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Predator–prey interactions are crucial components of populations and communities. Their dynamics depend on the covariation of traits of the interacting organisms, and there is increasing evidence that intraspecific trade‐off relationships between defense and competitive traits are important drivers of trophic interactions. However, quantifying the relevant traits forming defense–competitiveness trade‐offs and how these traits determine prey and predator fitness remains a major challenge. Here, we conducted feeding and growth experiments to assess multiple traits related to defense and competitiveness in six different strains of the green alga Chlamydomonas reinhardtii exposed to predation by the rotifer Brachionus calyciflorus. We found large differences in defense and competitive traits among prey strains and negative relationships between these traits for multiple trait combinations. Because we compared trait differences among strains whose ancestors evolved previously in controlled environments where selection favored either defense or competitiveness, these negative correlations suggest the presence of a trade‐off between defense and competitiveness. These differences in traits and trade‐offs translated into differences in prey and predator fitness, demonstrating the importance of intraspecific trade‐offs in predicting the outcome of predator–prey interactions. [ABSTRACT FROM AUTHOR]

We quantified the effect of two cyclopoids, an invasive (Mesocyclops pehpeiensis) and a native (Mesocyclops longisetus curvatus) species on the population growth of the rotifers Brachionus havanaensis and Brachionus calyciflorus. We hypothesized that the invasive copepod would have a greater adverse effect on the test rotifers. The population growth of B. havanaensis was tested in the indirect presence of B. calyciflorus (used as prey for the predatory copepods), and the predatory copepods, M. pehpeiensis and M. longisetus curvatus. For B. calyciflorus the experimental design was as above except that we used B. havanaensis as prey. The test rotifers were separated from the competitors and predators by mesh cages placed in the experimental jars. Rotifer density and the egg ratios were quantified, followed by a daily medium change, until the population density declined. The population growth rate of B. havanaensis ranged between 0.26 and 0.30 day−1, while that of B. calyciflorus between 0.19 and 0.21 day−1. The presence of the invasive copepod had an adverse effect on the smaller (< 110 µm) B. havanaensis, but not on the larger (> 180 µm) B. calyciflorus. The results are discussed with emphasis on the differences in the indirect impact invasive and native predatory copepods. [ABSTRACT FROM AUTHOR]

Maternal effect plays important role in adaptive evolution and population dynamics. Methylparaben (Mep) is a common organic pollutant exerting diverse impacts on aquatic organisms. However, the impact of maternal Mep exposure on offspring remains poorly understood. This study was designed to explore whether maternal Mep exposure can affect the offspring's population performance, either by amictic mothers in parthenogenesis phase, or by mictic mothers in sexual reproduction phase of the rotifer Brachionus calyciflorus. Here, we exposed either amictic or mictic mothers from one clonal laboratory population to 20 mg/L Mep (T environment) until the offspring or resting eggs were collected. A parallel control group without Mep (C environment) was also set. Thereafter, offspring from amictic mothers or stem female from resting eggs of mictic mothers were treated similarly in T or C environment. Population growth, life history traits and antioxidant indices of the offspring were examined. The results demonstrated that maternal Mep exposure inhibited population performance of offspring in both life history phases, while the negative effects were markedly buffered in sexual reproduction phase. This study clarifies toxicity of Mep on rotifers and highlights the different response patterns of maternal Mep exposure in different life history phase. [ABSTRACT FROM AUTHOR]

Copyright of Asian Journals of Ecotoxicology is the property of Gai Kan Bian Wei Hui and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Toxic effects of tribromomethane (TBM), a most used drinking water disinfection byproduct, on rotifers are unknown. we investigated the effects of TBM (0, 0.001, 15, 30, 45, 60, and 75 mg/L) on the life table demography of the freshwater rotifer, Brachionus calyciflorus, fed with three densities (1.0, 2.0, and 4.0 × 106 cells/mL) of Scenedesmus obliquus. It showed that the TBM exposure decreased survivorship and fecundity of the rotifer and significantly affected the developmental stages and life table demographic parameters of B. calyciflorus. Compared with the control, treatments with 30-75 mg/L TBM significantly prolonged the juvenile period of rotifer under different algal densities. Treatments with 0.001 and 15 mg/L TBM significantly decreased the net reproductive rate of rotifer under the algal density of 1.0 × 106 cells/mL, while increased and did not affect it under the algal density of 2.0 and 4.0 × 106 cells/mL, respectively. These results demonstrate that TBM is toxic to B. calyciflorus, and the increased algal density can reduce the toxic effects of TBM on rotifers. The current safety limit of TMB in natural water could affect the community structure of organisms in the aquatic system. [ABSTRACT FROM AUTHOR]

Cytostatic drugs are one of the most important therapeutic options for cancer, a disease that is expected to affect 29 million individuals by 2040. After being excreted, cytostatics reach wastewater treatment plants (WWTPs), which are unable to efficiently remove them, and consequently, they will be released into the aquatic environment. Due to the highly toxic properties of cytostatics, it is particularly relevant to evaluate their potential ecological risk. Yet, cytostatics toxicity data is still not available for various species. In this work, the ecotoxicity of two widely consumed cytostatics, cyclophosphamide (CYP—as a model cytostatic) and mycophenolic acid (MPA—as a priority cytostatic), was evaluated on three freshwater species—Raphidocelis subcapitata, Brachionus calyciflorus, and Danio rerio, and the risk quotient (RQ) was assessed. Both drugs significantly affected the yield and growth inhibition of the microalgae, while for rotifers, the least sensitive species, only significant effects were registered for CYP. These drugs also caused significant effects on the mortality and morphological abnormalities on zebrafish. The estimation of the RQ discloses that CYP seems to pose a low risk to aquatic biota while MPA poses a very high risk. Altogether, these results emphasize the need for more complete environmental risk assessments, to properly prioritize and rank cytostatics according to their potentially toxic effects on the environment and aquatic biota. [ABSTRACT FROM AUTHOR]

Zooplankton provides bacteria with a complex microhabitat richen in organic and inorganic nutrients, and the bacteria community also changes the physiochemical conditions for zooplankton, where the symbiotic relationship between them plays an important role in the nutrient cycle. However, there are few studies on the effect of associated bacteria on the population dynamics of rotifers. In order to make clear their relationships, we reconstructed the associated bacterial community in Brachionus calyciflorus culture, and examined the life history and population growth parameters, and analyzed the diversity and community composition of the associated bacteria at different growth stages of B. calyciflorus. The results showed that the addition of bacteria from natural water can promote the population growth and asexual reproduction of B. calyciflorus, but has no significant effect on sexual reproduction, exhibited by the improvement of its life expectancy at hatching, net reproduction rates and intrinsic growth rate, no significant effects on the generation time and mixis ratio of offspring. It was found that the B. calyciflorus-associated bacterial community was mainly composed of Proteobacteria, Bacteroidota, Actinobacteriota, Cyanobacteria and Firmicutes. Through correlation network analysis, the members of Burkholderiales, Pseudomonadales, Micrococcales, Caulobacterales and Bifidobacteriales were the keystone taxa of B. calyciflorus-associated bacteria. In addition, the relative abundance of some specific bacteria strains increased as the population density of B. calyciflorus increased, such as Hydrogenophaga, Acidovorax, Flavobacterium, Rheinheimera, Novosphingobium and Limnobacter, and their relative abundance increased obviously during the slow and exponential phases of population growth. Meanwhile, the relative abundance of adverse taxa (such as Elizabethkingia and Rickettsiales) decreased significantly with the increase in rotifer population density. In conclusion, the closely associated bacteria are not sufficient for the best growth of B. calyciflorus, and external bacterioplankton is necessary. Furthermore, the function of keystone and rare taxa is necessary for further exploration. The investigation of the symbiotic relationship between zooplankton-associated bacterial and bacterioplankton communities will contribute to monitoring their roles in freshwater ecosystems, and regulate the population dynamics of the micro-food web. [ABSTRACT FROM AUTHOR]

