Epizoic mode of life in Brachionus rubens Ehrenberg as a deterrent against predation by Asplanchna intermedia Hudson

The planktonic rotifer Brachionus rubens has a propensity for an epizoic mode of life, and in nature is often found attached to cladocerans. In this way the rotifer avoids to a certain extent the adverse effects of interference competition with cladocerans. We test the hypothesis that the epizoic habit of B. rubens acts also as a deterrent against invertebrate predation. Using Asplanchna intermedia as predator, we followed the population growth patterns of B. rubens alone and in the presence of the host species Daphnia carinata and Ceriodaphnia rigaudi. In the absence of cladocerans, the prey was eliminated within three days, followed by extinction of the predator due to starvation. With D. carinata in the medium, the prey-predator system persisted much longer, with B. rubens reaching high population densities. With the smaller-sized C. rigaudi, allowing a significantly smaller fraction of B. rubens population to be epizoic, the system persisted longer than in the controls, but both the prey and predator eventually became extinct. We conclude that the epizoic habit of B. rubens, by acting as a prey refugium, helps a portion of the population to escape from predation, and facilitates its coexistence with Asplanchna intermedia.     

An evolutionary perspective on the resistance of Daphnia to the epizoic rotifer Brachionus rubens

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Effect of lead on the reaction of O-demethylase in p-nitro anisole in the cladoceran Moina macrocopa

The presence of the Mixed-Function Oxydase (MFO) system, in Moina macrocopa was detected through the transformation of p-nitroanisole to para-nitrophenol. The presence of this enzymatic system suggested that this cladoceran participates in the biotransformation of xenobiotics in aquatic ecosystems. This capacity, in conjunction with the aquatic flea's high tolerance to environmental stress, suggested that M. macrocopa could be used in bioremediation efforts to increase ecosystem health. The effects of lead on the MFO system in M. macrocopa, were also studied. Lead acted as an inhibitor of the enzymatic complex. Therefore, induction of MFO-activity as an early warning may not work in waterbodies affected by both inducers of MFO and inhibitors like lead.     

Effects of three organophosphorus pesticides on population growth and sexual reproduction of rotifer Brachionus calyciflorus Pallas

Effects of organophosphorus pesticides including dichlorvos, triazophos and chlorpyrifos on population growth and sexual reproduction of freshwater rotifer Brachionus calyciflorus were studied by 3-d population growth and 4-d resting egg production tests. The results showed that all the three organophosphorus pesticides influenced significantly the population growth rate, the ratio ovigerous females/non-ovigerous females in the rotifer populations and the resting egg production of the rotifers. Both dichlorvos and chlorpyrifos influenced markedly the mictic rate of the rotifers, but triazophos did not. Compared to the controls, both dichlorvos at 10.0–1000.0 μg/L and chlorpyrifos at 0.01–100.0 μg/L increased the population growth rate, but the reverse was also true for dichlorvos and triazophos both at 10000.0 μg/L. Chlorpyrifos at 10000.0 μg/L made the rotifers dead after 24-hr exposure. Dichlorvos and triazophos both at 10000.0 μg/L, and chlorpyrifos at 1000.0 μg/L all increased the ratio ovigerous females/non-ovigerous females. Both dichlorvos at 10000.0 μg/L and chlorpyrifos at 0.1–100.0 μg/L increased the mictic rate. Dichlorvos at 10.0 μg/L and 100.0 μg/L, and triazophos and chlorpyrifos both at 0.1–100.0 μg/L increased the resting egg production. Both population growth rate and ratio ovigerous females/non-ovigerous females are suitable endpoints for assessing the effects of dichlorvos, triazophos and chlorpyrifos, and mictic rate is a suitable endpoint for monitoring the effects of dichlorvos and chlorpyrifos on the reproduction of the rotifers. Both population growth rate and ratio ovigerous females/non-ovigerous females are more sensitive to dichlorvos and chlorpyrifos than mictic rate.     

Hatching of Brachionus Rubens O. F. Muller resting eggs (Rotifers)

After a dormant period at low temperature (5°C) and darkness, hatching of Brachionus rubens resting eggs is induced by an increase of temperature (10–22°C) in presence of light.     

