ω -( o -Alkylphenyl)alkanoic acids are known to form in vitro from triunsaturated fatty acids following protracted heating. These compounds have recently been identified in absorbed lipid extracts obtained from archaeological pottery vessels, providing a potentially valuable new class of indicator for the processing of commodities, such as marine oils, which contain high abundances of polyunsaturated fatty acids. Experiments were conducted to assess whether ω -( o -alkylphenyl)alkanoic acids form when pure compounds and complex triacylglycerol mixtures are heated with a fired clay. The results demonstrate that ω -( oalkylphenyl)alkanoic acids are only produced following heating of unsaturated fatty acids (tri-, di-and monounsaturated species) or complex unsaturated fatty acyl lipids at around 270 ° C. Heating saturated fatty acyl lipids does not yield ω -( o -alkylphenyl)alkanoic acids. Thus, when searching for evidence for the processing of marine derived animal fats in archaeological pottery vessels, it is essential that: ω -( o -alkylphenyl)alkanoic acids of carbon length C 18 and C 20 should be present, ideally with C 22 also detectable (if only in trace abundances), together with at least one of the three isoprenoid fatty acids (phytanic, pristanic or 4,8,12-tetramethyltridecanoic acid).
Studies of the trophic interactions between organisms in opaque environments where direct observation can be difficult, such as soil or leaf litter, often require the use of indirect inferential approaches. Here, the use of compound-specific 13 C-tracing of dietary biomarker fatty acids is evaluated as a method for studying predation by larvae of the dung-breeding fly, Mesembrina meridiana (Diptera: Muscidae); the technique was used to differentiate dung from high-enrichment 13 C-labelled prey in their gut contents. Potential prey, 13 C-labelled larvae of the dungbreeding fly, Neomyia cornicina (Diptera: Muscidae), were placed into unlabelled dung microcosms in the laboratory. A single 7-day-old M. meridiana larva was allowed to feed in each microcosm for 8 h. The magnitude of increases in the δ 13 C values of fatty acids (i14:0, 14:0, i15:0, a15:0, 15:0, 16:0 and 18:0) in the gut contents, relative to those of M. meridiana deprived of prey, demonstrated the predation of N. cornicina larvae which were estimated to have constituted at least 35% of the average dietary wet mass of these M. meridiana larvae. The tracing of specific labelled compounds increased confidence in dietary assessment and helped to avoid systematic errors associated with compound-dependent efficiency of assimilation in the gut. The results demonstrate the potential value of this method in helping to elucidate trophic interactions in predator-prey systems within opaque environments. The precision of the quantitative dietary estimation that arose from these isotopic data was superior to that generated using fatty acid distributional data, a widely used and evidentially independent line of evidence.
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