Magna Individuals Research Articles

Co-cultivation of Daphnia magna (Straus) and Desmodesmus armatus (chod.) Hegew. in recirculating aquaculture system wastewater

AbstractThe study focused on the development of co-cultivation schemes for Daphnia magna (Straus) and Desmodesmus armatus (Chod.) Hegew. Wastewater from a recirculating aquaculture system (RAS) was used as a medium for co-cultivation. Three schemes for D. magna and algae co-cultivation that differed in the timing of the introduction of Daphnia into the system were tested. Initially, D. armatus algae were cultivated to the exponential growth phase until cell numbers reached 5 × 104 cell × 1-1. This algal culture was introduced into the system for joint cultivation. D. magna was added immediately on the same day or three or six days after the algae. The number of D. magna individuals and the number of D. armatus cells were analyzed. It was established that the optimal scheme is the simultaneous introduction of algae and crustaceans into the cultivating system. By implementing this system it was possible to increase the number and biomass of D. magna by ten times in comparison to initial values.The biochemical composition of the D. magna obtained after co-cultivation and Daphnia that was fed traditionally once every 48 h with the same algae or yeast, Saccharomyces cerevisiae, was also compared. The scheme applied for D. magna and D. armatus simultaneous co-cultivation rendered it possible to obtain a biomass of Daphnia that was characterized by a protein content of 82.5% lipids of 6.7%, and carotenoids of 15.3 mg × g-1.

Habitat orientation alters the outcome of interspecific competition: A microcosm study with zooplankton grazers.

Habitat orientation has recently been demonstrated to affect the foraging behavior, growth, and production of plankton grazers. Because the orientation effect may vary with species, we hypothesize that habitat orientation may alter interspecific interactions between animal species. We experimentally investigated how habitat orientation (placing cuboid chambers in three orientations with long, medium, and small side as the chamber height) affected the interaction between two common cladoceran species, Daphnia magna and Moina micrura, which competitively exploited green algae of Chlorella pyrenoidosa at two volume scales (64 and 512 ml). Results show that chamber orientation and volume additively affected the behavior and species performance of the grazers. Specifically, both grazer species generally decreased their average swimming velocity, grazing rate (on algal cells), body size, and survival and reproduction rates with increasing chamber height for both chamber volumes and with decreasing chamber volume regardless of chamber orientation. Nevertheless, the decrease magnitude was greater for M. micrura with increasing chamber height but was greater for D. magna with decreasing chamber volume. Correspondingly, when cocultured, the density ratio of D. magna to M. micrura increased with increasing chamber height but decreased with decreasing chamber volume. At the end of the experiment, none of D. magna individuals survived in the small and short (large‐based) chambers, and few M. micrura individuals survived in large and tall (small‐based) chambers. These results indicate that both habitat orientation and size affect the outcome of interspecific competition between grazer species. We suggest that variation in habitat orientation may improve community coexistence and species diversity in nature.

Daphnia magna filtration efficiency and mobility in laminar to turbulent flows

Daphnia are filter feeder organisms that prey on small particles suspended in the water column. Since Daphnia individuals can feed on wastewater particles, they have been recently proposed as potential organisms for tertiary wastewater treatment. However, analysing the effects of hydrodynamics on Daphnia individuals has scarcely been studied. This study focuses then, on quantifying the filtration and swimming velocities of D. magna individuals under different hydrodynamic conditions. Both D. magna filtration and movement responded differently if the flow was laminar or if it was turbulent. In a laminar-dominated flow regime Daphnia filtration was enhanced up to 2.6 times that of a steady flow, but in the turbulent-dominated flow regime D. magna filtration was inhibited. In the laminar flow regime D. magna individuals moved freely in all directions, whereas in the turbulent flow regime they were driven by the streamlines of the flow. A model based on Daphnia-particle encountering revealed that the filtration efficiency in the laminar regime was driven by the length of the D. magna individuals and the shear rate imposed by the system.

