TY - GEN A1 - Wacker, Alexander A1 - von Elert, Eric T1 - Polyunsaturated fatty acids : evidence for non-substitutable biochemical resources in Daphnia galeata N2 - The factors that determine the efficiency of energy transfer in aquatic food webs have been investigated for many decades. The plant-animal interface is the most variable and least predictable of all levels in the food web. In order to study determinants of food quality in a large lake and to test the recently proposed central importance of the long-chained eicosapentaenoic acid (EPA) at the pelagic producer-grazer interface, we tested the importance of polyunsaturated fatty acids (PUFAs) at the pelagic producerconsumer interface by correlating sestonic food parameters with somatic growth rates of a clone of Daphnia galeata. Daphnia growth rates were obtained from standardized laboratory experiments spanning one season with Daphnia feeding on natural seston from Lake Constance, a large pre-alpine lake. Somatic growth rates were fitted to sestonic parameters by using a saturation function. A moderate amount of variation was explained when the model included the elemental parameters carbon (r2 = 0.6) and nitrogen (r2 = 0.71). A tighter fit was obtained when sestonic phosphorus was incorporated (r2 = 0.86). The nonlinear regression with EPA was relatively weak (r2 = 0.77), whereas the highest degree of variance was explained by three C18-PUFAs. The best (r2 = 0.95), and only significant, correlation of Daphnia's growth was found with the C18-PUFA α-linolenic acid (α-LA; C18:3n-3). This correlation was weakest in late August when C:P values increased to 300, suggesting that mineral and PUFA-limitation of Daphnia's growth changed seasonally. Sestonic phosphorus and some PUFAs showed not only tight correlations with growth, but also with sestonic α-LA content. We computed Monte Carlo simulations to test whether the observed effects of α-LA on growth could be accounted for by EPA, phosphorus, or one of the two C18-PUFAs, stearidonic acid (C18:4n-3) and linoleic acid (C18:2n-6). With >99 % probability, the correlation of growth with α-LA could not be explained by any of these parameters. In order to test for EPA limitation of Daphnia's growth, in parallel with experiments on pure seston, growth was determined on seston supplemented with chemostat-grown, P-limited Stephanodiscus hantzschii, which is rich in EPA. Although supplementation increased the EPA content 80-800x, no significant changes in the nonlinear regression of the growth rates with α-LA were found, indicating that growth of Daphnia on pure seston was not EPA limited. This indicates that the two fatty acids, EPA and α-LA, were not mutually substitutable biochemical resources and points to different physiological functions of these two PUFAs. These results support the PUFA-limitation hypothesis for sestonic C:P < 300 but are contrary to the hypothesis of a general importance of EPA, since no evidence for EPA limitation was found. It is suggested that the resource ratios of EPA and α-LA rather than the absolute concentrations determine which of the two resources is limiting growth. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 063 KW - alga KW - consumer KW - Daphnia KW - fatty acid KW - food quality KW - grazer KW - herbivore KW - Lake Constance KW - European Alps KW - PUFA KW - seston Y1 - 2001 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17587 ER - TY - JOUR A1 - Wacker, Alexander A1 - von Elert, Eric T1 - Polyunsaturated fatty acids : evidence for non-substitutable biochemical resources in daphnia galeata N2 - The factors that determine the efficiency of energy transfer in aquatic food webs have been investigated for many decades. The plant-animal interface is the most variable and least predictable of all levels in the food web. In order to study determinants of food quality in a large lake and to test the recently proposed central importance of the long-chained eicosapentaenoic acid (EPA) at the pelagic producer-grazer interface, we tested the importance of polyunsaturated fatty acids (PUFAs) at the pelagic producer-consumer interface by correlating sestonic food parameters with somatic growth rates of a clone of Daphnia galeata. Daphnia growth rates were obtained from standardized laboratory experiments spanning one season with Daphnia feeding on natural seston from Lake Constance, a large pre-alpine lake. Somatic growth rates were fitted to sestonic parameters by using a saturation function. A moderate amount of variation was explained when the model included the elemental parameters carbon (r2 = 0.6) and nitrogen (r2 = 0.71). A tighter fit was obtained when sestonic phosphorus was incorporated (r2 = 0.86). The nonlinear regression with EPA was relatively weak (r2 = 0.77), whereas the highest degree of variance was explained by three C18-PUFAs. The best (r2 = 0.95), and only significant, correlation of Daphnia's growth was found with the C18-PUFA a-linolenic acid (a-LA; C18:3n-3). This correlation was weakest in late August when C:P values increased to 300, suggesting that mineral and PUFA- limitation of Daphnia's growth changed seasonally. Sestonic phosphorus and some PUFAs showed not only tight correlations with growth, but also with sestonic alpha-LA content. We computed Monte Carlo simulations to test whether the observed effects of alpha-LA on growth could be accounted for by EPA, phosphorus, or one of the two C18-PUFAs, stearidonic acid (C18:4n-3) and linoleic acid (C18:2n-6). With >99% probability, the correlation of growth with alpha-LA could not be explained by any of these parameters. In order to test for EPA limitation of Daphnia's growth, in parallel with experiments on pure seston, growth was determined on seston supplemented with chemostat-grown, Plimited Stephanodiscus hantzschii, which is rich in EPA. Although supplementation increased the EPA content 80-800x, no significant changes in the nonlinear regression of the growth rates with alpha-LA were found, indicating that growth of Daphnia on pure seston was not EPA limited. This indicates that the two fatty acids, EPA and alpha-LA, were not mutually substitutable biochemical resources and points to different physiological functions of these two PUFAs. These results support the PUFA-limitation hypothesis for sestonic C:P < 300 but are contrary to the hypothesis of a general importance of EPA, since no evidence for EPA limitation was found. It is suggested that the resource ratios of EPA and alpha-LA rather than the absolute concentrations determine which of the two resources is limiting growth. Y1 - 2001 UR - http://www.esajournals.org/esaonline/?request=get-abstract&issn=0012-9658&volume=082&issue=09&page=2507 ER - TY - GEN A1 - Wacker, Alexander A1 - von Elert, Eric T1 - Strong influences of larval diet history on subsequent post-settlement growth in the freshwater mollusc Dreissena polymorpha N2 - Significant seasonal variation in size at settlement has been observed in newly settled larvae of Dreissena polymorpha in Lake Constance. Diet quality, which varies temporally and spatially in freshwater habitats, has been suggested as a significant factor influencing life history and development of freshwater invertebrates. Accordingly, experiments were conducted with field-collected larvae to test the hypothesis that diet quality can determine planktonic larval growth rates, size at settlement and subsequent post-metamorphic growth rates. Larvae were fed one of two diets or starved. One diet was composed of cyanobacterial cells which are deficient in polyunsaturated fatty acids (PUFAs), and the other was a mixed diet rich in PUFAs. Freshly metamorphosed animals from the starvation treatment had a carbon content per individual 70% lower than that of larvae fed the mixed diet. This apparent exhaustion of larval internal reserves resulted in a 50% reduction of the postmetamorphic growth rates. Growth was also reduced in animals previously fed the cyanobacterial diet. Hence, low food quantity or low food quality during the larval stage of D. polymorpha lead to irreversible effects for postmetamorphic animals, and is related to inferior competitive abilities. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 064 KW - Dreissena polymorpha KW - food quality KW - fatty acid KW - life history KW - metamorphosis KW - PUFA Y1 - 2002 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17627 ER - TY - JOUR A1 - Wacker, Alexander A1 - Becher, Paul A1 - von Elert, Eric T1 - Food quality effects of unsaturated fatty acids on larvae of the zebra mussel Dreissena polymorpha N2 - In standardized growth experiments, newly hatched larvae of the zebra mussel Dreissena polymorpha were fed diets representing different biochemical compositions. Algae that were rich in (n-3) polyunsaturated fatty acids (PUFAs), except for long-chained (.C18) PUFAs (Chlorella minutissima and Monoraphidium minutum) were of low food quality. Higher growth than on C. minutissima or M. minutum was supported by a culture of the cyanobacterium Aphanothece sp., which contained traces of a long-chained (n-3) PUFA, docosahexaenoic acid (DHA, 22 : 6n-3). The alga Isochrysis aff. galbana, which contained high amounts of the longchained (n-3) PUFAs DHA and eicosapentaenoic acid (EPA, 20 : 5n- 3), supported the highest growth. The alga Nannochloropsis limnetica, which differed from I. galbana by a defi- ciency in DHA, allowed slightly, but significantly lower, growth. Growth of larvae on N. limnetica was increased by enrichment of N. limnetica cells with a lipid extract of I. galbana, showing that larval growth on N. limnetica was limited by the deficiency of a compound that was present in I. galbana. Growth was also enhanced by feeding N. limnetica cells supplemented with DHA, but not by cells enriched with EPA, indicating that DHA was the limiting factor. We conclude that, on DHA-deficient food, the larvae of D. polymorpha were not able to sufficiently convert C18-PUFAs into long- chained (n-3) PUFAs and that the rates for elongation and desaturation of EPA into DHA limited growth. Y1 - 2002 UR - http://aslo.org/lo/toc/vol_47/issue_4/1242.pdf ER - TY - JOUR A1 - Wacker, Alexander A1 - von Elert, Eric T1 - Strong influences of larval diet history on subsequent post-settlement growth in the freshwater mollusc Dreissena polymorpha N2 - A significant seasonal variation in size at settlement has been observed in newly settled larvae of Dreissena polymorpha in Lake Constance. Diet quality, which varies temporally and spatially in freshwater habitats, has been suggested as a significant factor influencing the life history and development of freshwater invertebrates. Accordingly, experiments were conducted with field-collected larvae to test the proposal that diet quality can determine planktonic larval growth rates, size at settlement and subsequent post-metamorphic growth rates. Larvae were fed one of two diets or starved. One diet was composed of cyanobacterial cells, which are de; cient in polyunsaturated fatty acids (PUFAs) and the other was a mixed diet rich in PUFAs. Freshly metamorphosed animals