Physiological effects of chronic silver exposure in Daphnia magna

Daphnia magna were exposed to a total concentration of 5.0+/-0.04 microg Ag/l, added as AgNO(3) (dissolved concentration, as defined by 0.45 microm filtration = 2.0+/-0.01 microg Ag/l) in moderately hard synthetic water under static conditions (total organic carbon = 4.80+/-1.32 mg/l) with daily feeding and water renewal, for 21 days. There was no mortality in control daphnids and 20% mortality in silver-exposed animals. Silver exposure caused a small but significant reduction of reproductive performance manifested as a 13.7% decrease in the number of neonates produced per adult per reproduction day over the 21-day exposure. However, silver exposed daphnids also exhibited a much more marked ionoregulatory disturbance, which was characterized by a 65% decrease in whole body Na(+) concentration, and an 81% inhibition of unidirectional whole body Na(+) uptake. Previous work on the acute toxicity of Ag(+) to daphnids has shown that Na(+) uptake inhibition is directly related to inhibition of Na(+),K(+)-ATPase activity. Therefore, we suggest that the Na(+) uptake inhibition seen in response to chronic silver exposure was explained by an inhibition of the Na(+) channels at the apical 'gill' membrane, since a 60% increase in whole body Na(+),K(+)-ATPase activity was observed in the chronically silver-exposed daphnids. Our findings demonstrate that, in broad view, the key mechanism involved in chronic silver toxicity in D. magna, the most acutely sensitive freshwater organism tested up to now, resembles that described for acute toxicity-i.e. ionoregulatory disturbance associated with inhibition of active Na(+) uptake, though the fine details may differ. Our results provide encouragement for future extension of the current acute version of the Biotic Ligand Model (BLM) to one that predicts chronic silver toxicity for environmental regulation and risk assessment. The results strongly suggest that Na(+) uptake inhibition is the best endpoint to determine sensitivity to both acute and chronic toxicity in the scope of future versions of the BLM for silver.     

Maternal effects after sexual reproduction in Daphnia magna

In this study we investigated the relationship between maternalsize and size of ephippial hatchlings in Daphnia magna. We observedthat larger females produce larger ephippia; these larger ephippiahave a higher hatching probability, yield larger neonates, whichin turn yield larger adults, producing more eggs. We interpretthese observations as an explanation why older and larger femalesof D.magna continue to produce ephippia despite a higher predationrisk.     

Calcium accumulation and regulation in Daphnia magna: Links with feeding, growth and reproduction

Calcium is involved in a wide variety of biological processes and has an important structural role in crustaceans. The present study aimed at exploring the possible link between Ca body concentrations and the ingestion rate and the role of soft tissue vs. total tissue Ca accumulation in Daphnia magna. D. magna was cultured for 21 days at different water Ca concentrations ranging from 3.4 to 32.5 mg/L. Every week Ca body concentrations (soft and total tissues), ingestion rate, growth, survival and reproduction were measured. Daily, algal food that was not deficient in Ca was supplied. Ca in the soft tissues represented 8 to 26% of the total Ca body concentrations. The ratio Ca in soft tissue/Ca in total tissue was generally not influenced by the Ca exposure concentration but decreased with time, i.e., age (from an average of 0.24 at day 7 to 0.09 at day 21). During week 1, a 54% decrease in Ca body concentrations was observed in daphnids exposed in medium with 3.4 mg/L Ca compared to those exposed to 32.5 mg/L. The concurrent decrease in ingestion rate was 14%. No significant differences among Ca treatments were observed during week 2 for ingestion rate and week 3 for calcium body concentrations. Also, no effects on growth and reproduction were observed, although these were expected at the lowest Ca concentration tested. It is hypothesised that Ca absorption from food in combination with an increased ingestion rate is used to maintain Ca homeostasis under Ca limiting conditions.     

