Effect of different densities of live and dead Chlorella vulgaris on the population growth of rotifers Brachionus calyciflorus and Brachionus patulus (Rotifera)

In order to maintain rotifer populations during periods of low algal production, it is necessary to offer alternate diets, some of which include forms of preserved algae. The present work is based on the effect of live and dead Chlorella vulgaris on the population growth of Brachionus calyciflorus and Brachionus patulus. The experimental design consisted of three algal levels (0.5 x 10(6), 1.5 x 10(6) and 4.5 x 10(6) cells ml-1) offered in three forms (living, frozen and heat-killed). The maximal population density values for B. calyciflorus ranged from 55 +/- 1 ind. ml-1 (at 0.5 x 10(6) cells ml-1) to 471 +/- 72 ind. ml-1 (at 4.5 x 10(6) cells ml-1) with live Chlorella, but was much lower (6 +/- 1 to 26 +/- 6 ind. ml-1) with frozen or heat-killed alga under comparable food levels. However, the maximum population density of B. patulus under live or or heat-killed Chlorella was similar at comparable algal levels but when offered frozen algae it was four times less. The highest mean peak population density was 1,277 +/- 83 ind. ml-1 under 4.5 x 10(6) cells ml-1. The rate of population increase for B. calyciflorus varied from 0.50 to 0.79 using live Chlorella, but under comparable conditions, this range was lower (0.21 to 0.31) for B. patulus. Results have been discussed in light of possible application for aquaculture.     

Effect of three food types on the population growth of Brachionus calyciflorus and Brachionus patulus (Rotifera: Brachionidae).

We compared the population growth of B. calyciflorus and B. patulus using the green alga Chlorella vulgaris, baker's yeast Saccharomyces cerevisiae or their mixture in equal proportions as food. Food was offered once every 24 h in two concentrations (low: 1 x 10(6) and high: 3 x 10(6) cells ml-1) separately for each species. The experiments were terminated after 15 days. In general, at any food type or concentration, B. patulus reached a higher population density. A diet of Chlorella alone supported a higher population growth of both rotifer species than yeast alone. B. calyciflorus and B. patulus achieved highest population densities (103 +/- 8 ind. ml-1 and 296 +/- 20 ind. ml-1, respectively) on a diet of Chlorella at 3 x 10(6) cells ml-1. When cultured using the mixture of Chlorella and yeast, the maximal population densities of B. calyciflorus were lower than those grown on Chlorella. Under similar conditions, the maximal abundance values of B. patulus were comparable in both food types. Regardless of food type and density the rate of population increase per day (r) for B. calyciflorus varied from 0.13 +/- 0.03 to 0.63 +/- 0.04. These values for B. patulus ranged from 0.19 +/- 0.01 to 0.37 +/- 0.01. The results indicated that even though Chlorella was a superior food for the tested rotifers, yeast can be effectively used at low concentrations to supplement algal requirements in rotifer culture systems.     

在培养基和食料中添加铅和镉对轮虫种群动态的影响

由于工业活动的影响,墨西哥水体环境中的重金属浓度在上升.浮游动物,尤其是轮虫类,由于对环境变化十分敏感而且是淡水中的常见组成部分,因此被广泛用于生态毒理试验以确定水质标准.在不同的胁迫途径下(如通过培养基或食料),重金属的毒性是不同的.在本研究中,通过在轮虫Brachionus rubens的培养基和食料中添加重金属这两种途径,我们评估了镉和铅的效应.对于这两种重金属,均采用将轮虫置于含0.5×106个/ml绿藻的培养基中或每天喂食经5倍于LC50值的金属处理(1,2和4h)的绿藻.对于在培养基中添加镉,使用了三个毒性水平(0.1,0.2和0.4 mg/L),铅的浓度分别为0.005,0.010 和0.015 mg/L.基于LC50的数据,B.rubens对铅的敏感性要比镉高24倍.镉浓度为0.4 mg/L时,培养基中加入镉造成B.rubens的生长趋缓.而喂食经不同时间处理的绿藻后,轮虫的密度随着食料在重金属中处理时间的延长而减小.培养基中或食料中添加铅时,轮虫种群生长的的趋势与在镉处理下的情况类似.随着培养基中重金属浓度的增加,每天种群增长率(r值)会减小.在培养基和食料处理两种不同途径下,r值会在0.33(对照)到0.02 d-1(经重金属处理)间变化[动物学报 51(1)46-52,2005].     

