Daphnia Magna Feeding Research Articles

Dissolved nitrogen uptake versus nitrogen fixation: Mode of nitrogen acquisition affects stable isotope signatures of a diazotrophic cyanobacterium and its grazer.

Field studies suggest that changes in the stable isotope ratios of phytoplankton communities can be used to track changes in the utilization of different nitrogen sources, i.e., to detect shifts from dissolved inorganic nitrogen (DIN) uptake to atmospheric nitrogen (N2) fixation by diazotrophic cyanobacteria as an indication of nitrogen limitation. We explored changes in the stable isotope signature of the diazotrophic cyanobacterium Trichormus variabilis in response to increasing nitrate (NO3-) concentrations (0 to 170 mg L-1) under controlled laboratory conditions. In addition, we explored the influence of nitrogen utilization at the primary producer level on trophic fractionation by studying potential changes in isotope ratios in the freshwater model Daphnia magna feeding on the differently grown cyanobacteria. We show that δ 15N values of the cyanobacterium increase asymptotically with DIN availability, from -0.7 ‰ in the absence of DIN (suggesting N2 fixation) to 2.9 ‰ at the highest DIN concentration (exclusive DIN uptake). In contrast, δ 13C values of the cyanobacterium did not show a clear relationship with DIN availability. The stable isotope ratios of the consumer reflected those of the differently grown cyanobacteria but also revealed significant trophic fractionation in response to nitrogen utilization at the primary producer level. Nitrogen isotope turnover rates of Daphnia were highest in the absence of DIN as a consequence of N2 fixation and resulting depletion in 15N at the primary producer level. Our results highlight the potential of stable isotopes to assess nitrogen limitation and to explore diazotrophy in aquatic food webs.

Is color a matter of concern during microplastic exposure to Scenedesmus obliquus and Daphnia magna?

Toxicities of microplastics (MPs) on aquatic organisms have been widely investigated often by using white or transparent MPs. However, various colored MPs scatter in the real aquatic environment. Here we investigated four colored MPs’ effects on Scenedesmus obliquus algal growth first. Under the light condition, algal growth increased initially due to hormesis stimulation and then decreased gradually at higher MP concentrations. Green colored MPs exhibited the lowest inhibition effect, probably due to their resemblance to algae; white MPs inhibited the algal growth significantly, which was attributed to the presence of ethanol. Turbulence condition seemed to diminish algal growth differences among groups, but it led to slight oxidative stress. Furthermore, we also tested MP effects on Daphnia magna feeding ability. Results indicated that daphnids were probably not able to distinguish colored MPs from algae. But their algae ingestion amounts increased when MPs reached to 40% of algal cells, probably because daphnids could widen their filtering gapes when food quality decreases. However, this phenomenon did not last until the 3rd day, as the agglomeration of MPs and algae made them settle down. Overall, our results highlighted the color may alter some MP effects and is necessary to be considered in (eco)toxicological studies.

Metabolomic method to detect a metabolite corona on amino-functionalized polystyrene nanoparticles

Protein coronas on nanoparticles (NPs) affect their physicochemical properties, cellular uptake, and toxicity, and have been described extensively. To date, studies of the occurrence of small molecule (metabolite) coronas are limited. We sought to determine whether a metabolite corona forms on NPs, using high-sensitivity metabolomics combined with a model system for freshwater ecotoxicology (Daphnia magna feeding on Chlorella vulgaris). Using amino-functionalized polystyrene NPs (NH2-pNPs), we showed the impact of this material on Daphnia feeding to provide a rationale for the detailed molecular investigations. We then employed a targeted LC-MS/MS approach for sodium dodecyl sulfate (SDS) as an analog to signaling molecules known to occur in our freshwater model system and optimized a corona extraction method for this representative metabolite. Next, we performed an untargeted discovery-based metabolomics study – using high-sensitivity nanoelectrospray direct infusion mass spectrometry (DIMS) – to enable an unbiased assessment of the metabolite corona of NH2-pNPs in the freshwater model system. Our results demonstrate that SDS was successfully recovered from NH2-pNPs, confirming that the extraction protocol was fit-for-purpose. Untargeted DIMS metabolomics reproducibly detected 100 s of small molecule peaks extracted from NH2-pNPs exposed to conditioned media from the D. magna–C. vulgaris model system. Attempts to annotate these extracted metabolites, including by using van Krevelen and Kendrick Mass Defect plots, indicate a diverse range of metabolites that were not clustered into any particular class. Overall we demonstrate the existence of an ecologically relevant metabolite corona on the surface of NPs through application of a high-sensitivity, untargeted mass spectrometry metabolomics workflow.