from the starvation treatment had a carbon content per individual 70% lower than that of larvae fed the mixed diet. This apparent exhaustion of larval internal reserves resulted in a 50% reduction of the post-metamorphic growth rates. Growth was also reduced in animals previously fed the cyanobacterial diet. Hence, low food quantity or low food quality during the larval stage of D. polymorpha, lead to irreversible effects for post-metamorphic animals and are related to inferior competitive abilities. Y1 - 2002 UR - http://www.journals.royalsoc.ac.uk/openurl.asp?genre=article&eissn=1471- 2954&volume=269&issue=1505&spage=2113 ER - TY - JOUR A1 - Wacker, Alexander A1 - von Elert, Eric T1 - Food quality controls reproduction of the zebra mussel (Dreissena polymorpha) N2 - Species such as Dreissena polymorpha sometimes contribute substantially in the transfer of primary to secondary production. During the ontogenetic cycle, the reproductive investment of adult mussels is one of the main parameters that affect recruitment success. We studied how food quality and temperature affect the reproductive investment in term of egg mass of D. polymorpha in a lake by sampling mussels monthly from 4 m and 15 m depths. Temperature affected reproduction directly and also indirectly through the food. To assess whether temperature and/or food conditions led to the differences observed in mussels sampled from the two depths, mussels were reared in the laboratory under two different temperature regimes for 3 months, simulating the temperature of the lake at 4 m and 15 m depth. Possible effects of food quality were tested at each temperature using four diets differing in fatty acid composition. Temperature played an important role as a trigger for spawning, and the type of diet clearly affected the reproductive investment. When the heterokont chromophyte alga Nannochloropsis limnetica, which is rich in polyunsaturated fatty acids (PUFAs) and long-chained PUFAs (>C18), was fed to mussels, an increased egg mass was obtained. This result was in contrast to that found when the green alga Scenedesmus obliquus and the cyanobacterium Aphanothece sp., both of which are deficient in long-chained PUFAs, were offered as food to the mussels. Such a PUFA-dependent food quality may affect reproduction in lakes. Food quality effects vary seasonally in a lake and may be most important in summer, when low-food- quality green algae and cyanobacteria are abundant. The low biochemical quality of these blooms may affect at least the later period of gametogenesis of D. polymorpha, which reproduces from June to August. Y1 - 2003 UR - http://www.link.springer.de/link/service/journals/00442/contents/03/01208/paper/s00442-003-1208- 5ch000.html ER - TY - JOUR A1 - Wacker, Alexander A1 - von Elert, Eric T1 - Settlement pattern of the zebra mussel, Dreissena polymorpha, as a function of depth in Lake Constance N2 - Settlement on suitable substrata under favourable environmental conditions is an important factor for a successful recruitment of adult populations of Dreissena polymorpha. Therefore, the pattern of settlement of zebra mussel (Dreissena polymorpha) larvae at different depths was studied in Lake Constance. Maximum densities of larvae and newly settled juvenile mussels were observed at 4m depth, while only single settlement episodes were recorded at greater depths (15 m and 30 m). Temperature fluctuation was used as a surrogate parameter for internal seiches. Biotic and abiotic parameters were subjected to a principal component analysis (PCA). The tight coupling of the internal seiches, larval abundance and settlement at 4-m depth vs. the lack of coupling of the latter two variables at greater depths indicated that water currents transported settling larvae to the substrata at greater depth. Our data suggest that physical factors, such as boundary mixing and internal seiches, should be considered as sources of variability in settlement. Y1 - 2003 ER - TY - JOUR A1 - Wacker, Alexander A1 - von Elert, Eric T1 - Food quality controls egg quality of the zebra mussel Dreissena polymorpha : The role of fatty acids N2 - We investigated the investment of adult Dreissena polymorpha to the eggs by sampling mussels monthly from 4- and 15-m water depth. The fatty acid composition of eggs differed significantly between depths and over time. To assess whether temperature and food conditions led to the differences observed for mussels sampled from the two depths, mussels were reared in the laboratory under two different 3-month temperature regimes, simulating the temperature of the lake at 4- and 15-m depth. Possible effects of food quality were tested in each simulation using four diets differing in fatty acid composition: Cryptomonas erosa, Nannochloropsis limnetica [rich in polyunsaturated fatty acids (PUFAs) and long- chained PUFAs (.C18)], Scenedesmus obliquus, and the cyanobacterium Aphanothece sp. (deficient in long-chained PUFAs). In newly released eggs, specific (n-3) and (n-6) long-chained PUFAs increased when these fatty acids were available in the natural seston or in the laboratory diets. Mussels fed organisms deficient in long-chained PUFAs were still able to allocate arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid into eggs, which suggests that minimum levels of particular fatty acids were maintained in eggs by transfer from internal reserves of the female mussels to oocytes. In contrast to the diet, there were no effects of the temperature on the fatty acid composition of eggs. Y1 - 2004 UR - http://aslo.org/lo/toc/vol_49/issue_5/1794.pdf ER - TY - JOUR A1 - Wacker, Alexander A1 - Baur, Bruno T1 - Effects of protein and calcium concentrations of artificial diets on the growth and survival of the land snail Arianta arbustorum N2 - Animals depend on a large set of essential compounds in their food. However, not all units of food are equal from a nutritional point of view. A reduced supply of protein and calcium might be critical for the growth, reproduction and survival of herbivorous gastropods. We experimentally examined the effects of different protein and calcium supplies on the growth and survival of the land snail Arianta arbustorum. Groups of snails were reared on agar-based diets with each of three levels of protein and calcium (nine treatments). Snails fed a high-protein diet grew faster and reached adulthood earlier and at a larger adult size than snails fed intermediate and low-protein diets. Surprisingly, the calcium concentration did not affect shell growth and adult size. Snails reared on intermediate- and low-calcium diets increased their consumption rates, but, despite this compensatory feeding, these snails were unable to take up the amount of calcium required for metabolism and shell growth and had a higher mortality. The calcium deficiency could partly be mitigated by the snails' internal calcium storage and reallocation capacity. A depletion of internal calcium reserves adversely affects the entire nutrient metabolism and was the probable cause for the high mortality rates associated with the intermediate- and low calcium diets observed in the present study Y1 - 2004 SN - 0168-8170 ER - TY - JOUR A1 - Wacker, Alexander T1 - Lipids in the food of a terrestrial snail N2 - Animals depend on a large set of essential compounds in their food. A reduced supply of specific lipid compounds has been shown to be critical for growth, reproduction and survival of aquatic molluscs and might also be critical for terrestrial gastropods. The effects were investigated of different fatty acid and cholesterol supplies on the growth, reproduction, and survival of the land snail Arianta arbustorum. Surprisingly, differences in diet did not affect shell growth, time to reach adulthood, and reproductive traits such as the number of eggs, dry mass and volume of spermatophores. However, snails reared on low cholesterol diets and low polyunsaturated fatty acid (PUFA) diets decreased their consumption rates and had a higher mortality. Snails fed a PUFA-rich diet showed higher mating activity than snails fed a diet deficient in PUFAs. A depletion of internal PUFA reserves may affect the regulation of mating behaviour because PUFAs play an important role as precursors for signal-transduction involved in the regulation of mating and reproduction. In contrast, when the diets were deficient in cholesterol, mating activity was not affected Y1 - 2005 ER - TY - JOUR A1 - Martin-Creuzburg, Dominik A1 - Wacker, Alexander A1 - von Elert, Eric T1 - Life history consequences of sterol availability in the aquatic keystone species Daphnia N2 - The absence of essential biochemical nutrients, such as polyunsaturated fatty acids or sterols, has been considered as a mechanism determining trophic interactions between the herbivore Daphnia and its phytoplankton food source. Here, we experimentally quantify the sensitivity of two Daphnia species to decreasing amounts of dietary sterols by measuring variations in life history traits. The two species Daphnia magna and D. galeata were fed different mixtures of the sterol-containing green alga Scenedesmus obliquus and the sterol-free cyanobacterium Synechococcus elongatus; a higher proportion of Synechococcus in the food is equivalent to a decrease in dietary sterols. To address the significance of sterol limitation, the Daphnia species were also fed Synechococcus supplemented with cholesterol. In both species, somatic and population growth rates, maternal dry mass, the number of viable offspring, and the probability of survival were significantly reduced with the lower availability of sterols. A high correlation between the sterol content of the mixed diet and the somatic and population growth rates was found, and growth on cholesterol- supplemented Synechococcus fitted well into this correlation. Somatic growth of first-clutch neonates grown on 100% Synechococcus exhibited a pattern similar to that of somatic growth of their mothers grown on the different food regimes, which demonstrated the significance of maternal effects for sterol-limited population growth. Daphnia galeata had a twofold higher incipient limiting sterol level than D. magna, which indicated interspecific differences in sterol requirements between the two Daphnia species. The results suggest a strong impact of dietary sterols on life history traits and therefore, population dynamics of the keystone species Daphnia Y1 - 2005 SN - 0029-8549 ER - TY - JOUR A1 - Weithoff, Guntram A1 - Wacker, Alexander T1 - The mode of nutrition of mixotrophic flagellates determines the food quality for their consumers Y1 - 2007 UR - http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2435.2007.01333.x/full U6 - https://doi.org/10.1111/j.1365-2435.2007.01333.x ER - TY - JOUR A1 - Wacker, Alexander T1 - Allocation of essential lipids in Daphnia magna during exposure to poor food quality Y1 - 2007 UR - http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2435.2007.01274.x/full U6 - https://doi.org/10.1111/j.1365-2435.2007.01274.x ER - TY - JOUR A1 - Wacker, Alexander A1 - Weithoff, Guntram T1 - Carbon assimilation mode in mixotrophs and the fatty acid composition of their rotifer consumers N2 - P>1. We examined an important ecophysiological link between the mixotrophic flagellate Chlamydomonas acidophila and its consumers, the rotifers Elosa worallii, Cephalodella sp. and Brachionus sericus, by comparing their fatty acid profiles. 