Influence of phytoplankton fractions on growth and reproduction of tropical cladocerans

The influence of two seston fractions, < 20 μm (nanoplankton) and ≥ 20 μm (microplankton), on growth and reproduction of cladoceran species with different sizes, from Lake Monte Alegre, was evaluated through individual growth and life table experiments. Size, shape and other features of the algae in the fractions were described. The procedure of filtering lake water through a 20 μm net for seston fractionation caused mutual contamination. The smallest cladoceran species, Ceriodaphnia cornuta Sars and Moina micrura Kurz, produced larger clutch sizes and exhibited higher intrinsic rates of population growth (r) in the nanoplankton, despite contamination of their food by inedible algae. The largest species, Simocephalus mixtus Sars, produced larger clutch sizes in the microplankton. There were no differences in juvenile biomass growth between treatments for M. micrura and Daphnia gessneri Herbst, but lower value of the exponential growth rate (g) in the microplankton was significant for M. micrura. Fecundity (eggs/total female) of M. micrura was significantly lower in the microplankton, while D. gessneri did not reproduce in this fraction, at the end of growth experiments. Spines, colonies, cenobium, filaments, hard cell wall, and gelatinous sheaths, represented constraints to cladoceran reproductive performance, besides algae size. Microplankton contamination by nanoplanktonic algae, in the experiments, probably minimized the negative effect of inedible algae. Nanoplankton was more suitable for the smallest species and microplankton for the largest one.     

Effects of food limitation and temperature on cladocerans from a tropical Brazilian lake

Food limitation was tested in the laboratory by individual growth and reproduction of two cladoceran species, Ceriodaphnia richardi and Daphnia gessneri, from the shallow tropical Brazilian Lake Monte Alegre. The cladocerans were fed cultivated green alga Scenedesmus spinosus in concentrations of 0.20, 0.10, 0.05, and 0.025 mg C l⁻¹. Higher biomass and growth rates occurred in the two highest-food concentrations; the two lowest ones negatively affected clutch size and first reproduction. The threshold food concentration is lower than 0.025 mg C l⁻¹ and the incipient limiting level is a value between 0.10 and 0.20 mg C l⁻¹. The largest species, D. gessneri, was more sensitive to low food concentrations. The effects of low and high temperatures (19 and 27°C) were evaluated by life table experiments with three cladocerans from the lake—Daphnia ambigua, D. gessneri, and Moina micrura—with no food limitation (1 mg C l⁻¹ of S. spinosus). Higher population growth rates for the three species were found at 27°C; better performance in most life table parameters was observed for the former two species at the highest temperature, D. gessneri being the most sensitive to the lowest temperature. There are indications that temperature is an important abiotic factor that constrains populations of cladocerans for a short period in winter in the lake, when temperature decreases to 18–19°C. However, its influence cannot be separated from a biotic factor such as food, whose effect is stronger in the cool season, when concentrations are lower and contribution of inedible algae is relatively higher.     

Influence of seston quantity and quality on growth of tropical cladocerans.

The seston of the small, shallow, and tropical lake Monte Alegre was tested for quantity and quality for cladocerans by growth bioassays, which were carried out in spring (Daphnia gessneri and Moina micrura), summer (D. gessneri, M. micrura, Ceriodaphnia cornuta, and Simocephalus mixtus), and winter (D. gessneri and D. ambigua). Cohorts of newborns originating from ovigerous females collected in the lake or from laboratory cultures were submitted, at a room temperature of 23 degrees C to the following treatments: (1) the chlorophytes Ankistrodesmus falcatus and/or Scenedesmus spinosus; (2) lake seston; and (3) lake seston + chlorophytes. Growth rate, clutch size, and fecundity were evaluated. Seston alone was not the best food for promoting cladoceran growth. There were seasonal differences in food quantity and quality with spring and summer seston being better for growth than that of the winter. Adding chlorophytes to the seston increased clutch size and fecundity for most species in summer and winter, but not in spring. Energy limitation seems to be the most important factor influencing cladoceran growth in summer and especially in winter.     