Acute and chronic toxicity of the pesticide methyl parathion to the rotifer Brachionus angularis (Rotifera) at different algal (Chlorella vulgaris) food densities

Methyl parathion is a commonly used insecticide in Mexico to eradicate insect pests. We evaluated the effects of this insecticide on rotifer B. angularis using both acute and chronic toxicity tests. Median lethal concentration (LC₅₀) of methyl parathion for B. angularis for a 24-h bioassay in the presence and absence of an algal diet was derived. Elevated LC₅₀ due to the survival of a greater number of test individuals in the presence of food was observed. Regardless of the toxicant concentration, population growth curves of the animals maintained at the low food level (0.75×10⁶ cells ml^-1) had a longer lag phase than those at the high food level (1.5×10⁶ cells ml^-1). Regardless of food level, an increase in the toxicant concentration in the medium resulted in decreased population growth. The lowest peak population density (50 ind. ml^-1) was observed at the highest toxicant concentration and the lower food level. The highest population density (200 ind. ml^-1) was observed in the controls at high food level. The rates of population increase per day (r) in the controls were higher (from 0.14 to 0.37 depending on the food level). Irrespective of food level, there was a decrease in the r values with increasing pesticide concentration in the medium. In order to detect the effect of population density on the growth rates in relation to the toxicant stress, we plotted the daily growth rate against initial density for the entire duration of the experiment. We observed the existence of a significantly inverse relation at all treatments except at the low food level and high toxicant concentrations (0.625 and 1.25 mg l^-1). We discuss the role of algae in the toxicity of methyl parathion to zooplankton.     

Demographic parameters of Brachionus patulus Muller (Rotifera) exposed to sublethal DDT concentrations at low and high food levels

The combined effects of sublethal levels of DDT (0, 15, 30, 45, and 60 µg·l^–1) and food (Chlorella at 1 and 3 × 10⁶ cells ml^–1) on the demography of the rotifer Brachionus patulus were studied. The average lifespan, life expectancy, net reproductive rate (R_o) and intrinsic rate of increase (r) were significantly greater at the higher food level, but declined with increasing DDT concentration. A significant DDT food interaction was manifested in the toxicity-mitigating action of the higher food density at higher DDT levels. The r values were negative at DDT levels 30 µg · l^–1 and above, only when food density was low. The effective DDT concentration at which a given parameter value was reduced to 50% of that in the controls (EC50) was lower at lower food levels for both survivorship and reproduction, and lower for reproduction than for survivorship at either food level.     

Combined effects of food level and inoculation density on competition between Brachionus patulus (Rotifera) and the cladocerans Ceriodaphnia dubia and Moina macrocopa

Competition among cladocerans and rotifers is of considerable interest not only due to their close similarity in life history strategies, but also due to the considerable overlap they exhibit in their feeding habits. In tropical waterbodies, several genera of cladocerans, including Ceriodaphnia and Moina occur, simultaneously with rotifers. We tested over a period of 3 weeks the combined effects of food (0.5×10⁶ and 1.5×10⁶ cells ml^–1 of Chlorella) level and rotifer density on the competition between B. patulus and C. dubia and M. macrocopa using population growth experiments. For each cladoceran species we used 30 test jars of 50 ml capacity. The initial density of cladocerans was 0.2 ind ml^–1, while for B. patulus it was either 1 ind ml^–1 or 5 ind ml^–1. Neither the maximal population density nor the rate of population increase (r) of C. dubia was significantly affected by B. patulus. However, for M. macrocopa, both these variables were negatively affected by the rotifers. The combined effects of low food level and high initial density of B. patulus resulted in a 50% reduction in the peak population density of M. macrocopa. The population growth of B. patulus was negatively influenced by the presence of C. dubia and M. macrocopa. The results of the competition experiments conducted in the present study between cladocerans and rotifers suggest the existence of a more complex and delicate interaction than is generally thought.     