2. The mixotrophic flagellate was grown under either exclusively autotrophic conditions in the light, under exclusively heterotrophic conditions in the dark with an organic carbon source (glucose), or in the light plus the organic carbon sources (=mixotrophic). 3. Under heterotrophic growth conditions, C. acidophila strongly reduced its content of the n-3 polyunsaturated fatty acid (PUFA) alpha-linolenic acid (ALA, C18:3n-3) compared with auto- and mixotrophic growth conditions. Although PUFAs with more than 18 carbon atoms were not detected in C. acidophila, significant amounts of eicosatetraenoic (ETA, 20:4n-3) and eicosapentaenoic acid (EPA, 20:5n-3) were found in three rotifer consumers. 4. Species-specific differences in the fatty acid profiles with respect to ETA, EPA and the precursor ALA were found in the rotifers: Brachionus and Cephalodella fed on the heterotrophic diets synthesised less EPA. In Elosa, smaller amounts of ALA were detected but were converted efficiently to a constant content of EPA and to an exceptionally high content of ETA. 5. Since in nature the mode of carbon assimilation among mixotrophic organisms differs, and their fatty acid composition varies depending on their mode of carbon assimilation, the availability of ALA might be critical for their consumers. An insufficient dietary supply of this precursor for the synthesis of ETA and EPA can prevent consumers from regulating their content of ETA and EPA. Therefore, observed differences in values of the latter might underly species-specific differences in the competitive capability of consumers. Y1 - 2009 UR - http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=0046-5070 U6 - https://doi.org/10.1111/j.1365-2427.2009.02251.x SN - 0046-5070 ER - TY - JOUR A1 - Sperfeld, Erik A1 - Wacker, Alexander T1 - Effects of temperature and dietary sterol availability on growth and cholesterol allocation of the aquatic keystone species Daphnia N2 - Enhanced water temperatures promote the occurrence of cyanobacterial blooms, which may be detrimental to aquatic herbivores. Especially, the often-dominant crustaceans could be negatively affected because cyanobacteria are deficient in phytosterols, which are required by the crustaceans to form the membrane component cholesterol, which in turn plays a role in thermal adaptation. Here, we determined the influence of temperature on growth, reproduction and the allocation of dietary sterol into somatic tissues and eggs of the keystone species Daphnia magna raised along a dietary cholesterol gradient. Mass-specific growth rates of D. magna increased with the increasing availability of dietary cholesterol up to an incipient limiting level, which increased with increasing temperature. This indicates a higher demand for cholesterol for growth at higher temperatures and may explain the consistently smaller clutch sizes of reproducing females at the highest temperature. The cholesterol content of the individuals increased with increasing dietary cholesterol; this increase was enhanced at higher temperatures, indicating a higher demand for cholesterol for tissues and probably specifically for membranes. Surprisingly, the daphnids showed different allocation strategies with regard to temperature and dietary sterol availability. The cholesterol content of eggs was enhanced at higher temperature, which suggested that females allocate more cholesterol to their offspring, presumably to ensure sufficient egg development. When dietary cholesterol was limiting, however, females did not allocate more cholesterol to their eggs. Our data suggest that during cyanobacterial blooms, a potential dietary sterol limitation of Daphnia can be intensified at higher water temperatures, which can occur with global warming. Y1 - 2009 UR - http://jeb.biologists.org/ U6 - https://doi.org/10.1242/Jeb.031401 SN - 0022-0949 ER - TY - JOUR A1 - Martin-Creuzburg, Dominik A1 - Sperfeld, Erik A1 - Wacker, Alexander T1 - Colimitation of a freshwater herbivore by sterols and polyunsaturated fatty acids N2 - Empirical data providing evidence for a colimitation of an herbivore by two or more essential nutrients are scarce, particularly in regard to biochemical resources. Here, a graphical model is presented, which describes the growth of an herbivore in a system with two potentially limiting resources. To verify this model, life-history experiments were conducted with the herbivore Daphnia magna feeding on the picocyanobacterium Synechococcus elongatus, which was supplemented with increasing amounts of cholesterol either in the presence or the absence of saturating amounts of eicosapentaenoic acid (EPA). For comparison, D. magna was raised on diets containing different proportions of S. elongatus and the cholesterol- and EPA-rich eukaryotic alga Nannochloropsis limnetica. Somatic and population growth of D. magna on a sterol- and EPA-deficient diet was initially constrained by the absence of sterols. With increased sterol availability, a colimitation by EPA became apparent and when the sterol requirements were met, the growth- limiting factor was shifted from a limitation by sterols to a limitation by EPA. These data imply that herbivores are frequently limited by two or more essential nutrients simultaneously. Hence, the concept of colimitation has to be incorporated into models assessing nutrient-limited growth kinetics of herbivores to accurately predict demographic changes and population dynamics. Y1 - 2009 UR - http://rspb.royalsocietypublishing.org/content/by/year U6 - https://doi.org/10.1098/rspb.2008.1540 SN - 0962-8452 ER - TY - JOUR A1 - Hartwich, Melanie A1 - Wacker, Alexander A1 - Weithoff, Guntram T1 - Changes in the competitive abilities of two rotifers feeding on mixotrophic flagellates N2 - The competitive abilities of two rotifer species (Elosa worallii, Cephalodella sp.) were influenced by the mode of carbon acquisition of the osmo-mixotrophic flagellate Chlamydomonas acidophila due to changes in cell biochemistry. Y1 - 2010 UR - http://plankt.oxfordjournals.org/ U6 - https://doi.org/10.1093/plankt/fbq081 SN - 0142-7873 ER - TY - JOUR A1 - Lukas, Marcus A1 - Sperfeld, Erik A1 - Wacker, Alexander T1 - Growth Rate Hypothesis does not apply across colimiting conditions cholesterol limitation affects phosphorus homoeostasis of an aquatic herbivore JF - Functional ecology : an official journal of the British Ecological Society N2 - 1. Herbivores show stronger control of element homoeostasis than primary producers, which can lead to constraints in carbon and nutrient transfer efficiencies from plants to animals. Insufficient dietary phosphorus (P) availability can cause reduced body P contents along with lower growth rates of animals, leading to a positive relationship between growth and body P. 2. We examined how a second limiting food component in combination with dietary P limitation influences growth and P homoeostasis of a herbivore and how this colimitation influences the hypothesized positive correlation between body P content and growth rates. Therefore, we investigated the responses in somatic growth and P stoichiometry of Daphnia magna raised on a range of diets with different amounts of P and the sterol cholesterol. 3. Somatic growth rates of D. magna increased asymptotically with increasing P as well as with increasing cholesterol availability. The body P content increased with increasing dietary P and stabilized at high dietary P availability. The observed plasticity in D. magna's P stoichiometry became stronger with increasing cholesterol availability, i.e. with decreasing colimitation by cholesterol. 4. At P-limiting conditions, the positive correlation between body P content and growth rate, as predicted by the growth rate hypothesis (GRH) applied to the within-species level, declined with increasing cholesterol limitation and disappeared entirely when cholesterol was not supplied. Thus, even when Daphnia shows no growth response owing to strong limitation by the colimiting nutrient, the body P content may vary substantially, calling into question the unconditional use of herbivores' P content as predictor of a potential P limitation in nature. 5. The observed interaction between dietary P and cholesterol on Daphnia's growth and stoichiometry can be used as a conceptual framework of how colimiting essential nutrients affect herbivore homoeostasis, and provide further insights into the applicability of the GRH within a consumer species. KW - colimitation KW - Daphnia KW - ecological stoichiometry KW - essential resources KW - food quality KW - imbalanced diet KW - nutrient limitation KW - nutritional ecology KW - zooplankton Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-2435.2011.01876.x SN - 0269-8463 VL - 25 IS - 6 SP - 1206 EP - 1214 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Spijkerman, Elly A1 - Wacker, Alexander T1 - Interactions between P-limitation and different C conditions on the fatty acid composition of an extremophile microalga JF - Extremophiles : life under extreme conditions N2 - The extremophilic microalga Chlamydomonas acidophila inhabits very acidic waters (pH 2-3.5), where its growth is often limited by phosphorus (P) or colimited by P and inorganic carbon (CO(2)). Because this alga is a major food source for predators in acidic habitats, we studied its fatty acid content, which reflects their quality as food, grown under a combination of P-limited and different carbon conditions (either mixotrophically with light + glucose or at high or low CO(2), both without glucose). The fatty acid composition largely depended on the cellular P content: stringent P-limited cells had a higher total fatty acid concentration and had a lower percentage of polyunsaturated fatty acids. An additional limitation for CO(2) inhibited this decrease, especially reflected in enhanced concentrations of 18:3(9,12,15) and 16:4(3,7,10,13), resulting in cells relatively rich in polyunsaturated fatty acids under colimiting growth conditions. The percentage of polyunsaturated to total fatty acid content was positively related with maximum photosynthesis under all conditions applied. The two factors, P and CO(2), thus interact in their effect on the fatty acid composition in C. acidophila, and colimited cells P-limited algae can be considered a superior food source for herbivores because of the high total fatty acid content and relative richness in polyunsaturated fatty acids. KW - Acidophilic algae KW - Cellular P quota KW - Chlamydomonas acidophila KW - Chlorophyceae KW - Colimitation KW - CO(2) KW - Fatty acid composition KW - Food quality KW - Glucose KW - Mixotrophy KW - Photosynthesis KW - Phytoplankton KW - Phosphorus limitation Y1 - 2011 U6 - https://doi.org/10.1007/s00792-011-0390-3 SN - 1431-0651 VL - 15 IS - 5 SP - 