Complementary impact of copepods and cladocerans on phytoplankton

The differences in the impact of two major groups of herbivorous zooplankton (Cladocera and Copepoda) on summer phytoplankton in a mesotrophic lake were studied. Field experiments were performed in which phytoplankton were exposed to different densities of two major types of herbivorous zooplankton, cladocerans and copepods. Contrary to expectation, neither of the two zooplankton groups significantly reduced phytoplankton biomass. However, there were strong and contrasting impacts on phytoplankton size structure and on individual taxa. Cladocerans suppressed small phytoplankton, while copepods suppressed large phytoplankton. The unaffected size classes compensated for the loss of those affected by enhanced growth. After contamination of the copepod mesocosms with the cladoceran Daphnia , the combined impact of both zooplankton groups caused a decline in total phytoplankton biomass.     

Some preliminary observations on the enhancement of phytoplankton growth by low levels of mineral hydrocarbons

From field and laboratory experiments it has been observed that low concentrations (ppb) of mineral hydrocarbons can cause an increase in photosynthesis among the nanoplankton. In field experiments, the increase in photosynthetic activity among the nanoplankton led to a bloom of µ-flagellates predominated by a member of the Haptophyceae,Chrysochromulina kappa.     

Influence of biochemical,mineral and morphological features of natural food on tropical cladocerans

Five laboratory experiments were performed to evaluate the effect of supplements of fatty acids and a green alga on the individual growth and reproduction of three species of tropical cladocerans Ceriodaphnia richardi, Daphnia ambigua, and D. gessneri feeding on natural seston from the Brazilian Lake Monte Alegre. Cohorts of newborns from cultivated females were submitted to one of the following treatments: (1) Natural seston, (2) Natural seston + microcapsules of EPA and DHA or linoleic and linolenic fatty acids, (3) Natural seston + oil-free microcapsules, and (4) Natural seston + green alga Scenedesmus spinosus (1 mg C l⁻¹). Particulate organic carbon, algal carbon, C:P ratios of seston and green alga, polyunsaturated fatty acids (PUFA) content of seston and cladocerans, as well as phytoplankton composition, size, and shape were measured. The addition of fatty acids to seston did not significantly enhance growth and reproduction of the cladocerans, suggesting that sestonic PUFA content is sufficient for promoting cladoceran development, even in the cool–dry season when the fatty acids used in the experiments were 5–10 times lower in the seston than in the warm–wet season. Despite high C:P molar ratios in most experiments, there was only one indication of growth limitation by P. Reproduction was more affected than individual growth on some occasions by food quantity (energy) caused apparently by algal size, morphology, and digestion resistance. Energy availability, which is affected by algae morphological characteristics, seems to prevail over PUFA and P in controlling growth and reproduction of cladocerans in tropical Lake Monte Alegre.     

Influence of mineral nutrient availability on growth of tree seedlings from the tropical deciduous forest

The effects of different nutrient availabilities on growth and biomass partitioning in seedlings from the tropical deciduous forest in Mexico were compared. The tree species studied were Heliocarpus pallidus, a species associated with disturbed parts of the forest, and Caesalpinia eriotachys, Jacquinia pungens and Recchia mexicana, species from mature, undisturbed habitats. The tropical deciduous tree seedlings were grown in pure silica sand for 50 days inside growth chambers under four nutrient regimes; 5, 20, 100 and 200% Long Ashton nutrient solutions. Data showed contrasting responses among species to different nutrient availabilities. Except Jacquinia pungens, all species had increased growth and productivity as nutrient level increased from 5 to 100%; however, no significant differences in these parameters were detected between 100 and 200% in all species. Compared with mature forest species, pioneer species showed higher variations in biomass production, relative growth rate and net assimilation rate. In contrast to mature forest species, root/ shoot ratios in Heliocarpus pallidus were greater and thus showed higher biomass allocation to roots when nutrient supply was limited. This response suggests higher phenotypic plasticity in pioneer species. Species from mature parts of the forest (Caesalpinia eriostachys, Recchia mexicana) showed less dependency on nutrient supply than pioneer species. These responses appear to support observations from studies with temperate plants investigating growth responses to soil fertility.     

