Molecular analysis of intact preen waxes of Calidris canutus (Aves : Scolopacidae) by gas chromatography/mass spectrometry

The intact preen wax esters of the red knot Calidris canutus were studied w ith gas chromatography/mass spectrometry (GC/MS) and GC/MS/MS. In this latt er technique, transitions from the molecular ion to fragment ions represent ing the fatty acid moiety of the wax esters were measured, providing additi onal resolution to the analysis of wax esters. The C-21-C-32 wax esters are composed of complex mixtures of hundreds of individual isomers. The odd ca rbon-numbered wax esters are predominantly composed of even carbon-numbered n-alcohols (C-14, C-16, and C-18) esterified predominantly with odd carbon -numbered 2-methyl fatty acids (C-7, C-9, C-11, and C-13), resulting in rel atively simple distributions. The even carbon-numbered wax esters show a fa r more complex distribution due to a number of factors: (i) Their n-alcohol moieties are not dominated by even carbon-numbered n-alcohols esterified w ith odd carbon-numbered 2-methyl fatty acids, but odd and even carbon-numbe red n-alcohols participate in approximately equal amounts; (ii) odd carbon- numbered methyl-branched alcohols participate abundantly in these wax ester clusters; and (iii) with increasing molecular weight, various isomers of t he 2,6-, 2,8-, and 2,10-dimethyl branched fatty acids also participate in t he even carbon-numbered wax esters. The data demonstrate that there is a cl ear biosynthetic control on the wax ester composition although the reasons for the complex chemistry of the waxes are not yet understood.