Asexual and sexual reproduction in the rotifer Brachionus plicatilis cultured at different salinities

Two strains of the rotifer Brachionus plicatilis (L-type) differing in the levels of mictic female and male production, were grown in batch cultures with the alga Nannochloropsis gaditana as food, at two low (2.5 and 10), and two high (40 and 50) salinities. While both the low (strain S-1) and the high (strain S-3) sexual reproducing strains developed similar growth cycles at 2.5 and 10, the population growth response at 40 and 50 showed that; 1) in strain S-1, mixis can be suppressed in conditions that still allow asexual reproduction, and 2) in strain S-3 mictic female and male production are possible at nearly zero asexual population growth rates. In strain S-3, a double log linear relationship between the densities of males and females was found. These results show that mixis can occur over a wide ranges of female population density, and support the hypothesis that sexual reproduction is a strain dependent component of the general reproductive response.     

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.     

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.     

The effect of prey morphology on the feeding behaviour and population growth of the predatory rotifer Asplanchna sieboldi: a case study using five species of Brachionus (Rotifera)

1. We investigated the numerical response, functional response and prey preference of Asplanchna sieboldi to five different prey brachionids. We also analysed the feeding behaviour of the predator in terms of encounters, attacks, capture and prey ingested per unit time. 2. The five prey species (Brachionus havanaensis, B. rubens, B. patulus, B. macracanthus and B. calyciflorus) differed in their body size and spine length. 3. The population growth rates of A. sieboldi ranged from 0.074 ± 0.03 to 0.431 ± 0.02 depending on prey type and density. There was a significant impact of the spine length rather than body size per se on the population growth rates of the predator. 4. The maximum number of prey consumed depended on both body size and spine length. In the functional response analyses, the plateau was reached at a prey density of 4–8 ind. mL^?1. 5. There was a significant impact of prey density on the prey preference of the predator.     

Competitive interactions between the rotifer Synchaeta oblonga and the cladoceran Scapholeberis kingi Sars

Competition experiments showed that the small cladoceran Scapholeberis kingi rapidly excluded the rotifer Synchaeta oblonga from mixed-species cultures, but was itself unaffected by the presence of S. oblonga. Short-term experiments testing the effect of S. kingi on the survivorship and reproduction of S. oblonga showed that the former imposed a high mortality on the latter, even though shared food resources were abundant. These results indicate that adult S. kingi mechanically interferes with S. oblonga either by ingesting, or by rejecting in a damaged condition, individuals swept into its branchial chamber. In contrast to many other small species of cladocerans, and like large species of Daphnia, S. kingi has the potential to markedly suppress populations of some rotifer species through a combination of interference and exploitative competition.     

Continuous culture of the rotifer Brachionus plicatilis fed recycled algal diets

A culture system for the rotifer Brachionus plicatilis was designed to maintain higher food conversion rates and stable population densities. Two 2001 plastic tanks were employed in the culture experiments, tank A for feedback culture and tank B for a control culture. The experiments were carried out for 70 days at 24 °C, light intensity, 1500 lux, and a photoperiod of L:D 15:9. B. plicatilis were fed once a day on baker's yeast and Chlorella.Food conversion rates in tanks A and B were 24.7% and 10.1%, respectively. Population density of B. plicatilis in tank A was consistently stable at 100–150 ind. ml^–1 throughout the culture period. Density in tank B, however, showed large fluctuations after 40 or 50 days and by the end of the experiment, declined to zero.     

Particle size dependent feeding by the rotifer Brachionus plicatilis

Size selective feeding by Brachionus plicatilis was investigated with algae and bacteria (0.3–3.5 µm) and mono-disperse latex beads (0.3–3.0 µm) in short term feeding experiments. B. plicatilis demonstrated maximum clearance rate of particles with diameter 2µm, but particles with diameter down to 0.3 µm were also ingested. The clearance rate of bacteria was 15–55% of that obtained for optimal sized particles (2 µm), and was related to particle size. The relative reduction in retention of particles with diameter < 2 µm was more pronounced for latex beads than for natural food particles, suggesting other mechanisms than size to be important for the particle retention by the rotifer. This is emphasized by the fact that the clearance rates were much lower for latex beads than for natural food particles of comparable size. Efficient retention of bacteria was observed for rotifers in poor physiological condition, i.e. rotifers with low maximum clearance rate. This may reflect a strategy to optimize energy utilization by reducing locomotion costs and increasing energy intake.The results indicate that B. plicatilis has a low to medium ability to feed on bacteria. In natural ecosystems, its importance as a bacterial grazer is of limited importance. At high population densities, such as in live feed cultures, the rotifer may, however, efficiently remove bacteria from the culture.     