The relative importance of sexual and clonal reproduction for population growth in the perennial herb Fragaria vesca

The relative importance of sexual and clonal reproduction for population growth in clonal plants is highly variable. Clonal reproduction is often more important than sexual reproduction but there is considerable interspecific variation and the importance of the two reproductive modes can change with environmental conditions. We carried out a demographic study on the woodland strawberry (Fragaria vesca), a widespread clonal herb, at 12 sites in Switzerland during 2 years. Study sites were selected in two different habitats, i.e., forest and forest edge. We used periodic matrix models to estimate annual population growth rates and carried out prospective analyses to identify life cycle components that influence population growth rates most. Retrospective analyses were applied to study how the two different habitats affected population dynamics. Furthermore, we tested whether trade-offs between sexual and clonal reproduction occurred. There were large differences in annual population growth rates between sites and large within-site differences between years. Results of the prospective analyses clearly indicate that clonal reproduction is the dominant reproductive pathway whereas sexual reproduction is rather insignificant for population growth. Compared to forest habitats, forest edge habitats had higher population growth rates in the first year but smaller growth rates in the second year. We attribute these differing habitat effects to different water availabilities during consecutive years. No trade-offs between sexual and clonal reproduction were found. In conclusion, population growth of F. vesca relies heavily on clonal reproduction. Furthermore, reproduction and survival rates of F. vesca depend highly on spatio-temporal variation of environmental conditions.     

Experimental studies of food and suspended sediment effects on growth and reproduction of six planktonic cladocerans

Life-long somatic growth and egg production responses of Daphniabarbata, Daphnia gibba, Daphnia laevis, Daphnia pulex, Moinamicrura and Diaphanosoma excisum were examined in relation todifferent food and suspended sediment levels, in factorial experimentsat 20°C. Food treatments involved additions of 0, 100, 500and 2500 µg C l^–1 of Selenastrum to 20 µmfiltered water, generally from source lakes. These food levelswere tested at two suspended sediment levels in all species,viz. (i) natural source-lake nephelometric turbidities of 7–65nephelometric turbidity units (NTU) ({small tilde}10–70mg l^–1 TSS) and (ii) {small tilde}3- to 4-fold enrichmentof natural levels (8-fold in D.excisum). A third sediment-freetreatment was tested in all species of Daphnia other than D.gibba.Growth in body length and reproductive output were assesseddaily for individual animals. Main and interactive effects offood and sediment on growth were assessed at selected ages fromday 3 through subsequent life using analysis of variance (ANOVA).Strong and highly significant positive food effects were apparentat all ages in all species examined, with the curious exceptionof D.excisum. The onset of maturity and fecundity were alsopositively related to food level. Sediment effects on growth,age of maturity and fecundity were variable, but tended to bemuch weaker than food effects. Both stimulatory (positive, especiallyat low food levels) and inhibitory (negative) effects of sedimenton growth were apparent, both between and within species. Performancein sediment-free water was very poor, except in D.pulex. Food-sedimentinteraction effects were variable. Generally, turbidwater specieswere influenced less adversely by sediment than clear-waterspecies, indicating the existence of environmentally appropriateadaptive responses. Overall, the findings indicate that lightlimitation of algal resources by suspended sediments, ratherthan the condition of high turbidity per se, is responsiblefor the apparently negative impact of suspended sediments frequentlyobserved on natural populations of cladoceran zooplankters.     

