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

点击翻译按钮获取中文摘要

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.