The growth rate hypothesis (GRH) posits that the relative body phosphorus content of an organism is positively related to somatic growth rate, as protein synthesis, which is necessary for growth, requires P‐rich rRNA. This hypothesis has strong support at the interspecific level. Here, we explore the use of the GRH to predict microevolutionary responses in consumer body stoichiometry. For this, we subjected populations of the rotifer Brachionus calyciflorus to selection for fast population growth rate (PGR) in P‐rich (HPF) and P‐poor (LPF) food environments. With common garden transplant experiments, we demonstrate that in HP populations evolution toward increased PGR was concomitant with an increase in relative phosphorus content. In contrast, LP populations evolved higher PGR without an increase in relative phosphorus content. We conclude that the GRH has the potential to predict microevolutionary change, but that its application is contingent on the environmental context. Our results highlight the potential of cryptic evolution in determining the performance response of populations to elemental limitation of their food resources. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Hydrobiology is the property of Editorial Department of Journal of Hydrobiology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Simple Summary: This study explored the relationship between Brachionus calyciflorus-associated bacterial and bacterioplankton communities in freshwater. We believe that our study makes a significant contribution because zooplankton and bacterioplankton are the basic components in the aquatic ecosystem, zooplankton has an important role between lower (phyto-, protozooplankton) and higher (fish) trophic levels, and bacteria participate in biogeochemical cycle processes such as nitrogen and carbon cycle, where the symbiotic relationship between them plays an important role in the nutrient cycle, so researching the symbiotic relationship between them will contribute to monitoring the process of environmental change and ecological restoration. Overall, our study expands the current understanding of zooplankton–bacteria interaction and promotes the combination of two different research fields. Zooplankton bodies are organic-rich micro-environments that support fast bacterial growth. Therefore, the abundance of zooplankton-associated bacteria is much higher than that of free-living bacteria, which has profound effects on the nutrient cycling of freshwater ecosystems. However, a detailed analysis of associated bacteria is still less known, especially the relationship between those bacteria and bacterioplankton. In this study, we analyzed the relationships between Brachionus calyciflorus-associated bacterial and bacterioplankton communities in freshwater using high-throughput sequencing. The results indicated that there were significant differences between the two bacterial communities, with only 29.47% sharing OTUs. The alpha diversity of the bacterioplankton community was significantly higher than that of B. calyciflorus-associated bacteria. PCoA analysis showed that the bacterioplankton community gathered deeply, while the B. calyciflorus-associated bacterial community was far away from the whole bacterioplankton community, and the distribution was relatively discrete. CCA analysis suggested that many environmental factors (T, DO, pH, TP, PO43-, NH4+, and NO3-) regulated the community composition of B. calyciflorus-associated bacteria, but the explanatory degree of variability was only 37.80%. High-throughput sequencing revealed that Raoultella and Delftia in Proteobacteria were the dominant genus in the B. calyciflorus-associated bacterial community, and closely related to the biodegradation function. Moreover, several abundant bacterial members participating in carbon and nitrogen cycles were found in the associated bacterial community by network analysis. Predictive results from FAPROTAX showed that the predominant biogeochemical cycle functions of the B. calyciflorus-associated bacterial community were plastic degradation, chemoheterotrophy, and aerobic chemoheterotrophy. Overall, our study expands the current understanding of zooplankton–bacteria interaction and promotes the combination of two different research fields. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Hydrobiology is the property of Editorial Department of Journal of Hydrobiology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Simple Summary: Many animals that have to cope with predation have evolved mechanisms to reduce their predation risk. One of these mechanisms is change in morphology, for example, the development of spines. These spines are induced, when mothers receive chemical signals of a predator (kairomones) and their daughters are then equipped with defensive spines. We studied the behaviour of a prey and its predator when the prey is either defended or undefended. We used common aquatic micro-invertebrates, the rotifers Brachionus calyciflorus (prey) and Asplanchna brightwellii (predator) as experimental animals. We found that undefended prey increased its swimming speed in the presence of the predator. The striking result was that the defended prey did not respond to the predator's presence. This suggests that defended prey has a different response behaviour to a predator than undefended conspecifics. Our study provides further insights into complex zooplankton predator-prey interactions. Predation is a strong species interaction causing severe harm or death to prey. Thus, prey species have evolved various defence strategies to minimize predation risk, which may be immediate (e.g., a change in behaviour) or transgenerational (morphological defence structures). We studied the behaviour of two strains of a rotiferan prey (Brachionus calyciflorus) that differ in their ability to develop morphological defences in response to their predator Asplanchna brightwellii. Using video analysis, we tested: (a) if two strains differ in their response to predator presence and predator cues when both are undefended; (b) whether defended individuals respond to live predators or their cues; and (c) if the morphological defence (large spines) per se has an effect on the swimming behaviour. We found a clear increase in swimming speed for both undefended strains in predator presence. However, the defended specimens responded neither to the predator presence nor to their cues, showing that they behave indifferently to their predator when they are defended. We did not detect an effect of the spines on the swimming behaviour. Our study demonstrates a complex plastic behaviour of the prey, not only in the presence of their predator, but also with respect to their defence status. [ABSTRACT FROM AUTHOR]

A new cultivation system with the chlorophyte Monoraphidium contortum combined with a self-sustaining culture of the freshwater rotifer Brachionus calyciflorus was applied for Sander lucioperca (L.) larviculture. Survival, morphometrics, as well as fatty acid composition of pikeperch larvae were analyzed after a ten-day feeding period. By using the pseudo-green water technique with improved aeration and water movement at the surface, survival rates reached up to 94%, with a total larval length of 8.1 ± 0.3 mm and a specific length growth rate of up to 4.1% day−1 for S. lucioperca. The biochemical composition of B. calyciflorus and especially its contents in C18 PUFAs and suitable n-3/n-6 ratios met the nutritional requirements of pikeperch larvae. The high abundance of highly unsaturated fatty acids (HUFAs) in the diet appeared to be less important in the first feeding due to a possible retention of essential fatty acids, which originate from the yolk sac reserves, at adequate levels. Exponential growth of microalgae and zooplankton under the applied conditions was most effective when stocking M. contortum five days and B. calyciflorus three days before adding the fish larvae. Appropriate timing and sufficient live feed density allowed a successful integration of B. calyciflorus into pikeperch larviculture. We hypothesize that feeding pikeperch larvae with a self-sustaining Brachionus-culture under pseudo-green water conditions with minor disruptions during larviculture will improve survival and growth. This system is a first step towards pikeperch larviculture inside recirculated aquaculture systems (RAS) under continuous feed supply with live feed within the same aquaculture unit. [ABSTRACT FROM AUTHOR]

