Brachionus Species Research Articles

Evaluation of DNA methodologies in identifying Brachionus species used in European hatcheries

Few efforts have dealt with the genetic make up of the Brachionus plicatilis rotifers which are often used as live feed in the larviculture of many marine fish. Recent results have demonstrated that the B. plicatilis species is actually a species complex. In this study a number of molecular markers (Restriction Fragment Length Polymorphism (RFLP) analysis of mitochondrial COI gene, Single-Stranded Conformation Polymorphism (SSCP) analysis and Denaturing Gradient Gel Electrophoresis (DGGE) of mitochondrial 16S rRNA gene as well as microsatellite genotyping of nuclear loci) have been developed and applied to identify genetically rotifer strains used in European hatcheries. All methods have proven highly efficient for the reliable diagnosis of the genetic variability within hatchery strains at bulk or individual level. Results point towards an absence of the typical B. plicatilis and Brachionus rotundiformis species and a predominance of the Brachionus sp. Cayman biotype ( Brachionus SM morphological type). All the other biotypes/species were either rarely found or were coexistent with B. sp. Cayman. These biotypes were B. plicatilis sensu stricto, B. sp. Nevada and B. sp. Austria, all belonging to the Brachionus L group. Minimal genetic variability was detected within strains. The above results have important implications for rotifer cultures, with respect to the different temperature and salinity optima of each biotype/species. Caution is needed regarding the common practice used by hatcheries around the world of exchanging samples based solely on morphological criteria.

Combined Effects of Food Concentration and Temperature on Competition Among Four Species of Brachionus (Rotifera)

Combined Effects of Food Concentration and Temperature on Competition Among Four Species of Brachionus (Rotifera)

Removal of Surface Glycoproteins and Transfer among Brachionus species

Removal of Surface Glycoproteins and Transfer among Brachionus species

Desenvolvimento de juvenis de Piracanjuba (Brycon orbignyannus), Vallencienes (1849) (Teleostei: characidae) em tanques experimentais fertilizados com adubação orgânica

The objective of this paper was to study the development of Piracanjuba (Brycon orbignyanus ) in tanks under differents organic fertilizers. The experiment, entirely randomized, was accomplished in 16 tanks of 1000 liters, fertilized with manures of bovine (BOV), pigs (SUI), chickens (FRG) and others without fertilizer (SAO), using 15 fish/m 3 with an initial average weight and length of 10,87+0,31 g e 9,78+0,07 cm. After 30 days, the experiment showed a uniform development of the fish and high survival rate in the studied density. The treatments presented significant statistical differences (P Scenedesmus species, and the Cianophyta, with the Microcystis species, and among the zooplankton, the largest presence was of the rotifera from the species Brachionus and Keratella , followed by the copepods. The treatment fertilized with manure of chickens made possible a larger development of the plankton community, and better results of the development of the fish, demonstrating the importance of natural food in its diet.

Seasonal Variations in the Species Diversity of Planktonic Rotifers in Lake Xochimilco, Mexico

ABSTRACT We collected rotifers during one year (2002–2003) from four different sites in Lake Xochimilco and analyzed the species diversity. We found on an average 25–30 species co-existing at any one site, and rotifer species density was highest in the summer months. The common genera found throughout the year were Brachionus, Keratella, Polyarthra, Trichocerca, Filinia and Asplanchna, and we often found six to eight species of Brachionus in the same sample. Keratella cochlearis and K. tropica were often found together, as were Trichocerca similis, T. pusilla and T. cylindrica. The genus Asplanchna was represented almost exclusively by A. brightwelli.

