Desert mammal shrinks organ mass to reduce exergy expenditure during drought

[Guy Leahy <xrciseguy@sbcglobal.net>]

Interesting stuff... one could imagine dinosaurs which
lived in strongly seasonal environments utilizing a
similar strategy...

Guy Leahy
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Source: University of Chicago Press Journals

Posted: June 9, 2006

Gazelles Shrink Liver And Heart To Reduce Oxygen
Consumption During Drought
How do gazelles and other large desert mammals adjust
their physiology to survive when food and water are in
short supply? A fascinating new study from the
July/August issue of Physiological and Biochemical
Zoology reveals that gazelles in the deserts of Saudi
Arabia have evolved the ability to shrink
oxygen-demanding organs such as the liver and heart,
allowing them to breathe less. Fewer breaths reduce
the amount of water lost to respiratory evaporation
during prolonged periods of drought.

There are few sources of drinking water in the desert,
so sand gazelles must rely on vegetation for both food
and water requirements.

"We found that gazelles had the lowest total
evaporative water loss ever measured in an arid zone
ungulate [hoofed animal]," write Stéphane Otrowski
(National Wildlife Research Center, Saudi Arabia),
Pascal Mésochina (National Wildlife Research Center,
Saudi Arabia), and Joseph B. Williams (Ohio State
University). Sand gazelles' livers and hearts -- which
are important determinants of metabolic rate --
decrease significantly in mass during four months of
food and water restriction. Conversely, the gut walls,
which are responsible in ruminants for 28-46% of
whole-body protein synthesis, an energy demanding
process, did not decrease significantly in mass. There
are few sources of drinking water in the desert, so
sand gazelles must rely on vegetation for both food
and water requirements.

"The deserts of the Arabian Peninsula are among the
most austere of terrestrial environments, with low,
unpredictable rainfall, and high ambient temperature,"
explain the authors. "The sand gazelle has evolved a
remarkable capacity to reduce its evaporative water
losses, which is likely a component of their success."

Unexpectedly, the researchers also found that deprived
sand gazelles had a higher fat content in the brain,
revealing that gazelles may store fats in the brain to
secure brain metabolism during prolonged food and
water deprivation.

Reference: Ostrowski, Stéphane, Pascal Mésochina, and
Joseph B. Williams. "Physiological adjustments of sand
gazelles (Gazella subgutturosa) to a boom or burst
economy: standard fasting metabolic rate, total
evaporative water loss and changes in the size of
organs during food and water restriction."
Physiological and Biochemical Zoology 79:4.