Classic population regulation theories usually concern the influence of immediate factors on current populations, but studies investigating the effect of parental environment factors on their offspring populations are scarce. The maternal environments can affect offspring life-history traits across generations, which may affect population dynamics and be a mechanism of population regulation. In cyclical parthenogens, sexual reproduction is typically linked with dormancy, thereby providing a negative feedback to population growth. In this study, we manipulated population sex ratios in the mother's environment to investigate whether this factor affected future population dynamics by regulating offspring sexual reproduction in the rotifer Brachionus calyciflorus. Compared with females in male-biased environments, those in female-biased environments produced fewer mictic (sexual) offspring, and their amictic (asexual) offspring also produced a lower proportion of mictic females at a gradient of population densities. Moreover, populations that were manipulated under male-biased conditions showed significantly smaller population sizes than those under female-biased conditions. Our results indicated that in cyclical parthenogens, mothers could adjust the sexual reproduction of their offspring in response to the current population sex ratio, thus providing fine-scale regulation of population dynamics in addition to population density. [ABSTRACT FROM AUTHOR]

One of the major research goals in ecology is to understand predator–prey interactions. However, our understanding of how prey express phenotypic plasticity in response to co‐occurring multiple predators is limited in many systems.Here, we use the rotifer Brachionus calyciflorus as model organism to test how prey responds to co‐occurring predators through a series of related experiments. Firstly, we examined the effects of the density of a fish predator Carassius auratus on morphological traits in B. calyciflorus. Secondly, we examined the effects of larval C. auratus and Asplanchna brightwellii (a rotifer predator) on morphological defensive traits (body length, body width, anterior spine length, and posterolateral spine length) of B. calyciflorus.We show that B. calyciflorus develops smaller body size and shorter spine length when exposed to media conditioned using larval fish, and that high larval fish densities induce more pronounced responses than low densities. We also show that B. calyciflorus is able to discriminate between the two predators by producing opposing morphological adaptations (i.e., larger body size and longer posterolateral spines against A. brightwellii, but smaller body size and shorter spine length when exposed to the visual predator [larval fish]). However, B. calyciflorus develops intermediate, trade‐off responses in all morphological traits when exposed to conflicting threats from a combination of predators with different size and feeding strategies.These results show how prey are not necessarily passive victims, but rather, use countermeasures against predation – they actively develop responses to counteract their vulnerability to different predators by rapidly adjusting their morphology and life‐history traits to the existing predator regimes. [ABSTRACT FROM AUTHOR]

Global change encompasses many co‐occurring anthropogenic stressors. Understanding the interactions between these multiple stressors, whether they be additive, antagonistic or synergistic, is critical for ecosystem managers when prioritizing which stressors to mitigate in the face of global change. While such interactions between stressors appear prevalent, it remains unclear if and how these interactions change over time, as the majority of multiple‐stressor studies rarely span multiple generations of study organisms. Although meta‐analyses have reported some intriguing temporal trends in stressor interactions, for example that synergism may take time to emerge, the mechanistic basis for such observations is unknown. In this study, by analysing data from an evolution experiment with the rotifer Brachionus calyciflorus (~35 generations and 31,320 observations), we show that adaptation to multiple stressors shifts stressor interactions towards synergism. We show that trade‐offs, where populations cannot optimally perform multiple tasks (i.e. adapting to multiple stressors), generate this bias towards synergism. We also show that removal of stressors from evolved populations does not necessarily increase fitness and that there is variation in the evolutionary trajectories of populations that experienced the same stressor regimes. Our results highlight outstanding questions at the interface between evolution and global change biology, and illustrate the importance of considering rapid adaptation when managing or restoring ecosystems subjected to multiple stressors under global change. [ABSTRACT FROM AUTHOR]

Various types of pollutants derived from rapid industrialization and urbanization have largely threaten biodiversity and functioning of freshwater ecosystems globally. Morphological plasticity, especially body size–associated traits, is considered a functional response to water pollution in species, as such changes are often directly related to functioning of freshwater ecosystems through dynamics of food webs. However, detailed dynamics of pollution impacts on morphological plasticity remain largely unknown, particularly in the wild. Here, we used the model planktonic rotifer Brachionus calyciflorus to assess morphological response to chemical pollution in a river reach disturbed by sewage discharges. Multiple analyses showed dynamic morphological response to water pollution in wild B. calyciflorus populations. The distance between anterior lateral spines, lorica length, and egg short diameter were the most sensitive morphological indicators to water pollution, while spine length was stable in varied pollution conditions. Interestingly, body size and egg size were increased with accentuated water pollution, suggesting that wild populations maintain fitness by increasing feeding efficiency and reducing vulnerability to predation and ensure survival by producing large newborns in polluted environments. Total ammonia nitrogen was the leading nitrogen pollutant affecting body size, while total phosphorus and elements of Mn and As were the key factors relating to egg size. The results obtained here provide new sights into biological consequences of environmental pollution in the wild, thus advancing our understanding of pollution impacts on structure and functioning of freshwater ecosystems. [ABSTRACT FROM AUTHOR]

The success of genetically depauperate populations in the face of environmental change is contrary to the expectation that high genetic diversity is required for rapid adaptation. Alternative pathways such as environmentally induced genetic modifications and non‐genetic heritable phenotypes have been proposed mechanisms for heritable adaptation within an ecologically relevant time frame. However, experimental evidence is currently lacking to establish if, and to what extent, these sources of phenotypic variation can produce a response.To test if adaptation can rapidly occur in the absence of initial standing genetic variation and recombination in small populations, we (a) exposed replicate monoclonal populations of the microzooplankton Brachionus calyciflorus to a culturing regime that selected for phenotypic variants with elevated population growth with either high or low phosphorus food for a period of 55 days and (b) examined population level response in two fully factorial common garden experiments at day 15 and 35 of the exposure experiment.Within six generations, we observed heritable local adaptation to nutrient limitation. More specifically, populations with a history of exposure to low P food exhibited higher population growth rates under low P food conditions than populations with a high P exposure history. However, the capacity for such a response was found to vary among clones.Our study finds that although standing genetic variation is considered essential for rapid heritable adaptation, the rapid emergence of de novo genetic variation or alternative sources of phenotypic variation could aid in the establishment and persistence of low‐diversity populations. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