597 EP - 609 PB - Springer CY - Tokyo ER - TY - JOUR A1 - Sperfeld, Erik A1 - Wacker, Alexander T1 - Temperature- and cholesterol-induced changes in eicosapentaenoic acid limitation of Daphnia magna determined by a promising method to estimate growth saturation thresholds JF - Limnology and oceanography N2 - We present data on eicosapentaenoic acid (EPA)-limited growth responses of Daphnia magna under different temperatures and different dietary cholesterol availabilities to assess how EPA growth saturation thresholds depend on changing environmental conditions. D. magna was raised on gradients of dietary EPA at 15 degrees C and 20 degrees C with high cholesterol supply and at 20 degrees C with low and high cholesterol supply in laboratory experiments. A new method was applied to estimate EPA growth saturation thresholds on the basis of fitted saturation curves using bootstrapped data. The EPA threshold at which 75% and 90% of maximum growth was reached ranged from 0.7 to 1.6 mu g EPA (mg dietary C)(-1) and 2.0 to 4.9 mu g EPA (mg dietary C)(-1), respectively. Previously reported EPA concentrations in natural seston of many different lakes suggest that the thresholds measured here indicate a frequent potential for at least moderate EPA limitation in nature. Furthermore, the calculated EPA thresholds were higher in treatments of low compared with high temperature and higher in treatments of low compared with high cholesterol availability. The EPA-dependent growth responses were more strongly affected by temperature than by cholesterol availability. Our results suggest that EPA growth saturation thresholds for a particular Daphnia species probably vary in nature under different environmental conditions. Y1 - 2011 U6 - https://doi.org/10.4319/lo.2011.56.4.1273 SN - 0024-3590 VL - 56 IS - 4 SP - 1273 EP - 1284 PB - Wiley CY - Waco ER - TY - JOUR A1 - Hartwich, Melanie A1 - Straile, Dietmar A1 - Gaedke, Ursula A1 - Wacker, Alexander T1 - Use of ciliate and phytoplankton taxonomic composition for the estimation of eicosapentaenoic acid concentration in lakes JF - Freshwater biology N2 - 1. The polyunsaturated fatty acid eicosapentaenoic acid (EPA) plays an important role in aquatic food webs, in particular at the primary producerconsumer interface where keystone species such as daphnids may be constrained by its dietary availability. Such constraints and their seasonal and interannual changes may be detected by continuous measurements of EPA concentrations. However, such EPA measurements became common only during the last two decades, whereas long-term data sets on plankton biomass are available for many well-studied lakes. Here, we test whether it is possible to estimate EPA concentrations from abiotic variables (light and temperature) and the biomass of prey organisms (e.g. ciliates, diatoms and cryptophytes) that potentially provide EPA for consumers. 2. We used multiple linear regression to relate size- and taxonomically resolved plankton biomass data and measurements of temperature and light intensity to directly measured EPA concentrations in Lake Constance during a whole year. First, we tested the predictability of EPA concentrations from the biomass of EPA-rich organisms (diatoms, cryptophytes and ciliates). Secondly, we included the variables mean temperature and mean light intensity over the sampling depth (020 m) and depth (08 and 820 m) as factors in our model to check for large-scale seasonal- and depth-dependent effects on EPA concentrations. In a third step, we included the deviations of light and temperature from mean values in our model to allow for their potential influence on the biochemical composition of plankton organisms. We used the Akaike Information Criterion to determine the best models. 3. All approaches supported our proposition that the biomasses of specific plankton groups are variables from which seston EPA concentrations can be derived. The importance of ciliates as an EPA source in the seston was emphasised by their high weight in our models, although ciliates are neglected in most studies that link fatty acids to seston taxonomic composition. The large-scale seasonal variability of light intensity and its interaction with diatom biomass were significant predictors of EPA concentrations. The deviation of temperature from mean values, accounting for a depth-dependent effect on EPA concentrations, and its interaction with ciliate biomass were also variables with high predictive power. 4. The best models from the first and second approaches were validated with measurements of EPA concentrations from another year (1997). The estimation with the best model including only biomass explained 80%, and the best model from the second approach including mean temperature and depth explained 87% of the variability in EPA concentrations in 1997. 5. We show that it is possible to predict EPA concentrations reliably from plankton biomass, while the inclusion of abiotic factors led to results that were only partly consistent with expectations from laboratory studies. Our approach of including biotic predictors should be transferable to other systems and allow checking for biochemical constraints on primary consumers. KW - ciliates KW - diatoms KW - eicosapentaenoic acid KW - light KW - temperature Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-2427.2012.02799.x SN - 0046-5070 VL - 57 IS - 7 SP - 1385 EP - 1398 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Sperfeld, Erik A1 - Wacker, Alexander T1 - Temperature affects the limitation of Daphnia magna by eicosapentaenoic acid, and the fatty acid composition of body tissue and eggs JF - Freshwater biology N2 - 1. Poikilothermic animals incorporate more polyunsaturated fatty acids (PUFAs) into their cellular membranes as temperature declines, suggesting an increased sensitivity to PUFA limitation in cool conditions. To test this we raised Daphnia magna at different temperatures and investigated the effect of varying dietary PUFA on life history parameters (i.e. growth, reproduction) and the PUFA composition of body tissue and eggs. 2. Upon a PUFA-rich diet (Cryptomonas sp.) females showed higher concentrations of several omega 3 PUFAs in their body tissue at 15 degrees C than at 20 degrees C and 25 degrees C, indicating a greater structural requirement for omega 3 PUFAs at low temperature. Their eggs had an equal but higher concentration of omega 3 PUFAs than their body tissue. 3. In a life history experiment at 15 and 20 degrees C we supplemented a diet of a PUFA-free cyanobacterium with the omega 3 PUFA eicosapentaenoic acid (EPA). The growth of D. magna was more strongly EPA limited at low temperature. A greater requirement for structural EPA at 15 degrees C was indicated by a steeper increase in somatic EPA content with dietary EPA compared to 20 degrees C. 4. At 20 degrees C the development of eggs to successful hatching was high when EPA was supplied to the mothers. At 15 degrees C the hatching success was generally poor, despite of a higher maternal provision of EPA to eggs, compared to that at 20 degrees C, suggesting that EPA alone was insufficient for proper neonatal development at the low temperature. The growth of offspring from mothers raised at 20 degrees C without EPA supplementation was very low, indicating that the negative effects of EPA deficiency can be carried on to the next generation. 5. The fatty acid composition of Daphnia sp. in published field studies shows increasing proportions of saturated fatty acids with increasing environmental temperature, whereas omega 3 PUFAs and EPA show no clear pattern, suggesting that variations in dietary PUFA may mask temperature-dependent adjustments in omega 3 PUFA concentrations of cladocerans in nature. KW - food quality KW - maternal effects KW - polyunsaturated fatty acids KW - resource allocation KW - zooplankton Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-2427.2011.02719.x SN - 0046-5070 VL - 57 IS - 3 SP - 497 EP - 508 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Piepho, Maike A1 - Arts, Michael T. A1 - Wacker, Alexander T1 - Species-specific variation in fatty acid concentrations of four phytoplankton species does phosphorus supply influence the effect of light intensity of temperature? JF - Journal of phycology N2 - We tested, in the laboratory, the influence of light intensity, temperature, and phosphorus (P) supply on fatty acid (FA) concentrations of four freshwater algae: the green algae Scenedesmus quadricauda (Turpin) Breb. and Chlamydomonas globosa J. Snow, the cryptophyte Cryptomonas ovata Ehrenb., and the diatom Cyclotella meneghiniana Kutz. We investigated the main and interactive effects of two variables on algal FA concentrations (i.e., light intensity and P supply or temperature and P supply). Interactive effects of light intensity and P supply were most pronounced in C. meneghiniana, but were also found in S. quadricauda and C. ovata. Changes in several saturated and unsaturated FA concentrations with light were more distinct in the low-P treatments than in the high-P treatments. Interactive effects of temperature and P supply on various FA concentrations were observed in all four species, but there was no consistent pattern. In lake ecosystems, P limitation often coincides with high light intensities and temperatures in summer. Therefore, it is important to examine how combinations of these environmental conditions affect FA concentrations of primary producers that are important sources of FAs for higher trophic levels. KW - Chlamydomonas KW - Cryptomonas KW - Cyclotella KW - fatty acids KW - light KW - lipids KW - phosphate KW - PUFA KW - Scenedesmus KW - temperature Y1 - 2012 U6 - https://doi.org/10.1111/j.1529-8817.2011.01103.x SN - 0022-3646 VL - 48 IS - 1 SP - 64 EP - 73 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Spijkerman, Elly A1 - Wacker, Alexander A1 - Weithoff, Guntram A1 - Leya, Thomas T1 - Elemental and fatty acid composition of snow algae in Arctic habitats JF - Frontiers in microbiology N2 - Red, orange or green snow is the macroscopic phenomenon comprising different eukaryotic algae. Little is known about the ecology and nutrient regimes in these algal communities. Therefore, eight snow algal communities from five intensively tinted snow fields in western Spitsbergen were analysed for nutrient concentrations and fatty acid (FA) composition. To evaluate the importance of a shift from green to red forms on the FA-variability of the field samples, four snow algal strains were grown under nitrogen replete and moderate light (+N+ML) or N-limited and high light (-N+HL) conditions. All eight field algal communities were dominated by red and orange cysts. Dissolved nutrient concentration of the snow revealed a broad range of NH4+ (<0.005-1.2 mg NI-1) and only low PO43- (< 18 mu g P I-1) levels. The external nutrient concentration did not reflect cellular nutrient ratios as C:N and C:P ratios of the communities were highest at locations containing relatively high concentrations of NH4- and PO43-. Molar N:P ratios ranged from 11 to 21 and did not suggest clear