Molecular biological analysis of Bt-transgenic (Bt-9) rice and its effect on Daphnia magna feeding

Molecular biological analysis of Bt-transgenic (Bt-9) rice and its effect on Daphnia magna feeding

Acute toxicity evaluation of drought-tolerant transgenic rice Agb0103 to Daphnia magna

A drought-tolerant transgenic rice (Agb0103) was developed using a pepper methionine sulfoxide reductase (CaMsrB2) under the control of rice Rab21 promoter with a selection marker, the phosphinothricin acetyltransferase (PAT) gene. Commercialization of genetically modified (GM) crops will require the evaluation of risks associated with the release of GM crops. With the potential problems associated to GM crops safety testing, the investigation of their effects on non-target organisms is necessary for environmental risk research. This study was carried out to assess acute toxicity of a GM crop using the water flea (Daphnia magna) for non-target organism risk evaluation. The effect of acute toxicity on Daphnia magna of Agb0103 rice and a non-GM rice, Ilmibyeo, were investigated at different concentrations (0, 625, 1,250, 2,500, 5,000, and 10,000 mg/L). The Agb0103 rice used for the test was confirmed to express the CaMsrB2/PAT gene by the PCR and ELISA. Daphnia magna feeding tests showed no significant differences in cumulative immobility or abnormal response with either Agb0103 rice or non-GM rice. The 48hr-EC50 values showed no difference between Agb0103 rice (2243 mg/L) and non-GM rice (2694 mg/L). These results suggest that there is no significant difference in toxicity to Daphnia magna between Agb0103 rice and its non-GM counterpart.

Food quality of heterotrophic bacteria for Daphnia magna: evidence for a limitation by sterols

The quality of heterotrophic bacteria as food for metazoan grazers has been investigated poorly. We conducted growth experiments with juvenile Daphnia magna feeding on different strains of heterotrophic bacteria that represent typical pelagic bacteria of five phylogenetically distinct groups. The bacterial food suspensions were supplemented with cholesterol and/or the polyunsaturated fatty acid eicosapentaenoic acid (EPA), two essential nutrients that are either absent or scarcely represented in bacteria. Our data imply that the selected heterotrophic bacteria are of poor food quality for D. magna, which was indicated either by very low somatic growth rates or by high mortality. However, with four out of six bacterial strains tested, the somatic growth rates increased significantly upon supplementation with cholesterol, which shows that the lack of sterols in bacteria is a major food quality constraint. We did not find clear evidence for a limitation by EPA on bacterial diets within our growth experiments. High mortality was observed when D. magna was fed with Hydrogenophaga sp. or Pseudomonas sp., which indicates that these two bacterial strains are toxic to D. magna. Our findings highlight the limitations of bacteria as a carbon source for Daphnia and point to a so far underestimated diversity of interactions between grazers and its bacterial food.

Identification of water soluble and particle bound compounds causing sublethal toxic effects. A field study on sediments affected by a chlor-alkali industry

A combination of cost effective sublethal Daphnia magna feeding tests, yeast- and cell culture-based bioassays and Toxicity Identification Evaluation (TIE) procedures was used to characterize toxic compounds within sediments collected in a river area under the influence of the effluents from a chlor-alkali industry (Ebro River, NE Spain). Tests were designed to measure and identify toxic compounds in the particulate and filtered water fractions of sediment elutriates. The combined use of bioassays responding to elutriates and dioxin-like compounds evidenced the existence of three major groups of hazardous contaminants in the most contaminated site: (A) metals such as cadmium and mercury bound to sediment fine particles that could be easily resuspended and moved downstream, (B) soluble compounds (presumably, lye) able to alkalinize water to toxic levels, and (C) organochlorine compounds with high dioxin-like activity. These results provided evidence that elutriate D. magna feeding responses can be used as surrogate assays for more tedious chronic whole sediment tests, and that the incorporation of such tests in sediment TIE procedures may improve the ability to identify the toxicity of particle-bound and water-soluble contaminants in sediments.

A Daphnia magna feeding bioassay as a cost effective and ecological relevant sublethal toxicity test for Environmental Risk Assessment of toxic effluents

