This photograph shows a member of a species of leaf-eared mouse called Phyllotis vaccarum. Credit: Marcial Quiroga-Carmona
The
dry, wind-swept summits of volcanoes in the Puna de Atacama of Chile and
Argentina are the closest thing on Earth to the surface of Mars due to their
thin atmosphere and freezing temperatures. At their extreme elevations of more
than 6,000 meters above sea level, experts had concluded that mammalian life
simply wasn't possible. But researchers reporting October 23 in the journal Current Biology on their discovery of
mummified mice in those tough environs now expand the physiologic limits of
vertebrate life on Earth.
"The most surprising thing about
our discovery is that mammals could be living on the summits of volcanoes in
such an inhospitable, Mars-like environment," says senior author Jay
Storz, a biologist at University of Nebraska, Lincoln.
"Well-trained mountain climbers can
tolerate such extreme elevations during a one-day summit attempt, but the fact
that mice are actually living at such elevations demonstrates that we have
underestimated the physiological tolerances of small mammals."
Storz and his colleagues discovered the
first mouse mummy on the summit of Volcán Salín by chance when they stumbled
across the desiccated cadaver at the edge of a rock pile. But, now knowing what
to look for, they soon turned up others.
"Once my climbing partner and I
started searching through the rest of the rocks, we found seven more mummies on
the same summit," Storz recalls.
Video showing the site where 4 mummies were
excavated from a site on the summit of Volcán Púlar (6,233 m), Chile. Credit:
Jay Storz
They then started searching
systematically on the summits of all the Andean volcanoes. So far, they've
searched 21 volcano summits, including 18 with elevations over 6,000
meters. All told, they've found 13 mummified mice on the summits of multiple
volcanoes with an elevation greater than 6,000 meters. In some cases, the
mummies were accompanied by skeletal remains of numerous other mice.
Radiocarbon dating showed that the
mummified mice found on the summits of two volcanoes were a few decades old at
most. Those from a third site were older, estimated at 350 years old at most.
Genetic analysis of the summit mummies demonstrated that they represent a
species of leaf-eared mouse called Phyllotis vaccarum, which is known to occur
at lower elevations in the region.
"The discovery of the mouse mummies on the summits of these freezing, wind-scoured volcano summits was a huge surprise," Storz says. "In combination with our live-capture records of mice on the summits and flanks of other high elevation Andean volcanoes, we are amassing more and more evidence that there are long-term resident populations of mice living at extreme elevations."
A
view from the summit of Volcán Salín, one of three Andean volcanoes where
researchers uncovered the mummified cadavers of mice. Analyses of the mummies,
combined with the capture of live specimens, suggest that the rodents scaled
the Mars-like peaks on their own—and are somehow managing to live on them.
Credit: Jay Storz, University of Nebraska–Lincoln
This
photograph shows a member of the research team at the summit of Ojos del
Salado, 6,893 m (Puna de Atacama, Chile-Argentina). Credit: Mario Pérez Mamani.
The
finding now raises important questions, including how mammals can live in a
barren world of rock, ice, and snow where the temperatures are never above
freezing, and there is roughly half the oxygen available at sea level. It's not
clear why the mice would have climbed to such heights.
Over 500 years ago, Incas were known to
conduct human and animal sacrifices on the summits of some Andean peaks.
However, the researchers note that the mummified mice from the volcano summits
couldn't have been transported there by the Incas, given that none are old
enough to have co-existed with them.
In ongoing work, the researchers are
investigating whether the high-elevation mice have special physiological traits
that enable them to survive and function in low-oxygen conditions. They're
conducting physiological experiments on captive mice that
were collected from high elevations to find out. They're also continuing their
mountaineering surveys of small mammals on high Andean peaks in Argentina,
Bolivia, and Chile.
"With our mountaineering biological surveys in the Andes, we keep making surprising new discoveries about the ecology of extreme high-elevation environments," Storz says.
by Cell Press
Source: Mouse mummies point to mammalian life in 'Mars-like' Andes (phys.org)
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