Norfloxacin disrupts Daphnia magna-induced colony formation in Scenedesmus quadricauda and facilitates grazing

Environmental pollutants can negatively affect grazer-induced defenses in phytoplankton species and lead to the disruption of phytoplankton-zooplankton relationships. However, it is still not known whether norfloxacin (NOR), a widely used antibiotic, has such effects on plankton systems when released into the environment. Here, we investigated the colony-forming ability of the green alga Scenedesmus quadricauda as well as the behavior (hopping frequency and duration of quiescence) and grazing rate of the cladoceran Daphnia magna, when exposed to different NOR concentrations (0, 50, 500, 5000 and 50,00ugL−1), to determine the effects of NOR on the S. quadricauda-D. magna relationship. Colony size was generally unaffected by NOR but significantly increased when subjected to the stress of adding grazers; however, the combined effects of adding grazers and increasing NOR concentrations led to consistently decreased colony size compared to only adding grazers. The hopping frequency and the time spent on swimming of D. magna individuals decreased while their grazing rate increased with increasing NOR concentrations. Thus, NOR seemed to inhibit grazer-induced colony formation in S. quadricauda, resulting in more algal cells being consumed by grazers, despite inhibiting grazers’ feeding behavior. Considering that phytoplankton-zooplankton interaction plays an important role in determining ecological process of aquatic ecosystems, ecosystem function might be more affected by NOR contamination than previously recognized.

Lethal/sublethal responses of Daphnia magna to acute norfloxacin contamination and changes in phytoplankton-zooplankton interactions induced by this antibiotic

Although the well-known antibiotic norfloxacin (NOR) is recognized as an important environmental pollutant, little is known about its impacts on ecological processes, particularly on species interactions. In this paper, we quantified Daphnia magna (Crustacea, Cladocera) responses in mortality rate at lethal NOR concentrations (0, 25, 50, 100, 200, 300 and 400 mg L−1), and in heartbeat rate, swimming behavior and feeding rate (on the green alga Chlorella pyrenoidosa) at sublethal NOR concentrations (0, 25, 50 and 100 mg L−1) to determine the effects of this antibiotic in plankton systems. In 96-h-long lethal experiment, mortality rates of D. magna increased significantly with increasing NOR concentration and exposure time. In sublethal experiments, heartbeat rate decreased, while time ratio of vertical to horizontal swimming (TVH) and the duration of quiescence increased in D. magna individuals exposed to increasing NOR concentrations after 4 and 12 h of exposure. These collectively led to decreases in both average swimming ability and feeding rate, consistent with the positive relationship between average swimming ability and feeding rate. Overall, results indicate that, by affecting zooplankton heartbeat rate and behavior, NOR decreased feeding efficiency of D. magna even at low doses, therefore, it might seriously compromise ecosystem health and function.

Effects of dietary exposure to herbicide and of the nutritive quality of contaminated food on the reproductive output of Daphnia magna

Risk assessment of pesticides has been based on direct toxic effects on aquatic organisms. Indirect effects data are taken into account but with limitations, as it is frequently difficult to predict their real impacts in the ecosystems. In this context the main aim of this work was to assess how the exposure to the herbicide pendimethalin (Prowl®), under environmentally relevant concentrations, may compromise the nutritional composition of food for a relevant group of primary consumers of freshwater food webs—the daphnids, thus affecting their reproduction performance and subsequently the long-term sustainability of active populations of this grazer. Therefore, Daphnia magna individuals were chronically exposed in a clean medium to a control diet (NCF – i.e., non-contaminated green algae Raphidocelis subcapitata) and to a contaminated diet (CF – i.e., the same monoalgal culture grown in a medium enriched with pendimethalin in a concentration equivalent to the EC20 for growth inhibition of algae), during which reproductive endpoints were assessed. The algae were analysed for protein, carbohydrate and fatty acid content. The chemical composition of R. subcapitata in the CF revealed a slight decrease on total fatty acid levels, with a particular decrease of essential ω9 monounsaturated fatty acids. In contrast, the protein content was high in the CF. D. magna exposed to CF experienced a 16% reduction in reproduction, measured as the total number of offspring produced per female. Additionally, an internal pendimethalin body burden of 4.226μgg−1 was accumulated by daphnids fed with CF. Hence, although it is difficult to discriminate the contribution of the pesticide (as a toxic agent transferred through the food web) from that of the food with a poor quality—compromised by the same pesticide, there are no doubts that, under environmentally relevant concentrations of pesticides, both pathways may compromise the populations of freshwater grazers in the long term, with consequences in the control of the primary productivity of these systems.