The stoichiometric knife-edge refers to the reduced performance of consumers encountering food with excess phosphorus (P) relative to carbon (C) or nitrogen (N). Studies that provide evidence for such knife-edge in aquatic systems often apply phosphate supplementation to create P-rich food treatments. However, this method may suffer from artifacts, because after uptake algae may store P in a form different from the P-rich biomolecules typically consumed by zooplankton. Our aim was to test if P supplementation results in potential biases. We experimentally exposed populations of the herbivore rotifer species, Brachionus calyciflorus (Pallas), to four different food quality treatments: algae grown under P-saturating (HPchem, molar C:P ratio = 59.7 ± 2.7) and P-sufficient (MPchem, molar C:P = 116.3 ± 5.2) conditions in chemostats, and algae grown under P-limiting conditions, but with molar C:P ratios equal to HPchem and MPchem treatments, respectively (HPLP+P, molar C:P = 59.8 ± 0.14; MPLP+P, molar C:P = 121.0 ± 4.3). The latter two treatments were achieved through P-supplementation of P-limited algae. Results show that for rotifers fed algae with either excess or intermediate P content, population growth rates were consistently higher on algae grown in chemostats than algae treated with the P supplementation method. Importantly, growth rates were also consistently lower in HP than in MP treatments and the magnitude of this negative impact was independent on algal growth history. The latter result confirms the existence of a stoichiometric knife-edge and indicates that P supplementation is a reliable method to study the relative effect of excess P on zooplankton performance in a standardized way. [ABSTRACT FROM AUTHOR]

There is often intense competition among species in an environment with limited resources and space, leading to the exclusion of inferior competitors, reduced species diversity, and changes in zooplankton communities. This study investigated the interspecific competition between two dominant rotifer species in the Pearl River Basin, Brachionus calyciflorus and Keratella valga, through laboratory experiments at different temperatures, food concentrations, and initial rotifer densities. In separate cultures, the population growth of both rotifer species was affected by changes in temperature, food density, and initial density. In mixed cultures, B. calyciflorus was inhibited by competition, leading to an overall decrease in its population growth rate and maximum population density. K. valga was also affected by competition, leading to an increase in its population growth rate and maximum population density at 20 ℃ or at an initial density of 1.0 × 106 cells/mL. B. calyciflorus was excluded by K. valga at low and medium food concentrations (0.5 × 106 and 1.0 × 106 cells/mL), whereas the opposite was found at high food concentration (3.0 × 106 cells/mL). Food concentration is obviously the main factor affecting outcome. Temperature, initial density, and interactions between the three factors also have an effect on it. [ABSTRACT FROM AUTHOR]

This work was involved DNA extraction from cultured Brachionus calyciflorus subjected to PCR .The PCR reaction was performed with Brachionus calyciflorus which having identical sequences of 18S rDNA and recorded as a global isolates of Brachionus calyciflorus in the (NCBI of USA, ENA of Europe and DDBJ of Japan) with Genbank ID: KM191796.1.

Zooplankton bodies are organic-rich micro-environments that support fast bacterial growth. Therefore, the abundance of zooplankton-associated bacteria is much higher than that of free-living bacteria, which has profound effects on the nutrient cycling of freshwater ecosystems. However, a detailed analysis of associated bacteria is still less known, especially the relationship between those bacteria and bacterioplankton. In this study, we analyzed the relationships between Brachionus calyciflorus-associated bacterial and bacterioplankton communities in freshwater using high-throughput sequencing. The results indicated that there were significant differences between the two bacterial communities, with only 29.47% sharing OTUs. The alpha diversity of the bacterioplankton community was significantly higher than that of B. calyciflorus-associated bacteria. PCoA analysis showed that the bacterioplankton community gathered deeply, while the B. calyciflorus-associated bacterial community was far away from the whole bacterioplankton community, and the distribution was relatively discrete. CCA analysis suggested that many environmental factors (T, DO, pH, TP, PO43-, NH4+, and NO3-) regulated the community composition of B. calyciflorus-associated bacteria, but the explanatory degree of variability was only 37.80%. High-throughput sequencing revealed that Raoultella and Delftia in Proteobacteria were the dominant genus in the B. calyciflorus-associated bacterial community, and closely related to the biodegradation function. Moreover, several abundant bacterial members participating in carbon and nitrogen cycles were found in the associated bacterial community by network analysis. Predictive results from FAPROTAX showed that the predominant biogeochemical cycle functions of the B. calyciflorus-associated bacterial community were plastic degradation, chemoheterotrophy, and aerobic chemoheterotrophy. Overall, our study expands the current understanding of zooplankton–bacteria interaction and promotes the combination of two different research fields.

Climbing perch, A. testudineus (Bloch, 1792), is a widely consumed fish in Asian nations due to its high nutritional value and delicate meat. The main obstacles to the spread of its cultural practises are a scarcity of high-quality seed and larval rearing due to the low survival rates in the initial stages of larval development. The key to improving the seed production of this species may lie in strategies to improve larval survival in the early stages. As a result, the goal of current study was to evaluate the impact of vitamin C, selenium, and highly unsaturated fatty acid (HUFA) enriched Brachionus calyciflorus on the development, nutrient availability, and fatty acid profile of climbing perch larvae. A total of 180 numbers of 3 days post-hatch (dph) larvae (0.021 ± 0.001 mg) were uniformly distributed among five treatments in triplicates. The larvae were fed thrice a day for 15 days with selenium (D 1), vitamin-C (D 2), HUFA (D 3) and combination of selenium-vitamin C- HUFA enriched (D 4) and non-enriched rotifer (C). The proximate analysis of various enriched and unenriched B. calyciflorus groups revealed that the vitamin C and HUFA-enriched treatment groups, respectively, had the highest percentages of crude protein (7.50%) and crude lipid (2.51%). Whereas, larvae fed a combination of selenium-vitamin C- HUFA enriched (D 4) rotifer showed the highest percentages of crude protein (12.40%) and crude lipid (1.81%). The findings of the fatty acid analysis demonstrate that feeding Se-VC-HUFA enriched B. calyciflorus to larvae resulted in significantly greater concentrations of Eicosapentaenoic acid (9.38%) and Docosahexaenoic acid (11.05%) that are 3.07 and 7.67 times higher, respectively, than feeding unenriched B. calyciflorus to larvae. The highest DHA/EPA ratio (1.18) was also observed with larvae fed Se-VC-HUFA enriched B. calyciflorus. The survivorship analysis revealed that the D 4 treatment group fed a combination of Se-VC-HUFA-enriched B. calyciflorus had the highest survival (37.41%) and the lowest (18.70%) observed in the control group. The highest average body weight gain and increased growth (30.79 ± 1.11 mg) were seen in the fishes given the rotifer supplemented with D 4 group, which performed substantially better than the other treatment groups (P < 0.05). Weight-specific growth rate (W-SGR) and Length-specific growth rate (L-SGR) of the fish exhibited similar trends across all treatment groups, whereas significantly (P < 0.05) lowest condition factor was observed in D 4 (2.63 ± 0.01) and highest in control group (3.21 ± 0.01). The results showed that larvae fed with enriched rotifer had significantly higher (P < 0.05) growth, nutrient availability, and fatty acid profile compared to un-enriched rotifer. The ideal first food for A. testudineus larval growth and survival must be a combination of Se-VC-HUFA enriched B. calyciflorus. • Enrichment of rotifer with nutraceuticals such as selenium, HUFA and vitamin C will improve the nutritional profile of rotifer as well as improves the larvae performance. • Better larval growth and survival could be achieved by feeding with enriched B. calyciflorus. • Feeding B. calyciflorus enriched with Selenium-Vitamin C-HUFA leads to increased body weight gain and specific growth rate in climbing perch larvae. • Higher larval growth and survival rates are positively correlated, suggesting that dietary DHA and EPA levels are essential for the proper development of climbing perch larvae. [ABSTRACT FROM AUTHOR]

