- ENGLAND -- Hikers trekking
through unfamiliar territory are well advised to carry a compass, if not
a GPS unit, to stay on course. Other animals are lucky enough to have complex
navigational equipment in-built. New research reveals that Israel's blind
mole rat (Spalax ehrenbergi) uses the Earth's magnetic field on long journeys,
much like a compass, to continuously monitor and maintain its course.
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- But that's not where the burrowing rodent's abilities
end. The mole rat also has an uncanny habit of burrowing around obstacles
- such as ditches or concrete blocks - without ever coming in to physical
contact with them.
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- "One of the most interesting characteristics of
this unique subterranean mammal is that it is [totally] blind," said
Tali Kimchi, who studies the brain and behavior at Tel Aviv University
in Israel. "This created a strong evolutionary pressure on the mole
rat to develop specialized, non-visual mechanisms of orientation that enable
it to find its way underground."
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- Making navigational mistakes underground is expensive
business too. Excavating soil uses between 360 and 3,400 times as much
energy as moving the same distance above ground.
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- Internal Map
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- Israel's blind mole rats live most of their lives underground
in pitch-black, complex tunnel systems. They have to dig over great distances
when foraging for bulbs and roots, and then have to find their way home
again.
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- Like other rodents, dogs, even people, mole rats can
predict where they are simply by keeping track of their own balance and
movement, said Kimchi. But over long distances in a mish-mash of winding
tunnels, that internal map may not be enough, she said.
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- Sighted animals use visual landmarks to keep correcting
mistakes, but the blind mole ratówhich may have lost its eyes in
an irreversible evolutionary step up to 30 million years ago - had to be
using something else, said Kimchi.
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- Researchers already knew that a related species, the
Zambian mole rat (Cryptomys anselli), could detect the Earth's magnetic
field. So, Kimchi along with biologists Joseph Terkel, also in Tel Aviv,
and Ariane Etienne of the University of Geneva in Switzerland decided to
test if the Middle Eastern species might be using that ability to deftly
navigate in the dark.
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- As they reported online January 21 in the science journal
Proceedings of the National Academy of Sciences, the team put wild mole
rats into two types of laboratory maze.
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- One maze was wheel-shaped and made up of eight radial
spokes with a central hub. The animals were required to find their way
from a feeding place to a nesting box by the most direct route. When the
maze was placed between two massive electromagnets - which had the effect
of turning the Earth's magnetic field by 90 - the mole rats were much more
likely to lose their way.
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- In a second rectangular maze, the mole rats were tested
on their ability to use their internal map along with the magnetic compass
to find new shortcuts to a food reward. Again, once the magnetic field
was unexpectedly turned by 90, they were much less likely to discover a
shortcut.
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- The mole rats lost their way less often under the altered
magnetic field when they only had to travel short distances, noted Kimchi,
suggesting that they switch to using the Earth's magnetic field as a reference
point when navigating over long distances.
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- Rat Radar
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- While some birds, fish, amphibians, insects, and several
other rodents can use the Earth's magnetic field to assess direction when
they begin an excursion, the blind mole rat is the first animal to be shown
to use it to regularly correct errors as it travels.
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- "The change in navigation strategy [over long distances]
is very interesting indeed," agreed Roswitha Wiltschko, behavioral
physiologist at the J.W. Goethe University in Frankfurt, Germany. Though
she says that the idea that mole rats switch from an internal map to an
external reference such as the Earth's magnetic field has been suggested
before but not tested.
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- Another study by Kimchi and Terkel, published in the
November 2003 issue of the science journal Animal Behaviour, shows that
blind mole rats have additional radar-like abilities to detect obstacles
before they come into contact with them. Another talent human hikers would
kill for.
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- The pair found that when they blocked wild mole rats'
tunnels, the animals carefully dug out the shortest route around the obstacles
to reconnect them. Furthermore, they left a safe margin of 10 to 20 centimeters
(4 to 8 inches) when the obstacle was a hollow ditch, but closely followed
the shape of solid concrete obstacles by just 3 to 8 centimeters (1 to
3 inches). Ingeniously, when an obstacle was placed asymmetrically across
the tunnel, the mole rats always detoured it on the shorter side.
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- The scientists believe that the animals could be using
seismic waves generated by banging their heads against the earth, much
like radar, to detect any dangers that lie ahead. "It's totally clear
that mole rats drum their heads to communicate and have a good sense of
hearing low frequency sounds," commented Pavel Nemec, zoologist at
Charles University in Prague, the Czech Republic. "And it is quite
possible that they use vibrations to test proximal surroundings."
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- "It is amazing that mole rats live in a permanently
dark environment and are able to navigate so well," added Nemec. "Other
animals use sight to correct their mistakes. Mole rats use the Earth's
magnetic field."
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- © 2004 National Geographic Society. All rights reserved.
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- http://news.nationalgeographic.com/news/2004/01/0129_040129_blindmolerat.html#main
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