limitation of a single nutrient. On a per carbon basis, we found a 6-fold difference in total FA content between the eight snow algal communities, ranging from 50 to 300 mg FA g C-1. In multivariate analyses total FA content opposed the cellular N:C quota and a large part of the FA variability among field locations originated from the abundant FAs C181n-9, C18 2n-6, and C183n-3. Both field samples and snow algal strains grown under -N+HL conditions had high concentrations of C181n-9. FAs possibly accumulated due to the cessation of growth. Differences in color and nutritional composition between patches of snow algal communities within one snow field were not directly related to nutrient conditions. We propose that the highly patchy distribution of snow algae within and between snow fields may also result from differences in topographical and geological parameters such as slope, melting water rivulets, and rock formation. KW - Arctic snow algal bloom KW - cellular C:N:P ratio KW - ecology KW - extremophiles KW - lipids KW - nutrients KW - psychrophilic. KW - Spitsbergen Y1 - 2012 U6 - https://doi.org/10.3389/fmicb.2012.00380 SN - 1664-302X VL - 3 PB - Frontiers Research Foundation CY - Lausanne ER - TY - JOUR A1 - Hartwich, Melanie A1 - Martin-Creuzburg, Dominik A1 - Rothhaupt, Karl-Otto A1 - Wacker, Alexander T1 - Oligotrophication of a large, deep lake alters food quantity and quality constraints at the primary producer-consumer interface JF - Oikos N2 - To assess nutritional consequences associated with lake oligotrophication for aquatic consumers, we analyzed the elemental and biochemical composition of natural seston and concomitantly conducted laboratory growth experiments in which the freshwater key herbivore Daphnia was raised on natural seston of the nowadays (2008) oligotrophic Lake Constance throughout an annual cycle. Food quality mediated constraints on Daphnia performance were assessed by comparing somatic growth rates with seston characteristics (multiple regression analysis) and by manipulating the elemental and biochemical composition of natural seston experimentally (nutrient supplementation). Results were compared to similar experiments carried out previously (1997) during a mesotrophic phase of the lake. In the oligotrophic phase, particulate carbon and phosphorus concentrations were lower, fatty acid concentrations were higher, and the taxonomic composition of phytoplankton was less diverse, with a more diatom- and cryptophytes-dominated community, compared to the previous mesotrophic phase. Multiple regression analysis indicated a shift from a simultaneous limitation by food quantity (in terms of carbon) and quality (i.e. a-linolenic acid) during the mesotrophic phase to a complex multiple nutrient limitation mediated by food quantity, phosphorus, and omega-3 fatty acids in the following oligotrophic phase. The concomitant supplementation experiments also revealed seasonal changes in multiple resource limitations, i.e. the prevalent limitation by food quantity was accompanied by a simultaneous limitation by either phosphorus or omega-3 fatty acids, and thus confirmed and complemented the multiple regression approach. Our results indicate that seasonal and annual changes in nutrient availabilities can create complex co-limitation scenarios consumers have to cope with, which consequently may also affect the efficiency of energy transfer in food webs. Y1 - 2012 U6 - https://doi.org/10.1111/j.1600-0706.2011.20461.x SN - 0030-1299 VL - 121 IS - 10 SP - 1702 EP - 1712 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Wacker, Alexander A1 - Martin-Creuzburg, Dominik T1 - Biochemical nutrient requirements of the rotifer Brachionus calyciflorus co-limitation by sterols and amino acids JF - Functional ecology : an official journal of the British Ecological Society N2 - It has been proposed that growth and reproduction of animals is frequently limited by multiple nutrients simultaneously. To improve our understanding of the consequences of multiple nutrient limitations (i.e. co-limitation) for the performance of animals, we conducted standardized population growth experiments using an important aquatic consumer, the rotifer Brachionus calyciflorus. We compared nutrient profiles (sterols, fatty acids and amino acids) of rotifers and their diets to reveal consumerdiet imbalances and thus potentially limiting nutrients. In concomitant growth experiments, we directly supplemented potentially limiting substances (sterols, fatty acids, amino acids) to a nutrient-deficient diet, the cyanobacterium Synechococcus elongatus, and recorded population growth rates. The results from the supplementation experiments corroborated the nutrient limitations predicted by assessing consumerdiet imbalances, but provided more detailed information on co-limiting nutrients. While the fatty acid deficiency of the cyanobacterium appeared to be of minor importance, the addition of both cholesterol and certain amino acids (leucine and isoleucine) improved population growth rates of rotifers, indicating a simultaneous limitation by sterols and amino acids. Our results add to growing evidence that consumers frequently face multiple nutrient limitations and suggest that the concept of co-limitation has to be considered in studies assessing nutrient-limited growth responses of consumers. KW - consumer KW - consumer-diet imbalance KW - dietary mismatch KW - fatty acid KW - global change KW - lipid KW - nutrition KW - phytoplankton KW - tetrahymanol KW - zooplankton Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-2435.2012.02047.x SN - 0269-8463 VL - 26 IS - 5 SP - 1135 EP - 1143 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Martin-Creuzburg, Dominik A1 - Wacker, Alexander A1 - Ziese, Christine A1 - Kainz, Martin J. T1 - Dietary lipid quality affects temperature-mediated reaction norms of a freshwater key herbivore JF - Oecologia N2 - 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. KW - Daphnia KW - Food quality KW - Phenotypic plasticity KW - Polyunsaturated fatty acids KW - Sterols Y1 - 2012 U6 - https://doi.org/10.1007/s00442-011-2155-1 SN - 0029-8549 VL - 168 IS - 4 SP - 901 EP - 912 PB - Springer CY - New York ER - TY - JOUR A1 - Piepho, Maike A1 - Martin-Creuzburg, Dominik A1 - Wacker, Alexander T1 - Phytoplankton sterol contents vary with temperature, phosphorus and silicate supply a study on three freshwater species JF - European journal of phycology N2 - The understanding of environmentally induced changes in the biochemical composition of phytoplankton species is of great importance in both physiological studies and ecological food web research. In extensive laboratory experiments we tested the influence of two different temperatures (10 degrees C and 25 degrees C) and a phosphorus supply gradient on the sterol concentrations of the three freshwater phytoplankton species Scenedesmus quadricauda, Cryptomonas ovata and Cyclotella meneghiniana. The diatom C. meneghiniana was additionally exposed to a silicate gradient. In two separate experiments we analysed (1) possible interactive effects of temperature and phosphorus supply and (2) the effect of four phosphorus levels and three silicate levels on algal sterol concentrations. We observed that sterol concentrations were higher at 25 degrees C than at 10 degrees C in S. quadricauda and C. meneghiniana, but were not affected by temperature in C. ovata. Interactive effects of temperature and phosphorus supply on sterol concentrations were found in C. meneghiniana. This presumably was due to the bioconversion of one sterol (24-methylenecholesterol) into another (22-dihydrobrassicasterol). Increasing phosphorus supply resulted in species-specific effects on sterol concentrations, viz. an optimum curve response in S. quadricauda, a saturation curve response in C. meneghiniana and no change in sterol concentration in C. ovata. Effects of silicate supply on the sterols of C. meneghiniana equalled the effects of phosphorus supply. Albeit we did not observe a general trend in the three phytoplankton species tested, we conclude that sterol concentrations of phytoplankton are strongly affected by temperature and nutrient supply. Interactive effects point out the importance of taking into account more than just one environmental factor when assessing the effects of environmentally induced changes on phytoplankton sterol concentrations. KW - algae KW - Chlorophyta KW - Cryptomonas KW - Cryptophyta KW - Cyclotella KW - diatoms KW - phosphorus KW - Scenedesmus KW - silicate KW - sterols KW - temperature Y1 - 2012 U6 - https://doi.org/10.1080/09670262.2012.665484 SN - 0967-0262 VL - 47 IS - 2 SP - 138 EP - 145 PB - Routledge, Taylor & Francis Group CY - Abingdon ER - TY - JOUR A1 - Sperfeld, Erik A1 - Martin-Creuzburg, Dominik A1 - Wacker, Alexander T1 - Multiple resource limitation theory applied to herbivorous consumers Liebig's minimum rule vs. interactive co-limitation JF - Ecology letters N2 - There is growing consensus that the growth of herbivorous consumers is frequently limited by more than one nutrient simultaneously. This understanding, however, is based primarily on theoretical considerations and the applicability of existing concepts of co-limitation has rarely been tested experimentally. Here, we assessed the suitability of two contrasting concepts of resource limitation, i.e. Liebigs minimum rule and the multiple limitation hypothesis, to describe nutrient-dependent growth responses of a freshwater herbivore (Daphnia magna) in a system with two potentially limiting nutrients (cholesterol and eicosapentaenoic acid). The results indicated that these essential nutrients interact, and do not strictly follow Liebigs minimum rule, which consistently overestimates growth at co-limiting conditions and thus is not applicable to describe multiple nutrient limitation of herbivorous consumers. We infer that the outcome of resource-based modelling approaches assessing herbivore population dynamics strongly depends on the applied concept of co-limitation. KW - Cholesterol KW - Daphnia magna KW - eicosapentaenoic acid KW - essential resources KW - food quality KW - herbivore KW - multi-nutrient limitation KW - nutritional ecology KW - von Liebig Y1 - 2012 U6 - https://doi.org/10.1111/j.1461-0248.2011.01719.x SN - 1461-023X VL - 15 IS - 2 SP - 142 EP - 150 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Lukas, Marcus A1 - Frost, Paul C. A1 - Wacker, Alexander T1 - The neonate nutrition hypothesis - early feeding affects the body stoichiometry of Daphnia offspring JF - Freshwater biology N2 - Aquatic herbivores consume variable quantities and qualities of food. In freshwater systems, where phosphorus (P) is often a primary limiting element, inadequate dietary P can slow maternal growth and reduce body P content. There remains uncertainty about whether and how dietary effects on mothers are transferred to offspring by way of egg provisioning. Using the keystone herbivore Daphnia, we tested a novel explanation (the neonate nutrition hypothesis') to determine whether the early nutrition of newborns affects their