Meeting Abstract

P2.54  Saturday, Jan. 5  Functional morphology of dorsal acoustic structures in pygmy (Kogia breviceps) and dwarf (K. sima) sperm whales THORNTON, S.W.*; MCLELLAN, W.A.; ROMMEL, S.A.; PABST, D.A.; Univ. of North Carolina Wilmington swt9459@uncw.edu

Odontocete cetaceans produce echolocation clicks to interrogate their environment and search for prey. These clicks are generated by pneumatically-driven phonic lips within their nasal passage, and propagated through specialized lipid structures within the forehead into the water. The echolocation clicks of kogiids, the pygmy and dwarf sperm whales, are produced using nasal morphologies that deviate dramatically from those of other odontocetes. Kogiids display marked left-right soft tissue asymmetry and possess accessory structures within their nasal system whose functions have not yet been adequately described. Our goal is to investigate the functional morphology of this system through gross and histological examinations, computed tomography (CT) imaging, and physical tissue manipulations. Preliminary results indicate that the kogiid phonic lips likely serve as sound generators and are composed of epithelial, connective, and muscular tissues. A labyrinth of air crypts and dense connective tissues are found within a dome-shaped “vocal cap,” a tough yet deformable structure that envelops the phonic lips. The morphology of the vocal cap, an autapomorphic feature of kogiids, suggests it functions as a sound reflector/absorber. The vocal cap, phonic lips, and spermaceti organ (a cornucopia-shaped fat channel that contacts the caudal-most phonic lip) are all acted on by facial muscles, suggesting that the kogiid acoustic system is highly tunable. Such muscular control may permit these animals to change the acoustic characteristics of their echolocation sounds and/or focus the sound “beam” in a desired direction.