@article{MartinCreuzburgOexleWacker2014,
  author    = {Martin-Creuzburg, Dominik and Oexle, Sarah and Wacker, Alexander},
  title     = {Thresholds for sterol-limited growth of Daphnia magna: A comparative approach using 10 different sterols},
  series = {Journal of chemical ecology},
  volume    = {40},
  journal   = {Journal of chemical ecology},
  number    = {9},
  publisher = {Springer},
  address   = {Dordrecht},
  issn      = {0098-0331},
  doi       = {10.1007/s10886-014-0486-1},
  pages     = {1039 -- 1050},
  year      = {2014},
  abstract  = {Arthropods are incapable of synthesizing sterols de novo and thus require a dietary source to cover their physiological demands. The most prominent sterol in animal tissues is cholesterol, which is an indispensable structural component of cell membranes and serves as precursor for steroid hormones. Instead of cholesterol, plants and algae contain a variety of different phytosterols. Consequently, herbivorous arthropods have to metabolize dietary phytosterols to cholesterol to meet their requirements for growth and reproduction. Here, we investigated sterol-limited growth responses of the freshwater herbivore Daphnia magna by supplementing a sterol-free diet with increasing amounts of 10 different phytosterols and comparing thresholds for sterol-limited growth. In addition, we analyzed the sterol composition of D. magna to explore sterol metabolic constraints and bioconversion capacities. We show that dietary phytosterols strongly differ in their potential to support somatic growth of D. magna. The dietary threshold concentrations obtained by supplementing the different sterols cover a wide range (3.5-34.4 mu g mg C-1) and encompass the one for cholesterol (8.9 mu g mg C-1), indicating that certain phytosterols are more efficient in supporting somatic growth than cholesterol (e.g., fucosterol, brassicasterol) while others are less efficient (e.g., dihydrocholesterol, lathosterol). The dietary sterol concentration gradients revealed that the poor quality of particular sterols can be alleviated partially by increasing dietary concentrations, and that qualitative differences among sterols are most pronounced at low to moderate dietary concentrations. We infer that the dietary sterol composition has to be considered in zooplankton nutritional ecology to accurately assess potential sterol limitations under field conditions.},
  language  = {en}
}
@article{MartinCreuzburgWackerZieseetal.2012,
  author    = {Martin-Creuzburg, Dominik and Wacker, Alexander and Ziese, Christine and Kainz, Martin J.},
  title     = {Dietary lipid quality affects temperature-mediated reaction norms of a freshwater key herbivore},
  series = {Oecologia},
  volume    = {168},
  journal   = {Oecologia},
  number    = {4},
  publisher = {Springer},
  address   = {New York},
  issn      = {0029-8549},
  doi       = {10.1007/s00442-011-2155-1},
  pages     = {901 -- 912},
  year      = {2012},
  abstract  = {Temperature-mediated plasticity in life history traits strongly affects the capability of ectotherms to cope with changing environmental temperatures. We hypothesised that temperature-mediated reaction norms of ectotherms are constrained by the availability of essential dietary lipids, i.e. polyunsaturated fatty acids (PUFA) and sterols, as these lipids are involved in the homeoviscous adaptation of biological membranes to changing temperatures. A life history experiment was conducted in which the freshwater herbivore Daphnia magna was raised at four different temperatures (10, 15, 20, 25A degrees C) with food sources differing in their PUFA and sterol composition. Somatic growth rates increased significantly with increasing temperature, but differences among food sources were obtained only at 10A degrees C at which animals grew better on PUFA-rich diets than on PUFA-deficient diets. PUFA-rich food sources resulted in significantly higher population growth rates at 10A degrees C than PUFA-deficient food, and the optimum temperature for offspring production was clearly shifted towards colder temperatures with an increased availability of dietary PUFA. Supplementation of PUFA-deficient food with single PUFA enabled the production of viable offspring and significantly increased population growth rates at 10A degrees C, indicating that dietary PUFA are crucial for the acclimation to cold temperatures. In contrast, cumulative numbers of viable offspring increased significantly upon cholesterol supplementation at 25A degrees C and the optimum temperature for offspring production was shifted towards warmer temperatures, implying that sterol requirements increase with temperature. In conclusion, essential dietary lipids significantly affect temperature-mediated reaction norms of ectotherms and thus temperature-mediated plasticity in life history traits is subject to strong food quality constraints.},
  language  = {en}
}