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Problems of Size and Scale: The Importance of Body Size in Metabolic Rate

Delve into the significance of body size in metabolic rate scaling, discussing key concepts and examples from Gulliver's Travels to LSD research on elephants. Understand the metabolic scaling laws and their implications.

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Problems of Size and Scale: The Importance of Body Size in Metabolic Rate

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Presentation Transcript

  1. PROBLEMS OF SIZE AND SCALE Why Size is So Important

  2. We know that a whale requires more energy (food, calories) per day than a mouse. Metabolic Rate vs. Body Size Scaling But how much more?

  3. written by Jonathan Swift in 1726 Gulliver in Lilliput - Lilliputian King is faced with a physiological problem - How much to feed Gulliver? King calculated 1728 Lilliputian portions.

  4. The story begins with early research on LSD using cats. If we’re not careful, we can run afoul of assumptions - to wit LSD and the Elephant It was discovered that a dose of 0.1 mg of LSD in a 2.6 kg cat caused aggressive behavior. It was subsequently decided that this might be a good model for studying musth in bull elephants.

  5. Musth is a condition of violent and uncontrollable rage. The elephant weighed 7722 kg. The “investigators” scaled up the dose by weight: (7722 kg /2.6 kg) = 2970 2970 X 0.1 mg = 297 mg (approximately 1500 X the human dose for a “trip”)

  6. Following injection, the elephant: • began trumpeting & running around • stopped • swayed • collapsed • convulsed • defecated, and • died The scientists concluded that elephants are particularly sensitive to LSD. Not so! Assumptions were incorrect!

  7. • • VO2 (or Em) = aMb • log VO2 = log(aMb) log VO2 = log(a) + b log(M) which has the form y = a + bx, where b is the slope of the line • There is an exponentialrelation between metabolic rate and mass: on a log-log plot this equation becomes a straight line:

  8. • Em (kcal • d-1) • log VO2 = log(a) + b log(M) 10000 1000 100 10 slope = b ~0.75 0.1 1.0 10 100 1000 Body Mass (kg)

  9. • VO2 / M (l O2 • h-1) / (kg) aM b VO2/M = = a M b-1 = aM -0.25 M • What about the weight-specific metabolic rate?

  10. mouse elephant • • Em (kcal • d-1) Em’ (kcal•kg-1•d-1) slope = -0.25 10000 1000 100 10 slope = 0.75 0.1 1.0 10 100 1000 Body Mass (kg)

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