Foraging behaviour of Brachionus calyciflorus (Pallas): variations in the swimming path according to presence or absence of algal food (Chlorella)

Both swimming and attachment behaviour of immature female Brachionus calyciflorus (Pallas) from a young orthoclone were analyzed under four experimental conditions: with and without algae (Chlorella), and with fed and starved individuals. Eighteen hours before the recording, two random groups were formed. To the first group, Chlorella was added. The second was placed in pure water. Both were filmed in red light to avoid a phototactic effect. Video-recorded swimming behaviour of B. calyciflorus was analyzed by automatic tracking. Each B. calyciflorus was filmed alternately in the presence or absence of Chlorella for five periods of 15 min. Under indentical light and temperature conditions the number of animals attached to the culture dish was measured with both starved and fed females. We observed a significant difference in swimming paths depending on the presence or absence of food, and the physiological state of the individuals. In the presence of Chlorella the linear speed was lower and the angular speed was greater. This increase in angular speed was more pronounced when females were subjected to a period of starvation before the experimentation. The attachment behaviour increased in the algal environment. This modification of swimming behaviour enables females to increase the time spent in a favorable food environment.     

Transgenerational and within-generational induction of defensive morphology in Brachionus calyciflorus (Rotifera): importance of maternal effect

Maternal effects on the induction of defensive morphology are regarded as an adaptive strategy. For instance, a female can transmit environmental conditions related to predation risk to offspring of the same generation or succeeding generations. However, studies have presented limited information regarding such an adaptive maternal effect on monogonont rotifers. In the present study, the maternal effects on the spine development of rotifers were evaluated using Brachionus calyciflorus-Asplanchna models. Asplanchna can release soluble kairomones into the environments, thereby inducing B. calyciflorus to form defensive morphs (e.g., elongated posterolateral spines). Our empirical data supported the hypothesis that an amictic Brachionus-experienced Asplanchna kairomones could produce offspring with longer posterolateral spine in the current or succeeding generation than those of a non-experienced amictic female. On the basis of our data, we speculated that the maternal effect of B. calyciflorus may involve the transfer and dilution of inducers (e.g., hormone) within and between generations. On one hand, our results reinforced the within-generation maternal effects on induction of defensive morphology of rotifers; on the other hand, our results enhanced transgenerational inducible defense to other planktonic taxa that have been only observed in cladocera.     

Rotifer neuropharmacology--II. Synergistic effect of acetylcholine on local anesthetic activity in Brachionus calyciflorus (Rotifera, Aschelminthes)

A number of compounds showing general anesthetic action in the rotifer Brachionus calyciflorus were investigated in the presence of acetylcholine. Non-ionizing anesthetics, including tricaine, showed no interaction with acetylcholine. However, highly ionized compounds like the local anesthetics procaine and lidocaine, the muscarinic blocker and local anesthetic atropine, and the beta-adrenergic blocker propranolol showed a synergistic effect with acetylcholine. ACh increased the general anesthetic effect of these compounds in a statistically highly significant dose-dependent fashion. To account for the mechanism of this unusual and novel effect it is proposed that these compounds interact with the anesthetic binding site of the rotifer cholinoceptor ionophore in the open state. It is also proposed that non-ionizing compounds have a general membrane effect only. In addition to anesthesia, atropine and propranolol cause foot paralysis in B. calyciflorus. This other novel effect is also enhanced by acetylcholine as well as decamethonium, a neuromuscular blocker.     

食物浓度对方形臂尾轮虫发育历期与实验种群增长参数的影响

为探讨富营养化水体中大量发生的轮虫与微藻之间的关系 ,在实验室条件下 ,观测了不同藻类食物浓度下方形臂尾轮虫生命周期中各发育阶段的历时以及种群增长参数的变化。实验选用蛋白核小球藻为食物 ,浓度梯度为 0 1× 10 6、 0 5× 10 6、 1 0× 10 6、 2 0× 10 6、 4 0× 10 6、 8 0× 10 6、 12× 10 6cells/ml。结果表明 :食物浓度对方形臂尾轮虫的胚胎发育时间与繁殖前期历时、产卵量、世代净生殖率、世代时间和种群的内禀增长率均有明显影响。在食物浓度为 2 0× 10 6cells/ml时 ,方形臂尾轮虫的繁殖前期最短 ,产卵量最大 ,世代净生殖率和种群增长率最高 ,世代时间最短。方形臂尾轮虫可在高于其最适食物浓度的较宽的食物浓度范围内 ,保持较高的种群增长率 ,表现出较强的对环境中高浓度藻类的适应     