Compounds altering fat storage in Daphnia magna

The analysis of lipid disruptive effects in invertebrates is limited by our poor knowledge of the lipid metabolic pathways. A recent study showed that tributyltin activated the ecdysteroid, juvenile hormone and retinoic X receptor signaling pathways, and disrupted the dynamics of neutral lipids in the crustacean Daphnia magna impairing the transfer of triacylglycerols to eggs and hence promoting their accumulation in post-spawning females. Tributyltin disruptive effects correlated with lower fitness for offspring and adults. The present study aims to addresses effects of existing compounds on storage lipids in post-spawning females and their health effects. D. magna individuals were exposed 12 chemicals that included vertebrate obesogens (tributyltin, triphenyltin, bisphenol A, nonylphenol, di-2-ethylhexyl phthalate), other contaminants known to affect arthropods (pyriproxyfen, fenarimol, methoprene, emamectin benzoate and fluoxetine), as well as the natural hormones methyl farnesoate and 20-hydroxyecdysone. Reproductive effects were also assessed. Quantitative changes in storage lipids accumulated in lipid droplets were studied using Nile red staining, which showed a close relationship with whole organism levels of triacylglycerols. Ten compounds altered storage lipids in a concentration related manner enhancing (tributyltin, bisphenol A, methyl farnesoate, pyriproxyfen and 20-hydroxyecdysone) or decreasing (nonylphenol, fenarimol, emamectin benzoate, methoprene and fluoxetine) their levels in post-spawning females. Eight compounds that altered lipid levels also had detrimental effects on growth and/or reproduction.

Species interactions and chemical stress: combined effects of intraspecific and interspecific interactions and pyrene on Daphnia magna population dynamics.

Species interactions are often suggested as an important factor when assessing the effects of chemicals on higher levels of biological organization. Nevertheless, the contribution of intraspecific and interspecific interactions to chemical effects on populations is often overlooked. In the present study, Daphnia magna populations were initiated with different levels of intraspecific competition, interspecific competition, and predation and exposed to pyrene pulses. Generalized linear models were used to test which of these factors significantly explained population size and structure at different time points. Pyrene had a negative effect on total population densities, with effects being more pronounced on smaller D. magna individuals. Among all species interactions tested, predation had the largest negative effect on population densities. Predation and high initial intraspecific competition were shown to interact antagonistically with pyrene exposure. This was attributed to differences in population structure before pyrene exposure and pyrene-induced reductions in predation pressure by Chaoborus sp. larvae. The present study provides empirical evidence that species interactions within and between populations can alter the response of aquatic populations to chemical exposure. Therefore, such interactions are important factors to be considered in ecological risk assessments.

Obesogens beyond Vertebrates: Lipid Perturbation by Tributyltin in the Crustacean Daphnia magna

BackgroundThe analysis of obesogenic effects in invertebrates is limited by our poor knowledge of the regulatory pathways of lipid metabolism. Recent data from the crustacean Daphnia magna points to three signaling hormonal pathways related to the molting and reproductive cycles [retinoic X receptor (RXR), juvenile hormone (JH), and ecdysone] as putative targets for exogenous obesogens.ObjectiveThe present study addresses the disruptive effects of the model obesogen tributyltin (TBT) on the lipid homeostasis in Daphnia during the molting and reproductive cycle, its genetic control, and health consequences of its disruption.MethodsD. magna individuals were exposed to low and high levels of TBT. Reproductive effects were assessed by Life History analysis methods. Quantitative and qualitative changes in lipid droplets during molting and the reproductive cycle were studied using Nile red staining. Lipid composition and dynamics were analyzed by ultra-performance liquid chromatography coupled to a time-of-flight mass spectrometer. Relative abundances of mRNA from different genes related to RXR, ecdysone, and JH signaling pathways were studied by qRT-PCR.Results and ConclusionsTBT disrupted the dynamics of neutral lipids, impairing the transfer of triacylglycerols to eggs and hence promoting their accumulation in adult individuals. TBT’s disruptive effects translated into a lower fitness for offspring and adults. Co-regulation of gene transcripts suggests that TBT activates the ecdysone, JH, and RXR receptor signaling pathways, presumably through the already proposed interaction with RXR. These findings indicate the presence of obesogenic effects in a nonvertebrate species.CitationJordão R, Casas J, Fabrias G, Campos B, Piña B, Lemos MF, Soares AM, Tauler R, Barata C. 2015. Obesogens beyond vertebrates: lipid perturbation by tributyltin in the crustacean Daphnia magna. Environ Health Perspect 123:813–819; http://dx.doi.org/10.1289/ehp.1409163

