought the Incas committed tiny animal sacrifices, in addition to human ones.
“You can’t fault the archaeologists for thinking this way because what other explanation is there?” Jay Storz, a Willa Cather Professor of biological sciences at the University of Nebraska–Lincoln, said. “Nothing could be living up there, so they had to have been brought there.”
Storz inadvertently cast doubt on the hypothesis three years ago. Along with friend and fellow mountaineer Mario Pérez Mamani, he captured a live specimen of a leaf-eared mouse atop the 22,000-foot peak of Llullaillaco (zhoo-zhuh-ZHEYE’-koh), a volcano on the Chile-Argentina border.
No mammal had been found alive at an altitude that high. Since then, Storz and his colleagues have reported the discovery of 13 leaf-eared mouse cadavers across the summits of three neighboring volcanoes — Salín, Púlar, and Copiapó.
Each of those volcanoes peaks nearly four miles above sea level.
“These are basically freeze-dried, mummified mice,” Storz said.
The researchers measured concentrations of carbon-14, an atom that decays at a known rate, and found that eight of the mummies atop Salín and one on Copiapó most likely died after 1955. Plus, the four mummies on Púlar died, at most, 350 years ago — well after the fall of the Incan empire.
“It now seems more and more clear,” Storz said, “that the mice got there of their own accord.”
The mice being in a mummified state helped preserve their DNA, letting Storz’s collaborators from the University of Montana compare the genetic makeup of these mice to those in the lowlands, midlands, and highlands of the Atacama Desert.
“Our genomic data indicate no: that the mice from the summits, and those from the flanks or the base of the volcanoes in the surrounding desert terrain, are all one big happy family,” Storz said. He added that the DNA evidence further clarified that the mummies were mountaineers, not hitchhikers.
The team concluded that two pairs of leaf-eared mummies on Salín were closely related, and there was an equal ratio of males to females among the mummies.
Therefore, Storz thinks the mice live on the volcanic summits and are not merely visiting them.
“It’s exactly what you’d expect,” he said, “if you were to capture a set of mice from some localized area in an environment that’s habitable.”
“Even at the base of the volcanoes, the mice are living in an extreme, Martian environment,” he continued. “And then, on the summits of the volcanoes, it’s even more so. It feels like outer space.
“It just boggles the mind that any kind of animal, let alone a warm-blooded mammal, could be surviving and functioning in that environment,” he concluded. “When you experience it all firsthand, it even further impresses upon you: How in God’s name is anything living up there?”
Members of Storz’s lab and colleagues in Santiago, Chile, have since established colonies of mice they collected from different altitudes.
The researchers want to acclimate each group to conditions like Puna de Atacama at 20,000 feet to see what physiological adaptations help the rodents cope.
They also want to know why the rodents would go to such high altitudes. They grow to be about two ounces and spend much of their time avoiding predators. Therefore, the researchers want to know if the mice see the harsh conditions as a worthwhile tradeoff to avoid being eaten.
“Certainly, if you’re hunkering down on top of a 6,000-meter volcano, you’re at least safe from that,” Storz said. “You just have other things to worry about. But why they’re ascending to these extreme elevations is still a mystery.”
Storz told The Center Square in an email that his research team’s field work in the Andes was funded via an Explorer Award from the National Geographic Society rather than the school itself. The grants are usually $50-60,000, but can go up to $100,000 according to the society’s website.
