Daphnia magna as a test animal in acute and chronic toxicity tests

Daphnia magna is a commonly used test animal in aquatic toxicology.Test procedures for acute and chronic test are described, together with the influence of several variables on their results.The practicability of the methods was checked with four model compounds, viz. 1,1,2-trichloroethane, dieldrin, pentachlorophenol and 3,4-dichloroaniline. Toxicity data of these compounds for Daphnia magna are given.     

Effect of food concentration on the chronic toxicity of sodium dodecyl sulphate to Daphnia magna

Food concentration supplied during subchronic and chronic toxicity tests, is one of the most important factors that might influence the response of test organisms to toxicants. The green microalga Scenedesmus incrassatulus was used as food for the cladoceran Daphnia magna, in a chronic toxicity test with the toxicant sodium dodecyl sulphate (SDS). Test concentrations were 0.625, 1.25, and 2.5 mg l^-1 of SDS, equivalent to 1/40, 1/20, and 1/10 of the average 48-h LC50 previously determined. Food concentrations were 9.5, 19, and 38 mg l^-1 (dry wt.). Survival and reproduction were recorded, and the data were analyzed using a life-table approach. After 55 days, the main findings were as follows:

Toxicity of the new pyrethroid insecticide,deltamethrin, to Daphnia magna

The toxicity of deltamethrin, a synthetic pyrethroid insecticide, was determined under standardized conditions (ISO, 1982) in neonates and juveniles of Daphnia magna. Neonates (6 to 24 h old) were more sensitive than juveniles (48 to 72 h old). The 24- and 48-h EC₅₀s (immobilization) in neonates were 0.113 and 0.031 µg l^–1, respectively. The toxicity of deltamethrin was highly toxic. The 96-h EC₅₀ was in the ppt (µg l^–1) range. Toxicity tests with Daphnia may be used to detect toxic residues in water and sediment in areas treated with deltamethrin and other highly toxic pyrethroid pesticides.     

The influence of Nickel on population dynamics and on some demographic parameters of Daphnia magna

Daphnia magna was cultured with two different techniques at sublethal nickel concentrations from 0 up to 200 µg Ni l^-1. The results of the experiments run with cohorts of single individuals in static cultures were compared with the results obtained with populations held in flow through cultures. The most sensitive demographic parameters in cohorts were life span, the total number of progeny and the achievable maximum body length. The investigated nickel concentrations lowered the mean animal density in populations. Size class distribution was affected and the oscillation of the percentage of ovigorous adults increased with increasing nickel concentrations. In 200 µg Ni l^-1 one population extincted. Individuals in static cultures exposed to the same nickel concentration produced at least two neonates. Both employed techniques are discussed.     

Population dynamics of Daphnia magna as modified by chronic bromide stress

Two chronic toxicity experiments were conducted with Daphnia magna. In a semi-static experiment with cohorts, the no effect level for bromide in respect of the intrinsic rate of natural increase (derived from age-specific survival and fecundity) was 10 mg l^–1. A second test was started with small populations in an intermittent-flow system. These populations had a stable age distribution, were composed of cohorts of different ages, and showed an almost perfect logistic growth. Model calculations showed that bromide reduced the upper numerical limit (carrying capacity). It also increased the time-lag required to attain the maximum reproduction rate. For the first parameter, a no effect level of 14 mg l^–1 was calculated. For the latter a threshold could not be detected. The EC₅₀ and EC₁₀ were 27 and 18 mg l^–1, respectively. Additional experiments showed that individual growth of D. magna in time could also be described by a logistic equation. The age structure of the populations changed when food became limiting. This was parallelled by a reduction of the mean brood size. In conclusion it is stated that the results of the toxicity studies with populations support Halbach's view (1984), that population dynamics can be used like a magnifying glass to detect small sublethal ecotoxicological effects of environmental pollutants.     

Toxicity of metal polluted sediments to Daphnia magna and Tubifex tubifex

Sediments from four lakes polluted by effuents from steel industries and from two reference lakes were investigated. The sediments contained elevated concentrations of oil, Pb, Cd, Hg, Zn, Ni and Cr in different combinations. The toxicity of the polluted sediments to Daphnia was much higher than reported elsewhere (24-h LC50 0.5–1.5 vol%). Tubifex survived more than 3 months in the polluted sediments, but growth and reproduction were inhibited.     

The effect of parthenogenic eggs in Daphnia magna on prey location by the bluegill sunfish (Lepomis macrochirus)

The distance at which the bluegill sunfish (Lepomis macrochirus) can locate Daphnia magna with parthenogenic eggs is shown to be significantly greater than the reactive distance for non-gravid Daphnia of the same size. This difference is due to greater visibility of the gravid prey and not to different locomotor behavior, since there was no correlation between the number of eggs carried by a Daphnia and the antennal beat frequency. Based on this experiment and other observations, an explanation is given for selective predation of polymorphic cladoceran populations.     

