One amino acid, a whale of a difference

ANN ARBOR'A single amino-acid variation in a key receptor in whales may help explain why some species of cetaceans evolved sleek, muscular bodies to hunt fish and seals, while others grow to massive sizes by filter-feeding on large volumes of plankton, an international research team has found. The work was led by Roger Cone, an obesity researcher at the University of Michigan Life Sciences Institute who has spent his career studying the melanocortin system. Just like the thermostat on a wall determines how much heat energy is in a room, the melanocortin circuits characterized by the Cone lab determine how much energy is stored as fat. Mutations in this system are the most common genetic cause of early-onset obesity in humans. Given the melanocortin system's importance to feeding and energy balance in fish and mammals, Cone and his collaborators thought variations in the melanocortin genes may play a critical role in the evolution of different types of feeding behaviors and body sizes. When Liyuan Zhao, a marine biologist and scholar from Ocean University in China, came to the Cone lab for a visiting fellowship, she decided to examine this idea in whales. She wanted to know: Could variation in the melanocortin system play a role in the differences between the two main suborders of whales-Odontoceti, which include dolphins and killer whales, and Mysticeti, which include humpback and blue whales? The Odontoceti feed by hunting prey, while the enormous Myticeti are filter feeders.