Transcriptomic, biochemical and individual markers in transplanted Daphnia magna to characterize impacts in the field

Daphnia magna individuals were transplanted across 12 sites from three Spanish river basins (Llobregat, Ebro, Jucar) showing different sources of pollution. Gene transcription, feeding and biochemical responses in the field were assessed and compared with those obtained in re-constituted water treatments spiked with organic eluates obtained from water samples collected at the same locations and sampling periods. Up to 166 trace contaminants were detected in water and classified by their mode of action into 45 groups that included metals, pharmaceuticals, pesticides, illicit drugs, and other industrial compounds. Physicochemical water parameters differentiated the three river basins with Llobregat having the highest levels of conductivity, metals and pharmaceuticals, followed by Ebro, whereas the Jucar river had the greatest levels of illicit drugs. D. magna grazing rates and cholinesterase activity responded similarly than the diversity of riparian benthic communities. Transcription patterns of 13 different genes encoding for general stress, metabolism and energy processes, molting and xenobiotic transporters corroborate phenotypic responses differentiated sites within and across river basins. Principal Component Analysis and Partial Least Square Projections to Latent Structures regression analyses indicated that measured in situ responses of most genes and biomarkers and that of benthic macroinvertebrate diversity indexes were affected by distinct environmental factors. Conductivity, suspended solids and fungicides were negatively related with the diversity of macroinvertebrates cholinesterase, and feeding responses. Gene transcripts of heat shock protein and metallothionein were positively related with 11 classes of organic contaminants and 6 metals. Gene transcripts related with signaling paths of molting and reproduction, sugar, protein and xenobiotic metabolism responded similarly in field and lab exposures and were related with high residue concentrations of analgesics, diuretics, psychiatric drugs, β blockers, illicit drugs, trizoles, bisphenol A, caffeine and pesticides. These results indicate that application of omic technologies in the field is a promising subject in water management.

Population growth of the Cladoceran, Daphnia magna: a quantitative analysis of the effects of different algal food.

In this study, we examined the effects of two phytoplankton species, Chlorella vulgaris and Stephanodiscus hantzschii, on growth of the zooplankton Daphnia magna. Our experimental approach utilized stable isotopes to determine the contribution of food algae to offspring characteristics and to the size of adult D. magna individuals. When equal amounts of food algae were provided (in terms of carbon content), the size of individuals, adult zooplankton, and their offspring increased significantly following the provision of S. hantzschii, but not after the provision of C. vulgaris or of a combination of the two species. Offspring size was unaffected when C. vulgaris or a mixture of the two algal species was delivered, whereas providing only S. hantzschii increased the production of larger-sized offspring. Stable isotope analysis revealed significant assimilation of diatom-derived materials that was important for the growth of D. magna populations. Our results confirm the applicability of stable isotope approaches for clarifying the contribution of different food algae and elucidate the importance of food quality for growth of D. magna individuals and populations. Furthermore, we expect that stable isotope analysis will help to further precisely examine the contribution of prey to predators or grazers in controlled experiments.

To flee or not to flee: detection, avoidance and attraction of profitable resources by Daphnia magna studied with olfactometer

The cladoceran herbivore Daphnia magna is a major consumer of phytoplankton in lakes. Therefore, this organism may control the phytoplankton community and the proliferation of some algae or cyanobacteria. Cladoceran behaviour and migration in relation to temperature, light or presence of planktivorous fishes have been well studied. In particular, it is known that the detection of kairomones produced by predators may induce avoidance. Avoidance could also occur with other semiochemicals such as cyanotoxins. In order to explore this hypothesis, we used an olfactometer to observe and measure the exploratory behaviour of D. magna individuals based on the motivation for food. Daphnids were allowed to choose between different compounds: water, a pure cyanotoxin, i.e. the microcystin-RR [(MC)-RR], extracts of one MC-producing strain (PMC 75.02) and one MC-free strain (PMC 87.02) of Planktothrix agardhii, or a green algae Scenedesmus obliquus. With this experimental design, we observed that i) cladocerans are able to detect resources with different qualities, ii) they can explore before exhibiting preferences, and iii) daphnids are able to avoid compounds that are potentially toxic (e.g., microcystins). First, daphnids explored the environment, subsequently (after about 1.5 h), they showed a significant tendency to stay where there is a profitable resource such as S. obliquus. These results also suggest that specimens of D. magna cannot detect MC compounds from P. agardhii, but they respond to it as a food resource. The study of zooplankton ability to explore the environment when exposed to semiochemicals needs further investigation.