Acute toxicity of water extract of Tephrosia vogelii Hook to species relevant in aquaculture ponds: rotifers, Cyclops, mosquito larvae and fish

Summary Rotenone is used to clear ponds of unwanted organisms and trash fish which may predate on fish when the ponds are stocked. Toxicity tests using water extract of the leaves of Tephrosia vogelii Hook, which contains rotenone, were conducted on rotifers (Brachionus species), Cyclops, mosquito larvae (Culex species) and fish (Aphyosemion gardneri nigerianum) in static bioassays. The 48-h LC50s were derived from probit curves using the probit-analysis method, while chisquare was used to test for significant differences between observed mean mortalities and predicted mean mortality values. These showed no significant differences (P > 0.05). The variance ratio of the replicates in each treatment also showed no significant difference (P > 0.05). The 48-h LC50s were found to be 2.89, 1.04, 4.48 and 0.24 mg L )1 for rotifers, Cyclops, mosquito larvae and fish, respectively. The probit mortalities were positively correlated with the log-concentration, except for the rotifers bioassay, which was negative. The fish, A. gardneri nigerianum, was the most sensitive; the mosquito larvae were the least sensitive.

Population density, sexual reproduction and diapause in monogonont rotifers: new data for Brachionus and a review

Diapausing, fertilized eggs in monogonont rotifers typically are formed after an environmental signal induces amictic females to produce mictic daughters. Mictic females lay haploid eggs that may develop parthenogenetically into males, or that may be fertilized and develop into diapausing, female embryos called resting eggs. Laboratory experiments demonstrate that crowding is the signal for production of mictic females in strains of Brachionus calyciflorus from Texas, Spain and Germany, and in a strain of Brachionus variabilis from Spain. In these experiments, newborn amictic females were cultured singly in large and small volumes to give lowand high-density treatments. Therefore, the induction of mictic females is due exclusively to population density and cannot be attributed to a grouping effect involving some interaction among individuals. B. variabilis is very sensitive to population density; females had to be cultured in 30 ml to prevent appreciable production of mictic daughters. Crowding is now known to be the signal for initiation of sexuality and diapause in four species of Brachionus, two species of Epiphanes, and Rhinoglena frontalis. The chemical that mediates this response somehow influences oocytes in the maternal body cavity to differentiate into mictic females. Aggregation of individuals in natural systems may facilitate the production of mictic females. In some of these rotifers, the response to crowding is suppressed in early generations from the resting egg, assuring that clonal populations will attain higher population densities before committing to sexual reproduction. Fitness benefits of the mictic-female response to crowding, and to other environmental signals in other rotifers (dietary tocopherol, long photoperiod), are discussed.

The ciliate epibiont Epistylis pygmaeum: selection for zooplankton hosts, reproduction and effect on two rotifers

SUMMARY1. A clonal culture of the peritrich Epistylis pygmaeum was used for all observations and experiments. Motile cells preferentially attached to the eggs of three species of Brachionus but also attached to the body of adult B. angularis. Zooids on the transitory egg substratum developed only short stalks, while those on the body often developed long stalks and branched colonies. Selection for the eggs positions the ciliate near the cloaca, and thus high concentrations of fine particulate material excreted by the host. Settlement on eggs occurred equally well in the light and dark, and on moving and stationary eggs.2. Motile Epistylis cells attached to a wide variety of rotifer and crustacean zooplankton, but exhibited some pronounced selectivity. They readily settled on the eggs of other rotifers (Epiphanes, Polyarthra), on the carapace of several cladocerans (Ceriodaphnia, Daphnia, Diaphanosoma), and on the egg sacs of a copepod (Tropocyclops). They settled less readily on the bodies of the rotifers Asplanchna and Synchaeta, and rarely or never settled on the rotifer Keratella, the cladocerans Bosmina and Scapholeberis, and the body of the copepod.3. Epistylis populations initiated with a single zooid on Brachionus increased exponentially and often contained several hundred attached zooids and motile cells after 3 days at 20 °C. Observations of a culture initiated from a single telotroch provided new information about peritrich life cycles: (1) motile cells reproduced themselves at a rapid rate (λ = 4.26 day−1); (2) telotrochs produced or transformed into swimming zooids and vice versa. Functions of the two types of motile cells remain to be clarified. Telotrochs likely are specialised for finding and attaching to hosts. Swimming zooids can feed and reproduce, producing both their own cell type and telotrochs. Together, they should enhance dispersal and population growth, especially when hosts are rare.4. Life‐table experiments with two species of Brachionus showed that colonisation by Epistylis had no effect on adult survival but significantly decreased fecundity, by 29% in both cases. Zooids attached to eggs could be a weight burden, increase drag, and possibly inhibit egg development. Those on the body of B. angularis also could interfere with coronal cilia, inhibiting feeding and further slowing locomotion. The ability of E. pygmaeum to select and then interfere with its hosts indicates that this epibiont has the potential to influence the species structure of zooplankton communities.