Predation is a strong species interaction causing severe harm or death to prey. Thus, prey species have evolved various defence strategies to minimize predation risk, which may be immediate (e.g., a change in behaviour) or transgenerational (morphological defence structures). We studied the behaviour of two strains of a rotiferan prey (Brachionus calyciflorus) that differ in their ability to develop morphological defences in response to their predator Asplanchna brightwellii. Using video analysis, we tested: (a) if two strains differ in their response to predator presence and predator cues when both are undefended; (b) whether defended individuals respond to live predators or their cues; and (c) if the morphological defence (large spines) per se has an effect on the swimming behaviour. We found a clear increase in swimming speed for both undefended strains in predator presence. However, the defended specimens responded neither to the predator presence nor to their cues, showing that they behave indifferently to their predator when they are defended. We did not detect an effect of the spines on the swimming behaviour. Our study demonstrates a complex plastic behaviour of the prey, not only in the presence of their predator, but also with respect to their defence status.

Nghiên cứu được thực hiện với 2 thí nghiệm nhằm đánh giá ảnh hưởng của liều lượng tảo Chlorealla sp. và ảnh hưởng của thay thế tảo với men bánh mì lên sự tăng trưởng của luân trùng Brachionus calyciflorus như sau: thí nghiệm 1 gồm 5 nghiệm thức, luân trùng được cho ăn bằng tảo tăng lũy tuyến 20.000 tế bào/luân trùng/ngày cho mỗi nghiệm thức xuất phát từ 60.000 tế bào/luân trùng/ngày. Dựa vào kết quả của thí nghiệm 1, mật độ tảo cho kết quả tốt về tăng trưởng quần thể được chọn để tiến hành bố trí thí nghiệm tiếp theo, thí nghiệm 2 được bố trí với số lượng tảo được thay thế bằng men bánh mì, số lượng thay thế tăng 25% từ nghiệm thức thứ 2 đến nghiệm thức cuối tương ứng với lượng tảo giảm, mỗi nghiệm thức với 3 lần lặp lại. Luân trùng được thả nuôi với mật độ ban đầu là 200 luân trùng/mL. Kết quả cho thấy, mật độ luân trùng đạt cao nhất ở nghiệm thức cho ăn 80.000 tế bào/luân trùng/ngày vào ngày thứ 4 là 688 luân trùng/mL và đạt 898 luân trùng/mL ở nghiệm thức cho ăn 75% tảo + 25% men bánh mì sau 5 ngày nuôi. Từ kết quả thí nghiệm khẳng định rằng thay thế 25% tảo bằng men bánh mì có cải thiện tăng trưởng quần thể của B. calyciflorus.

The baking industries and disinfection of tap water released a considerable amount of bromate into surface water, which has been reported as a carcinogenic compound to mammals. Rotifers play an important role in freshwater ecosystems and are model organisms to assess environmental contamination. In the present study, the effects of different concentrations (0.001, 0.01, 0.1, 1, 10, 100 and 200 mg/L) of bromate on the life-table and population growth parameters were investigated in the rotifer Brachionus calyciflorus. The results showed that the 24-h LC50 of bromate to B. calyciflorus was 365.29 mg/L (95%Cl: 290.37–480.24). Treatments with 0.01, 10 and 200 mg/L bromate shorten the reproductive period. High levels of bromate (100 and 200 mg/L) significantly decreased net reproductive rate, intrinsic rate of population increase, life span, mictic rate of B. calyciflorus. To investigate the underlying mechanisms, swimming speed and antioxidative biomarkers were compared between bromate treatments and the control. The results showed that glutathione (GSH) and malondialdehyde (MDA) contents, total superoxide dismutase (T-SOD) and peroxidase (POD) activities decreased significantly in response to bromate exposure and the reasons required further investigation. Treatments with 0.001–200 mg/L bromate all significantly reduced swimming linear speed to rotifer larvae and treatments with 100–200 mg/L bromate significantly suppressed the swimming linear speed of adult rotifer. These changes would reduce filtration of algal food and could explain the decreased survival and reproduction. Overall, bromate may not show acute toxicity to rotifers, but still have potential adverse effects on rotifer behavior, which may then influence the community structure in aquatic ecosystems.

In recent years, increasing concerns have been raised about the environmental risk of microplastics in freshwater ecosystems. Small microplastics enter the water either directly or accumulate through disintegration of larger plastic particles. These particles might then be ingested by filter-feeding zooplankton, such as rotifers. Particles released into the water may also interact with the biota through the formation of aggregates, which might alter the uptake by zooplankton. In this study, we tested for size-specific aggregation of polystyrene microspheres and their ingestion by a common freshwater rotifer Brachionus calyciflorus. The ingestion of three sizes of polystyrene microspheres (MS) 1-, 3-, and 6-μm was investigated. Each MS size was tested in combination with three different treatments: MS as the sole food intake, MS in association with food algae and MS aggregated with biogenic matter. After 72 h incubation in pre-filtered natural river water, the majority of the 1-μm spheres occurred as aggregates. The larger the particles, the higher the relative number of single particles and the larger the aggregates. All particles were ingested by the rotifer following a Type-II functional response. The presence of algae did not influence the ingestion of the MS for all three sizes. The biogenic aggregation of microspheres led to a significant size-dependent alteration in their ingestion. Rotifers ingested more microspheres (MS) when exposed to aggregated 1- and 3-μm MS as compared to single spheres, whereas fewer aggregated 6-μm spheres were ingested. This indicates that the small particles when aggregated were in an effective size range for Brachionus, while the aggregated larger spheres became too large to be efficiently ingested. These observations provide the first evidence of a size- and aggregation-dependent feeding interaction between microplastics and rotifers. Microplastics when aggregated with biogenic particles in a natural environment can rapidly change their size-dependent availability. The aggregation properties of microplastics should be taken into account when performing experiments mimicking the natural environment.

