Fatty acid patterns as biomarker for trophic interactions: Changes after dietary switch and starvation

Fatty acid (FA) analysis is becoming increasingly important for investigating trophic interactions in soil food webs. FA profiles of neutral lipids are affected by diet, and the occurrence and amount of certain FAs can reflect feeding strategies. However, to draw conclusions on feeding strategies in the field it is necessary to know physiological parameters of fatty acid metabolism such as the detection time and storage period of FAs. In this study we investigated the chronological change of FA biomarkers in the Collembola Heteromurus nitidus when switched between different food sources: leaves (Tilia europaea), a fungus (Chaetomium globosum) and two bacteria (Stenotrophomonas maltophilia, Bacillus amyloliquefaciens). Additionally, we followed the change of bacterial FA biomarkers during starvation. After 14 days of food deprivation bacterial FAs were still detectable in a sufficient amount to use them as dietary markers. Switching diet experiments demonstrated that FAs typical for a specific diet are already present after one day and are still detectable after 14 days of feeding on a different food source, suggesting that FA analysis can integrate the food choice of Collembola over a longer period of time, in contrast to snapshot methods such as gut content analysis.