In complex food webs, it is often difficult to classify all trophic interactions, especially when the number of potential energy sources and interacting species can be high. Biochemical markers (biomarkers) can help trace energy-flow pathways from basal sources up to top predators, but can suffer from poor resolution when multiple sources all produce the same biomarker (e.g. many algae produce long-chain unsaturated fatty acids). Highly branched isoprenoids (HBIs) are unique lipids produced by diatoms, which have been successfully applied as biomarkers of diatom-derived energy pathways through marine food webs. However, currently, the existence and trophic transfer of HBIs has not been explored in freshwater food webs. Here, we confirm, for the first time, the presence of two HBI isomers (IIb and IIc) across two temperate-lake food webs, from lower basal sources up to higher trophic-position consumers (predatory fishes). Lake ecosystems are facing multiple interacting threats that could influence food-web structure and function in complex ways. HBIs could provide a novel method for tracing the outcome of altered temperature, nutrient loading and water clarity on high-quality, diatom-derived energy pathways through freshwater food webs.

中文翻译：

---

高度分支的类异戊二烯：淡水食物网中基于硅藻的能量途径的新型示踪剂

在复杂的食物网中，通常很难对所有营养相互作用进行分类，尤其是当潜在能源和相互作用物种的数量可能很高时。生化标志物（生物标志物）可以帮助追踪从基础来源到顶级捕食者的能量流通路，但是当多个来源都产生相同的生物标志物（例如，许多藻类产生长链不饱和脂肪酸）时，分辨率可能会很差。高度支化的类异戊二烯 (HBI) 是由硅藻产生的独特脂质，已成功用作通过海洋食物网的硅藻衍生能量途径的生物标志物。然而，目前尚未在淡水食物网中探索 HBI 的存在和营养转移。在这里，我们首次确认了两个温带湖泊食物网中存在两种 HBI 异构体（IIb 和 IIc），从较低的基础来源到较高营养位置的消费者（掠食性鱼类）。湖泊生态系统正面临多种相互作用的威胁，这些威胁可能以复杂的方式影响食物网的结构和功能。HBI 可以提供一种新方法，用于通过淡水食物网追踪温度、养分负荷和水透明度变化对高质量硅藻衍生能量途径的影响。