The disruption of Daphnia magna sodium metabolism by humic substances: mechanism of action and effect of humic substance source

Humic substances have important functions in aquatic systems. While these roles are primarily indirect, influencing the physicochemical environment, recent evidence suggests these materials may also have direct biological actions. This study investigated the mechanism by which humic substances perturb sodium metabolism in a freshwater invertebrate, the water flea Daphnia magna. Aldrich humic acid (AHA) stimulated the maximal rate of whole-body sodium influx (Jmax) when experimental pH was 6 and water calcium content was 0.5 mM. This effect persisted at pH 8 and 1 mM calcium but not at pH 8 in the absence of calcium. An indirect action of AHA on apical transporter activity was proposed to explain this effect. At pH 4 AHA promoted a linear sodium uptake kinetic relationship, attributed to altered membrane permeability due to enhanced membrane binding of humic substances at low pH. In contrast, a real-world natural organic matter sample had no consistent action on sodium influx, suggesting that impacts on sodium metabolism may be limited to commercially available humic materials. These findings question the applicability of commercially available humic substances for laboratory investigations and have significant implications for the study of environmental metal toxicity.     

The effect of humic substances on the toxicity of copper and zinc for Daphnia magna]

The results of laboratory experiments of humic matter influence on toxic resistance of Daphnia magna to zinc and copper using water samples from a few Karelia water bodies are presented. The increasing of humic matter content in water samples has been shown to promote the binding of a part of metals in organic complexes that leads to decrease of their toxicity for hydrobionts.     

有毒和无毒微囊藻对大型溞生长和繁殖的影响

近年来,随着工农业的快速发展和人们生活水平提高,一些城市生活污水和工农业废水流入江河、湖泊等淡水水体中,加剧了水体的富营养化和污染,导致蓝藻过度生长繁殖而形成水华,其中最常见的是微囊藻水华[1,2].     

Effects of fluoride on growth, reproduction and survival in Daphnia magna

The effects of waterborne fluoride (NaF) on growth, reproduction and survival in Daphnia magna were studied from subnormal to toxic concentrations in hard reconstituted water. The 24- and 48-hr EC50S for immobilization were 205 and 98 mg F (fluoride) 1(-1). Median survival times for fed and unfed Daphnia were reduced at concentrations of F above 8.9 and 10 mg F1(-1), respectively. Growth, determined as body length after 7 and 21 days, was partially inhibited at all concentrations above 3.7 mg F1(-1). Parthenogenetic reproduction was stimulated by all concentrations (dilution factor 0.5) between 0.45 X 10(-3) mg F1(-1) and 3.7 mg F1(-1) and inhibited by all concentrations above 3.7 mg F1(-1), compared to the control with no waterborne fluoride. The highest concentration with a reproduction (number of live progeny/live female) equivalent to the control after 21 days was 4.4 mg F1(-1). However, a progressive decline in reproduction between 14 and 21 days indicates a slight long-term inhibition above 0.58 mg F1(-1). The "safe" concentration equivalent to the geometric mean of NOEC or MATC for D. magna in hard water is 4.4 mg F1(-1), derived as ZEP, the Zero Equivalent Point, for reproduction after 21 days.     

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.     

不同藻类对大型溞存活和生殖的影响

通过生命表技术观察了大型溞（Daphnia magna）在实验室恒定温度（25 ℃）下分别以梅尼小环藻、铜绿微囊藻905、铜绿微囊藻469和斜生栅藻为饵料时的存活率和生殖量变化,并据此探讨了不同藻类对大型溞生活史特征的影响。结果表明：大型溞食用梅尼小环藻和铜绿微囊藻469后生长良好,大型溞在斜生栅藻中也能较好生长,而铜绿微囊藻905对大型溞的生长和繁殖均有不良影响;大型溞对不同藻类的净生殖率(R₀)、世代历期(T)和内禀增长率(r_m)及存活率有不同的影响,梅尼小环藻分别为44.35、11.86、0.32、5%;铜绿微囊藻469分别为48.20、14.25、0.27、30%;斜生栅藻分别为8.10、12.47、0.17、15%;铜绿微囊藻905分别为0、0、0、0。     

