Sunday, February 17, 2013
Room 310 (Hynes Convention Center)
Large body size is associated with a wide range of physiological advantages in air-breathing marine vertebrates, ranging from more efficient metabolism to enhanced diving capacity. As a consequence, these benefits are generally thought to drive the evolution of greater body sizes in many different groups of animals. The fossil record suggests that extant baleen whales are the largest animals that have ever existed, but it is unknown why whales are not any larger. Such extreme body sizes require very high energetic demands and baleen whales are able to meet these needs by filter feeding large quantities of small prey, ranging from krill to fish. Filter feeding in baleen whales involves the engulfment of prey-laden water that is subsequently filtered by racks of keratinized baleen plates that hang down from the top of the mouth. A family of baleen whales called rorquals, which include many of the largest baleen whale species (i.e., blue and fin whales), use a distinct filter feeding strategy called lunge feeding - a dynamic process that entails the engulfment of a large volume of prey and water at high speed. By lunge feeding on dense patches of prey, many rorqual species are able to efficiently exploit abundant oceanic resources and acquire energy that is needed for growth, long distance migration, and reproduction. Using suction-cup attached, multi-sensor tags researchers have elucidated the fine-scale details of rorqual feeding behavior during foraging dives. Researchers have used these data in combination with advanced hydrodynamic and morphometric models to calculate the energetic costs and benefits of this complex foraging mechanism. Across a range of body sizes, these data demonstrate that larger rorquals exhibit relatively larger mouths and therefore have the ability to take relatively bigger gulps of water during each lunge. Although this allows larger rorquals to capture more prey, the energetic cost and power (rate of energy delivery) required to perform each lunge becomes increasingly higher. Such a trend decreases both diving capacity and the energetic efficiency of foraging in larger rorquals. These results suggest a physiological limit to larger body sizes and may explain why whales are not larger than present day blue whales. Therefore, the bulk-filter feeding mechanism that facilitates gigantism in baleen whales may also limit maximum body size of the largest animals of all-time.