Minimal algal food requirements in the presence of protozoan prey for the rotifer Brachionus calyciflorus

As recent experiments demonstrated that protozoans support reproductionof the rotifer Brachionus calyciflorus only in the presenceof algal prey, we addressed the question of minimal algal foodrequirements in a mixed diet of algae and protozoans to ensurepositive growth of B. calyciflorus. In numerical response experiments,we determined the algal threshold concentration for zero populationgrowth of B. calyciflorus when feeding on a pure algal dietof Monoraphidium minutum, and on a mixed diet of M. minutumplus the ciliate Coleps sp. Under pure algal and under mixedfood conditions, a minimum amount of 0.3 µg carbon (C)ml^-1 M. minutum was needed to ensure zero population growthof B. calyciflorus. At lower algal concentrations, Coleps sp.was of low nutritional value. However, when offered in conjunctionwith a concentration of 0.8 µg C ml^-1 M. minutum, Colepssp. contributed equally to the reproductive success of B. calyciflorusas compared to a sole M. minutum diet. Overall, Coleps sp. canbe an adequate supplement in the diet of B. calyciflorus ifa sufficient amount of algal prey is available. However, attimes of low phytoplankton biomass, consumption of ciliatesdoes not necessarily confer a reproductive advantage for thisrotifer.     

Isolation and purification of glutathione S-transferases from Brachionus plicatilis and B. calyciflorus (Rotifera)

1. The enzyme glutathione S-transferase (GST), a critical element in xenobiotic metabolism, was isolated from the marine rotifer Brachionus plicatilis and its freshwater congener B. calyciflorus. 2. In B. plicatilis, GST comprised 4.2% of cytosolic protein and was present as three separate isozymes with mol. wts 30,000, 31,400 and 33,700. Specific activity of crude homogenates was 56 nmol min-1 mg-1 protein, while that of affinity chromatography purified GST was 1850. 3. In B. calyciflorus, GST was present as two isozymes with mol. wts of 26,300 and 28,500, representing 1.0% of cytosolic protein. Crude GST specific activity was 1750 nmol min-1 mg-1 protein and purified was 72,400. 4. Rotifer GSTs are unusual because they are monomers whereas all other animals thus far investigated posses dimeric GSTs.     

The effect of pH onBrachionus calyciflorus Pallas (Rotifera)

Cohorts of the rotiferBrachionus calyciflorus were grown in media with pH of between 2.5 and 11.5 in increments of 1 unit. pH was shown to exert a major influence on the growth rate and reproductive capacity of theB. calyciflorus. At pH 2.5 theB. calyciflorus showed a negative capacity for population increase (r _c). Ther _c values of the cohorts reared at pH 3.5 and 4.5 were positive and these cohorts showed high net reproductive rates (R₀). Ther _c's of cohorts reared at pH of 5.5 and 6.5 were negative, while those of cohorts reared at pH 7.5 to 10.5 were positive with a peak in theR ₀ and cohort generation time (T _c) at pH 8.5 and 9.5. Total mortality occurred in less that 24 h at pH 11.5.Successive generations of the progeny from the cohort held at pH 3.5 were reared under the same conditions. Although ther _c of the F₁ and F₂ cohorts increased, the organism was unable to maintain the increased population growth rate, and the F₄ generation showed anr _c of almost 0.     