食物种类和浓度对红臂尾轮虫种群增长、个体大小及卵大小的影响

采用群体累积培养法,研究了藻类食物的种类和浓度对红臂尾轮虫种群增长、个体大小及卵大小的影响．结果表明,藻种类和浓度对红臂尾轮虫种群增长率、个体体积及卵体积均有极显著影响．不同食堕种空中,种群增长率以小球藻组最小,栅藻组最大;个体体积以小球藻组最小,栅藻组和混合藻组问无显著差异．种群增长率(Y,d^-1)与食物浓度(X,×10^6cells·ml^-1)间呈曲线相关,两者间的关系符合方程：y＝-0．0040x^2+0．0409X+0．4471。在所研究的食物浓度范围内,当浓度分别高于或低于6．0×10^cells·m1^-1和3．0×10^6cells·ml^-1时,轮虫个体体积和卵体积均分别呈减小的趋势。     

Disentangling the morphological stasis in two rotifer species of the <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> species complex

The taxonomic uncertainty surrounding cryptic species complexes has traditionally been resolved using lengthy experimental approaches, while, since the advent of PCR based techniques the number of cryptic species described in a variety of taxa is increasing steadily. Here we formally describe a new rotifer species of the Brachionus plicatilis complex: Brachionus manjavacas n.sp., disentangling what was known as a morphological stasis. Detailed morphological analyses demonstrated significant differences in body shape and size between B. manjavacas and B. plicatilis s.s., analysed by geometric morphometrics; unfortunately these statistical differences are not taxonomically reliable because of wide overlaps. Size and asymmetry of masticatory apparatus, named trophi, observed by SEM, gave similar results, with taxonomic ambiguity. Only the shape of small pieces of the trophi, named satellites, were consistently different between the species. On a strictly classical taxonomical basis it is absolutely useful to name new species on morphological bases, as we did, and to assess their status as distinct entities. Nevertheless, the two species are broadly similar; therefore, we do not suggest using the small differences in shape of satellites of trophi to identify the species for further ecological studies, but to continue discriminating them on genetic marker bases. Handling editor: K. Martens     

Effect of algal diet and temperature on the embryonic development time of the rotifer Brachionus plicatilis in culture

The embryonic development times of two strains of Brachionus plicatilis (Bs and S-1) cultured on three different algal diets (Nannochloris oculata, N. maculata and Nannochloropsis gaditana), have been determined at 20°C, 25°C and 30°C. As expected, the embryonic development times decreased with increasing temperature in all cases. However, embryos from adults fed on N. gaditana tended to develop more slowly than those of individuals fed on the other algal species. Mean egg volume was also affected by diet, larger eggs being produced by females fed on N. gaditana. No obvious relationship between egg size and temperature was detected.Two principal factors seemed to affect the embryonic development time. The first was temperature which acts through its well known effect on metabolic rates. The second was maternal diet which probably affects development time through its effect on yolk content, as reflected in the size of the egg.     

Effect of diazinon on life stages and resting egg hatchability of rotifer Brachionus plicatilis

The effects of organophosphate pesticide, diazinon, on life history parameters and hatchability of resting eggs of rotifer Brachionus plicalitis were assessed. Newly hatched (<1 h-old) neonates were individually cultured in six varying concentrations (0/control, 0.1, 1.0, 2.5, 5.0 and 10.0 mg/l) of diazinon. The life history parameters such as time (h) the rotifers bear first egg and release first neonate, reproductive period, net reproductive rate, mixis, intrinsic rate of population increase, and life span were evaluated. Results showed that among the life history parameters, the time the rotifers took to release neonates is the most sensitive, giving the lowest EC₅₀ value of 1.24 mg/l. The fecundity of maternal females, amictic and mictic daughters was also investigated. Rotifers exposed to 10.0 mg/l produced significantly fewer amictic daughters, and at this concentration, rotifers did not produce any mictic daughter. At 5.0 mg/l, the number of male offspring was significantly lower than the control. Furthermore, the hatchability of resting eggs produced by the rotifers was evaluated when exposed to diazinon: from birth until they produced resting eggs (early development); during late developmental stage of resting eggs (before diapause); and during diapausing stage. The hatchability of the resting eggs was not affected when exposure was timed at late developmental and diapausing stages. Overall results showed that even though amictic females reproduced normally in the presence of low-concentration of diazinon, sexual reproduction is severely affected, especially the hatchability of resting eggs when the exposure was timed on its early developmental stages. Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez Advances in Rotifer Research     

