BIO 358 1st Edition Lecture 9 Outline of Last Lecture I Review II How do marine mammals dissipate body heat A Counter current heat exchange III Enhanced sensory systems A Echolocation biosonar Outline of Current Lecture I Review II Receiving system of biosonar A Odontocete lower jaw B Bullock et al 1968 C Brill et al 1988 III Transmitting System of biosonar A Cranford 1996 B Melon C Harper et al 2008 Current Lecture Sensory Biology Review water attenuation physical property of water Sound travels very efficiently through water These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Odontocete echolocation animals can make extremely high ultra sonic sounds 50 130 kHz that emanated from the head and bounce off an object and come back to the head perception of the world Human hearing pinnae funnel sound in sound pressure way hits ear drum vibration vibration of oscicles stathes pushes across the oval window which sets up pressure waves in the liquid of the inner ear hairs deformed sensory nerve Dolphins external air is a tiny hole and a narrow channel is it really the way sound enters the head alternative hypothesis Bone in jaw very thin fat body inside boney channel and inserts DIRECTLY on to the inner ear the specialized bulla Ken Norris hypothesis Fat in the lower jaw has very low sound absorption attenuation it is called acoustic fat Varanasi and Malins 1971 1972 Unusual fats not insulating unusual combination of lipids and interesting sound propagation qualities Lower jaw fats have specific spatial topography that direct sound to the bulla distribution of fat sound travels faster on inner lipids Selective pressure specialized fats arranged in a specialized manner How to test the two alternative hypothesis of normal mammal hearing vs traditional mammal hearing our hearing Cover external ear holes or cover the jaw Bullock et al 1968 Pre MMPA electrophysiological studies largest response when hydrophone placed on pan acoustic window o Anesthetized dolphin electrodes in brain or inner ear o Placed hydrophones on the head of the anesthetized dolphin and measure the brain or the ears response o Darker pigments more brain response from inputs of the animals o Darkest at the jaw most sensitive area to sound o Sound can also be activated through external ear o Problems with this approach doesn t say sound cannot enter through the ear o Why is the top of the head so sensitive o They placed the hydrophones right on the surface on the head different then transmitted through water o Animal anesthetized head out of water artificial condition Brill et al 1988 behavioral study kinder gentler version blindfolded dolphins to do discrimination tasks o 3 conditions 1 no shield 2 shield that did NOT block sound 3 shield that did block sound o No difference between conditions 1 and 2 o Dolphins with the sound blocking shield failed the test o This affects the receiving system so it could not do the discrimination Transmitting system monkey lips dorsal bursae MLDB nasal system melon People thought sound was coming from the larynx Odontocete larynx lacks vocal chords problem for sound production Sound production anatomy Bony nasal passage goes through the skull and connects to the blow hole larynx is permanently INTRANARIAL shoved into the base of the bony nasal cavity and is sometimes called the goose beak muscle holds the larynx to the bony cavity vestibular sacs sit directly below the blow hole these sacs expand and contract when filled with air the monkey lips dorsal bursae complex monkey lips sit in the vestibular sacs one dorsal bursae made of fat sits behind the nasal passage and another made of fat sits in front of the nasal passage in contact with the melon Ted Cranford 1996 Unified hypothesis of sound generation Gross morphology of lots of animals 19 speceis including kogiids monodontids delphinids phyceterids CT scanning Sound generators monkey lips dorsal bursae complex dorsal bursae small fat bodies Specialized sound transmission path melon rich with specialized acoustic fat Melon Sits in front of nasal passage Specialized fatty structure in forehead Compose of acoustic fats Shared derived trait unique to odontocetes Synapomorphy not found in Mysticetes 2 dorsal bursae one behind the nasal passage one in front of it connected to the melon monkey lips in nasal passage Harper et al 2008 Muscles surround and act upon the entire sound transmission path suggesting that the sound path is a tunable system visualized tendons working on the melon from the muscle change in shape or pressure Ziphiuscavirostris Mesoplodondentirostris different system complex we do not understand how it works