上海滴水湖两种枝角类牧食对浮游植物群落影响的模拟研究

于2012年9月通过浮游动物添加实验,研究了大型溞(Daphnia magna)和隆腺溞(Daphnia carinata)对上海滴水湖浮游植物群落结构的影响.结果表明,实验组氨氮和可溶性活性磷浓度与空白组相比显著增加,大型溞组浮游植物密度较空白组降低了70.3％,隆腺溞组浮游植物密度较空白组降低了80.0％,叶绿素a浓度分别下降了80.4％和75.2％,叶绿素a与氨氮、可溶性活性磷呈显著相关性.浮游植物的群落结构较空白组也发生较大变化,硅藻、蓝藻和绿藻密度比例明显降低,隐藻、裸藻和甲藻在实验结束时没有检出,说明大型溞和隆线溞能有效控制水体中浮游植物密度,并能够对浮游植物群落结构产生影响.同时,附着藻类密度较空白组也有明显减少,说明大型溞和隆线溞对附着藻类也有一定的牧食作用.     

Oxygen preference of Daphnia magna is influenced by Po2 acclimation and biotic interactions

Oxygen preference of the planktonic crustacean Daphnia magna was observed within an oxygen gradient. Long-term acclimation to specific oxygen conditions determined the preferred oxygen tension. Animals from hypoxic acclimation stayed in oxygen-poor water at first. They chose oxygen tensions above the critical partial pressure, thus maintaining aerobic energy supply, but they avoided higher oxygen concentrations. However, they gradually took more oxygen-rich positions within 2 d. Animals from severe hypoxic and hyperoxic acclimation showed stenoxic behavior. Specimens raised in moderately hypoxic or normoxic medium spread out more widely in the oxygen gradient (euryoxic behavior). The possible role of hemoglobin and antioxidant defense capacity limiting the animals' distribution at low or high oxygen concentrations, respectively, is discussed. In tests with mixed groups of D. magna from opposing oxygen acclimation conditions, the animals clustered at intermediate oxygen conditions. However, the acclimation condition of the major group was found to determine the position taken within the gradient to a greater extent. Selected oxygen tensions were closer to the preference values of the larger group, yet the influence of the minority prevented the majority in heterogeneous groups from taking their originally determined preference position. Thus, aggregation behavior interfered with the acclimation-dependent oxygen preference behavior.     

Supplementation with sterols improves food quality of a ciliate for Daphnia magna

Experimental results provide evidence that trophic interactions between ciliates and Daphnia are constrained by the comparatively low food quality of ciliates. The dietary sterol content is a crucial factor in determining food quality for Daphnia. Ciliates, however, presumably do not synthesize sterols de novo. We hypothesized that ciliates are nutritionally inadequate because of their lack of sterols and tested this hypothesis in growth experiments with Daphnia magna and the ciliate Colpidium campylum. The lipid content of the ciliate was altered by allowing them to feed on fluorescently labeled albumin beads supplemented with different sterols. Ciliates that preyed upon a sterol-free diet (bacteria) did not contain any sterols, and growth of D. magna on these ciliates was poor. Supplementation of the ciliates' food source with different sterols led to the incorporation of the supplemented sterols into the ciliates' cells and to enhanced somatic growth of D. magna. Sterol limitation was thereby identified as the major constraint of ciliate food quality for Daphnia. Furthermore, by supplementation of sterols unsuitable for supporting Daphnia growth, we provide evidence that ciliates as intermediary grazers biochemically upgrade unsuitable dietary sterols to sterols appropriate to meet the physiological demands of Daphnia.     

Changes in food quality of the green alga Scenedesmus induced by Daphnia infochemicals: biochemical composition and morphology

1. The effects of Daphnia infochemicals on the morphology and biochemical composition of Scenedesmus were studied and subsequently their influence on Daphnia life history. Three species of Scenedesmus ( S. acutus, S. obliquus and S. subspicatus ) were tested for Daphnia -induced colony formation. Life history experiments were performed with Daphnia cucullata and D. magna feeding on unicellular or colonial S. acutus.
2. Colony formation was promoted when S. acutus and S. obliquus were exposed to filtered water from a D. magna culture. S. subspicatus did not form colonies when exposed to culture water, but showed some colony formation when exposed to live D. magna.
3. No clear differences were found in total lipid, protein or carbohydrate content between the unicellular and colonial ecomorphs of the three Scenedesmus species. However, fatty acid (FA) concentration and composition were changed. Total FA as a percentage of frozen dry weight (DW) were increased in colonies. The ratio of monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA) and the ratio of ω3 : ω6 fatty acids decreased in colonies.
4. A short-term grazing experiment with three size classes of Scenedesmus revealed lower clearance rates for small Daphnia when feeding on large colonial Scenedesmus.
5. Life history parameters of both Daphnia species were influenced by food type. The intrinsic rate of population increase ( r) was significantly lower for daphnids feeding on colonies.
6. The negative influence of colonial Scenedesmus on population growth of Daphnia seems to be determined by algal morphology rather than biochemical composition.     

