The molecular basis of essential fatty acid limitation in Daphnia magna: A transcriptomic approach

Abstract

It is widely accepted that in many food webs, the trophic transfer efficiency among primary producers and herbivores is determined by the nutritional value of primary producers. In pelagic freshwater and marine ecosystems, secondary production by herbivorous crustacean zooplankton is often limited by the seston's content of essential ω3 polyunsaturated fatty acids (ω3 PUFAs). However, little is known about the genetic network behind the positive relationship between phytoplankton ω3 PUFA content and zooplankton growth and reproduction. In our experimental study, we analysed gene expression changes of the freshwater cladoceran Daphnia magna under different food regimes differing in their ω3 PUFA composition. To disentangle ω3 PUFA effects from other factors, we fed D. magna with different pure phytoplankton cultures (i.e., algal and cyanobacterial diets) with or without supplementing the essential ω3 PUFA eicosapentaenoic acid (EPA). As hypothesized, we observed enhanced growth on diets supplemented with EPA. We applied an Illumina RNA-seq approach to D. magna from different diet treatments to find and monitor genes that are regulated dependent on EPA availability. Of 26,646 potential protein products (mapped to the D. magna genome), we identified transcriptomic signatures driven by the different food sources. Further analyses revealed specific candidate genes involved in EPA metabolism, irrespective of the basal food source. This allows a first functional annotation of previously uncharacterized genes involved in the EPA-specific response of D. magna and may finally provide a link to molecular processes connected to ω3 PUFA metabolism and conversion and thus trophic transfer efficiency in pelagic food webs.

Equal relevance of omega‐3 and omega‐6 polyunsaturated fatty acids for the fitness of Daphnia spp.

“…Limitation of Daphnia by an ω-6 PUFA and subsequently evaporated at 40 C under a stream of nitrogen gas and the remaining FAMEs were redissolved in 50 μL isohexane per sample. One microliter of each sample was injected splitless into a 6890-N GC System (Agilent Technologies, Waldbronn, Germany) and analyzed using the same method as described by Windisch and Fink (2018). We found 122 ng μL −1 of ARA and $ 142 ng μL −1 of EPA in the respective liposomes, while we confirmed the control liposomes to be PUFA-free.…”

“…One microliter of each sample was injected splitless into a 6890‐N GC System (Agilent Technologies, Waldbronn, Germany) and analyzed using the same method as described by Windisch and Fink (). We found 122 ng μ L −1 of ARA and ∼ 142 ng μ L −1 of EPA in the respective liposomes, while we confirmed the control liposomes to be PUFA‐free.…”

High nutrient availability leads to weaker top‐down control of stream periphyton: Compensatory feeding in Ancylus fluviatilis

“…(). Furthermore, nutrient enrichment is likely to alter not only periphyton nutrient content, but also its taxonomic (Stelzer & Lamberti, ) and fatty acid composition (Hill, Rinchard, & Czesny, ), which are further components of algal nutritional quality (Brett, Müller‐Navarra, & Park, ; Wacker & von Elert, ; Windisch & Fink, ). As a consequence, more studies are needed to investigate the long‐term effects of eutrophication on periphyton food quality and grazer behaviour in stream communities.…”

“…Significant effects (p < 0.05) are highlighted in bold Values are mean ± SD of n = 3 replicate flumes. Different letters indicate significant differences between treatments Lamberti, 2001) and fatty acid composition (Hill, Rinchard, & Czesny, 2011), which are further components of algal nutritional quality (Brett, Müller-Navarra, & Park, 2000;Wacker & von Elert, 2004;Windisch & Fink, 2018). As a consequence, more studies are needed to investigate the long-term effects of eutrophication on periphyton food quality and grazer behaviour in stream communities.…”

Transcriptome sequencing of a keystone aquatic herbivore yields insights on the temperature-dependent metabolism of essential lipids

“…Further, they can provide an unbalanced supply (stoichiometry) of nutrients [4]. In many cases their biochemical composition does not meet the herbivores' demands in essential nutritional compounds, such as essential fatty acids [5,6], sterols [7,8], vitamins [9], or amino acids [10,11].…”