Effects of endosulfan on survival,growth and reproduction of Daphnia magna

1. Acute and chronic toxicity tests with endosulfan were conducted on Daphnia magna. The 24-hr static lc₅₀ was 0.62 mg/l with a coefficient of variation of 14.2%.2. The sublethal effects of 0.12, 0.15, 0.20, 0.25 and 0.31 mg/l endosulfan on the survival, reproduction and growth of D. magna were monitored for 21 days.3. The parameters used to determined the effect of the pesticide on reproduction were: mean total young per female, maximum number of broods, mean brood size, mean number of broods, mean time to first reproduction and intrinsic rate of natural increase (r).4. Growth, as measured by body length, was depressed significantly at all endosulfan concentrations tested. The highest concentrations used (0.20, 0.25 and 0.31 mg/l) caused a decrease in survival and mean total young per female, and an increase in the time to first reproduction. The intrinsic rate of natural increase (r) and the mean number of broods were decreased significantly at all the sublethal concentrations of endosulfan tested.     

Effects of algal food quality on sexual reproduction of Daphnia magna

The objective of our study was to investigate sexual reproduction of Daphnia magna associated with mating behaviors and hatching rates, according to different algal food sources. Since a diatom is known to contain more abundant long‐chain poly unsaturated fatty acids (PUFAs), we hypothesized that the diatom‐consuming D. magna would exhibit more successful reproduction rates. Upon the hypothesis, we designed three experiments using two algal species, a green alga (Chlorella vulgaris) and a diatom (Stephanodiscus hantzschii). From the results, we found that the mating frequency and copulation duration increased in the treatment with S. hantzschii, resulting in a significant increase of hatching rates of resting eggs. In the other two repetitive mating strategies (e.g., one female vs. multiple males, and one male vs. multiple females), we found that the hatching rates of resting eggs were greater in the S. hantzschii treatment. In addition to the mating strategy, male body size significantly increased in the diatom treatment, hence average diameter of penis was also statistically different among the treatments (greater diameter in the S. hantzschii treatment). To examine the effect of algal food quality, we estimated quantity of fatty acids in the two algal species. Our result showed that S. hantzschii had a higher proportion of long‐chain PUFAs than C. vulgaris. Furthermore, a stable isotope analysis revealed that carbon and nitrogen originated from S. hantzschii were more assimilated to D. magna. In summary, our study manifested that diatom consumption of D. magna leads to more successful sexual reproduction. We then discussed how the diatom consumption of zooplankton influences food web dynamics in a freshwater ecosystem.     

Protective effects of ectoine on heat-stressed Daphnia magna

Ectoine (ECT) is an amino acid produced and accumulated by halophilic bacteria in stressful conditions in order to prevent the loss of water from the cell. There is a lack of knowledge on the effects of ECT in heat-stressed aquatic animals. The purpose of our study was to determine the influence of ECT on Daphnia magna subjected to heat stress with two temperature gradients: 1 and 0.1 °C/min in the range of 23–42 °C. Time to immobilisation, survival during recovery, swimming performance, heart rate, thoracic limb movement and the levels of heat shock protein 70 kDa 1A (HSP70 1A), catalase (CAT) and nitric oxide species (NOx) were determined in ECT-exposed and unexposed daphnids; we showed protective effects of ECT on Daphnia magna subjected to heat stress. Time to immobilisation of daphnids exposed to ECT was longer when compared to the unexposed animals. Also, survival rate during the recovery of daphnids previously treated with ECT was higher. ECT significantly attenuated a rapid increase of mean swimming velocity which was elevated in the unexposed daphnids. Moreover, we observed elevation of thoracic limb movement and modulation of heart rate in ECT-exposed animals. HSP70 1A and CAT levels were reduced in the presence of ECT. On the other hand, NOx level was slightly elevated in both ECT-treated and unexposed daphnids, however slightly higher NOx level was found in ECT-treated animals. We conclude that the exposure to ectoine has thermoprotective effects on Daphnia magna, however their mechanisms are not associated with the induction of HSP70 1A.     

