November 26, 2018
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With funds from a National Science Foundation grant—and the help of a monstrous caterpillar—interdisciplinary teams of Kenyon students and professors have been exploring one of life's most intriguing mysteries. The focus is metabolism itself, "the fire of life," and more specifically a remarkable consistency seen in creatures from bacteria to blue whales.
Faculty in both biology and mathematics are investigating metabolic scaling, or how the rate of metabolism changes with the size of organisms. Across the living world, metabolic scaling takes on a consistent mathematical form, says Associate Professor of Biology Drew Kerkhoff, a specialist in the increasingly important field of mathematical biology and one of five professors involved in the project.
Attacking the problem from a number of angles, and using sophisticated statistical methods as well as mathematical modeling, the faculty-student teams are studying the factors that underpin metabolic scaling. Working with Kerkhoff are biologists Chris Gillen and Harry Itagaki, along with mathematicians Brad Hartlaub and Judy Holdener, plus students participating in the Summer Science Scholars Program.
"It's not practical to work on bacteria and blue whales," Kerkhoff said. "So we need an animal that spans a wide range of body sizes." Enter Manduca sexta, the larva of the tobacco hawkmoth. This caterpillar grows to 10,000 times its egg mass in 18 days. "In other words," Kerkhoff said, "it doubles its mass every day, growing from a tiny one-milligram egg to about 10 grams in weight, and a few inches long. For comparison, a bull elephant is about 10,000 times heavier than a guinea pig."
"Our main focus is on understanding how metabolic scaling relates to resource exchange," Kerkhoff said. "The caterpillar eats plant leaves, taking up nutrients. Does that exchange process determine scaling?" The work has implications for understanding life at every level of organization, from molecules to ecosystems.
One of the studies looks at transporter proteins in the tissue of the Manduca midgut, where digestion takes place. Another focuses on the surface area of the midgut and entails a painstaking process of taking cross sections (with techniques developed at Kenyon) and using digital photography, image-processing software, and mathematical modeling to produce a three-dimensional picture of the midgut. Another measures the caterpillar's metabolic rate by tracking oxygen consumption and carbon dioxide production.
"This is a truly unique project," Kerkhoff said. "Other researchers are working on specific, specialized problems. But here's a whole collection of faculty and students working collectively, seeing how all the aspects of the question fit together."