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.

"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.

Since 1928, Physiological and Biochemical Zoology has presented original, current research in environmental, adaptational, and comparative physiology and biochemistry.

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.

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