1,8-二羟基蒽醌对大型溞的毒性效应

The study on the acute,sublethal and chronic toxicity of 1,8-dihydroxyanthraquinone (1,8-dihAQ) to Daphnia magna showed that the 48 h LC₅₀ was 0.37 mg稬^-1,and the feeding behavior of Daphnia magna was severely affected by the compound.When exposed to 0.2 mg稬^-1 of 1,8-dihAQ for 5 h,the filtration and ingestion rate of Daphnia magna was inhibited by 97%.Chronic toxicity test results indicated that the reproduction ability decreased dramatically after exposing to sublethal concentration of 1,8-dihAQ.It could be inferred that reproduction parameters and intrinsic rate of natural increase were the sensitive parameters in characterizing sublethal toxicity.The NOEC and LOEC values for reproduction parameters were also given.     

Long-term temperature acclimation in Daphnia magna: effects on filtering rates

Populations of a laboratoiy clone of Daphnia magna were acclimatedat 5, 10, 15 and 24C, and a varying temperature regin for aminimum of 70 days. The effect of temperature (5–25C)on filtering rates was measured for animals acclimated to theconstant temperatures and for a wild population collected froma reservoir. Acclimation temperature strongly influenced ffltcrmgrates at test temperatures. Animals with acclimation temperaturesclosest to the test temperature tended to have highest filteringrates at that temperature.     

Food availability modulates temperature‐dependent effects on growth,reproduction, and survival in Daphnia magna

Reduced body size and accelerated life cycle due to warming are considered major ecological responses to climate change with fitness costs at the individual level. Surprisingly, we know little about how relevant ecological factors can alter these life history trade‐offs and their consequences for individual fitness. Here, we show that food modulates temperature‐dependent effects on body size in the water flea Daphnia magna and interacts with temperature to affect life history parameters. We exposed 412 individuals to a factorial manipulation of food abundance and temperature, tracked each reproductive event, and took daily measurements of body size from each individual. High temperature caused a reduction in maximum body size in both food treatments, but this effect was mediated by food abundance, such that low food conditions resulted in a reduction of 20% in maximum body size, compared with a reduction of 4% under high food conditions. High temperature resulted in an accelerated life cycle, with pronounced fitness cost at low levels of food where only a few individuals produced a clutch. These results suggest that the mechanisms affecting the trade‐off between fast growth and final body size are food‐dependent, and that the combination of low levels of food and high temperature could potentially threaten viability of ectotherms.     

Effects of copper on growth, reproduction, survival and haemoglobin in Daphnia magna

The effects of additions of CuSO4 X 5H2O to final concentrations between 0.0004 and 105 micrograms Cu l-1 on growth, reproduction, survival and haemoglobin content of Daphnia magna were studied in hard reconstituted water and compared to the response in the dilution water without addition of copper. Concentrations of copper are nominal values. The 48-hr EC50 (immobilization) for unfed neonates was 6.5 micrograms Cu l-1 and the 48-hr and 21-day LC50 for fed neonates were 18.5 and 1.4 microgram Cu l-1, respectively. Growth expressed as body length of juveniles after 7 days and adult females after 21 days was only reduced in survivors at the highest non-lethal concentration (6.6 micrograms Cu l-1). Reproduction was stimulated by low concentrations of copper. Optimal reproduction after 21 days was found between 0.001 and 0.1 microgram Cu l-1. Higher concentrations were partially inhibitory (0.4 microgram Cu l-1), stimulatory (0.8 and 1.6 microgram Cu l-1) or completely inhibitory (3.2 micrograms Cu l-1 and above). The stimulatory peak around 1 microgram Cu l-1 was accompanied by a reduced survival (above 0.4 microgram Cu l-1). The Zero Equivalent Point (ZEP) for reproduction at non-reduced survival was 0.23 microgram Cu l-1. This concentration should be "safe" for D. magna under prevailing conditions (reconstituted water with a hardness of 250 mg l-1 as CaCo3 and a synthetic diet based on fish food and baby gruel). The haemoglobin content was affected by copper in a complex pattern which was not related to growth, reproduction or survival.     