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     

The Influence of Toxic and Filamentous Blue-green Algae on Feeding and Population Growth of the Rotifer Brachionus rubens

The effect of toxic and of filamentous blue-green algae on feeding and population growth of the rotifer Brachionus rubens was investigated in laboratory experiments. A toxic strain of Microcystis aeruginosa was ingested, but rotifers cultured with Microcystis died faster than nonfed controls. The rigid filaments of Cylindrospermopsis raciborskii were not ingested, reduced the ingestion of simultaneously offered algae, and depressed population growth rates. The soft filaments of Anabaena flos-aquae were ingested at a moderate rate, did not reduce ingestion of other algae, and were used as an additional food in population growth experiments.     

High density culture of the freshwater rotifer,Brachionus calyciflorus

The freshwater rotifer, Brachionus calyciflorus is one of the live food organisms used for the mass production of larval fish. In this study possibility of obtaining high density cultures of the freshwater rotifer B. calyciflorus were investigated. The two culture systems used differed in their air and dissolved oxygen supplies using three temperatures in each case: 24, 28 and 32 °C. Rotifers were batch-cultured using 5 l-vessels and fed with the freshwater Chlorella. The growth rate of rotifers significantly increased with an increase in temperature. The maximum density of the rotifers with air-supply at 24 °C, 6500 ind. ml^–1, was significantly lower than those cultured at 28 and 32 °C, i.e. 8600 and 8100 ind. ml^–1, respectively. Dissolved oxygen levels decreased with time and ranged from 0.8 to 1.4 mg l^–1 when the density of freshwater rotifer was the highest at each temperature. The highest density (19200 ind. ml^–1) of freshwater rotifer was obtained in cultures with a supply of oxygen at 28 °C. Densities of 13500 and 17200 ind. ml^–1 were found at 24 and 32 °C, respectively. Levels of NH₃-N increased with time and a dramatic increase of NH₃-N was observed at high temperatures. Levels of NH₃-N at 24, 28 and 32 °C were 13.2, 18.5 and 24.5 mg l^–1, respectively. These levels coincided with the highest rotifer density at each of the three temperatures. When rotifers were cultured with an oxygen-supply and pH was adjusted to 7, the maximum density of rotifer reached 33500 ind. ml^–1 at 32 °C . These results suggested that high density culture of freshwater rotifer, B. calyciflorus could be achieved under optimal conditions with DO value of exceeding 5 mg l^–1 and NH₃-N values of lower than 12.0 mg l^–1.     

Effect of unionized ammonia,viscosity and protozoan contamination on reproduction and enzyme activity of the rotifer Brachionus rotundiformis

We determined the effect of environmental stressors on the physiological condition of Brachionus rotundiformis. For two morphologically distinct B. rotundiformis strains: Hawaii (average lorica length = 222 m) and Langkawi strains (average lorica length 180 m), neonates hatched from resting eggs were exposed to different levels of unionized ammonia (0.7–9.8 mg l^–1), viscosity (relative viscosity against natural seawater = 1–1.17) and Euplotes sp. (protozoan) contamination (1–40 cells ml^–1). Increasing stress decreased fecundity and lifespan of both rotifer strains. Glucosidase and phospholipase activities were correlated with reproductive responses of both the strains exposed to unionized ammonia. When culture water viscosity was changed, the activity of esterase and phospholipase was correlated with reproductive responses of the Hawaiian strain, and glucosidase activity was correlated with those of Langkawi strain.With the protozoan contamination, esterase and glucosidase activities were correlated only with reproductive responses of the Hawaiian strain, while activity of all three enzymes was correlated to those of the Langkawi strain. Glucosidase activity proved to be a reliable indicator of stress for cultured B. rotundiformis.