Compound-specific isotope analyses (CSIA) of fatty acids (FA) constitute a promising tool for tracing energy flows in food-webs. However, past applications of FA-specific carbon isotope analyses have been restricted to a relatively coarse food-source separation and mainly quantified dietary contributions from different habitats. Our aim was to evaluate the potential of FA-CSIA to provide high-resolution data on within-system energy flows using algae and zooplankton as model organisms. First, we investigated the power of FA-CSIA to distinguish among four different algae groups, namely cyanobacteria, chlorophytes, haptophytes and diatoms. We found substantial within-group variation but also demonstrated that δ 13 C of several FA (e.g. 18:3 ω 3 or 18:4 ω 3) differed among taxa, resulting in group-specific isotopic fingerprints. Second, we assessed changes in FA isotope ratios with trophic transfer. Isotope fractionation was highly variable in daphnids and rotifers exposed to different food sources. Only δ 13 C of nutritionally valuable poly-unsaturated FA remained relatively constant, highlighting their potential as dietary tracers. The variability in fractionation was partly driven by the identity of food sources. Such systematic effects likely reflect the impact of dietary quality on consumers' metabolism and suggest that FA isotopes could be useful nutritional indicators in the field. Overall, our results reveal that the variability of FA isotope ratios provides a substantial challenge, but that FA-CSIA nevertheless have several promising applications in food-web ecology. This article is part of the theme issue ‘The next horizons for lipids as ‘trophic biomarkers’: evidence and significance of consumer modification of dietary fatty acids’.

中文翻译：

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脂肪酸同位素追踪水生食物网营养转移的潜力

脂肪酸 (FA) 的化合物特异性同位素分析 (CSIA) 是追踪食物网能量流的有前途的工具。然而，过去 FA 特异性碳同位素分析的应用仅限于相对粗略的食物来源分离，并且主要量化来自不同栖息地的饮食贡献。我们的目的是评估 FA-CSIA 使用藻类和浮游动物作为模型生物提供系统内能量流高分辨率数据的潜力。首先，我们研究了 FA-CSIA 区分四种不同藻类（即蓝藻、叶绿藻、触生藻和硅藻）的能力。我们发现了显着的组内差异，但也证明了 δ13几个FA的C（例如18:3ω3或18:4ω3）类群之间存在差异，从而产生特定群体的同位素指纹。其次，我们评估了 FA 同位素比率随营养转移的变化。接触不同食物来源的水蚤和轮虫的同位素分馏变化很大。仅δ13具有营养价值的多不饱和脂肪酸的 C 值保持相对稳定，突显了它们作为膳食示踪剂的潜力。分馏的可变性部分是由食物来源的特性造成的。这种系统效应可能反映了膳食质量对消费者新陈代谢的影响，并表明 FA 同位素可能是该领域有用的营养指标。总的来说，我们的结果表明 FA 同位素比率的变化带来了巨大的挑战，但 FA-CSIA 在食物网生态学中仍然有一些有前景的应用。本文是主题“脂质作为‘营养生物标志物’的下一个前景：消费者改变膳食脂肪酸的证据和意义”的一部分。