elemental composition and whether the indications of differences in maternal P nutrition found previously might be overestimated. We thus examined the P content of mothers and their eggs from deposition through development to the birth of neonates. We examined further whether very short periods of ingestion (3h) by the offspring alter the overall P content of juvenile Daphnia. We showed that strong dietary P effects on mothers were not directly transferred to their eggs. Irrespective of the supply of P in the maternal diet, the P content of eggs in different developmental stages and in (unfed) neonates did not differ. This indicates that Daphnia mothers do not reduce the quality (in terms of P) of newly produced offspring after intermittent periods (i.e. several days) of poor nutrition. In contrast, the P content of neonates reflected that of their food after brief periods of feeding, indicating that even temporary exposure to nutrient poor food immediately after birth may strongly affect the elemental composition of neonates. Our results thus support the neonate nutrition hypothesis, which, like differential maternal provisioning, is a possible explanation for the variable elemental quality of young Daphnia. KW - ecological stoichiometry KW - food quality KW - maternal effects KW - nutrient limitation KW - zooplankton Y1 - 2013 U6 - https://doi.org/10.1111/fwb.12213 SN - 0046-5070 VL - 58 IS - 11 SP - 2333 EP - 2344 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Wagner, Nicole D. A1 - Hillebrand, Helmut A1 - Wacker, Alexander A1 - Frost, Paul C. T1 - Nutritional indicators and their uses in ecology JF - Ecology letters N2 - The nutrition of animal consumers is an important regulator of ecological processes due to its effects on their physiology, life-history and behaviour. Understanding the ecological effects of poor nutrition depends on correctly diagnosing the nature and strength of nutritional limitation. Despite the need to assess nutritional limitation, current approaches to delineating nutritional constraints can be non-specific and imprecise. Here, we consider the need and potential to develop new complementary approaches to the study of nutritional constraints on animal consumers by studying and using a suite of established and emerging biochemical and molecular responses. These nutritional indicators include gene expression, transcript regulators, protein profiling and activity, and gross biochemical and elemental composition. The potential applications of nutritional indicators to ecological studies are highlighted to demonstrate the value that this approach would have to future studies in community and ecosystem ecology. KW - Ecological stoichiometry KW - lipid profiling KW - metabolism KW - nutrient-stress KW - nutrition KW - proteomics KW - transcriptomics Y1 - 2013 U6 - https://doi.org/10.1111/ele.12067 SN - 1461-023X VL - 16 IS - 4 SP - 535 EP - 544 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Hartwich, Melanie A1 - Martin-Creuzburg, Dominik A1 - Wacker, Alexander T1 - Seasonal changes in the accumulation of polyunsaturated fatty acids in zooplankton JF - Journal of plankton research N2 - In aquatic food webs, consumers, such as daphnids and copepods, differ regarding their accumulation of polyunsaturated fatty acids (PUFAs). We tested if the accumulation of PUFAs in a seston size fraction containing different consumers and in Daphnia as a separate consumer is subject to seasonal changes in a large deep lake due to changes in the dietary PUFA supply and specific demands of different consumers. We found that the accumulation of arachidonic acid (ARA) in Daphnia increased from early summer to late summer and autumn. However, ARA requirements of Daphnia appeared to be constant throughout the year, because the accumulation of ARA increased when the dietary ARA supply decreased. In the size fraction 140 m, we found an increased accumulation of docosahexaenoic acid (DHA) during late summer and autumn. These seasonal changes in DHA accumulation were linked to changes in the proportion of copepods in this size fraction, which may have increasingly accumulated DHA for active overwintering. We show that consumer-specific PUFA demands can result in seasonal changes in PUFA accumulation, which may influence the trophic transfer of PUFAs within the food web. KW - accumulation KW - Daphnia KW - copepods KW - ARA KW - DHA Y1 - 2013 U6 - https://doi.org/10.1093/plankt/fbs078 SN - 0142-7873 VL - 35 IS - 1 SP - 121 EP - 134 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Lukas, Marcus A1 - Wacker, Alexander T1 - Constraints by oxygen and food quality on carbon pathway regulation: a co-limitation study with an aquatic key herbivore JF - Ecology : a publication of the Ecological Society of America N2 - In food webs, herbivores are often constrained by low food quality in terms of mineral and biochemical limitations, which in aquatic ecosystems can co-occur with limited oxygen conditions. As low food quality implies that carbon (C) is available in excess, and therefore a regulation to get rid of excess C is crucial for the performance of consumers, we examined the C pathways (ingestion, feces release, excretion, and respiration) of a planktonic key herbivore (Daphnia magna). We tested whether consumer C pathways increase due to mineral (phosphorus, P) or biochemical (cholesterol and fatty acid) limitations and how these regulations vary when in addition oxygen is low. Under such conditions, at least the capability of the upregulation of respiration may be restricted. Furthermore, we discussed the potential role of the oxygen-transporting protein hemoglobin (Hb) in the regulation of C budgets. Different food quality constraints led to certain C regulation patterns to increase the removal of excess dietary C: P-limited D. magna increased excretion and respiration, while cholesterol-limited Daphnia in addition upregulated the release of feces. In contrast, the regulative effort was low and only feces release increased when D. magna was limited by a long-chain polyunsaturated fatty acid (eicosapentaenoic acid, EPA). Co-limiting oxygen did not always impact the discharge of excess C. We found the food-quality-induced upregulation of respiration was still present at low oxygen. In contrast, higher excretion of excess C was diminished at low oxygen supply. Besides the effect that the Hb concentration increased under low oxygen, our results indicate a low food-quality-induced increase in the Hb content of the animals. Overall, C budgeting is phenotypically plastic towards different (co-) limiting scenarios. These trigger specific regulation responses that could be the result of evolutionary adaptations. KW - carbon budget KW - carbon stoichiometry KW - cholesterol KW - co-limitation KW - Daphnia KW - EPA KW - hemoglobin KW - oxygen KW - phosphorus KW - polyunsaturated fatty acid KW - zooplankton Y1 - 2014 SN - 0012-9658 SN - 1939-9170 VL - 95 IS - 11 SP - 3068 EP - 3079 PB - Wiley CY - Washington ER - TY - JOUR A1 - Lukas, Marcus A1 - Wacker, Alexander T1 - Daphnia's dilemma: adjustment of carbon budgets in the face of food and cholesterol limitation JF - The journal of experimental biology N2 - We studied the carbon (C) metabolism in Daphnia when the amount of C (food quantity) and/or the content of biochemical nutrients (food quality) was limiting. Growth performances and C budgets of Daphnia magna (assimilation, faeces egestion, excretion and respiration measured by [C-14]-tracing) were analysed when animals were raised on different food quantities and concentrations of cholesterol, an essential biochemical food compound. Cholesterol is of special interest because it not only acts as limiting nutrient but also contributes to the overall C pool of the animals. As the tissue cholesterol concentration in Daphnia is quite low, we hypothesized the selective exclusion of cholesterol from C budgeting and tested this using radiolabelled cholesterol. Somatic growth rates of D. magna were highest at high quantity and quality and were reduced to a moderate value if either the food quantity or the cholesterol concentration was low. Growth was lowest at low food quantity and quality. The measurements of C budgets revealed high regulative response to low food quality at high food quantity only. Here, low dietary cholesterol caused bulk C assimilation efficiency (AE) to decrease and assimilated (excess) C to be increasingly respired. Additionally, Daphnia enhanced efficient adjustment of C budgets when facing cholesterol limitation by (1) increasing the AE of the cholesterol itself and (2) not changing cholesterol respiration, which was still not detectable. In contrast, at low food quantity, Daphnia is unable to adjust for low food quality, emphasizing that food limitation could overrule food quality effects. KW - Biochemical limitation KW - Carbon budgets KW - Zooplankton KW - Carbon pathway KW - Food quality KW - Food quantity Y1 - 2014 U6 - https://doi.org/10.1242/jeb.094151 SN - 0022-0949 SN - 1477-9145 VL - 217 IS - 7 SP - 1079 EP - 1086 PB - Company of Biologists Limited CY - Cambridge ER - TY - JOUR A1 - Lukas, Marcus A1 - Wacker, Alexander T1 - Acclimation to dietary shifts impacts the carbon budgets of Daphnia magna JF - Journal of plankton research N2 - Daphnia responds to low availability of carbon (food quantity) or limiting concentrations of nutrients relative to carbon (C) in excess (food quality) by respectively saving or discharging C via different pathways. We investigated which kind of food limitation leads to a faster regulation in Daphnia C budgets, and whether the pre-assimilative C pathways, ingestion and faeces egestion and the post-assimilative C pathways, excretion and respiration, are regulated concurrently. Daphnia magna were exposed to dietary shifts in different food quantities or qualities; food quality was varied in terms of the essential component, cholesterol. After acclimation to the new diet ranging from 0 to 96 h, C budgets were measured by a radiotracer technique. Dietary shifts in quantity and quality caused Daphnia to quickly adjust their C budgets within 6 h, but different C pathways were affected. A shift to low food quantity reduced Daphnia respiration indicating C retention. In contrast, sudden low quality food caused increased faeces egestion to discharge excess C. Furthermore, we observed a delayed increase in excretion but no change in respiration within the time frame studied. Such time-shifted responses appear to be an appropriate means to keep the costs of physiological adjustments relatively low, which in turn would benefit Daphnia performance. KW - carbon pathway KW - cholesterol KW - zooplankton KW - food quality KW - food quantity Y1 - 2014 U6 - https://doi.org/10.1093/plankt/fbu018 SN - 0142-7873 SN - 1464-3774 VL - 36 IS - 3 SP - 848 EP - 858 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Martin-Creuzburg, Dominik A1 - Oexle, Sarah A1 - Wacker, Alexander T1 - Thresholds for sterol-limited growth of Daphnia magna: A comparative approach using 10 different sterols JF - Journal of chemical ecology