The origin of the giant liver fluke, Fascioloides magna (Trematoda: Fasciolidae) from Croatia determined by high-resolution melting screening of mitochondrial cox1 haplotypes

The high-resolution melting (HRM) method, recently optimized as a reliable technique for population study of the European Fascioloides magna populations, was applied to determine an origin of F. magna individuals from Croatia. The structure and frequency of mitochondrial cytochrome c oxidase subunit I (439 bp; cox1) haplotypes of 200 Croatian flukes coming from 19 red deer (Cervus elaphus elaphus) livers were screened and compared with recently determined reference samples of F. magna from all European foci-Italy, Czech Republic, and Danube floodplain forests. While the reference haplotypes Ha1 and Ha2 were specific for flukes from the first European focus of fascioloidosis, the Natural Park La Mandria in Italy, the remaining three haplotypes (Ha3, Ha4, and Ha5) represented parasites from the second focus, Czech Republic. Besides, Ha3 and Ha4 were found also in the third, latest, and still expanding European focus, the Danube floodplain forests. The HRM screening of cox1 haplotypes of Croatian F. magna individuals resulted in classification of samples into the two mitochondrial haplogroups characterized by well-distinguished melting curves. They corresponded to Ha3 and Ha4 reference haplotypes that confirmed the Danube origin of F. magna from Croatia. The results support the theory that the Danube floodplain forests population of F. magna represents uniform genetic pool of the parasite. The spread of F. magna alongside the Danube River down to Croatia was possible due to suitable ecological conditions for definitive and intermediate hosts present in this unique biotope.

Daphnia magna Straus, 1820 response to sediment samples from a contaminated river ( Rio Grande do Sul, Brazil)

AIM: The Sinos River, a tributary of Guaíba Lake, is 200 km long from the headwaters to the mouth and is influenced by several sources of pollution. A study to learn more about conditions in this river was performed in the middle and lower reaches. The study evaluated the effects of sediment contamination by xenobiotics on the survival and reproduction of Daphnia magna. METHODS: Eight sediment samples were collected per site from Dec/2007 to Aug/2009, as a substrate for 480 young cladocera (2-26 h old at the beginning of the trials) in chronic toxicity tests (21 days). For this purpose, D. magna individuals were exposed to sediment and M4 culture medium, at a proportion of 1:4 (v:v) using 50 mL beakers, kept at 20 ºC ± 2 ºC in 16h light:8h dark cycles. The test organisms came from lots with LC50-24h = 1.04 mgK2Cr2O7 ± 0.11 mg. Percentage survival and reproduction were considered to define acute and/or chronic responses. Duncan (p < 0.05) and T (p < 0.05) Tests, ANOVA and Spearman correlation of the biological data were used as statistical complementation. The Spearman correlation was also applied looking for dependencies between the rainfall measured at the sites and the biological parameters but there was no evidence of correlation. The presence of acute toxicity was diagnosed for the sample in which survival was less than 80%, and for chronic toxicity when the mean number of neonates was less than 20 daphniids. RESULTS: Reproductive delays were found coinciding with physical and chemical parameters, as well as the presence of metals at values that were not in accordance with the law. Statistical analysis suggested the predominance of point sources of contamination. An effect on survival was observed in 17% of the samples, and on reproduction in 87%. CONCLUSIONS: This study found that pollutants discharged into the Sinos River remain and can interfere in the equilibrium of the trophic network, since they increase mortality and diminish the production of offspring among the cladocera, representatives of the primary consumers in the food chain.