Environmental Risk Assessment of chemical products and effluents within EC countries require the use of cost effective standardized toxicity tests that in most cases are restricted to acute responses to high doses. Thus, subtle ecological effects are underestimated. Here we propose a short-term one day Daphnia magna feeding inhibition test as a cost effective and ecological relevant sublethal bioassay. The sensitivity and reliability of the proposed bioassay was tested in the laboratory against standardized bacteria, algae growth, D. magna and fish acute toxicity test by using 16 chemical mixture × water type combinations that included four different water types fortified with four complex chemical mixtures. Water types included ASTM hard water and three selected effluents diluted 1/10 in water to mimic worse field situations that many overexploited arid river ecosystems suffer during summer months when effluents are discharged into them with little dilution. The results obtained denoted a greater sensitivity of the proposed feeding bioassay in 51 out of 65 tests performed with an average sensitivity 50 fold greater than that of the standardized tests. The greater differences were obtained for mixtures that included narcotic chemicals and the lowest differences for those containing pesticides. Furthermore, feeding responses to the studied contaminant mixtures behaved differently to increasing TOC content than those based on bioluminescent bacteria and algae. Increasing TOC coming from sewage treated effluents decrease toxicity to the latter bioassays but increased those of D. magna feeding bioassays. These results empathize the need to include additional bioassays to monitor more accurately and realistically the toxicity of effluents or surface waters dominated by effluent discharges, a quite common situation in America and Mediterranean arid regions.

Nutritional constraints at the cyanobacteria—Daphnia magna interface: The role of sterols

In past decades, a considerable amount of research has been conducted to elucidate the factors that affect the carbon transfer across the cyanobacteria‐Daphnia interface. It is well accepted that cyanobacteria are a nutritionally inadequate food source for cladocerans, but the underlying mechanisms are still controversial. Morphological properties, toxicity, and the absence of essential lipids, i.e., polyunsaturated fatty acids (PUFAs) and sterols, are discussed as the most important factors that account for this nutritional inadequacy. Here, we conducted standardized growth experiments with the herbivore Daphnia magna feeding on coccal, filamentous, and putatively toxic cyanobacterial strains comprising the genera Synechococcus, Anabaena, Aphanizomenon, and Microcystis and on a cyanobacterial mixture containing strains of these genera. The relative importance of PUFAs and sterols in determining the food quality of cyanobacteria for Daphnia was assessed by supplementation of eicosapentaenoic acid‐ and/or cholesterol‐containing liposomes to the cyanobacterial carbon. We provide evidence that somatic growth of daphnids on coccal as well as on filamentous cyanobacteria is primarily constrained by the absence of sterols, provided that the cyanobacterial carbon is readily ingested and nontoxic. The absence of PUFAs in cyanobacteria appears to be of minor importance for somatic growth but potentially affects egg production in Daphnia. Thus, the absence of sterols has to be considered a major food‐quality constraint that potentially affects the efficiency of carbon transfer across the cyanobacteria‐Daphnia interface.

How Daphnia copes with excess carbon in its food.

Animals that maintain near homeostatic elemental ratios may get rid of excess ingested elements from their food in different ways. C regulation was studied in juveniles of Daphnia magna feeding on two Selenastrum capricornutum cultures contrasting in P content (400 and 80 C:P atomic ratios). Both cultures were labelled with (14)C in order to measure Daphnia ingestion and assimilation rates. No significant difference in ingestion rates was observed between P-low and P-rich food, whereas the net assimilation of (14)C was higher in the treatment with P-rich algae. Some Daphnia were also homogeneously labelled over 5 days on radioactive algae to estimate respiration rates and excretion rates of dissolved organic C (DOC). The respiration rate for Daphnia fed with high C:P algae (38.7% of body C day(-1)) was significantly higher than for those feeding on low C:P algae (25.3% of body C day(-1)). The DOC excretion rate was also higher when animals were fed on P-low algae (13.4% of body C day(-1)) than on P-rich algae (5.7% of body C day(-1)). When corrected for respiratory losses, total assimilation of C did not differ significantly between treatments (around 60% of body C day(-1)). Judging from these experiments, D. magna can maintain its stoichiometric balance when feeding on unbalanced diets (high C:P) primarily by disposing of excess dietary C via respiration and excretion of DOC.

Implications of element deficits for zooplankton growth

Daily measurements of mass and phosphorus (P) were made for Daphnia magna feeding on a high concentration (1 mg C l−1) of P-sufficient (molar C:P = 70–80, `P+') or P-deficient (C:P = 1000, `P−') green algae (Scenedesmus obliquus or Ankistrodesmus falcatus). Animals feeding on P+ algae for 12 d showed a sharp decline in growth during the last juvenile instar (mean ± SE from 0.57 ± 0.02 to 0.25 ± 0.03 d−1) and a modest decline in P-content at the first adult instar (from 1.55 ± 0.01 to 1.46 ± 0.02% mass). Animals feeding on P− algae showed declines in P-content to as low as 0.84% after 5 d, with the sharpest decline in the first day. Growth of animals feeding on P− algae declined sharply over time and showed a linear relationship with the grazer's P-content. Growth during the first day of exposure to P− algae was relatively high (mean 0.39 ± 0.03 d−1) but approached zero as P-content declined to <0.90% mass. For animals feeding on P+ algae, the ontogenetic decline in P-content resulted in only a small difference between growth calculated for mass and growth calculated for Daphnia P. In contrast, for animals feeding for 4 d on P− algae, growth calculated for mass was 2–5 times higher than growth based on P. Thus, this study shows that short-term growth assays may substantially underestimate the negative impact of P-deficient resources, unless the decline in the grazer's P-content is taken into account. In this situation, measurement of growth in terms of nutrient content (e.g. grazer's P-content) should provide a better indication of the potential for sustained growth than calculations based on change in mass. This study also supports the `integration of growth' hypothesis (Sterner & Schwalbach, 2001), in which animals undergoing diel migration between water layers with P-deficient and P-sufficient resources experience a reduced growth penalty.