Automated Recording of Vertical Negative Phototactic Behaviour in Daphnia magna Straus (Crustacea)

Diurnal vertical migration is a well-known phenomenon in the circadian activity rhythms of zooplankton. Our goal was to test whether negative phototaxis in Daphnia magna clone BEAK (provoked by artificially induced light stress, alternating light and dark phases in 2 h intervals), and its interference with the endogenous rhythm of diurnal vertical migration, can be automatically registered with a biomonitor. For the first time the vertical swimming behaviour of D. magna was recorded quantitatively based on non-optical data recording in a fully automated biotest system, the Multispecies Freshwater Biomonitor in a new experimental setup consisting of a column of three recording units (3-level chambers). Circadian vertical migration was clearly recorded in the 3-level chambers and the rhythm was more clear with 5 than with 1 organism per chamber. The organisms clearly responded to induced light stress with negative phototaxis, however best in larger chambers. The artificially induced rhythm was influenced by the endogenous rhythm. This approach may facilitate long-term observations of vertical swimming activity of zooplankton in the future.     

The effects of low pH on the respiration of Daphnia magna Straus.

The effect of low pH values on Daphnia magna is shown to severely depress the O₂ uptake rates. The reason for this is discussed with respect to a decrease in the ability of the gills to exchange CO₂ with the surrounding medium due to a reduction in the CO₂ diffusion gradient as a result of increasing acidity. Respiration in CO₂ free water at acid pH values is shown to be apparently unaffected.     

An estimation of the heritability of phototaxis in Daphnia magna Straus

Summary The phototactic responses of four clones of Daphnia magna were experimentally analysed. Broad-sense heritability of this behavioural character was estimated through an analysis of variance, and it was very high under the standardised experimental conditions of this study.     

The use of biomarkers in Daphnia magna toxicity testing

We investigated the effect of short-term exposure to cadmium and 2,4-dichlorophenoxy acetic acid on the digestive physiology of Daphnia magna and the consequences for the bioenergetics of the organism. In both cases, ingestion was more drastically reduced compared to digestive enzyme activity. Furthermore a differential shift in catabolism was noted: in general polysaccharidases were less affected than the enzymes responsible for protein and lipid digestion. Comparison of the ‘1 h in vivo fluorescence’ criterion (Janssen & Persoone, 1993) with the ingestion and digestive enzyme activity revealed that this rapid screening assay should be considered as a quantification of ingestion inhibition rather than a methodology assessing digestive enzyme inhibition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of river sediment elutriates on Daphnia magna

Laboratory sediment bioassays, both acute and chronic, were conducted on sediment elutriates from the River Eurajoki, SW Finland. The river is under impacts of industrial discharges, community effluents and agricultural run-offs. The water flea Daphnia magna Straus was used as a test organism. None of the elutriates tested were acutely toxic. In a long-term bioassay sediment elutriates had effects on survival, body growth and reproduction. Elutriates prepared from samples of a downstream station were characterized by low survival, small body size, reduced total offspring production, and delayed start of reproduction.     

The effect of temperature on maturation threshold body-length in Daphnia magna

Aquatic invertebrates are usually larger at maturity when water temperatures are lower. For the freshwater cladoceran Daphnia, it has been suggested that a threshold size must be attained to initiate maturation, which results two instars later in the deposition of eggs into the brood chamber. This threshold size is believed to temperature on maturation threshold body-length in Daphnia magna. Daphnids were raised from birth to maturity under three constant-temperature regimes (12°C, 16°C, 22°C), and two food-level conditions. Animals were measured daily, and a body-length based maturation threshold determined for each individual. We demonstrate that mean maturation threshold length is negatively correlated with ambient water temperature. Further, daphnids with a larger threshold length tended to be larger at maturity. A maturation threshold linked to body length suggests that reduced variation in size at maturity is adaptive, even at the cost of additional variation in instar number or age at maturity.     

The oculomotor system of Daphnia magna

Summary The highly mobile cyclopic compound eye of Daphnia magna is rotated by six muscles arranged as three bilateral pairs. The three muscles on each side of the head share a common origin on the carapace and insert dorsally, laterally and ventrally on the eye. The dorsal and ventral muscles are each composed of two muscle fibers and the lateral muscle is composed of from two to five fibers, with three the most common number. Individual muscle fibers are spindle-shaped mononucleated cells with organized bundles of myofilaments. Lateral eye-muscle fibers are thinner than those of the other muscles but are otherwise similar in ultrastructure. Two motor neurons innervate each dorsal and each ventral muscle and one motor neuron innervates each lateral muscle. The cell bodies of the motor neurons are situated dorsally in the supraesophageal ganglion (SEG) and are ipsilateral to the muscles they innervate. The dendritic fields of the dorsal-muscle motor neurons are ipsilateral to their cell bodies; those of the ventral-muscle motor neurons are bilateral though predominantly contralateral. The central projections of the lateral-muscle motor neurons are unknown. In the dorsal and ventral muscles one motor axon synapses principally with one muscle fiber; in each lateral muscle the single motor axon branches to, and forms synapses with, all the fibers. The neuromuscular junctions, characterized by pre- and postsynaptic densities and clear vesicles, are similar in all the eye muscles.     