Effects of nutrient recycling by zooplankton and fish on phytoplankton communities

In laboratory experiments we tested the hypothesis that nutrients supplied by fish and zooplankton affect the structure and dynamics of phytoplankton communities. As expected from their body size differences, fish released nutrients at lower mass-specific rates than Daphnia. On average, these consumers released nutrients at similar N:P ratios, although the ratios released by Daphnia were more variable than those released by fish. Nutrient supply by both fish and Daphnia reduced species richness and diversity of phytoplankton communities and increased algal biomass and dominance. However, nutrient recycling by fish supported a more diverse phytoplankton community than nutrient recycling by Daphnia. We conclude that nutrient recycling by zooplankton and fish have different effects on phytoplankton community structure due to differences in the quality of nutrients released. Received: 21 December 1998 / Accepted: 31 May 1999     

Effects of essential fatty acids and N and P-limited algae on the growth rate of tropical cladocerans

SUMMARY 1. In this study, the effects of nutrient (N and P) deficiency and the importance of essential polyunsaturated fatty acids (PUFA) [eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] to tropical cladocerans, growth and reproduction were determined in a growth bioassay.
2. The animals were fed N/P-sufficient, N-deficient and P-deficient algae, and also N and P-deficient algae supplemented with fish oil emulsions rich in EPA and DHA.
3. Cladocerans showed different responses to nutrient-deficient algae and also to supplements of fish oil emulsions. Moina micrura was most sensitive to P-deficient alga and, surprisingly, grew better and produced more eggs in N-deficient alga than in N/P sufficient alga. Ceriodaphnia cornuta was less sensitive, growing well in both N and P-deficient algae. This species, however, had a lower clutch size in N-deficient alga. On the other hand, Daphnia gessneri was the most sensitive to mineral limitation, showing decreased growth and clutch size in both nutrient-deficient algae.
4. The PUFA supplements to nutrient-deficient algae increased growth rates only for M. micrura and C. cornuta , suggesting that these fatty acids are important food requirements for these species.     

The effect of the nanoflagellateTetraselmis suecica on the growth and survival of grunion,Leuresthes tenuis,larvae

Synopsis The nanoflagellateTetraselmis suecica was tested both as the sole food source and as a diet complement toArtemia nauplii for grunion,Leuresthes tenuis, larvae. A total of 4800 grunion larvae, obtained through artificial insemination and incubation, were cultivated under laboratory conditions. Growth and survival rates were registered for 14 days in two experimental series. In the first series the nanoflagellateT. suecica was offered as the sole food source at five different concentrations. Survival and growth increased in agreement with the increase inT. suecica concentration. In the second series,Artemia nauplii were offered at six concentration levels. This series was divided into two groups: the nanoflagellateT. suecica was added to one group at a concentration of 5000 cells ml^–1; the other group was maintained without nanoflagellates. In this series, survival and growth were directly related to nauplii concentration, but significant effects of the nanoflagellates were evident only in relation to the survival; the greatest difference (58% without nanoflagellates vs. 69% with nanoflagellates) was observed at anArtemia concentration of 1000 nauplii 1^–1. The mechanism responsible for increased survival ofL. tenuis larvae in presence of phytoplankton is unclear.     

Associations between lake phytoplankton community and growth factors — a canonical correlation analysis

Canonical correlation analysis was used to study the associations between the most prevalent phytoplankton species and nine physical and chemical growth factors in a polyhumic Finnish lake. The analysis was made (a) to the ten species with the greatest mean biomass in the data over one growth season and (b) to the ten species providing the greatest canonical correlation with the growth factors. The latter species were detected using an exchange type procedure. The analysis showed strong associations within phyla. Especially the most problematic phylum with respect to the use of the lake, the cyanobacteria, had a pronounced mutual association, as they correlated negatively with the N/P ratio as positively with phosphorus.     

Effect of pH on survival,reproduction, egg viability and growth rate of five closely related rotifer species

In the laboratory we examined the effect of pH (5–10 with one interval) on survival, reproduction, egg viability and growth rate (intrinsic growth rate—r _m and population growth rate—r) of five Brachionus rotifer species (B. calyciflorus, B. quadridentatus, B. urceolaris, B. patulus and B. angularis). The pH was shown to exert a major influence on egg viability and growth rate (r _m and r) for each species. The age-specific survivorship curves within a species were not significantly different at pH 6–10. The optimal pH for each species is near-neutral pH (pH 6–8), and the fecundity decreased as the pH deviated from these values. For each Brachionus species, there was no significant difference between age-specific fecundity curves at pH 7 and 8. At acid pH (pH 5 or 6) higher egg mortality was observed for each species. The r _m and population r of the five Brachionus species incubated at different pHs were significantly influenced by pH. The pH supporting the highest r _m or r was obtained at pH 6–8, but varied due to species. In this study B. urceolaris and B. patulus could tolerate a broad range of pH, while the populations of B. calyciflorus, B. quadridentatus and B. angulari declined at acid conditions.     