The effects of potassium bromate (KBrO3), sodium bromate (NaBrO3), and potassium bromide (KBr) on the sexual reproduction of the rotifer Brachionus calyciflorus were studied by 2-d population growth, 4-d sexual reproduction, and 7-d resting egg production tests. The results showed that low concentrations of bromate promote 2-d and 4-d rotifer population growth, while high concentrations limit it. Bromate stress significantly affected parameters of rotifer sexual reproduction, including the ratio of mictic to amictic females, the mictic rate of rotifers, and the fertilization rate of mictic females. KBrO3 at 0.001, 0.01, 1, and 10 mg/L, NaBrO3 at 1 and 10 mg/L, and KBr at 100 and 200 mg/L significantly increased resting egg production, while KBrO3 at 100 and 200 mg/L, and NaBrO3 at 200 mg/L significantly decreased it. Resting egg production appears to provide a sensitive endpoint in evaluating the effect of bromate on rotifer sexual reproduction. [ABSTRACT FROM AUTHOR]

This work was involved DNA extraction from cultured Brachionus calyciflorus subjected to PCR .The PCR reaction was performed with Brachionus calyciflorus which having identical sequences of 18S rDNA and recorded as a global isolates of Brachionus calyciflorus in the (NCBI of USA, ENA of Europe and DDBJ of Japan) with Genbank ID: KM191796.1. [ABSTRACT FROM AUTHOR]

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The present study was undertaken to find out preferred food type, minimum effective algal cell requirement, effective harvest rate of rotifers and to design and construct re-circulatory aquaculture system (RAS) based rotifer, Brachionus calyciflorus production system at Aquatic Rainbow Technology Park, Dr MGR Fisheries College and Research Institute, TNJFU, Madhavaram campus, Chennai during 2017–2019. In the first experiment, food types, viz. Chlorella vulgaris, Spirulina major, Scenedismus obliquus and Baker’s yeast were extensively fed to rotifers with control (5000 L). The highest rotifer count was observed with C. vulgaris food type (365.33±2.18 rotifers/ml) followed by Baker’s yeast (245.33±5.36 rotifers/ml) on 8th day which started declining gradually to 30th day because of lower water quality. Second experiment on algal consumption rate by rotifer postulated that 22,000–25,000 cells/day/rotifer was the minimum cell requirement. Third experiment on standardizing effective harvest rate (10%, 30%, 50% and 70%) suggested that daily harvest at 30% maintained the rotifer culture at its stationary phase (381±19.45 rotifers/ml). After the experiments, we have designed, built and operated RAS based live food production unit for 17 months where the harvested water was treated using series of filters (rapidsand, cartridge, UV filters) and reused for algal culture. The seasonal data showed that temperature plays a major role with the highest production during summer (404.43±24.33 rotifers/ml) and consequently lower in winter (301.21±14.33 rotifers/ml). The system opens a new perspective of commercial scale production of rotifers with standard culture and harvesting practices.

This study evaluated the acute toxicity of herbicide paraquat and the insecticide permethrin and their impacts on growth and reproduction of freshwater rotifers Brachionus calyciflorus according to the guidelines OECD. The acute toxicity (LC50 24h) of paraquat and permethrin on freshwater rotifers B. calyciflorus were 0.541 and 8.997 mg l-1, respectively. The level of exposure responses of rotifers to four different concentrations of the pesticide paraquat (0.027, 0.054, 0.1 and 0.27 mg l-1) and permethrin (0.449, 0.899, 1.799 and 4.498 mg l-1) with three replicates per concentration was evaluated for ten days. The results showed that the specific growth rate and populations of rotifer decreased by increasing the concentration of toxins in the culture medium (p

The two complete mitochondrial genomes were sequenced from the Netherlands strain of the freshwater monogonont rotifer Brachionus calyciflorus. The mitochondrial genome sequences were 27,698 bp and 9,906 bp in size, respectively. The gene order and contents of the two B. calyciflorus strains were mostly identical to one another, except for the additional identification and translocation of several tRNAs in mitochondrial DNA I and II. Of 13 protein-coding genes (PCGs), three genes (ND1, ND5, and ND3) had incomplete stop codons. Furthermore, the start codon of ND2, CO2, and CO3 and ND4 genes was ATT, GTG, and ATA, respectively, while the start codon of other PCGs was ATG. The base composition of 13 PCGs of B. calyciflorus (the Netherlands strain) mitogenome showed 31.1% for A, 37.6% for T, 16.5% for C, and 14.8% for G, respectively.

Titanium dioxide nanoparticles (nTiO2) have raised environmental concerns and display potential hazards to aquatic organisms and even humans. However, only a few reports tested the toxicity of nTiO2 to rotifers. In the present study, acute and chronic toxicity of nTiO2 to the freshwater rotifer Brachionus calyciflorus was investigated at different temperatures. At 25°C, the 24 and 48‐hr LC50 was 117.14 and 60.11 mg/L, respectively. At 15°C, 20°C, 25°C, and 30°C, exposure to nTiO2 significantly decreased life expectancy at birth, net reproductive rate, generation time, average lifespan, and/or intrinsic rate of population increase of B. calyciflorus (p <.05). High temperature enhanced the toxicity of nTiO2 to rotifers. The swimming linear speed of rotifers significantly increased (p <.05) in treatments with 200 µg/L nTiO2, compared with the control. In addition, treatments with 8 µg/L to 5 mg/L nTiO2 significantly increased superoxide dismutase activity (p <.05). Glutathione content and catalase activity increased significantly after exposure to 8 µg/L nTiO2 but decreased significantly in treatments with nTiO2 concentrations ranging from 40 µg/L to 5 mg/L (p <.05). There were no significant changes in malondialdehyde contents among nTiO2 treatments and control. Overall, the present study indicated that nTiO2 revealed high toxicity to rotifers, displaying high environmental risks to aquatic ecosystems. HIGHLIGHTS: 1.High temperature enhanced the toxicity of nTiO2 to rotifers.2.The 24 and 48‐hr LC50 of nTiO2 to B. calyciflorus was 117.4 and 60.11 mg/L, respectively.3.nTiO2 displayed high environmental risk to aquatic ecosystems even at the µg/L levels. [ABSTRACT FROM AUTHOR]