Lifetable demography of four cladoceran species in relation to algal food (Chlorella vulgaris) density

Algal food density is known to influence life history variables of cladoceran species. It is not, however, well established whether both littoral and planktonic cladocerans show similar trends when exposed to increasing food concentrations. In the present work, we studied the life table demography of four cladoceran species (Ceriodaphnia cornuta, Moina macrocopa, Pleuroxus aduncus and Simocephalus vetulus) in relation to three algal food concentrations (low: 0.5 × 10⁶, medium: 1.5 × 10⁶ and high: 4.5 × 10⁶ cells ml^–1 of Chlorella vulgaris) (in terms of carbon content, these were equivalent to 0.15, 0.45 and 1.35 g ml^–1, respectively) at 25 °C. In general, for all the tested cladoceran species, values of average lifespan, gross reproductive rate, net reproductive rate, generation time and the rate of population growth were higher at lower food concentrations. Furthermore, high food concentration resulted in a negative population growth rate (mean ± standard error: –0.091 ± 0.026) for P. aduncus. The highest population growth rate (0.602 ± 0.014) was recorded for M. macrocopa at low food density. S. vetulus had the longest average lifespan (40 ± 1 d) while M. macrocopa had the lowest (5 ± 1 d). C. cornuta showed better performance at medium food concentration. We conclude that among the algal concentrations used here, 0.5 × 10⁶ – 1.5 × 10⁶ was beneficial not only to the planktonic species but also to the littoral P. aduncus and S. vetulus while 4.5 × 10⁶ cells ml^–1 was unsuitable for all the cladocerans tested.     

Life history characteristics of three types of females in Brachionus calyciflorus Pallas (Rotifera) fed different algae

This study describes the life history characteristics of amictic, unfertilized mictic and fertilized mictic females of the rotifer Brachionus calyciflorus cultured individually on two different algae at 0.1 mg ml^–1 food concentration and 27 °C. The duration of the juvenile period of amictic females was significantly shorter on Chlorella pyrenoidosa Chick than on Scenedesmus obliquus Kütz or both algae together. The duration of the juvenile period of unfertilized mictic females was significantly longer, and the number of eggs produced by amictic females was significantly larger on Chlorella pyrenoidosa than on S. obliquus. When fed the same type of alga, the duration of the juvenile period of the fertilized mictic females was the longest among the three types of females, and the durations of the reproductive period of the amictic females and the post-reproductive period of the fertilized mictic females were longer than, or equal to those of the other two types of females, respectively. The number of eggs produced by an unfertilized mictic female was the largest among the three types of females, and that of amictic females was larger than or equal to that of fertilized mictic females, depending on the type of diet.     

Life table demography and population growth of Brachionus variabilis Hempel, 1896 in relation to Chlorella vulgaris densities

We studied the life history variables and population growth characteristics of Brachionus variabilis, which was recorded for the first time from Mexico. The animals were fed Chlorella, using five concentrations (0.25, 0.5, 1, 2 and 4 × 10⁶ cells ml^–1) at 25 °C. Food density was observed to have significant effect on life expectancy, average lifespan, gross reproductive rate, net reproductive rate, generation time and population growth rate. The average lifespan ranged from 3 to 6 days depending on the food density. The net reproductive rate ranged from 2 to 7 neonates female^–1 d^–1. The rate of population increase per day varied from 0.14 to 0.35. The highest net reproductive rate and average lifespan and life expectancy were recorded at Chlorella concentrations of 1 × 10⁶ and 2 × 10⁶ cells ml^–1.     

邻苯二甲酸酯类物质对萼花臂尾轮虫种群增长和有性生殖的影响

以萼花臂尾轮虫(Brachionus calyciflourus)为受试动物,以17β-雌二醇(E2)为阳性对照,运用3d种群增长和4d休眠卵产量实验方法研究了不同浓度的邻苯二甲酸二丁酯(DBP)、邻苯二甲酸二异辛酯(DEHP)和邻苯二甲酸丁苄酯(BBP)对轮虫种群增长和有性生殖的影响。结果显示,与空白对照组相比,0.05-5000μg/L的E2和500μg/L的BBP显著提高了轮虫种群增长率,而0.5和5000μg/L的DBP以及0.05和0.5μg/L的BBP使轮虫种群增长率显著降低;0.5-500μg/L的E2、50和500μg/L的DBP、0.005和500μg/L的DEHP和500μg/L的BBP显著提高了轮虫的休眠卵产量,而5000μg/L的DBP和0.05μg/L的BBP却与其相反;5和500μg/L的E2、50和500μg/L的DEHP以及500μg/L的DBP和BBP均使轮虫混交率显著上升,而0.005和0.05μg/L的E2、5000μg/L的DBP和DEHP及0.5μg/L的BBP显著降低了轮虫种群中混交雌体受精率;除5000μg/L的E2显著降低轮虫种群中的混交雌体数/非混交雌体数之外,其它所有处理组均对其无显著性影响;5、500和5000μg/L的E2、5000μg/L的DBP和5-5000μg/L的DEHP均使轮虫种群中的带卵雌体数/不带卵雌体数显著升高,而BBP对其无显著影响。在实验设置浓度范围内,轮虫种群中的混交雌体数/非混交雌体数与E2浓度间、轮虫种群中的混交雌体受精率和种群增长率与DBP浓度间、轮虫休眠卵产量与DEHP浓度间、轮虫混交率与BBP浓度间均具有显著的效应-剂量关系     