Experimental evidence of negative interference in Daphnia magna

Individuals of Daphnia magna Straus living together in groups were found to influence each other in a density-dependent manner. The effect appeared as an inhibition in offspring production and was demonstrated to be induced in part or completely by metabolic products released by Daphnia itself (negative interference). Negative interference was measurable even when there were only two individuals in 50 ml medium (40 animals · 1^–1) and increased up to a density of six animals per 50 ml (120 animals · 1^–1). Also, animals living singly in Daphnia-conditioned water showed a decrease in reproduction. For the measurements a cascade of vessels was developed in which flow-through conditions ensured a constant concentration of algae throughout the system.     

Reproducibility of short-term and reproduction toxicity experiments with Daphnia magna and comparison of the sensitivity of Daphnia magna with Daphnia pulex and Daphnia cucullata in short-term experiments

Short-term toxicity tests with Daphnia magna are reasonably reproducible. The sensitivity of Daphnia pulex, Daphnia cucullata and Daphnia magna proved to be about the same in short-term tests with 15 different chemical compounds.Reproduction toxicity experiments with Daphnia magna can easily be carried out within three weeks. At least duplicate experiments are necessary to arrive at an approximate no-effect level.     

The genetics of phototaxis in Daphnia magna: Existence of three phenotypes for vertical migration among parthenogenetic females

Using a cloning technique, we revealed the existence of three phototactically distinct types in Daphnia magna, viz. negatives, positives, and gipsies. The latter migrate continuously between a low and a high light intensity. The expression of this behaviour is genetically determined, although positives and negatives can reversibly switch into gipsies.It is proposed that two opposite genotypes exist, with the gipsy behaviour epigenetically induced. All juveniles behave more or less uniformly, irrespective of their origin. The phototactic responses develop rather late during ontogenesis.     

Top-down control of natural phyto- and bacterioplankton prey communities by Daphnia magna and by the natural zooplankton community of the hypertrophic Lake Blankaart

Biomanipulation, through the reduction of fish abundance resulting in an increase of large filter feeders and a stronger top-down control on algae, is commonly used as a lake restoration tool in eutrophic lakes. However, cyanobacteria, often found in eutrophic ponds, can influence the grazing capacity of filter feeding zooplankton. We performed grazing experiments in hypertrophic Lake Blankaart during two consecutive summers (1998, with and 1999, without cyanobacteria) to elucidate the influence of cyanobacteria on the grazing pressure of zooplankton communities. We compared the grazing pressure of the natural macrozooplankton community (mainly small to medium-sized cladocerans and copepods) with that of large Daphnia magna on the natural bacterioplankton and phytoplankton prey communities. Our results showed that in the absence of cyanobacteria, Daphnia magna grazing pressure on bacteria was higher compared to the grazing pressure of the natural zooplankton community. However, Daphnia grazing rates on phytoplankton were not significantly different compared to the grazing rates of the natural zooplankton community. When cyanobacteria were abundant, grazing pressure of Daphnia magnaseemed to be inhibited, and the grazing pressure on bacteria and phytoplankton was similar to that of the natural macrozooplankton community. Our results suggest that biomanipulation may not always result in a more effective top-down control of the algal biomass.     

An analysis of the phototactic behaviour of Daphnia magna clones and their sexual descendants

Daphnia magna clones, isolated from different natural populations, were inbred and crossbred. Some aspects of the heredity of the phototactic behaviour, quantified by an index, were analysed. Heritability in the broad sense was determined for several assemblages of clones through calculation of the clonal repeatability. Heritability sensu strictu was determined by offspring-parent regressions. Frequency distributions of a phototactic index of several inbred and crossbred families are given.The results indicate a significant contribution of additive genetic variance to the total phenotypic variance. Comparison of heritability estimates suggests an important genetic interaction component.Some implications of these results on the variability of vertical migration patterns in natural populations are discussed.     

A laboratory study of the feeding of Mesostoma lingua (Schmidt) (Turbellaria: Neorhabdocoela) on Daphnia magna Straus at four different temperatures

Mesostoma lingua eats 0.8 Daphnia magna at 15 °C, and 2.04 at 30 °C. Below 0.5 Daphnia per day (D d^–1) hunger occurs, at any temperature, and mortality increases sharply. The functional response curve appears to be linear, but saturation was not fully reached at 5 D d^–1, the highest food level applied in the present study. All food regimes (above hunger level) and temperature regimes differed significantly from each other; factor interactions were of increasing importance at higher temperatures.Longevity, above hunger level, decreased with temperature. Peak longevity at low temperature may be weakly associated with relatively low food levels.