title: Demands of eicosapentaenoic acid (EPA) in Daphnia: are they dependent on body size?
abstract: 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.
authors.affiliation: Department of Hydrobiology, Faculty of Biology, Biological and Chemical Research Center, University of Warsaw, Żwirki i Wigury 101, 02-089, Warsaw, Poland. a.b.sikora@uw.edu.pl.|Aquatic Chemical Ecology, Cologne Biocenter, University of Cologne, Zülpicherstrasse 47b, 50674, Cologne, Germany. a.b.sikora@uw.edu.pl.
authors.forename: Anna B
authors.initials: AB
authors.lastname: Sikora
authors.affiliation: Institute of Hydrobiology, Technische Universität Dresden, Helmholtzstrasse 10, 01069, Dresden, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Petzoldt
authors.affiliation: Department of Hydrobiology, Faculty of Biology, Biological and Chemical Research Center, University of Warsaw, Żwirki i Wigury 101, 02-089, Warsaw, Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Dawidowicz
authors.affiliation: Aquatic Chemical Ecology, Cologne Biocenter, University of Cologne, Zülpicherstrasse 47b, 50674, Cologne, Germany.
authors.forename: Eric
authors.initials: E
authors.lastname: von Elert
mesh_terms: D000818:Animals; D049628:Body Size; D003621:Daphnia; D017753:Ecosystem; D015118:Eicosapentaenoic Acid; D010839:Phytoplankton
chemical_list: D015118:Eicosapentaenoic Acid
keywords: Body size; Daphnia; EPA; Polyunsaturated fatty acids; Threshold