Population growth of herbivorous rotifers and their predator ( Asplanchna ) on urban wastewaters

We studied the population growth of three Brachionus species ( B. calyciflorus , B. patulus and B. rubens ) using domestic (Mexico City) wastewater at different phases of treatment (treated: type C, partially treated: type B and crude: type A). We also evaluated growth characteristics of a predatory rotifer ( Asplanchna sieboldi ) fed B. rubens raised on wastewater and compared the growth rates of animals fed cultured algae. All the three tested brachionid species grew well in controls (i.e. fed on the alga Chlorella ). However, populations of B. calyciflorus and B. patulus did not grow on the fully treated wastewater (type C). All three brachionid species grew poorly on par tially treated wastewater (type B). In crude wastewater, B. rubens reached densities as high as 200 ind. ml –1 . Regardless of Brachionus species, the rates of population increase per day (r) varied between 0.29 and 0.4 in the controls. B. rubens in crude wastewater experienced steep mortality in the first two days but stabilized thereafter. It had generation times, which varied from 3 to 5 days depending on the treatment. Prey ( B. rubens ) raised on wastewater supported better population growth of A. sieboldi , the highest being from crude wastes. The growth rate of A. sieboldi fed B. rubens , raised on crude wastewater, was the highest (∽ 0.8 d –1 ). Thus, the present study showed that culturing of certain species of brachionid rotifers on crude wastewater or partially treated is feasible without addition of alga.

Resource competition and patterns of sexual reproduction in sympatric sibling rotifer species

We present experimental data on the reproduction patterns of three sympatric sibling rotifer species, belonging to the Brachionus plicatilis complex, as they compete for food. Variation existed in the amount and pattern of sexual reproduction among the three cyclical parthenogenetic species. Competitive exclusion between the three Brachionus species was related to a higher investment in sexual reproduction by the inferior competitor. In general, no correlation was found between sexual reproduction and population density in a given species. However, when pairs of competing species were compared, a negative relationship between sexual investment differences (between species) and average population density differences was frequently found. From the results we conclude that: (1) the characteristic sexual pattern of each species has some implications for the competitive outcome; (2) allocation of resources into sexual reproduction does not mediate coexistence; and (3) the response of sexual reproduction to competitive interaction is unlikely to determine competition outcome. Nevertheless, our results suggest that the competitively inferior species invests more in sexual reproduction, as a response to resource limitation, which would accelerate its exclusion.

Resource competition between sympatric sibling rotifer species

Mechanisms underlying competitive interactions are important in understanding the structure of planktonic communities, particularly the coexistence of similar species. Here we present experimental results of exploitative competition among three sympatric sibling species of the Brachionus plicatilis complex for two differently‐sized species of food microalgae. These three rotifer species are to be found in seasonal succession in brackish ponds on the Spanish Mediterranean coast; they can, however, co‐occur for long periods. The functional and numerical responses of the three Brachionus species to both food microalgae, although similar, differed. Neither rotifer population growth nor grazing rates showed a clear positive correlation between rotifer and alga sizes. Tilman's models were applied to these results in order to predict the outcome of competition in two rotifer, two resources systems. For testing predictions and addressing the possibility of rotifer coexistence, we performed pairwise competition experiments in semicontinuous cultures, which introduces periodic disturbance as an additional factor. Results confirmed the pattern expected from Tilman's models regarding the competitive superiority of each rotifer species, when food composition was biased toward one of the two resources. This shows the relevance of the food threshold concept to predict the superior competitor. However, coexistence of rotifers was found in conditions in which Tilman's models had predicted an unstable equilibrium, with the winning species depending on the initial conditions. We hypothesize that variance in food availability mediated coexistence. Our results suggest that both food partitioning and disturbance are important in explaining the coexistence of these sibling species in nature.

