Variation in the endogenous intact waxes of odontocetes: There is more than one way to build an acoustic receiver

Odontocetes possess specialized fat bodies in and around the mandibles for sound reception which have complex topographical distributions of unique endogenous lipids (triacylglycerols and wax esters [WE]). Although there is diversity across species in the fatty acid (FA) and fatty alcohol (FAlc) components of WE, little is understood about the composition and placement of the intact molecules, which will likely impact acoustic function. We aimed to determine the composition and distribution of intact waxes in the jaw fats from five species representative of three odontocete families: delphinids, kogiids, and ziphiids. Total lipid content was similar in all groups, but the WE content of that lipid (21.3%-53.3% of total lipid) and the identity of intact WE molecules showed a high degree of variation, especially in the short-chain fatty acid components. In contrast, the FAlc elements were surprisingly well conserved. There were 26 intact WE that were common to all species but the delphinids had 12 additional WE with short-chain fatty acids (i-5:0 specifically) not found in the other animals examined here. Our study suggests that this highly specialized tissue has evolved several different biochemical pathways, and that there may be multiple strategies for building acoustic fat bodies.