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

决定湖泊系统营养转移效率的一个主要因素是藻类和蓝藻对水蚤的食物质量。一些相关研究指出，天然浮游植物中低含量的多不饱和脂肪酸二十碳五烯酸(EPA，C20：5n-3)对水蚤有原位限制作用，大量实验研究表明，EPA限制对水蚤的体细胞生长和繁殖有负面影响。这些EPA限制的负面影响在较低的温度下比在20°C时更强。本建议旨在调查限制资源EPA是否影响水蚤之间的竞争，以及EPA限制如何影响水蚤群落的克隆组成。这里建议调查，如果EPA需求在同一物种的克隆之间和(Ii)不同执行Diel Vertical Mirgation(DVM)能力的水蚤之间存在差异。为了实现这一点，将对每个克隆人进行生活史实验，每个克隆人使用在两个不同温度下增加EPA含量的梯度食物。类似Monod的饱和函数将被用来估计EPA限制增长的阈值浓度。Bootstrapping将被用来估计这些阈值浓度的变异性，以便可以在不同的Daphnia基因型间进行统计比较。为了了解造成EPA阈值浓度差异的机理，将进行后续实验，通过比较摄入和同化的EPA量来确定不同基因型EPA的资源利用效率。最后，将进行竞争实验，以调查EPA限制如何影响不同EPA阈值浓度的Daphnia基因型群落的遗传组成。总体目的是调查不同类型的水蚤之间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一种机制。

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.