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.     

Molecular mass of macromolecules and subunits and the quaternary structure of hemoglobin from the microcrustacean Daphnia magna

The molecular masses of macromolecules and subunits of the extracellular hemoglobin from the fresh-water crustacean Daphnia magna were determined by analytical ultracentrifugation, multiangle laser light scattering and electrospray ionization mass spectrometry. The hemoglobins from hypoxia-incubated, hemoglobin-rich and normoxia-incubated, hemoglobin-poor Daphnia magna were analyzed separately. The sedimentation coefficient of the macromolecule was 17.4 +/- 0.1 S, and its molecular mass was 583 kDa (hemoglobin-rich animals) determined by AUC and 590.4 +/- 11.1 kDa (hemoglobin-rich animals) and 597.5 +/- 49 kDa (hemoglobin-poor animals), respectively, determined by multiangle laser light scattering. Measurements of the hemoglobin subunit mass of hemoglobin-rich animals by electrospray ionization mass spectrometry revealed a significant peak at 36.482 +/- 0.0015 kDa, i.e. 37.715 kDa including two heme groups. The hemoglobin subunits are modified by O-linked glycosylation in the pre-A segments of domains 1. No evidence for phosphorylation of hemoglobin subunits was found. The subunit migration behavior during SDS/PAGE was shown to be influenced by the buffer system used (Tris versus phosphate). The subunit mass heterogeneity found using Tris buffering can be explained by glycosylation of hemoglobin subunits. Based on molecular mass information, Daphnia magna hemoglobin is demonstrated to consist of 16 subunits. The quaternary structure of the Daphnia magna hemoglobin macromolecule was assessed by three-dimensional reconstructions via single-particle analysis based on negatively stained electron microscopic specimens. It turned out to be much more complex than hitherto proposed: it displays D4 symmetry with a diameter of approximately 12 nm and a height of about 8 nm.     

Development of empirical feeding models for a benthic predator

Feeding on Chironomus riparius, Glyptotendipes paripes (Chironomidae). and Daphnia magna by the predatory freshwater leech, Nephelopsis obscura , was investigated in the laboratory and predictive models developed to estimate prey capture rate in the field. Experimental arena (container) size significantly affected predation rates when arena diameter was less than twice the total body length of the predator. Both chironomid and Daphnia magna capture rates were influenced by predator size, temperature and prey density.     

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.     

Physiology of immunity in the water flea Daphnia magna: environmental and genetic aspects of phenoloxidase activity

In an attempt to understand the ecological correlates of immunocompetence in Daphnia magna (Crustacea, Cladocera), we tested for variation in immune function in relation to feeding conditions, host conditions, and host genotype. We investigated both phenotypic (environmental dependent and condition dependent) as well as genotypic aspects of the prophenoloxidase activating system (Pro-POAS), which has been described as a key factor in invertebrate immunity. Daphnia magna is an ideal study system to disentangle phenotypic and genetic variation because females can reproduce clonally. Well-fed Daphnia showed higher phenoloxidase (PO) activity than Daphnia kept at a low food level. Wounding provoked a higher level of PO activity, indicating that the Pro-POAS was condition dependent. Further, we found clonal variation in PO activity among four clones of D. magna isolated from four different populations. The same four clones were tested for their resistance to the bacterial pathogen Pasteuria ramosa. High resistance corresponded to high PO activity. Our results suggest adaptive variation in PO activity and suggest that its expression is costly. These costs may influence the evolution of the PO activity level and the maintenance of its genotypic variation.     

氯化高汞对大型溞的慢性毒性

在换水静置条件下(25℃),氯化高汞(以Hg++计)对大型溞的48小时LC50值及其可信限为13.5(±2.1)微克/升。试验个体饲以斜生栅藻单个培养,在汞含量为1—21微克/升浓度下,产仔总数经方差分析表明组间差异显著(FF0.05)。各浓度组(X)与产仔总数(Y)的关系为:Y=-51.823X+4320.960(r=-0.904,p0.01)。净增殖率(R0)随浓度升高而逐渐下降。存活和生长用方差分析及D值检验表明对照组与各浓度组之间(差异数分别小于各自的D值20.89和0.1749),没有显著差异。各浓度组对内禀增长能力(rm)和世代平均周期(T)影响不大。根据大型溞的生物学基本参数,其体长的生长模型为: lt=4.57-3.5177e-0.00838t.       