Live food organisms move in the water column and serve as a source of all the nutrients such as essential proteins, lipids, carbohydrates, vitamins, minerals, amino acids and fatty acids for larval stages of fish. Hence, they are commonly known as “living capsules of nutrition”. Most of the fish and shellfish larvae in nature feed on these small phytoplanktonic and zooplanktonic organisms. Zooplankton is required as the first food for much-cultured fish; for others, it contributes to faster growth and higher survival. Among zooplankton, rotifers (Phylum: Rotifera) popularly called as wheel animalcules forms an important group of live food organisms for use in aqua hatcheries. Rotifera includes three classes, the Monogononta, the Bdelloidea, and the marine Seisonidea. Most of the rotifer species vary between 200 to 500 micrometers in size, and are primarily omnivorous, but few species have been known to be cannibalistic. The diet of rotifers is decomposed or dead organic materials, unicellular algae and other phytoplankton. Such feeding habits make rotifers primary consumers. Rotifers in turn act as prey to carnivorous secondary consumers, including shrimp and crabs. Though rotifers are represented by about 2,500 species, the monogonont genus Brachionus is the most known form of all rotifers, and widely distributed in marine and freshwaters worldwide. They serve as an ideal starter diet for early larval stages of many fish and prawn species in marine as well as in freshwater, due to its smaller size as compared to Cladocerans. Among Brachionus, B. calyciflorus is the most commonly cultured freshwater rotifer for both freshwater and marine water fish species and shrimps, because of its numerous characteristics like small size, slow mobility and easy catchability. Moreover, B. calyciflorus has been found to conserve energy when food is scarce by decreasing its respiration rate, while other species of rotifers show no change in the respiration rate. Generally in laboratory their culture is maintained on algal concentrate with sufficient light, aeration at pH ranged between 6-8 and temperature at 25oC. However, there is need to conduct in-depth study to standardize the abiotic conditions like light, pH, and hardness for mass-scale production of rotifer to meet the nutritional requirements of young larvae of fishes that encounter huge mortality during their larval stages. Successful mass scale production of rotifers will hold the key to higher efficiency in the seed production of important species like Clarias magur, Anabas testudeneus, etc. [ABSTRACT FROM AUTHOR]

Anthropogenic activities have reshaped the relative supply rates of essential elements to organisms. Recent studies suggested that consumer performance is strongly reduced by food that is either very high or very low in relative phosphorus content. However, the generality of such 'stoichiometric knife‐edge' and its underlying mechanisms are poorly understood. We studied the response of a planktonic rotifer to a 10‐fold food carbon : phosphorus (C : P) gradient and confirmed the existence of the stoichiometric knife‐edge. Interestingly, we observed a complete homeostatic breakdown associated with strong growth reductions at high food C : P. In contrast, at low food C : P, animals maintained homeostasis despite pronounced performance reductions. Our results suggest that the mechanisms underlying adverse effects of stoichiometric imbalance are determined by both the identity of elements that are limiting and those that are present in excess. Negative effects of excess P reveal an additional way of how eutrophication may affect consumers. [ABSTRACT FROM AUTHOR]

Water pollution can be monitored through the use of indicator species, including Brachionus calyciflorus. To do this, it is necessary to understand the species’ population ecology. Four surveys of zooplankton were conducted in May, August, and December 2018 and February 2019 in the Pearl River Delta, China, to examine the population characteristics of B. calyciflorus. The temporal and spatial distribution of abundance, biomass, dominance, and occurrence frequency were compared with those from 2012 to investigate the relationship between changes in the population of B. calyciflorus and environmental factors. The average abundance, dominance, and occurrence of B. calyciflorus in this survey were significantly higher than those of 2012 in all seasons. Principal component analysis showed that environmental factors such as the temperature, transparency, total nitrogen, and total phosphorus of water had a major impact on the abundance of B. calyciflorus. There was a significant positive correlation with transparency, total nitrogen, and total phosphorus of water, and a very significant positive correlation with water temperature. Overall, these results demonstrated that the distribution characteristics of B. calyciflorus can reflect pollution in water bodies and can be used to evaluate water quality. These research results provide a reference for evaluating China’s river health and can help to manage water quality in the Pearl River Delta.

Ultraviolet radiation (UVR) is an environmental stressor in several ecosystems and can affect organisms' survival and reproduction, and community structure. Rotifers cope with UVR stress adopting preventive behavioral and metabolic mechanisms. However, the demonstration of an immediate behavioral response in rotifers is missing. We investigated the short-term response of rotifers to UVR, by combining video analysis and movement ecology methods, in three common species: Brachionus calyciflorus, Keratella cochlearis, and Keratella quadrata. We recorded the behavior of B. calyciflorus (both sexes), K. quadrata, and K. cochlearis (females) exposed to white light, and to intermittent cycles of UVR (30:30 s). Individual trajectories were extracted from videos with open-source software. We found that B. calyciflorus females exposed to UVR exhibited strong negative phototaxis with increased swimming speed, and a weak positive phototaxis in males. Keratella cochlearis and K. quadrata showed a weaker response. Our study reveals a species-specific behavioral response to UVR in rotifers. Furthermore, we highlight how sexual dimorphism in B. calyciflorus does not only occur in morphology and movement, but also in behavioral traits. Our results help to understand zooplankton community dynamics by providing a mechanistic explanation of UVR response in one major zooplankton taxonomic group. [ABSTRACT FROM AUTHOR]

Maternal effects are one of the most interesting topics in evolutionary ecology as they can affect the rate of evolution and population dynamics by phenotypic manipulation of offspring related to fitness. At present, studies examining the interaction between maternal environment effects and maternal age (birth order) effects are scarce. We designed an experiment to reveal whether environmentally induced maternal manipulation works equally on offspring across birth orders in rotifer Brachionus calyciflorus. In the experiment, newborn amictic mothers (F0) were cultured parallelly in low (LD) and high (HD) population density. Offspring (F1) of young (YF0) and old (OF0) mothers in both LD and HD groups were cultured under a crowded condition and the mixis ratios of both F1 and F2 were examined. Results show that F1 from HD-YF0 had a significantly higher mixis ratio and those amictic ones produced daughters (F2) with higher mixis ratio in response to crowding than those from HD-OF0. In contrast, no such differences among F1 siblings were found in the LD-F0 group. Therefore, the effect of maternal age on the sexual propensity of the offspring can be affected independently by the maternal population density. [ABSTRACT FROM AUTHOR]

Food quantity and quality are highly variable in natural systems. Therefore, their interplay and the associated effects on consumer population growth are important for predator–prey interactions and community dynamics. Experiments in which consumers were exposed to elemental nutrient limitations along food quantity gradients suggest that food quality effects on consumer performance are relevant only at high food quantities. However, elemental nutrients act differently on physiological processes than biochemical nutrients. So far, the interactive effects of food quantity and biochemical compounds on consumer performance have been insufficiently studied.We studied interactive effects of food quantity and biochemical food quality on population growth, including fecundity and survival, of the freshwater rotifer Brachionus calyciflorus. We hypothesised that these life history traits are differently affected by the availability of biochemical nutrients and that food quality effects gain importance with increasing food quantity. In a first experiment, we established food quantity and quality gradients by providing rotifers with different concentrations of a low‐quality food, the sterol‐free cyanobacterium Synechococcus elongatus, supplemented with increasing amounts of cholesterol. In a second experiment, food quantity and quality gradients were established by providing different proportions of two prey species differing in biochemical food quality, i.e. S. elongatus and the lipid‐rich alga Nannochloropsis limnetica, at different total food concentrations.We found that the effects of cholesterol supplementation on population growth increased with increasing food quantity. This interactive effect on population growth was mainly due to food quality effects on fecundity, as effects on survival remained constant along the food quantity gradient. In contrast, when feeding on the mixed algal diet, the food quality effect associated with increasing the proportion of the high‐quality alga did not change along the food quantity gradient. The data on survival and fecundity demonstrate the missing interactive effect of food quantity and quality on population growth, as both traits were oppositely affected. Survival was affected by food quality primarily at low food quantity, whereas food quality effects on fecundity were stronger at high food quantity.Our results highlight the significance of essential biochemicals in mediating the interactive effects of food quantity and quality on population growth. The interplay between food quantity and biochemical food quality limitation seems to influence resource allocation patterns in order to optimise survival or reproduction, which may strongly affect population dynamics in variable environments. As opposed to exploring the function of a single nutrient via supplementation, using algae mixtures allowed us to assess food quality effects on consumer performance in a more natural context by taking potential interactive effects of multiple co‐limiting nutrients into account. [ABSTRACT FROM AUTHOR]

