X-Message-Number: 119
From att!pdn!oz.paradyne.com!alan Wed Jul 12 19:56:21 1989
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Date: Wed, 12 Jul 89 19:55 EDT
From:  (Alan Lovejoy)
Subject: "Frozen" Mammals

Squirrel Sleeps at a Fluid Subzero
Science News, 8 July, 1989

Researchers have discovered for the first time a warm-blooded animal that can 
survive, without freezing, at a body temperature below the freezing point of 
water.  The hibernating arctic ground squirrel, Spermophilus parryii, can drop
as low as -2.9 degrees C, reports biologist Brian M. Barnes of the University
of Alaska at Fairbanks.  Although scientists have found a few cold-blooded
vertebrates that can live at subzero body temperatures, they previously had
found no mammal that survives below 0.5 degrees C, Barnes writes in the June
30 Science.  

Barnes and his co-workers captured 12 arctic round squirrels from their native
habitat on the North Slope of Alaska.  They implanted miniature temperature-
sensitive raddio transmitters in the squirrels' abdomens and released them in
partially buried outdoor wire cages in Fairbanks.  The squirrels dug burrows 
in the cages and hibernated for eight months starting in September, Barnes

The scientists recorded the lowest body temperatures in February and March.
The squirrels maintained these temperatures, which averaged -1.9 degrees C,
for over three weeks.  Then several days before the animals' brief monthly
arousal, the squirrels gradually warmed to about 0.5 degrees C before rapidly
climbing to normal body temperature, says Barnes' collaborator Alison D. York.

In a second experiment, the scientists held arctic ground squirrels in a
-4.3 degrees C laboratory chamber, where they could measure temperatures at
different locations and examine their blood for clues of freezing survival
mechanisms.  They found subzero temperatures only at the rear of the animal, 
not in the brain or heart, Barnes says.  And from measurements of molecules in 
blood plasma drawn from six squirrels with subzero body temperatures, Barnes 
concluded that the measured concentrations could not lower the blood's
freezing point enough to account for the squirrels' survival at the 
temperatures observed.

Barnes' team also found that the freezing and melting points of plasma from
these animals were identical, ruling out the presence of antifreeze molecules,
which lower freezing points below melting points.  And since these animals'
fluids do not freeze, the only possibility, Barnes reasons, is that the animals
use supercooling, in which a fluid is somehow prevented from freezing below its
freezing point.

Despite decades of research, no previous scientist has found a mammal able
to remain supercooled for longer than an hour.  Prolonged supercooling is
probably unique to arctic species, many of which must live for many months at 

extremely low temperatures, says H. Craig Heller of Stanford University.  Barnes
suggests that supercooling to -3 degrees C could save 10 times the energy
needed to keep up a body temperature above zero, giving the squirrels a
selective advantage.

[ Messages #43 and #95 also concerned animals that survived very low
  temperatures. - KQB ]

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