Isovaleric acid accumulation in odontocete melon during development.

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.