The role of polyunsaturated fatty acids for the competition in herbivorous zooplankton

决定生态系统营养转移效率的一个主要因素是水蚤所需藻类和蓝藻的食物质量。一些相关研究指出，天然浮游植物中多不饱和脂肪酸二十碳五烯酸（eicosapentaenoic acid, C20:5 n-3）的低含量限制了水蚤的原位生长，大量实验研究证明了EPA限制对水蚤体细胞生长和繁殖的负面影响。epa限制的这些负面影响在较低温度下比在20°C时更强烈。本文旨在研究限制资源EPA是否会影响水蚤间的竞争，以及EPA限制如何影响水蚤群落的克隆组成。在这里，我们提出了调查，如果epa需求不同(i)在同一物种的克隆和（ii）水蚤物种之间的能力不同，在执行Diel垂直迁移（DVM）。为了实现这一目标，将对每个克隆进行生活史实验，使用在两种不同温度下具有增加epa含量梯度的食物。monod类饱和函数将用于估计epa限制生长的阈值浓度。Bootstrapping将用于估计这些阈值浓度的变异性，以便对不同水蚤基因型的阈值浓度进行统计比较。为了了解造成EPA阈值浓度差异的机制，将进行后续实验，通过比较摄入和吸收的EPA量来确定不同基因型的EPA资源利用效率。最后，通过竞争试验研究EPA限制对不同EPA阈值浓度水蚤基因型群落遗传组成的影响。总体目的是研究不同水蚤基因型之间EPA阈值浓度的差异是否如此相关，以至于EPA限制是影响水蚤之间竞争的机制。

A major factor determining the trophic transfer efficiency in limnic systems is the food quality of algae and cyanobacteria for Daphnia. Several correlative studies point at an in-situ limitation of Daphnia by a low content of the polyunsaturated fatty acid eicosapentaenoic acid (EPA, C20:5 n-3) in natural phytoplankton, and numerous experimental studies have demonstrated negative effects of EPA-limitation on somatic growth and reproduction of Daphnia. These negative effects of EPA-limitation were stronger at lower temperatures than at 20°C. This proposal aims at investigating, if the limiting resource EPA affects the compe-tition among Daphnia and how an EPA-limitation affects the clonal composition of a Daphnia community.Here it is proposed to investigate, if the EPA-demand differs (i) between clones of the same species and (ii) between Daphnia species that differ in their ability to perform Diel Vertical Mirgation (DVM). To achieve this, life-history experiments will be performed with each clone using food with a gradient of increasing EPA-content at two different temperatures. Monod-like saturation functions will be used to estimate threshold concentrations for EPA-limited growth. Bootstrapping will be used to estimate the variability of these threshold concentrations, so that threshold concentrations can be statistically compared among Daphnia genotypes. In order to understand the mechanisms causing differences in EPA-threshold concentrations, a follow-up experiments will be conducted to determine the resource-use efficiency for EPA of the different genotypes by comparing ingested and assimilated EPA amounts. Finally a competition experiment will be performed to investigate, how EPA limitation affects the genetic composition of communities of Daphnia genotypes with different EPA threshold concentrations. The overall aim is to investigate if differences in EPA threshold concentrations among Daphnia genotypes are so relevant that EPA-limitation is a mechanism that affects competition among Daphnia.