The effects of fluid motion on toxicant sensitivity of the rotifer Brachionus calyciflorus

Standardized methods for estimating the toxicity of anthropogenic compounds to aquatic organisms frequently fail to consider key elements of the test organisms’ environment. Aquatic organisms exist in a fluid environment, and fluid dynamics may have an important influence on the response to toxicants. Rotifers are one of the three major groups of zooplankton and have been increasingly utilized in standardized toxicity testing. However, like other toxicity tests, assays with the species Brachionus calyciflorus are performed under static conditions in the absence of fluid motion. We investigated how fluid motion modifies pentachlorophenol (PCP) toxicity to B. calyciflorus using 24 h acute and 48 h reproductive toxicity tests. Estimates of PCP LC50s and reproduction EC50s in static conditions decreased from 738 and 1082 μg l −1, respectively, to as low as 262 and 136 μg l −1, respectively, in fluid motion. Flow analysis indicated that increased toxicant sensitivity can occur at ecologically relevant levels of fluid motion. Mechanistic studies indicated that fluid motion/toxicant interactions may result from the ability of fluid motion to cause shear stress, alter toxicant uptake, and/or alter the bioavailability of food. As fluid motion may have an important effect on the life histories of a wide variety of aquatic organisms, fluid motion/toxicant interactions may be an important consideration in other standard test organisms. These results raise questions about the accuracy of ecological risk assessments based on toxicity data from static conditions.

A routine method of DNA-extraction from extremely small metazoans, e.g. single rotifer specimens for RAPD-PCR analyses

A simple and efficient method has been developed for isolating genomic DNA from single specimens of extremely small metazoan animals, e.g. rotifers (Rotifera: Monogononta). The amount and quality of the extracted DNA allows the Random Amplified Polymorphic DNA Polymerase Chain Reaction (RAPD-PCR) to be employed with up to three random primers per specimen. Reproducibility of RAPD-fingerprints has been checked and verified. Exemplarily, RAPD patterns of three Brachionus species (B. angularis, B. calyciflorus, B. urceolaris) amplified with the primer OPA 07 are demonstrated.

Optimal prey size for early turbot larvae ( Scophthalmus maximus L.) based on mouth and ingested prey size

Mouth size and gut contents were examined in turbot ( Scophthalmus maximus L.) larvae from first exogenous feeding to day 10. The larvae were fed on three organisms (two Brachionus species and Artemia nauplii) differing in size. A logarithmic relationship was found between mouth size (width and height) and standard length (SL) of larvae, and a linear relationship between prey size and SL of larvae. Considering the mean size of prey found in the guts of larvae fed on a range of prey sizes, the optimal prey size was determined over the study period. The optimal prey width corresponded to 36±1% of the mouth height (MH). The relationship between optimal prey size and mouth width (MW) was more variable (40±4%). Therefore, the former relationship was found to be more adequate in determining optimal prey size. The optimal prey width for first feeding larvae (day 2 posthatching) was found to be 144 μm, increasing to 225 μm at day 10. The relationships were described by mathematical equations that can be useful to optimise both ingestion and growth rates under rearing conditions.

