Biomarker function and nutritional stoichiometry of neutral lipid fatty acids and amino acids in oribatid mites

- Neutral lipid fatty acids (NLFAs) are reliable and specific nutritional biomarkers for oribatid mites.
- Multivariate patters of neutral lipid fatty acid profiles can be used to unequivocally assign oribatid mites to their diet.
- Amino acid profiles are independent from dietary compositions.

Biomarkers (e.g. fatty acids, amino acids, stable isotopes, and molecular barcodes) have become increasingly important for investigating food web structure and nutrient flow in soil ecosystems. While the biomarker function of fatty acids has been investigated for some soil animal taxa (e.g. collembolans and nematodes), their role in soil-dwelling oribatid mites remained unknown. Here, we investigate the biomarker function and nutritional stoichiometry of neutral lipid fatty acids (NLFA) and amino acids in oribatid mites. We reared the opportunistic model oribatid mite species Archegozetes longisetosus on ten different resources of animal, bacterial, fungal and herbal origin. We analyzed the neutral lipid fatty acid and amino acid compositions of resources and consumers with gas chromatography/mass spectrometry (GC/MS) and ion-exchange chromatography (IEC), respectively. We found diet-dependent amounts and compositions of NLFA in the oribatid mites, but amino acids were stable and independent of diet. Consumer NLFA composition could be used as a reliable predictor of diet using data mining approaches (i.e., Random Forest), while amino acid profiles reflected diet-independent intrinsic physiological properties and confirm the homeostatic protein stoichiometry hypothesis for oribatid mites.