TY - JOUR A1 - Koussoroplis, Apostolos-Manuel A1 - Wacker, Alexander T1 - Covariance modulates the effect of joint temperature and food variance on ectotherm life-history traits JF - Ecology letters N2 - Understanding animal performance in heterogeneous or variable environments is a central question in ecology. We combine modelling and experiments to test how temperature and food availability variance jointly affect life-history traits of ectotherms. The model predicts that as mean temperatures move away from the ectotherm's thermal optimum, the effect size of joint thermal and food variance should become increasingly sensitive to their covariance. Below the thermal optimum, performance should be positively correlated with food–temperature covariance and the opposite is predicted above it. At lower temperatures, covariance should determine whether food and temperature variance increases or decreases performance compared to constant conditions. Somewhat stronger than predicted, the covariance effect below the thermal optimum was confirmed experimentally on an aquatic ectotherm (Daphnia magna) exposed to diurnal food and temperature variance with different amounts of covariance. Our findings have important implications for understanding ectotherm responses to climate-driven alterations of thermal mean and variance. KW - Biotic interactions KW - co-limitation KW - Daphnia KW - environmental fluctuations KW - heterogeneity KW - variability KW - vertical migration KW - zooplankton Y1 - 2016 U6 - https://doi.org/10.1111/ele.12546 SN - 1461-023X SN - 1461-0248 VL - 19 SP - 143 EP - 152 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Wacker, Alexander A1 - Piepho, Maike A1 - Harwood, John L. A1 - Guschina, Irina A. A1 - Arts, Michael T. T1 - Light-Induced Changes in Fatty Acid Profiles of Specific Lipid Classes in Several Freshwater Phytoplankton Species JF - Frontiers in plant science : FPLS N2 - We tested the influence of two light intensities [40 and 300 μmol PAR / (m2s)] on the fatty acid composition of three distinct lipid classes in four freshwater phytoplankton species. We chose species of different taxonomic classes in order to detect potentially similar reaction characteristics that might also be present in natural phytoplankton communities. From samples of the bacillariophyte Asterionella formosa, the chrysophyte Chromulina sp., the cryptophyte Cryptomonas ovata and the zygnematophyte Cosmarium botrytis we first separated glycolipids (monogalactosyldiacylglycerol, digalactosyldiacylglycerol, and sulfoquinovosyldiacylglycerol), phospholipids (phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, and phosphatidylserine) as well as non-polar lipids (triacylglycerols), before analyzing the fatty acid composition of each lipid class. High variation in the fatty acid composition existed among different species. Individual fatty acid compositions differed in their reaction to changing light intensities in the four species. Although no generalizations could be made for species across taxonomic classes, individual species showed clear but small responses in their ecologically-relevant omega-3 and omega-6 polyunsaturated fatty acids (PUFA) in terms of proportions and of per tissue carbon quotas. Knowledge on how lipids like fatty acids change with environmental or culture conditions is of great interest in ecological food web studies, aquaculture, and biotechnology, since algal lipids are the most important sources of omega-3 long-chain PUFA for aquatic and terrestrial consumers, including humans. KW - freshwater algae KW - light adaptation KW - lipid classes KW - fatty acid changes Y1 - 2016 U6 - https://doi.org/10.3389/fpls.2016.00264 SN - 1664-462X VL - 7 SP - 1 EP - 13 PB - Frontiers Media CY - Lausanne ER - TY - JOUR A1 - Grzesiuk, Malgorzata A1 - Wacker, Alexander A1 - Spijkerman, Elly T1 - Photosynthetic sensitivity of phytoplankton to commonly used pharmaceuticals and its dependence on cellular phosphorus status JF - Ecotoxicology N2 - Recently pharmaceuticals have become significant environmental pollutants in aquatic ecosystems, that could affect primary producers such as microalgae. Here we analyzed the effect of pharmaceuticals on the photosynthesis of microalgae commonly found in freshwater-two species of Chlorophyceae and a member of the Eustigmatophyceae, via PAM fluorometry. As pharmaceuticals, three medicines often consumed in households were chosen: (i) fluoxetine, an antidepressant, (ii) propranolol, a beta-blocker and (iii) ibuprofen, an anti-inflammatory and analgesic medicine. The EC50 for the quantum yield of photosystem II in phytoplankton acclimated to inorganic phosphorus (P-i)-replete and P-i-limited conditions was estimated. Acute toxicity experiments over a 5 h exposure revealed that Nannochloropsis limnetica was the least sensitive to pharmaceuticals in its photosynthetic yield out of all species tested. Although the estimation of sub-lethal effects can be vital in contrast to that of LC(50)s, the EC50 values in all species and for all medicines were orders of magnitude higher than concentrations found in polluted surface water. Chlamydomonas reinhardtii was the most sensitive to fluoxetine (EC50 of 1.6 mg L-1), and propranolol (EC50 of 3 mg L-1). Acutodesmus obliquus was most sensitive to ibuprofen (EC50 of 288 mg L-1). Additionally, the sensitivity to the pharmaceuticals changed under a P-i-limitation; the green algae became less sensitive to fluoxetine and propranolol. In contrast, P-i-limited algal species were more sensitive to ibuprofen. Our results suggest that the sensitivity of algae to pharmaceuticals is (i) highly compound- and species-specific and (ii) dependent on the cellular P status. KW - Freshwater algae KW - Medicine KW - EC50 KW - PAM fluorometry KW - Tolerance Y1 - 2016 U6 - https://doi.org/10.1007/s10646-016-1628-8 SN - 0963-9292 SN - 1573-3017 VL - 25 SP - 697 EP - 707 PB - Springer CY - Dordrecht ER -