Influence of the nitrogen source and concentration on N fractions and free amino acid levels of grape vine explants

The influence of the source of inorganic nitrogen (KNO₃, (NH₄)₂SO₄ and NH₄NO₃) and its concentration (5, 10, 20 and 30 mM N) on total N incorporation, as well as on N distribution into different fractions (amminiacal, amino, amide and protein) and on free amino acid levels has been determined in grape vine explants cultured in vitro.Increasing concentrations of the nitrogen source resulted in increased total N content in tissues. This effect was small for KNO₃, higher for (NH₄)₂SO₄ and maximal for NH₄NO₃. In addition, nitrate promoted an increase in amino-N only, whereas ammonium increased both the ammoniacal-N and the amino-N fractions. Incorporation of N into amide-N and protein-N were not affected significantly by the N sources tested.The application of increasing quantities of N enhanced the accumulation of most free amino acids, especially arginine, alanine and proline, but to different extents, depending on both the N source and its concentration. The combination of ammonium and nitrate resulted in a higher accumulation of amino acids than that observed with either one of the two forms alone.     

Influence of slurry applications on the EUF-N fractions in the soil

Summary Increasing quantities of slurry (30, 60 and 90 m³/ha as well as 60 m³/ha + DIDIN) were applied to two sandy soils both in September and in December 1982. During the 1982/83 winter EUF-N was determined in soil horizons (0–30 cm, 30–60 and 60–90 cm).EUF-NO₃ and EUF-N_org clearly reflected the different quantities of slurry applied. The retarding effect of DIDIN on nitrification could also be demonstrated by means of the EUF-N contents.Due to the mild and humid climate prevailing in the winter of 1982/83 slurry-NO₃ of the September applications had obviously been leached out of the 0–60 cm soil layer in all treatments by February and even out of the 60–90 cm layer by March 24. Translocation of NO₃ was also observed for slurry applied in December. But in this case on March 24 the EUF-NO₃ contents in the 60–90 cm layer still reflected the quantities of slurry applied four months earlier.After slurry application the EUF-N_org fraction of a soil initially consists mainly of NH ₄ ⁺ which is rapidly oxidized to NO₃ and transferred in this form to deeper layers. As a consequence a rapid decline in EUF-N_org fraction is observed. It could therefore be expedient to consider the N_org and EUF-NH ₄ ⁺ fractions separately when slurry applications are concerned.     

Sublethal effects of buprofezin on development,reproduction, and chitin synthase 1 gene (SfCHS1) expression in the white-backed planthopper,Sogatella furcifera (Hemiptera: Delphacidae)

The white-backed planthopper, Sogatella furcifera (Horváth) (Hemiptera: Delphacidae), is a major rice pest in some Asia-Pacific countries. Buprofezin is an insect growth regulator with relatively low mammalian toxicity but high efficacy to many rice pests. In this study, we estimated the toxicity of buprofezin against 3rd-instar nymphs of S. furcifera using the rice-stem dipping method. The results showed that the LC₅₀ of buprofezin to 3rd-instar nymphs were 0.89?mg/L. When 3rd-instar nymphs were exposed to the LC₁₀ and LC₂₅ (0.10 and 0.28?mg/L) of buprofezin, the duration of juvenile development was significantly prolonged in the F₀ and F₁ generations. The fecundity (eggs per female) of the F₁ females was reduced by 5.29% and 12.34%, respectively, in addition to the survival rate, emergence rate, copulation rate, and hatchability were decreased by treatment with buprofezin at LC₁₀ and LC₂₅, compared with the control group. The relative fitness of S. furcifera in LC₁₀ and LC₂₅ treatments was reduced by 47% and 63%, respectively. Furthermore, real-time quantitative PCR analyses revealed increased the expressions of SfCHS1 and its two variants following the exposure of nymphs to buprofezin. Increased these genes mRNA levels associated with reduced chitin biosynthesis may result from the inhibition of chitin synthase activity, and thereby leading to a higher mortality of S. furcifera. Overall, sublethal concentrations of buprofezin suppressed the population growth of S. furcifera.     