N2 - 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. KW - Cholesterol KW - Daphnia KW - Food quality KW - Nutrition KW - Phytosterols KW - Sterols Y1 - 2014 U6 - https://doi.org/10.1007/s10886-014-0486-1 SN - 0098-0331 SN - 1573-1561 VL - 40 IS - 9 SP - 1039 EP - 1050 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Wacker, Alexander A1 - Piepho, Maike A1 - Spijkerman, Elly T1 - Photosynthetic and fatty acid acclimation of four phytoplankton species in response to light intensity and phosphorus availability JF - European journal of phycology N2 - Photosynthetic acclimation of phytoplankton to lower irradiation can be met by several strategies such as increasing the affinity for light or increasing antenna size and stacking of the thylakoids. The latter is reflected by a higher proportion of polyunsaturated fatty acids (PUFAs). Additionally, photosynthetic capacity (P-max), respiratory losses, and proton leakage can be reduced under low light. Here we consider the effect of light intensity and phosphorus availability simultaneously on the photosynthetic acclimation and fatty acid composition of four phytoplankters. We studied representatives of the Chlorophyceae, Cryptophyceae and Mediophyceae, all of which are important components of plankton communities in temperate lakes. In our analysis, excluding fatty acid composition, we found different acclimation strategies in the chlorophytes Scenedesmus quadricauda, Chlamydomonas globosa, cryptophyte Cryptomonas ovata and ochrophyte Cyclotella meneghiniana. We observed interactive effects of light and phosphorus conditions on photosynthetic capacity in S. quadricauda and Cry. ovata. Cry. ovata can be characterized as a low light-acclimated species, whereas S. quadricauda and Cyc. meneghiniana can cope best with a combination of high light intensities and low phosphorus supply. Principal component analyses (PCA), including fatty acid composition, showed further species-specific patterns in their regulation of P-max with PUFAs and light. In S. quadricauda and Cyc. meneghiniana, PUFAs negatively affected the relationship between P-max and light. In Chl. globosa, lower light coincided with higher PUFAs and lower P-max, but PCA also indicated that PUFAs had no direct influence on P-max. PUFAs and P-max were unaffected by light in Cry. ovata. We did not observe a general trend in the four species tested and concluded that, in particular, the interactive effects highlight the importance of taking into account more than one environmental factor when assessing photosynthetic acclimation to lower irradiation. KW - chlorophyll content KW - dark respiration KW - FAME KW - light acclimation KW - oxygen evolution KW - photosynthesis KW - phytoplankton KW - polyunsaturated fatty acids Y1 - 2015 U6 - https://doi.org/10.1080/09670262.2015.1050068 SN - 0967-0262 SN - 1469-4433 VL - 50 IS - 3 SP - 288 EP - 300 PB - Routledge, Taylor & Francis Group CY - Abingdon ER - TY - JOUR A1 - Hixson, Stefanie M. A1 - Sharma, Bhanu A1 - Kainz, Martin J. A1 - Wacker, Alexander A1 - Arts, Michael T. T1 - Production, distribution, and abundance of long-chain omega-3 polyunsaturated fatty acids: a fundamental dichotomy between freshwater and terrestrial ecosystems JF - Environmental reviews = Dossiers environnement N2 - Long-chain polyunsaturated fatty acids (LC-PUFA) are critical for the health of aquatic and terrestrial organisms; therefore, understanding the production, distribution, and abundance of these compounds is imperative. Although the dynamics of LC-PUFA production and distribution in aquatic environments has been well documented, a systematic and comprehensive comparison to LC-PUFA in terrestrial environments has not been rigorously investigated. Here we use a data synthesis approach to compare and contrast fatty acid profiles of 369 aquatic and terrestrial organisms. Habitat and trophic level were interacting factors that determined the proportion of individual omega-3 (n-3) or omega-6 (n-6) PUFA in aquatic and terrestrial organisms. Higher total n-3 content compared with n-6 PUFA and a strong prevalence of the n-3 PUFA eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) characterized aquatic versus terrestrial organisms. Conversely, terrestrial organisms had higher linoleic acid (LNA) and alpha-linolenic acid (ALA) contents than aquatic organisms; however, the ratio of ALA: LNA was higher in aquatic organisms. The EPA + DHA content was higher in aquatic animals than terrestrial organisms, and increased from algae to invertebrates to vertebrates in the aquatic environment. An analysis of covariance (ANCOVA) revealed that fatty acid composition was highly dependent on the interaction between habitat and trophic level. We conclude that freshwater ecosystems provide an essential service through the production of n-3 LC-PUFA that are required to maintain the health of terrestrial organisms including humans. KW - aquatic ecosystems KW - conservation KW - eicosapentaenoic acid KW - docosahexaenoic acid KW - food webs Y1 - 2015 U6 - https://doi.org/10.1139/er-2015-0029 SN - 1208-6053 SN - 1181-8700 VL - 23 IS - 4 SP - 414 EP - 424 PB - NRC Research Press CY - Ottawa ER - TY - JOUR A1 - Sperfeld, Erik A1 - Wacker, Alexander T1 - Maternal diet of Daphnia magna affects offspring growth responses to supplementation with particular polyunsaturated fatty acids JF - Hydrobiologia : acta hydrobiologica, hydrographica, limnologica et protistologica N2 - Previous studies examining the effects of food quality on zooplankton often controlled for maternal effects of resource provisioning using standardized maternal diets. However, varying nutritional history of mothers may change resource provisioning to their progeny, especially regarding polyunsaturated fatty acids (PUFAs), which may change the interpretation of previously observed fitness responses of offspring. To assess PUFA-mediated maternal provisioning effects on offspring, we raised females of the cladoceran Daphnia magna on diets differing considerably in PUFA composition and raised their offspring on a PUFA-lacking diet supplemented with the omega 3 PUFAs alpha-linolenic acid (ALA) and/or eicosapentaenoic acid (EPA). The mass-specific growth responses of offspring to their own diets were affected by the maternal diet regime, probably due to varying maternal PUFA provisioning. A low maternal provisioning of EPA or ALA was sufficient to prevent growth limitation of offspring by these PUFAs until reaching maturity. A comparison with results of published ALA and EPA supplementation experiments suggests that the previously observed limitation effects depended on the usage of a single algae genus as maternal diet. Therefore, we suggest that maternal diets should be deliberately varied in future studies assessing ecological relevant food quality effects on zooplankton, especially regarding PUFAs. KW - Food quality KW - Maternal effects KW - Nutritional ecology KW - Resource provisioning KW - Zooplankton Y1 - 2015 U6 - https://doi.org/10.1007/s10750-015-2244-y SN - 0018-8158 SN - 1573-5117 VL - 755 IS - 1 SP - 267 EP - 282 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Wacker, Alexander A1 - Marzetz, Vanessa A1 - Spijkerman, Elly T1 - Interspecific competition in phytoplankton drives the availability of essential mineral and biochemical nutrients JF - Ecology : a publication of the Ecological Society of America N2 - The underlying mechanisms and consequences of competition and diversity are central themes in ecology. A higher diversity of primary producers often results in higher resource use efficiency in aquatic and terrestrial ecosystems. This may result in more food for consumers on one hand, while, on the other hand, it can also result in a decreased food quality for consumers; higher biomass combined with the same availability of the limiting compound directly reduces the dietary proportion of the limiting compound. Here we tested whether and how interspecific competition in phytoplankton communities leads to changes in resource use efficiency and cellular concentrations of nutrients and fatty acids. The measured particulate carbon : phosphorus ratios (C:P) and fatty acid concentrations in the communities were compared to the theoretically expected ratios and concentrations of measurements on simultaneously running monocultures. With interspecific competition, phytoplankton communities had higher concentrations of the monounsaturated fatty acid oleic acid and also much higher concentrations of the ecologically and physiologically relevant long-chain polyunsaturated fatty acid eicosapentaenoic acid than expected concentrations based on monocultures. Such higher availability of essential fatty acids may contribute to the positive relationship between phytoplankton diversity and zooplankton growth, and may compensate limitations by mineral nutrients in higher trophic levels. KW - biodiversity KW - C:P ratio KW - competition KW - eicosapentaenoic acid KW - elemental composition KW - EPA KW - food quality KW - minerals KW - phosphorus KW - polyunsaturated fatty acids KW - PUFA KW - resource use efficiency Y1 - 2015 U6 - https://doi.org/10.1890/14-1915.1 SN - 0012-9658 SN - 1939-9170 VL - 96 IS - 9 SP - 2467 EP - 2477 PB - Wiley CY - Washington ER - TY - JOUR A1 - Schwarzenberger, Anke A1 - Wacker, Alexander T1 - Melatonin synthesis follows a daily cycle in Daphnia JF - Journal of plankton research N2 - In freshwater systems, Daphnia has been demonstrated to show adaptive responses following the light-dark cycle. The adjustment of these responses to the change of day and night is probably transmitted via the hormone melatonin. The rate-limiting enzyme in melatonin synthesis is the arylalkylamine N-transferase (AANAT). We identified three genes coding for insect-like AANATs in Daphnia, of which we measured the gene expression in an ecologically relevant light-dark cycle. We demonstrated that Daphnia's insect-like AANAT gene expression oscillated in a daily manner, and that the highest peak of expression after the onset of darkness was followed by a peak of melatonin production at midnight. Moreover, we could show an oscillation of endogenous melatonin synthesis in Daphnia. In most organisms, melatonin synthesis is due to rhythmic expression of genes of the circadian clock, since transcription of aanats is directly linked to a circadian transcription factor. We could demonstrate that putative clock genes and insect-like AANAT genes of Daphnia were equally expressed. Therefore, we propose that melatonin synthesis is coupled to the expression of Daphnia clock genes, and that insect-like AANATs of crustaceans have a similar function as AANATs of vertebrates: The initiation of melatonin synthesis. In future studies with Daphnia, it will be necessary to take the time of day into account since melatonin concentrations might influence stress responses. KW - arylalkylamine N-transferase KW - insect-like AANAT KW - qPCR KW - circadian clock KW - clock genes Y1 - 2015 U6 - https://doi.org/10.1093/plankt/fbv029 SN - 0142-7873 SN - 1464-3774 VL - 37 IS - 3 SP - 636 EP - 644 