Isotope ratio mapping by means of laser ablation-single collector-ICP-mass spectrometry: Zn tracer studies in thin sections of Daphnia magna

In this paper, the possibilities of LA-single collector-ICP-mass spectrometry for obtaining isotope ratio images of thin sections of Daphnia magna specimens exposed to isotopically enriched Zn tracers were evaluated. Zn was selected considering its importance in ecotoxicological studies. All aspects of the analytical methodology deployed were carefully studied and optimized for obtaining the best isotope ratio precision and accuracy. The development of this methodological approach consisted of: (i) evaluation of the performance of two different medium mass resolution exit slits, a conventional one providing a mass resolution of m/Δm ≈ 4000 and triangular shaped peaks, and another (wider) one, offering a lower mass resolution (m/Δm ≈ 2000), but providing enhanced ion transmission and flat-topped peaks; (ii) the use of a wet plasma for improving plasma robustness; (iii) thorough optimization of the ablation conditions (such as laser spot size, repetition rate, scan speed and laser fluence) and data acquisition parameters (such as scan mode, the number of nuclides monitored, mass window, the number of samples per peak and dwell times); and (iv) adequate data treatment including the use of the moving average of 5 individual values. With the methodology developed, isotope ratio images with 30 micrometer spatial resolution scale were obtained for exposed and unexposed Daphnia magna individuals. The typical overall uncertainty of the measurements was approximately 5% RSD for the 66Zn/64Zn and 68Zn/64Zn ratios, which can be considered as satisfactory taking into account that the amount of Zn present per 30 μm × 30 μm pixel only reached a few picograms in the most favourable cases (giving rise to 10 000–20 000 counts per s for 64Zn). These results open the possibility for tracer studies with stable isotopes to be carried out using single collector instrumentation, a much more widespread analytical technique than multi-collector ICP-MS.

Effects of microcystin-producing and microcystin-free strains ofPlanktothrix agardhiion long-term population dynamics ofDaphnia magna

The effects of cyanobacterial toxins on herbivorous zooplankton depend on cyanobacterial strains, zooplankton species and environmental conditions. To explore the relationship between zooplankton and cyanobacteria, we investigated the effects of Planktothrix agardhii extracts on Daphnia magna population dynamics. We designed an experiment where individuals were grown in the presence of extracts of two P. agardhii strains. We monitored daily life-history parameters of D. magna individuals subjected to microcystin-RR (MC-RR), intracellular and extracellular extracts of a microcystin-producing strain (MC-strain, PMC 75.02) and a microcystin-free strain (MC-free strain, PMC 87.02) of P. agardhii. Measured life-history parameters of D. magna were used to build population dynamics models and compute expected population growth rate, replacement rate, generation time and proportion of adult and juveniles at demographic equilibrium. Results show that MC-RR tends to slow the life history (reduced growth rate and larger proportion of adults). In contrast, intracellular extracts of the two strains tend to accelerate the life history (increased growth rate, decreased generation time and lower proportion of adults). Extracellular extracts produce the same trends as the intracellular extracts but to a lesser extent. However, the MC-strain has stronger effects than the MC-free strain. Interestingly, extracellular extracts of the MC-free strain may have effects comparable to pure MC-RR. Moreover, in the presence of MC-RR and both cyanobacterial extracts, the daily fecundities present a cyclic pattern. These results suggest that MC-RR and unknown metabolites of cyanobacterial extracts have negative effects on D. magna reproduction processes such as those observed with endocrine-disruptive molecules.

Multiple origins of European populations of the giant liver fluke Fascioloides magna (Trematoda: Fasciolidae), a liver parasite of ruminants

The giant liver fluke, Fascioloides magna, a liver parasite of free-living and domestic ruminants of Europe and North America, was analysed in order to determine the origin of European populations and to reveal the biogeography of this originally North American parasite on the European continent. The variable fragments of the mitochondrial cytochrome c oxidase subunit I (cox1; 384bp) and nicotinamide dehydrogenase subunit I (nad1; 405bp) were used. Phylogenetic trees and haplotype networks were constructed and the level of genetic structuring was evaluated using population genetic tools. In F. magna individuals originating from all European foci of infection (Italy, Czech Republic and Danube floodplain forests involving the territories of Slovakia, Hungary and Croatia) and from four of five major North American enzootic areas, 16 cox1 and 18 nad1 haplotypes were determined. The concatenated sequence set produced 22 distinct haplotypes. The European fluke populations were less diverse than those from North America in that they contained proportionately fewer haplotypes (eight), while a more substantial level of genetic diversity and a greater number of haplotypes (15) were recorded in North America. Only one haplotype was shared between the European (Italy) and North American (USA/Oregon and Canada/Alberta) flukes, supporting a western North American origin of the Italian F. magna population. Haplotypes found in Italy were distinct from those determined in the remaining European localities which indicates that introduction of F. magna to the European continent occurred more than once. In the Czech focus of infection, a south-eastern USA origin was revealed. Identical haplotypes, common to parasites from the Czech Republic and from an expanding focus in Danube floodplain forests, implies that the introduction of F. magna to the Danube region came from an already established Czech focus of infection.

