Sikora Anna B, Petzoldt Thomas, Dawidowicz Piotr, von Elert Eric
Department of Hydrobiology, Faculty of Biology, Biological and Chemical Research Center, University of Warsaw, Żwirki i Wigury 101, 02-089, Warsaw, Poland.
Aquatic Chemical Ecology, Cologne Biocenter, University of Cologne, Zülpicherstrasse 47b, 50674, Cologne, Germany.
Oecologia. 2016 Oct;182(2):405-17. doi: 10.1007/s00442-016-3675-5. Epub 2016 Jun 27.
Fatty acids contribute to the nutritional quality of the phytoplankton and, thus, play an important role in Daphnia nutrition. One of the polyunsaturated fatty acids (PUFAs)--eicosapentaenoic acid (EPA)--has been shown to predict carbon transfer between primary producers and consumers in lakes, suggesting that EPA limitation of Daphnia in nature is widespread. Although the demand for EPA must be covered by the diet, the demand of EPA in Daphnia that differ in body size has not been addressed yet. Here, we hypothesize that the demand for EPA in Daphnia is size-dependent and that bigger species have a higher EPA demand. To elucidate this, a growth experiment was conducted in which at 20 °C three Daphnia taxa (small-sized D. longispina complex, medium-sized D. pulicaria, and large-bodied D. magna) were fed Synechococcus elongatus supplemented with cholesterol and increasing concentrations of EPA. In addition, fatty acid analyses of Daphnia were performed. Our results show that the saturation threshold for EPA-dependent growth increased with increasing body size. This increase in thresholds with body size may provide another mechanism contributing to the prevalence of small-bodied cladocera in warm habitats and to the midsummer decline of large cladocera in eutrophic water bodies.
脂肪酸有助于提高浮游植物的营养质量，因此在水蚤的营养中发挥着重要作用。多不饱和脂肪酸（PUFAs）之一的二十碳五烯酸（EPA）已被证明可以预测湖泊中初级生产者和消费者之间的碳转移，这表明自然界中水蚤的EPA限制很普遍。尽管EPA的需求必须由食物来满足，但不同体型水蚤对EPA的需求尚未得到研究。在此，我们假设水蚤对EPA的需求与体型有关，体型较大的物种对EPA的需求更高。为了阐明这一点，我们进行了一项生长实验，在20°C的条件下，用添加了胆固醇和浓度不断增加的EPA的细长聚球藻喂养三种水蚤分类群（小型的长刺溞复合体、中型的蚤状溞和大型的大型溞）。此外，还对水蚤进行了脂肪酸分析。我们的结果表明，依赖EPA生长的饱和阈值随着体型的增大而增加。这种阈值随体型的增加可能为小型枝角类在温暖栖息地的普遍存在以及富营养水体中大型枝角类在仲夏时数量下降提供了另一种机制。