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Wannicke, Nicola A1 - Frindte, Katharina A1 - Gust, Giselher A1 - Liskow, Iris A1 - Wacker, Alexander A1 - Meyer, Andreas A1 - Grossart, Hans-Peter T1 - Measuring bacterial activity and community composition at high hydrostatic pressure using a novel experimental approach: a pilot study JF - FEMS microbiology ecology N2 - In this pilot study, we describe a high-pressure incubation system allowing multiple subsampling of a pressurized culture without decompression. The system was tested using one piezophilic (Photobacterium profundum), one piezotolerant (Colwellia maris) bacterial strain and a decompressed sample from the Mediterranean deep sea (3044 m) determining bacterial community composition, protein production (BPP) and cell multiplication rates (BCM) up to 27 MPa. The results showed elevation of BPP at high pressure was by a factor of 1.5 +/- 1.4 and 3.9 +/- 2.3 for P. profundum and C. maris, respectively, compared to ambient-pressure treatments and by a factor of 6.9 +/- 3.8 fold in the field samples. In P. profundum and C. maris, BCM at high pressure was elevated (3.1 +/- 1.5 and 2.9 +/- 1.7 fold, respectively) compared to the ambient-pressure treatments. After 3 days of incubation at 27 MPa, the natural bacterial deep-sea community was dominated by one phylum of the genus Exiguobacterium, indicating the rapid selection of piezotolerant bacteria. In future studies, our novel incubation system could be part of an isopiestic pressure chain, allowing more accurate measurement of bacterial activity rates which is important both for modeling and for predicting the efficiency of the oceanic carbon pump. KW - hydrostatic pressure KW - pressure chamber KW - piezophilic bacteria KW - deep-sea bacterial community KW - bacterial production KW - stable isotopes KW - membrane fatty acids Y1 - 2015 U6 - https://doi.org/10.1093/femsec/fiv036 SN - 0168-6496 SN - 1574-6941 VL - 91 IS - 5 PB - Oxford Univ. Press CY - Oxford 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 - Sperfeld, Erik A1 - Raubenheimer, David A1 - Wacker, Alexander T1 - Bridging factorial and gradient concepts of resource co-limitation: towards a general framework applied to consumers JF - Ecology letters N2 - Organism growth can be limited either by a single resource or by multiple resources simultaneously (co-limitation). Efforts to characterise co-limitation have generated two influential approaches. One approach uses limitation scenarios of factorial growth assays to distinguish specific types of co-limitation; the other uses growth responses spanned over a continuous, multi-dimensional resource space to characterise different types of response surfaces. Both approaches have been useful in investigating particular aspects of co-limitation, but a synthesis is needed to stimulate development of this recent research area. We address this gap by integrating the two approaches, thereby presenting a more general framework of co-limitation. We found that various factorial (co-)limitation scenarios can emerge in different response surface types based on continuous availabilities of essential or substitutable resources. We tested our conceptual co-limitation framework on data sets of published and unpublished studies examining the limitation of two herbivorous consumers in a two-dimensional resource space. The experimental data corroborate the predictions, suggesting a general applicability of our co-limitation framework to generalist consumers and potentially also to other organisms. The presented framework might give insight into mechanisms that underlie co-limitation responses and thus can be a seminal starting point for evaluating co-limitation patterns in experiments and nature. KW - Consumer KW - essential nutrient KW - factorial design KW - food quality KW - growth rate KW - multi-nutrient limitation KW - nutritional ecology KW - performance landscape KW - substitutable resource KW - synergistic effect Y1 - 2016 U6 - https://doi.org/10.1111/ele.12554 SN - 1461-023X SN - 1461-0248 VL - 19 SP - 201 EP - 215 PB - Wiley-Blackwell CY - Hoboken ER - 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 - GEN 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 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 223 KW - fatty acid changes KW - freshwater algae KW - light adaptation KW - lipid classes Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-90682 SP - 1 EP - 13 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 - TY - JOUR A1 - Spijkerman, Elly A1 - Lukas, Marcus A1 - Wacker, Alexander T1 - Ecophysiological strategies for growth under varying light and organic carbon supply in two species of green microalgae differing in their motility JF - Phytochemistry : an international journal of plant biochemistry N2 - Mixing events in stratified lakes result in microalgae being exposed to varying conditions in light and organic carbon concentrations. Stratified lakes consist of an upper illuminated strata and a lower, darker strata where organic carbon accumulates. Therefore, in this contribution we explore the importance of dissolved organic carbon for growth under various light intensities by measuring some ecophysiological adaptations in two green microalgae. We compared the non-motile Chlorella vulgaris with the flagellated Chlamydomonas acidophila under auto-, mixo-, and heterotrophic growth conditions. In both algae the maximum photosynthetic and growth rates were highest under mixotrophy, and both algae appeared inhibited in their phosphorus acquisition under heterotrophy. Heterotrophic conditions provoked the largest differences as C. vulgaris produced chlorophyll a in darkness and grew as well as in autotrophic conditions, whereas Chl. acidophila bleached and could not grow heterotrophically. Although the fatty acid composition of both phytoplankton species differed, both species reacted in a similar way to changes in their growth conditions, mainly by a decrease of C18:3n-3 and an increase of C18:1n-9 from auto- to heterotrophic conditions. The two contrasting responses within the group of green microalgae suggest that dissolved organic carbon has a high deterministic potential to explain the survival and behaviour of green algae in the deeper strata of lakes. KW - Chlamydomonas acidophila KW - Chlorella vulgaris KW - Chlorophyceae KW - Ecophysiology on freshwater phytoplankton KW - Glucose KW - Mixotrophy KW - Osmotrophy KW - Heterotrophy KW - Photosynthesis KW - Fatty acids Y1 - 2017 U6 - https://doi.org/10.1016/j.phytochem.2017.08.018 SN - 0031-9422 SN - 1873-3700 VL - 144 SP - 43 EP - 51 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Colombo, Stefanie M. A1 - Wacker, Alexander A1 - Parrish, Christopher C. A1 - Kainz, Martin J. A1 - Arts, Michael T. T1 - A fundamental dichotomy in long-chain polyunsaturated fatty acid abundance between and within marine and terrestrial ecosystems JF - Environmental reviews = Dossiers environnement N2 - Polyunsaturated fatty acids (PUFA), especially long-chain (i.e., >= 20 carbons) polyunsaturated fatty acids (LC-PUFA), are fundamental to the health and survival of marine and terrestrial organisms. Therefore, it is imperative that we gain a better understanding of their origin, abundance, and transfer between and within these ecosystems. We evaluated the natural variation in PUFA distribution and abundance that exists between and within these ecosystems by amassing and analyzing, using multivariate and analysis of variance (ANOVA) methods, >3000 fatty acid (FA) profiles from marine and terrestrial organisms. There was a clear dichotomy in LC-PUFA abundance between organisms in marine and terrestrial ecosystems, mainly driven by the C-18 PUFA in terrestrial organisms and omega-3 (n-3) LC-PUFA in marine organisms. The PUFA content of an organism depended on both its biome (marine vs terrestrial) and taxonomic group. Within the marine biome, the PUFA content varied among taxonomic groups. PUFA content of marine organisms was dependent on both geographic zone (i.e., latitude, and thus broadly related to temperature) and trophic level (a function of diet). The contents of n-3 LC-PUFA were higher in polar and temperate marine organisms than those from the tropics. Therefore, we conclude that, on a per capita basis, high latitude marine organisms provide a disproportionately large global share of these essential nutrients to consumers, including terrestrial predators. Our analysis also hints at how climate change, and other anthropogenic stressors, might act to negatively impact the global distribution and abundance of n-3 LC-PUFA within marine ecosystems and on the terrestrial consumers that depend on these subsidies. KW - climate change KW - food webs KW - omega-3 KW - polyunsaturated fatty acids KW - trophic ecology Y1 - 2017 U6 - https://doi.org/10.1139/er-2016-0062 SN - 1208-6053 SN - 1181-8700 VL - 25 SP - 163 EP - 174 PB - NRC Research Press CY - Ottawa ER - TY - JOUR A1 - Raatz, Michael A1 - Gaedke, Ursula A1 - Wacker, Alexander T1 - High food quality of prey lowers its risk of extinction JF - Oikos N2 - The mineral and biochemical food quality of prey may limit predator production. This well-studied direct bottom-up effect is especially prominent for herbivore-plant interactions. Low-quality prey species, particularly when defended, are generally considered to be less prone to predator-driven extinction. Undefended high-quality prey species sustain high predator production thereby potentially increasing their own extinction risk. The food quality of primary producers is highly species-specific. In communities of competing prey species, predators thus may supplement their diets of low-quality prey with high-quality prey, leading to indirect horizontal interactions between prey species of different food quality. We explore how these predator-mediated indirect interactions affect species coexistence in a general predator-prey model that is parametrized for an experimental algae-rotifer system. To cover a broad range of three essential functional traits that shape many plant-herbivore interactions we consider differences in 1) the food quality of the prey species, 2) their competitive ability for nutrient uptake and 3) their defence against predation. As expected, low food quality of prey can, similarly to defence, provide protection against extinction by predation. Counterintuitively, our simulations demonstrate that being of high food quality also prevents extinction of that prey species and additionally promotes coexistence with a competing, low-quality prey. The persistence of the high-quality prey enables a high conversion efficiency and control of the low-quality prey by the predator and allows for re-allocation of nutrients to the high-quality competitor. Our results show that high food quality is not necessarily detrimental for a prey species but instead can protect against extinction and promote species richness and functional biodiversity. Y1 - 2017 U6 - https://doi.org/10.1111/oik.03863 SN - 0030-1299 SN - 1600-0706 VL - 126 SP - 1501 EP - 1510 PB - Wiley CY - Hoboken ER -