Differences in predation among morphotypes of the rotifer Asplanchna silvestrii

Summary1. Interactions were observed between three morphotypes of the predatory rotifer Asplanchna silvestrii and six different prey (Brachionus plicatilis, B. rotundiformis, B. pterodinoides, B. satanicus, Hexarthra jenkinae and copepod nauplii) to understand the differences in feeding abilities among morphotypes that may have led to the evolution of this predator polymorphism. The outcome of predation events was affected significantly, both by predator morphotype and prey type. Predator morphotypes also interacted differently with different prey types.2. The two smaller morphotypes, the saccate and the cruciform, responded similarly to prey overall, except that the smallest morphotype (saccate) was unable to ingest the most mobile prey (nauplii) and less able to ingest relatively large prey (B. plicatilis). The largest morphotype, the campanulate, had the highest encounter rate with prey, but the lowest probability of attack after encounter, so that it consumed far fewer prey per feeding bout than did the smaller morphotypes. This may have been because campanulates prefer larger prey than used in this study.3. Highly mobile prey (H. jenkinae and copepod nauplii) were much less susceptible to predation than the less mobile Brachionus species. While evasiveness reduced attacks by saccates and cruciforms, campanulates did not have a significantly lower attack rate on H. jenkinae and copepod nauplii than on less evasive prey. Large body size moderately defended B. plicatilis against ingestion by saccates only. The short‐spined B. satanicus was the only prey that was rejected after capture, resulting in lower ingestion probabilities for B. satanicus than other brachionid prey.

Dynamics of natural rotifer populations

New tools for analyzing ecological time series have permitted the construction of rigorous models from relatively short series. We have applied these techniques to abundance data for nine natural rotifer populations to construct realistic models of their dynamics. Species included are Asplanchna girodi, Filinia pejleri, Keratella tropica, Monostyla bulla, Brachionus rotundiformis, and four other Brachionus species. The overall shapes of the time series were similar with an initial peak followed by oscillations of varying amplitude around a mean of lower population density. Auto correlation functions (ACF) for all populations were positive at small time lags and decayed rapidly to zero. This suggest that these are stationary, exponentially damped time series, fluctuating arround a constant mean with constant variance. The rapid decay of the ACFs indicates that the effect of a perturbation on these populations is quickly removed in one or two days. Phase portrait plots of log current population density vs log lagged density indicate that the time series are stable and non-chaotic. One type of model yielded the highest R2 for four of the nine species and was designated the consensus model. The mean R2 of this model for all nine species was 0.53 with a coefficient of variation of 38%. Lyapanov exponents were strongly negative, indicating that these populations rapidly return to equilibrium after an exogenous perturbation. Rotifer populations appear to be tracking very recent perturbations and their dynamics cannot be predicted from perturbations in the more distant past. We investigated the effects of increasing the level of stochasticity in the consensus model on the length of the growing season and resting egg production. Increasing stochastic variance increased the probability of extremely low population densities, shortening the growing season. In shorter growing seasons, fewer resting eggs were produced, other factors being equal. Counteracting this negative effect, was an increased probability of extremely high populations densities which increased mixis and resting egg production. Constructing models accurately depicting the dynamics of natural zooplankton populations should improve aquatic ecosystem models.