Many organisms display oscillations in population size. Theory predicts that these fluctuations can be generated by predator–prey interactions, and empirical studies using life model systems, such as a rotifer‐algae community consisting of Brachionus calyciflorus as predator and Chlorella vulgaris as prey, have been successfully used for studying such dynamics. B. calyciflorus is a cyclical parthenogen (CP) and clones often differ in their sexual propensity, that is, the degree to which they engage into sexual or asexual (clonal) reproduction. Since sexual propensities can affect growth rates and population sizes, we hypothesized that this might also affect population oscillations. Here, we studied the dynamical behaviour of B. calyciflorus clones representing either CPs (regularly inducing sex) or obligate parthenogens (OPs). We found that the amplitudes of population cycles to be increased in OPs at low nutrient levels. Several other population dynamic parameters seemed unaffected. This suggests that reproductive mode might be an important additional variable to be considered in future studies of population oscillations. Many organisms find themselves in predator‐prey relationships where growth rates of prey and attack rates of predators determine the dynamics. Since sexual reproduction can affect growth rates and population sizes compared to asexual reproduction, we hypothesized that this might also affect population oscillations. Using a predator‐prey system with Brachionus calyciflorus rotifer clones representing either cyclical parthenogens (regularly inducing sex) or obligate parthenogens, feeding on Chlorella vulgaris algal populations, we found that the amplitudes of predator population cycles are increased in obligate parthenogens at low nutrient levels. [ABSTRACT FROM AUTHOR]

Current research on the effects of cladoceran allelochemicals on rotifers has been inconclusive and the allelopathic effects of rotifers on cladocerans are unknown. We sought to fill this knowledge gap with life table demography experiments assessing the interspecific effects of Moina macrocopa-conditioned mediums (MCM) and Brachionus calyciflorus-conditioned mediums (CCM) on the main life history variables under different temperatures and algal densities. Our results demonstrate that, when compared to the allelopathic effects of M. macrocopa on B. calyciflorus, M. macrocopa had higher sensitivity to the allelochemicals from B. calyciflorus. When compared to the controls, the chemically-mediated effects of M. macrocopa on the net reproductive rate (R0), intrinsic rate of population growth (rm) and total number of offspring (NO) of B. calyciflorus were non-significant in many cases while in a few the impacts were stimulatory or inhibitory under different concentrations of MCM, temperatures, and food densities. However, when compared to the controls, the allelopathic effects of B. calyciflorus on the R0, rm and NO of M. macrocopa were stimulatory in many cases; some impacts were inhibitory or non-significant under different concentrations of CCM, temperatures, and food densities. In addition, life expectancy at birth (e0), generation time (T), and average lifespan (LS) of B. calyciflorus and M. macrocopa cultured in the conditioned medium nearly did not differ significantly from the controls. Our results suggest that the interspecific allelopathic effects of B. calyciflorus and M. macrocopa are dependent on the origin and concentration of the allelochemical, life history variable, temperature, and food (algal) density. Additionally, the underlying mechanisms should be further investigated. Interspecific allelopathic effects of B. calyciflorus and M. macrocopa were dependent on the origin and concentration of allelochemical, life history variable, temperature and food density. M. macrocopa had higher sensitivity to the allelochemicals from B. calyciflorus. The underlying mechanisms should be further investigated. [ABSTRACT FROM AUTHOR]

While induced defense of aquatic organisms against predators has been considerably studied by both laboratory and field research, our understanding is still limited about, for example, whether induced defense is variable between microhabitats within the same lake and how multiple predators influence induced defense in the natural environment. Here, we examined whether a rotifer species, Brachionus calyciflorus showed a different development degree of induced defenses against its predator Asplanchna and cyclopoid copepods between the microhabitats of a macrophyte bed consisting of Trapa species and open water. B. calyciflorus was more abundant and had larger posterolateral spines as a defensive trait in open water than in the Trapa bed. Asplanchna was more abundant in open water than in the Trapa bed, whereas cyclopoids were more abundant in the Trapa bed. Both of the predators significantly affected the development of the defense trait. The effect of Asplanchna on the defense trait was positive, whereas the effect of cyclopoids was negative. Thus, a spatial difference in the development degree of induced defense between the microhabitats occurred as the dense Trapa bed influenced the abundance of the two predators. The results also suggest that the induced defense of B. calyciflorus was effective in reducing the predation pressure from Asplanchna while B. calyciflorus was not able to avoid predation by cyclopoids in the Trapa bed. [ABSTRACT FROM AUTHOR]

The chronic effects of deltamethrin and endosulfan on non-target organisms have been investigated several times. However, most of these studies were only performed under certain environmental conditions and ignored the effects of food density. In the present study, the effects of deltamethrin (0.3, 0.6, 1.2, and 2.4 mg/L) and endosulfan (0.27, 0.54, 1.08, and 2.16 mg/L) on the population growth of the rotifer Brachionus calyciflorus were investigated at two densities of Scenedesmus obliquus (1.0×106 and 3.0×106 cells/mL). Compared with the blank control, high levels of deltamethrin and endosulfan significantly decreased the population growth rate and the maximum population density of B. calyciflorus, suggesting that these two chemicals are toxic to rotifers. In comparison to high algal density, the toxic effects of 2.4 mg/L deltamethrin and 2.16 mg/L endosulfan on rotifers were much more obvious at low algal density. The present results show the important role of algal density on influencing the toxicities of deltamethrin and endosulfan to rotifers. [ABSTRACT FROM AUTHOR]

The two complete mitochondrial genomes were sequenced from the Netherlands strain of the freshwater monogonont rotifer Brachionus calyciflorus. The mitochondrial genome sequences were 27,698 bp and 9,906 bp in size, respectively. The gene order and contents of the two B. calyciflorus strains were mostly identical to one another, except for the additional identification and translocation of several tRNAs in mitochondrial DNA I and II. Of 13 protein-coding genes (PCGs), three genes (ND1, ND5, and ND3) had incomplete stop codons. Furthermore, the start codon of ND2, CO2, and CO3 and ND4 genes was ATT, GTG, and ATA, respectively, while the start codon of other PCGs was ATG. The base composition of 13 PCGs of B. calyciflorus (the Netherlands strain) mitogenome showed 31.1% for A, 37.6% for T, 16.5% for C, and 14.8% for G, respectively. [ABSTRACT FROM AUTHOR]