Influence of food quality on growth and reproduction in Daphnia

SUMMARY. 1. Growth and reproduction were measured for Daphnia pulex (Leydig) fed Scenedesmus obliquus (Turp.) Kutz. grown with nitrogen-sufficient and nitrogen-deficient media. The incorporation of carbon into the body of D. pulex was traced using ¹⁴C-labelled algae and biochemical fractionation.
2. Scenedesmus cultured on N-defkient media allocated more carbon to lipid and less to protein than when cultured on N-sufficient media.
3. In a short-term feeding experiment, Daphnia accumulated more lipid when fed N-deficient algal cells high in lipid content than when fed algae grown on N-sufficient media that were lower in lipid.
4. Animals grew faster and produced larger broods when fed algae grown on an N-sufficient medium over an 8-day period. Daphnids fed N-deficient algae had higher quantities of body lipid, suggesting it was not a lack of energy which limited their growth and reproduction.
5. Daphnia fed algae grown on N-deficient media allocated more lipid to eggs, and their offspring lived longer under starvation conditions.     

Changes in community structure and photosynthetic activities of total phytoplankton species during the growth,maintenance, and dissipation phases of a Prorocentrum donghaiense bloom

The potential interactions between the bloom-forming dinoflagellates and other phytoplankton during the algal bloom cycle are interesting, while the causes for the phytoplankton community changes were not fully understood. We hypothesized that phytoplankton community structure and photosynthetic activities of total phytoplankton have their special characteristics in different phases of the algal blooms. To test this hypothesis, a survey covering the process of a Prorocentrum donghaiense bloom in coastal waters between Dongtou and Nanji Islands was carried out from 9 to 20 May 2016, and the changes in the phytoplankton community and photosynthetic activities of total phytoplankton were determined. Surface seawater was sampled for microscopic analysis of phytoplankton composition and pulse amplitude modulated (PAM) chlorophyll fluorescence analysis of photosynthetic activities of the total phytoplankton species. A total of 25, 31, and 19 phytoplankton species were identified in its growth (9–12 May), maintenance (13–18 May) and dissipation phases (19–20 May), respectively. Diatoms were dominant in terms of species number while dinoflagellates were predominant at cell abundance. Dinoflagellates were the major dominant species during three phases of the bloom based on the dominance (Y) value, whereas the dominant species extended to dinoflagellates and diatoms including P. donghaiense, Coscinodiscus argus, Gonyaulax spinifera, Cyclotella sp. and Scrippsiella trochoidea in the dissipation phase. In the maintenance phase, the average cell abundances of the total phytoplankton and P. donghaiense were consistent with the chlorophyll a (Chla) concentration in the seawater; for the diversity indices of total phytoplankton species, Simpson index (C) was the highest while Shannon index (H′) and Pielou evenness index (J′) were the lowest. Furthermore, photosynthetic activities of the total phytoplankton species represented by the effective quantum yield (F_q'/F_m') and the maximum relative electron transport rate (rETR_max) in the maintenance phase were higher than those in the growth and dissipation phases. The results indicated that the characteristics of phytoplankton community structure and photosynthetic activities could be regarded as criteria in predicting the phases of algal blooms.     

麦蛾卵对南方小花蝽生长发育和繁殖的影响

南方小花蝽Orius strigicollis作为一种广食性捕食性天敌昆虫,可高效控制蓟马、蚜虫及螨类等多种害虫,极具生防潜能.但目前国内南方小花蝽商业化进程相对滞后,其中未找到适合的饲料来源是主要的限制因素之一.本研究以新鲜麦蛾Sitotroga cerealella卵和紫外线处理的麦蛾卵作为饲养南方小花蝽的替代猎物...