Chemical ecology of rotifers

One of the primary channels of sensory input for zooplankton are chemical signals. Much zooplankton behavior is triggered by chemical stimuli, including feeding, predator defense, mating, and migration. Chemically regulated zooplankton behavior affects larger scale ecosystem processes like grazing, recruitment and secondary production. Knowledge of how chemicals transmit information about location, food quality, conspecifics, competitors, and predators is critical for understanding how aquatic ecosystems function. This paper reviews the behavioral evidence that planktonic rotifers respond to a variety of chemical stimuli. Although a rich variety of rotifer behaviors are regulated by chemical signals, little progress has been made to isolate and characterize these stimuli. If aquatic ecology is to become a predictive science, knowledge of the mechanisms causing the observed interactions is necessary. Chemical signals need to be isolated, purified, and characterized, and their causal role in regulating population and community processes needs to be demonstrated. Rotifers have chemosensory neurons in their corona and electron microscopy has revealed chemoreceptive pores in the anterior integument of several species. Some rotifers use these chemoreceptors to discriminate food particles based on the flavors on the cell surface. In Asplanchna, prey are discriminated by contact chemoreception. Asplanchna releases a waterborne signal that induces spine formation in several Brachionus species, Keratella cochlearis, K. slacki, and Filinia longisecta. The colonial Sinatherina socialis is defended against fish predation by warts containing unpalatable chemicals that have yet to be identified. Larval settlement in Collotheca gracillipes is determined by the chemistry of aquatic plant surfaces. Larvae prefer the undersurface of leaves where there is a low Ca{++} microhabitat due to photosynthesis. Oviposition in Euchlanis dilatata is restricted to plant surfaces familiar to the maternal female. Hydrogen peroxide and certain prostaglandins stimulate resting egg hatching even in the dark. Sexual reproduction and polymorphism in Asplanchna sieboldi is regulated by dietary tocopherol. A chemical signal that allows assessment of conspecific population density is detected in conditioned media by several rotifer species. Water soluble extracts of Brachionus plicatilis increase mictic female production 1.7 times more than controls. Unknown compounds produced by certain bacteria also increase mixis 4–10 fold over controls. Mate recognition in B. plicatilis is determined by a 29 kD surface glycoprotein called the mate recognition pheromone (MRP). The MRP has been isolated, purified, and a polyclonal antibody against it has been prepared. The structure of the oligosaccharide and protein components of the MRP are currently being characterized. Elucidation of the chemicals regulating rotifer life cycles will make important contributions to the understanding of ecological processes in aquatic communities.

Brachionus species of some inland waters in Nigeria with a note on a new record and Zoogeography

Brachionus species of some inland waters in Nigeria with a note on a new record and Zoogeography

Morphology, reproduction, genetics, and mating behavior of small, tropical marine Brachionus strains (Rotifera)

Small, tropical marine Brachionus (SS strains) are distinguished by their lorica size and shape. Their relation to other marine Brachionus species, however, remains unknown. We examined morphometry, reproductive mode, allozyme patterns and mating behavior among marine Brachionus species in an attempt to classify SS strains. Based on morphological features, reproductive mode, and allozyme patterns, SS strains were most similar to those of B. rotundiformis Tschugunoff. Observations on mating behavior between different groups indicated that there is reproductive isolation between B. plicatilis O.F. Müller and B. rotundiformis and between B. plicatilis and SS strains. In contrast, copulation was observed between B. rotundiformis and SS strains. Thus, there is no evidence that SS strains are a new marine Brachionus species, and most likely should be included in B. rotundiformis.

Rotifer community structure in the south basin of Lake Biwa

Seasonal changes in abundance and species composition of rotifers were surveyed at five locations under different physical and chemical conditions in the south basin of Lake Biwa during July 1987–June 1988. Total density of rotifers showed similar seasonal fluctuation with three peaks, although the maximum density showed north (low)-south (high) gradient. Polyarthra spp. (P. vulgaris and P. dolichoptera with low density) dominated except during July–October 1987 and April–May 1988. In the former period the species of Brachionus, Trichocerca, Filinia and Hexarthra, and in the latter, those of Synchaeta, Keratella and Kellicottia had somewhat different proportions in the communities of north and south stations, respectively. The difference in composition during July–October suggests a difference of trophic state between the northern and southern areas in the south basin of Lake Biwa. However, the dominance of Polyarthra and the difference in the composition during April–May 1988 could not be explained by such a difference in trophic state. No critical difference was observed in the community structure of the eastern area of the south basin, where the seasonal fluctuations in nutrient levels and phytoplankton community structure were different from other areas in the south basin. The present results, therefore, suggest that physical and chemical conditions were not effective in controlling the rotifer community structure in the south basin of Lake Biwa.