Image analysis of Daphnia populations: non‐destructive determination of demography and biomass in cultures

SUMMARY 1. An image analysis technique was developed for the semiautomatic determination of abundance, size distribution and biomass in Daphnia cultures. This allowed detailed observations of growth, demography and biomass accumulation in live populations, avoiding artifacts caused by subsampling and sampling losses.2. The image analysis method gave fast, non‐destructive and reliable individual counts, even in cultures with high density and a large fraction of juveniles.3. In Daphnia, animal width changes with nutritional status and growth within instar, while length changes only at the moult. Thus, estimation of individual biomass using an ellipsoidal model based on animal width gave improved biomass calculations compared to manual counting, sizing, and length : weight regressions.4. The power of the image analysis technique for assessing population growth and size structure was demonstrated in two 40‐day experiments, with Daphnia magna feeding on the green algae Selenastrum capricornutum in a two‐stage chemostat system.

Daphnia magna Feeding Behavior after Exposure to Tetradifon and Recovery from Intoxication

The feeding behavior of the cladocera Daphnia magna subjected to a short-term exposure to the acaricide tetradifon (4-chlorophenyl 2,4,5-trichlorophenyl sulfone) was studied. The experiments were performed using the unicellular algae Nannochloris oculata at a density of 5×105 cells/ml as food for the organisms. In a first experiment, three generations (F0, F1, and F3) of the daphnids were exposed to sublethal levels of tetradifon (0.1, 0.18, 0.22, and 0.44 mg/l) and the effect of the toxicant on filtration and ingestion rates was determined. Rates of filtration and ingestion of D. magna declined in the three generations studied with increasing toxicant concentrations; however, toxicant effect was greater in daphnids from generations F1 and F3 than in those from the parental generation F0. A second experiment was conducted in order to evaluate whether animals of a first (1) or third (F3) generation coming from parental daphnids (F0) previously exposed to those pesticide concentrations exhibited any alteration in feeding behavior when transferred to clean water (recovery period). The results indicated that the feeding rates of D. magna generations F1 and F3 were still affected during the recovery period but to a less degree. The effective tetradifon concentrations D. magna at which feeding rates were reduced to 50% that of controls (EC50) were also calculated.

Accumulation of microcystin in Daphnia magna feeding on toxic Microcystis

The influence of toxic microcystis on the life processes of Daphnia magna was studied in a series of in vitro and in situ life table experiments. Using survival, body growth and fecundity as response parameters, the performance of D. magna incubated in suspensions of the toxic Microcystis aeruginosa CYA 228/1 (2 mg microcystin/g algal DW) and lake water containing natural Microcystis was compared to the performance of D. magna incubated in a high quality food suspension of Scene-desmus acutus and yeast and in tap water without addition of food. Accumulation of microcystin in D. magna was quantified by ELISA. Additional experiments were performed to study the grazing of D. magna in food suspensions containing varying quantities of M. aeruginosa CYA 228/1 mixed with S. acutus. The presence of M. aeruginosa CYA 228/1 reduced the survival of D. magna by 85-100% in the in situ life table experiments. No significant reduction was recorded in the in vitro experiments. M. aeruginosa CYA 228/1 reduced the growth and fecundity of D. magna in all experiments. Microcystin was detected in all D. magna populations incubated in food suspensions containing indigenous or cultured Microcystis. A strong negative correlation between toxin concentration and body length were found (r 2 = 0.72) as well as a weaker negative correlation between toxin concentration and fecundity (r 2 = 0.48) expressed as biovolume specific concentrations. These findings indicate that 1) microcystin has direct toxic effects on Daphnia life processes, 2) microcystin can accumulate in Daphnia and 3) Daphnia can potentially act as vectors for the transfer of microcystin to higher trophic levels in the aquatic food web. A possible pathway for the transfer of microcystin from the food particles to the daphniid body is suggested.