Effects of 4-nonylphenol, fish predation and food availability on survival and life history traits of Daphnia magna straus

This study aimed to investigate the compound effect of environmentally relevant 4-nonylphenol (NP) concentrations and natural stressors-namely fish predation and food availability-on Daphnia magna, which were exposed to four NP concentrations (0, 1, 5 and 10 microg l(-1)) under optimum or low food concentrations (1.00 and 0.075 mg C l(-1), respectively) in water (un)conditioned by a fish predator (Alburnus alburnus). A(n) "environmentally relevant" and "no observable effect" concentration (NOEC) of NP (10 microg l(-1)) resulted in a significant reduction (P < 0.01**) in daphnids' survival when it was encountered concurrently with conditions of low food availability and presence of fish predation. The significance of the results lies in the observation that not only environmentally relevant concentrations of NP but also NP concentrations reported to have no observable effect on daphnids may in reality have unexpected critical effects on D. magna survival under conditions more parallel to natural ecosystems. The deterioration of the life-history traits-namely, NP-induced delay in the age at first reproduction (P < 0.001***) and fish kairomone-induced reduction in the size at first reproduction (P < 0.001***)-of the D. magna individuals is also crucial, as such alterations could significantly influence future generations and result in ultimate adverse effects at the community level because large-bodied daphnids are key-stone species in freshwater ecosystems. The results of this study demonstrate the importance of taking into account environmentally realistic conditions while investigating the effects of NOEC levels of toxicants on non-target aquatic species.

Phototactic behavior in Daphnia magna Straus as an indicator of toxicants in the aquatic environment

In this study, the phototactic behavior of Daphnia magna was investigated as a possible bioindicator for the following 11 chemicals commonly found in the aquatic environment: benzo(b)fluoranthene, mercury (II) chloride, dimethoate, lindane, linuron, MCPA, TBTO, carbon tetrachloride, thiram, 2,4,6-trichlorophenol and arsenic trioxide. Phototactic response was monitored as the movement of 7 to 8 day-old D. magna individuals. The analysis was carried out using glass test tubes divided radially into two zones, with increasing distance from a light source. For each of the compounds, different concentrations and exposure times were analyzed, and the behavior of the D. magna in each of the treatments compared to the controls in which the chemicals were not added. Using the experimental model described here, all of the 11 chemicals could be detected following exposure times of between 15 min and 48 h. The lowest concentrations detected using this technique were between 2 and 43 times lower than the LC 50 and EC 50 values reported for D. magna. The results of this study show that the analysis of phototactism is a useful method for detecting the presence of a wide range of potentially toxic chemicals found in the aquatic environment.

Die Bedeutung der Untersuchungen des Lebenszyklus bei der Bestimmung fadenförmiger Grünalgen (Chlorophyta)

Summary Investigating the epibiontic algae growing on planctonic Entomostraca in a rural pond masses of green coloured Daphnia magna individuals were observed. The outer surface of the chitin shells of these Daphnias was densely overgrown with a small filamentous green alga resembling Protoderma daphnicola Fott . Protoderma however is a representative of pseudoparenchymatous algae with biflagellate zoospores. No one of these characters could be found in the studied alga. The alga produced under natural conditions short prostrate uni- or biseriate filaments, only sometimes with 2–3 erected cells as known in the genus Pseudendoclonium. Moreover quadriflagellate zoospores were arising. In cultures the mentioned alga produced as well prostrate as erected filaments and the plant has developed into a Stigeoclonium with all its typical features. Zoospores of two types were formed, large quadriflagellate macrozoospores and smaller quadri- or biflagellate microzoospores. The cultured Stigeoclonium belongs with regard to the prostrate system probably into the group of Stigeoclonium tenue ( Ag .) Kutzing . On this example authors call attention to the possibility of making mistakes in determination of filamentous green algae if they are not well developed. Therefore the knowledge of their whole life cycle is most important, both in nature and in culture.