OU researcher provides insights on survival of world’s highest dwelling mammal
University of Oklahoma
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Naim Bautista, Ph.D., is studying how Andean leaf-eared mice have defied the odds to survive at extreme elevations that even acclimated mountaineers struggle to cope with.
view moreCredit: Jonathan Kyncl / University of Oklahoma
NORMAN, Okla. – Mammals inhabit a variety of environments on Earth, but few are able to withstand the hostile conditions of low oxygen and freezing temperatures characteristic of extreme elevations. Thanks to the recent discovery of a resilient mouse species living at elevations exceeding 6,000 meters above sea level, University of Oklahoma professor Naim M. Bautista, Ph.D., is working to uncover how these rodents have adapted their physiology to cope with such conditions.
He is one of the leading co-authors of a study published this month in Science that explores how high-altitude Andean leaf-eared mice have evolved to survive these elements. This species has been known to exist from sea level at the northern Chilean coast through the Andes Mountains into Argentina. But they are now the highest-dwelling mammals currently known to researchers, due to their appearance at extreme elevations with such low levels of oxygen that well-trained, acclimated mountaineers can only tolerate for a one-day summit attempt.
Bautista, an assistant professor of ecological physiology at OU’s School of Biological Sciences, joined an international team – which includes his friend and colleague, University of Nebraska–Lincoln professor Jay Storz, Ph.D. – that traveled to the Andes starting in 2020 to collect these mice for examination. He said the study examined both high-altitude and sea-level members of the mouse species and simulated the effects of different elevations on both groups.
“We targeted physiological measurements related to thermogenic capacity: the capacity of a body to produce heat,” Bautista said. “We wanted to understand how these animals are able to live there, how they resist low oxygen conditions and cold stress, how they breathe, how their hemoglobin is working and how much saturation of oxygen they have in their blood. We wanted to learn everything about these animals.”
Among the researchers’ findings, mice collected from extreme elevations displayed two apparent local adaptations separating them from their lower-elevation counterparts. One is the ability to generate higher amounts of heat by shivering through their skeletal muscles, an important quality for living in such cold environments. The second was the discovery of an unexpected environmental adaptation: “These mice have genes that allow them to process plant-derived dietary toxins,” Bautista said. This means that much of the elevation-related selection of these mice is due to previously unrecognized aspects of their feeding ecology.
Another major finding is that populations of Andean leaf-eared mice from different altitudes exhibit very little genetic differentiation. “Instead of being like several genetically differentiated subpopulations of the same species, the whole species just behaves as one big population,” Bautista said.
This lack of genetic differentiation makes it hard for local, population-specific trait differences to evolve, because the gene variants with local benefits must compete with the other gene variants. But since highland mice have evolved different physiological traits than lowlanders, natural selection pressure favoring high-altitude traits seems to be strong enough to counteract the homogenizing effect of gene flow from low-altitude populations.
While their findings have now been published, Bautista and the team are continuing to explore the Andes. They plan to travel to the eastern, Argentinian side of the mountain region to study further populations of Andean leaf-eared mice and other small mammals. They aim to see if the same observations they’ve made are part of a larger pattern affecting other species.
For Bautista, the research is also helping shed more light on a discovery that remains fascinating.
“From a physiological point of view, the smaller you are, the easier it is for you to lose heat,” Bautista said. “Thinking about an extreme high-altitude environment where there is no oxygen, where it is freezing cold and there is virtually no food, why are these animals up there?”
About the research
This study was part of a large collaboration between scientists from the University of Oklahoma, the University of Nebraska, the University of Montana, and three universities in Chile: la Universidad Austral de Chile, la Universidad de Chile, y la Universidad San Sebastián.
While Andean leaf-eared mice have previously been spotted across a range of elevations in Chile and Argentina, their presence more than 6,000 meters above sea level has surprised researchers.
Credit
Marcial Quiroga-Carmona
Journal
Science
Article Title
Adaptation across an extreme elevational gradient in Andean leaf-eared mice, the world’s highest-dwelling mammal
Article Publication Date
9-Jul-2026
Researchers uncover how a mouse survives in one of Earth’s harshest environments
McMaster University
Hamilton, ON, July 9, 2026 –A tiny mouse living nearly 7,000 metres above sea level in the Andes is helping scientists rethink the limits of life on Earth.
The animal, a leaf-eared mouse, is the focus of a new international study co‑authored by McMaster University researchers, revealing how mammals can survive in conditions once thought uninhabitable.
Researchers had believed mammals could survive only up to about 5,500 metres — roughly the altitude of the highest permanent human settlements. The discovery of these mice living more than a kilometre higher challenged that assumption.
“It was completely unexpected. People did not think mammals could survive at these altitudes, but they’re there,” says Graham Scott, a professor in the Department of Biology who co-authored the study.
The extreme environment, often compared to conditions on Mars, is defined by freezing temperatures, extremely low oxygen levels, a lack of water and little to no plant life. That combination makes it difficult for most animals to survive.
To understand how the mice endure such extremes, Scott and colleague Grant McClelland joined an international team to study the animals in Chile, comparing animals from these high elevations with those from lower ones.
Their findings, published today in Science, suggests that survival in these conditions is not driven by a single adaptation, but by a combination of changes across the body.
“Evolution is a complex process,” says McClelland, a co-author of the study and a professor in the Department of Biology. “When animals encounter really challenging environments, there are a lot of different things they need to cope with, not just the obvious ones.”
High-altitude mice were better able to maintain body heat and sustain oxygen use in cold, low oxygen conditions than their lowland counterparts.
At a cellular level, their muscle tissue resembles that of endurance athletes.
“They’re more like a marathon runner than a sprinter,” explains Scott. “Their muscle cells are packed with mitochondria that allow them to sustain heat-producing activity for longer periods.”
This enhanced capacity lets the mice maintain high rates of oxygen consumption, which is critical for generating heat in freezing temperatures.
The animals also rely more heavily on fats as a fuel source, an effective way to provide energy to both shivering muscle and specialized heat-producing tissues.
But some of the most surprising findings had little to do with oxygen or temperature.
At such extreme elevations, food is scarce. The mice survive on unusual and unpredictable food sources, including lichens, which are symbiotic organisms that grow on rocks, and possibly seeds or insects carried up by the wind.
Genetic analyses revealed that the high-altitude mice have evolved changes in genes involved in metabolizing food and can detoxify plant compounds that would normally be harmful.
“We were initially focused on the most obvious environmental challenges, things like low oxygen and cold, but there were important factors we didn’t expect, including how these animals deal with what they’re eating,” says Scott.
The findings paint a picture of evolution as a multi-layered process, where multiple systems shift to meet complex environmental challenges.
It also highlights how much there still is to learn about the limits of life.
“Sometimes our assumptions about the most extreme environments animals can live in can be questioned,” says McClelland. “Evolution has a lot of room to experiment.”
That insight may have broader implications as species face a rapidly changing climate.
“We tend to focus on temperatures as the big challenge,” says Scott. “But animals are dealing with many pressures at once and evolution may push them in ways we don’t always anticipate.”
Journal
Science
Article Title
Adaptation across an extreme elevational gradient in Andean leaf-eared mice, the world’s highest-dwelling mammal
Article Publication Date
9-Jul-2026
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