Effect of vertebrate and invertebrate kairomones on the life history of Daphnia magna Straus (Crustacea: Branchiopoda)

The history of selection of Daphnia magna populations living in North African temporary ponds may differ from populations inhabiting permanent ponds. Laboratory experiments were conducted to examine the effect of fish Gambusia holbrooki and invertebrate Notonecta glauca kairomones on the life history traits of the freshwater Cladocera Daphnia magna Straus. With fish kairomones, Daphnia reproduced early and had a significantly smaller size at first reproduction (SFR) and a smaller size of neonates compared to control. In contrast, daphnids reared in water treated with Notonecta glauca had no effect on the age at first reproduction but females were also smaller and produced smaller neonates.     

Derivation of a toxicity-based model to predict how water chemistry influences silver toxicity to invertebrates

The effect of altering water chemistry on acute silver toxicity to three invertebrate species, two Daphnids, Daphnia magna and Daphnia pulex, as well as an amphipod Gammarus pulex was assessed. In addition, the physiological basis of Ag(I) toxicity to G. pulex was examined. Daphnia magna and D. pulex were more sensitive than G. pulex and 48 h LC(50) values in synthetic ion poor water were 0.47, 0.65 and 2.1 microg Ag(I) l(-1), respectively. Increasing water [Cl(-)] reduced Ag(I) toxicity in all species, and increasing water [Ca(2+)] from 50 to 1,500 microM reduced Ag(I) toxicity in G. pulex. Whole body Na(+) content, but not K(+) or Ca(2+) was significantly reduced in G. pulex exposed to 6 microg Ag(I) l(-1) for 24 h, but there was no inhibition of whole body Na(+)/K(+)-ATPase activity. Both increasing water [Cl(-)] and [Ca(2+)] reduced this Ag(I)-induced Na(+) loss. For D. magna, the presence of 10 mg l(-1) humic acid or 0.5 microM 3-mercaptoproprionic acid (3-MPA) increased the 48 h LC(50) values by 5.9 and 58.5-fold, respectively, and for D. pulex the presence of 1 microM thiosulfate increased the 48 h LC(50) value by four-fold. The D. magna toxicity data generated from this study were used to derive a Daphnia biotic ligand model (BLM). Analysis of the measured LC(50) values vs. the predicted LC(50) values for toxicity data from the present and published results where water Cl(-), Ca(2+), Na(+) or humic acid were varied showed that 91% of the measured toxicity data fell within a factor of two of the predicted LC(50) values. However, the daphnid BLM could not accurately predict G. pulex toxicity. Additionally, the Daphnia BLM was under-protective in the presence of the organic thiols 3-MPA or thiosulphate and predicted an increase in the LC(50) value of 114- and 74-fold, respectively. The Daphnia toxicity based BLM derived from the present data set is successful in predicting Daphnia toxicity in laboratory data sets in the absence of sulfur containing compounds, but shows its limitations when applied to waters containing organic thiols or thiosulphate.     

Essential fatty acid content and the phosphorus to carbon ratio in cultured algae as indicators of food quality for Daphnia

1. A series of experiments examined growth of Daphnia magna on three algal diets ( Rhodomonas minuta , Scenedesmus acutus and Synechococcus sp.) at varying physiological states [nitrogen and phosphorus (P) limitations] to test whether variation in algal fatty acid and/or elemental composition can predict Daphnia growth.
2. These algae differed widely in their essential fatty acid (EFA) composition while phosphorus (P) or nitrogen limitation had only a small influence on their ω3-polyunsaturated fatty acid (PUFA) content.
3. Individually, algal ω3-PUFA content explained 69% of the variation in the normalised growth of D. magna, while algal phosphorus content explained 11% of the variation. Quantitative models for D. magna growth used both algal ω3-PUFA content and algal C : P ratio as food quality indices. Together, algal ω3-PUFA content and C : P ratio explained 70% of the variation in the normalised growth rate of D. magna .
4. Our results indicate that EFA influenced algal food quality much more strongly than P. The EFA and mineral P impacts appear to be independent.     

Daphnia magna, a host for evaluation of bacterial virulence

We show that Daphnia magna can be used to assess acute virulence of pathogens relevant to human health, such as Pseudomonas aeruginosa or Photorhabdus asymbiotica. Analysis of bacterial mutants suggests that P. aeruginosa uses similar mechanisms to infect Daphnia and other hosts.     

Underestimation of the Effect of Biologiocal Invasions in Phylogeographic Reconstructions as Seen in Daphnia magna (Crustacea,Cladocera)

Biology Bulletin - A phylogeographic analysis of Daphnia magna Straus 1820 (Crustacea, Cladocera) was used to study the consequences of underestimating the effects of biological invasions, namely,...     

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.