Mechanisms of energy allocation to reproduction in the cladoceran Daphnia magna Straus

Understanding rules of resource allocation within individuals is helpful in explaining population dynamics. This is particularly the case under the conditions of resource limitation that are commonly experienced by zooplankton. Here, we evaluate assumptions underlying models of resource allocation in Daphnia and test the predictions of two models of response to starvation.
We also test the predictions of two simple models concerning the mechanisms of egg provisioning in Daphnia magna. Our results: (1) demonstrate that provisioning is discontinuous, occurring over a discrete period of the instar; (2) support the hypothesis that egg production occurs in a serial fashion; (3) show that Daphnia magna responds to starvation by ceasing egg production but that there is an increase in mean size of eggs provisioned during the instar, prior to starvation; and (4) broadly support predictions that the response of Daphnia to starvation is an instantaneous cessation of reproduction but that there is a time lag before death.     

The use of inorganic substances to stimulate gut evacuation in Daphnia magna

Observations were done on the effect of inorganic substances on the gut evacuation process in Daphnia magna. Procedures which accelerate this process are described.     

Effects of waterborne iron on growth, reproduction, survival and haemoglobin in Daphnia magna

The effects of waterborne iron (FeCl3 X 6H2O) on growth, reproduction, survival and haemoglobin content in Daphnia magna were studied from subnormal to toxic concentrations in hard reconstituted water. Low concentrations of iron stimulated reproduction and haemoglobin synthesis after chronic exposure for 21 days. Maximum reproduction occurred between 0.1 and 1 microgram Fe 1(-1). Juvenile growth was not stimulated by iron but was slightly inhibited between 1 and 8 micrograms Fe 1(-1) and above 128 micrograms Fe 1(-1). A slight inhibition of growth persisted for 21 days. Total haemoglobin content was above the control with no waterborne iron at all but one concentration (512 micrograms Fe 1(-1]. The highest value (3.8 X control value) was found at 2 micrograms Fe 1(-1). The haemoglobin content decreased between 64 and 512 micrograms Fe 1(-1) and increased at higher concentrations. The decrease coincided with an inhibited reproduction. The increase was found in non reproductive survivors. A comparison with a previous study in D. magna suggests that ambient conditions (hardness and pH) and ageing of the water are important for the effects of waterborne iron. At a hardness of 250 mg 1(-1) as CaCO3 and a pH range of 7.0-8.0 the ZEP (Zero Equivalent Point) for reproduction was 158 micrograms Fe 1(-1). Continuous exposure to higher concentrations is expected to lead to extinction of a D. magna population.     

温度和种间竞争对大型溞种群动态和两性生殖的影响

在20℃、25℃下,将大型溞和老年低额溞分别按7+3(B组),5+5(C组),3+7(D组)的组合进行混合培养,以及用单种培养(10+0(A组),0+10(E组))作为对照,研究了温度和种间竞争对大型溞种群动态和两性生殖的影响.实验结果表明:在混合培养时,大型溞对老年低额溞产生明显的竞争优势.20℃、25℃下,单种培养的老年低额溞最大种群密度分别为大型溞的2.31和1.97,而在混合培养下老年低额溞的种群密度明显低于大型溞,在实验25d后几乎全部死亡.25℃下两种溞的种群密度之间存在极显著的负相关性(C组:r=-0.508,n=30,P<0.01;D组:r=-0.483,n=30,P<0.01).在20℃、单种培养下,大型溞在首次产幼溞时即出现雄体,且种群密度与雄体密度呈显著的相关性(r=0.678,n=24,P<0.01).大型溞的最大雄体密度(106 ind.(200ml)~(-1))和最大雄体比例(36.8%)均出现在20℃、单种培养下.25℃下,大型溞在混合培养的B组和C组首次产幼溞时即出现雄体,且雄体在混合培养B组的比例达28.2%.大型溞在25℃、单种培养下没有产生卵鞍,在混合培养下总计产生66个卵鞍,其中空卵鞍占51.5%,而在20℃、混合培养下没有卵鞍产生.实验结果暗示:在较高的温度下,种间竞争刺激了大型溞雄体的产生和卵鞍的形成,高密度的雄体有助于大型溞孤雌生殖雌体向两性生殖雌体的转化.