At first glance, it's just a rodent. But the Andean leaf-eared mouse is, in fact, a natural marvel.
The small mammal is capable of living at altitudes exceeding 6,700 metres in the Andes, and its capabilities challenge our understanding of physiological limits.
Six years after discovering the animal living on some of the world's highest peaks – places where mammalian life was previously considered impossible – a team of international researchers is beginning to unravel the secrets of this extraordinary animal.
The mouse that can fit in the palm of a hand holds several world records, said Zachary Cheviron, a biology researcher at the University of Montana and co-author of a new study on the mammal published this week in the prestigious journal Science.
"They have literally the world's record for the highest dwelling mammal on the planet," the researcher told AFP, saying that it can live in areas where mountaineers can barely venture for more than a brief period.
The species was found hundreds of metrees above dwellings of Himalayan pika, the small animal that had previously held the title.
But on top of that, the little mouse has range.
The same species than can survive atop Chilean peaks has also been found at sea level: they "have the broadest elevational distribution of any mammal on the planet," Cheviron said.
The animal's vast range is made possible by a resilience and adaptability that is phenomenal in several respects, wrote the team of researchers, who believe their findings could offer valuable insights for human medicine.
Superpowers
The study shows that the mice living both down low and up high are genetically similar, not so different from humans who have evolved to life in deserts, tropical regions or at high altitudes.
"It's kind of a nice model of humans in a lot of ways," Cheviron said.
Mice living in snowy heights were found to have a handful of distinct genes, including one already known to be linked to adaptation to hypoxia – oxygen deprivation – in populations of Tibetan people.
But the bodies of these mice respond differently.
They "have gained these superpowers to be able to survive in a low oxygen environment," said Jay Storz, an evolutionary biologist at the University of Nebraska, who is also a climber.
Experiments conducted in a cold-chamber setting reveal that these mountain mice are particularly adept at maintaining body heat.
Initial findings also suggest that the rodent does not produce extra red blood cells to capture oxygen more efficiently – as other mammals do – but instead breathes more rapidly.
In order to counteract any harmful effects stemming from such accelerated breathing, the animal relies on a modified enzyme.
Other mechanisms are likely at play – but scientists say the preliminary findings could prove useful for future research.
Limits of life
Storz explained that many human diseases, particularly heart conditions, involve complications resulting from impaired oxygen delivery.
"So understanding the ways that animals like leaf-eared mice have evolved to cope with low oxygen availability in their natural habitat can help guide the design of treatments for human patients that are suffering basically the same physiological state for different reasons," he said.
Such insights could, for example, aid cancer research, Cheviron said, as tumors can create "a hypoxic environment" as well.
Beyond the implications for human medicine, Cheviron emphasised how the discovery of the mountaineering mice "really kind of pushed what we thought about the limits of mammalian life."
Not only can they survive in low-oxygen environments in a desert of snow and rock, the mice also subsist on scarce, toxic plants.
Genes that play key roles in the metabolism of dietary toxins have been identified in the genomes of Andean leaf-eared mice.
"Nothing comes easy to these guys," said Storz, saying the research lends new appreciation of "how resilient life is."
"Really we have a new understanding of, just kind of the environmental limits of vertebrate life." – AFP
