Isovaleric acid accumulation in odontocete melon during development
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Biosonar in odontocetes is a highly complex process for gathering information about the surrounding environment. The forehead melon lipid and mandibular lipid tissues, which comprise the region known as the acoustical window for cetacean sound production and reception, have a unique biochemical composition that is made up of unusual fatty deposits rich in isovaleric acid. Although the structure of these acoustical lipids was elucidated three decades ago, little work has been done to determine their origin during cetacean development. The objective of this research was to examine development of the acoustical region by characterizing the accumulation of isovaleroyl lipids throughout cetacean early life stages. Biochemical analyses of melon tissue of Phocoena phocoena and Tursiops truncatus of different sizes (as an indicator of age) demonstrated that the proportion of isovalerate increased significantly with length. These results indicate that the acoustic system is not fully developed at birth and that its biochemical structure changes throughout development.
This study would not have been possible without the generous contribution of tissue samples from John Nicolas (NEFSC), Wayne McFee (SEFSC), and Howard Braham, Jack Ceaserone, and Rich Ferrero (NMML of NMFS). The project was greatly improved by contributions made by William Nilsson and the assistance of the NWFSC’s Marine Mammal Team, Tom Hom, Sylvester Spencer and Karen Tilbury, and the technical support provided by Jo Ann Lund with the GC analyses, Hoa Dung with the Iatroscan work, and Samuel Chávez Rosales and Paul Tontz. This research was performed while S.C. Gardner held a National Research Council–NWFSC Research Associateship.
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