Demographic parameters of Brachionus calyciflorus Pallas (Rotifers) exposed to sublethal endosulfan concentrations

The effects of sublethal levels of endosulfan (0, 1, 1.5, 2.5 and 3.3 mg 1^–1) on the demography of the rotifer Brachionus calyciorus were studied. Life expectancy at birth (e _o), net reproductive rate (Ro), generation time (T) and intrinsic rate of natural increase (r) were significant differentes between blank controls and controls with acetone. The effective endosulfan concentration at which a given parameter value was reduced to 50% of the controls (EC50) was calculated for life expectancy.     

食物种类对萼花臂尾轮虫种群增长率的影响

在短期慢性观测过程中,食物类型可能是造成萼花臂尾轮虫(Brachionuscalyciflorus)种群繁殖率变化的一种原因。共观测了分别单独投喂10种不同绿藻对轮虫种群增长率的影响。为验证藻青菌是藻类饵料(如绿藻Scenedesmus)有价值的佐剂这一假说,还用蓝细菌单独投喂或与斜生栅藻(Scenedesmusobliquus)混合投喂轮虫进行实验观测。结果发现食物种类对萼花臂尾轮虫种群增长率影响显著。斜生栅藻组获得最大种群增长(1.6/d),而Desmodesmus组增长率最低(0.3/d)。以占斜生栅藻组最大增长的百分率来表示,其它几种绿藻组种群增长由高到低依次为:Desmodesmussubspicatus88%,小球藻(Chlorellavulgaris)83%,单壳缝藻(Monoraphidiumminutum)77%,D.quadricauda74%,S.falcatus71%,S.acuminatus69%,S.pectinatus64%,莱茵衣藻(Chlamydomonasreinhardtii)57%,D.abundans19%。轮虫增长率的差异不能用藻类饵料的大小差异来解释。蓝细菌(Microcystisaeruginosa)和(Synechococcuselongates)不论是单独投喂还是与优良藻类饵料(斜生栅藻)混合投喂都对萼花臂尾轮虫种群增长有抑制作用。这种副作用似乎与微囊藻素无关。该结果不支持无毒蓝细菌可作为与其他绿藻饵料配合使用的优良佐剂这一假说。本研究所观察到的生长变化显示了饵料种类对萼花臂尾轮虫种群增长的影响,也预示了对毒性实验结果的影响     

Nutritional effect of freshwater Chlorella on growth of the rotifer Brachionus plicatilis

Mass production of Brachionus plicatilis is usually accomplished by feeding so-called marine Chlorella (Nannochloropsis oculata) to the rotifers in marine fish hatcheries. If the marine Chlorella are in short supply, baker's yeast is usually used as a supplementary food. Recently, a condensed suspension of freshwater Chlorella (Chlorella vulgaris, k-22) was commercially developed as another supplementary food. We have evaluated the dietary value of this freshwater Chlorella for growth of the rotifer by means of individual and batch cultures. Rotifers cultured with the freshwater Chlorella suspension under almost bacteria-free conditions, showed very suppressed growth. However if the Chlorella was supplemented with vitamin B₁₂ by adding the vitamin solution into the suspension or by culturing the Chlorella in a medium containing vitamin B₁₂, the nutritional value of freshwater Chlorella was greatly improved and almost at the same level as that of marine Chlorella. Condensed Chlorella may therefore be effective as a supplementary food if vitamin B₁₂ is supplied.