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Plastic contamination in aquatic ecosystems all around the world is on the rise. Microplastics (MPs) interfere with the ecological functions of different aquatic animals, including zooplankton. Other contaminants can also be transported by microplastics, resulting in higher toxicity. Here, we evaluated the effect of microplastics alone and in combination with cyanotoxins (CT) on the demographic and feeding responses of the freshwater rotifer Brachionus calyciflorus. The microplastics used were polystyrene spheres of 30 μm diameter. The cyanobacteria were obtained from a sample collected from the Valle de Bravo reservoir in Central Mexico, and the secondary metabolites were obtained after 5 cycles of freezing, thawing and sonication. We conducted acute (LC 50 , 24h bioassay) and chronic toxicity tests involving population growth, life table experiments, and feeding experiments. The LC 50 value using microplastics was 21.91 mg/L, and for the cyanobacterial crude extract it was 2.56 μg/L, but the combination of both resulted in a higher adverse effect (16.64 mg/L) due to the microplastics. Rotifer survival, reproduction, and feeding decreased in the presence of either MPs or CT but the adverse effect was more in the presence of both contaminants. We found that the adverse effects of MPs and CT on the test rotifer species were enhanced when exposed to both contaminants simultaneously., Competing Interests: Declaration of competing interest We have no conflicts of interest to declare., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Microplastics (MPs) are becoming increasingly common in freshwater ecosystems. Rotifers may involuntarily ingest MPs through non-selective filtration, thus causing non-real satiety, leading to adverse effects on their demography. Here, we evaluated the acute and chronic effects of MPs (30 µm) on two successive generations of Brachionus calyciflorus s.s. at 20 and 25 °C. Demographic variables and ingestion rates were compared in the absence and presence of microplastics (550 spheres mL -1 ). For the life table experiments, cohorts of twenty neonates were introduced into 20 mL medium with four replicates per treatment. Ingestion rates of the rotifer were tested at both test temperatures in the absence and presence of the microplastics in 20 mL containers with 1 ind. mL -1 per container. The rotifer population growth rates ranged from 0.55 to 1.05 d -1 depending on the treatment. MPs decreased the fecundity by 20-24 %. The average lifespan of rotifers exposed to MPs in the F 0 generation was lower than that in the F 1 generation at both temperatures, indicating that pre-exposure of mothers may offer some protection to the offspring. The population growth rate was higher at 25 °C. The ingestion rates were significantly lower in the presence of the microplastics. Our observations indicated that this strain of B. calyciflorus was better adapted to 20 °C; microplastics and higher test temperature resulted in a pronounced changes in the demographic variables of the rotifer., Competing Interests: Declaration of competing interest We have no Conflict of Interest to declare., (Copyright © 2024. Published by Elsevier B.V.)

The emerging contaminant 4-nonylphenol is an active ingredient in many surfactants. Though 4-nonylphenol has been reported in Mexican waterbodies, no stringent law is available to establish its permissible limits. Most ecotoxicological assays using zooplankton species are based on previously unexposed populations, and multigenerational experiments are rare. Plationus patulus and Brachionus havanaensis are widely distributed species in Mexico and have been used in ecotoxicological assessments. In this work, the median lethal concentration of 4-nonylphenol (LC 50 , 24 h) for both rotifer species was derived. Based on our acute toxicity data (24 h LC 50 of 4-nonylphenol for P. patulus and B. havanaensis were 500 and 250 µg L -1 , respectively), three sublethal concentrations (µg L -1 ) (7.81, 15.82 and 31.25 for B. havanaensis and 15.62, 31.25 and 62.5 for P. patulus ) were used in the life table demography tests for two successive generations (F0 and F1) of either rotifer species. Regardless of the concentrations used, 4-nonylphenol had an adverse effect on both rotifer species over two successive generations. P. patulus was more sensitive than B. havanaensis in chronic toxicity tests. F1 generation of both rotifer species was far more adversely affected than the F0 in all toxicant treatments.

Diurnal temperature fluctuations affect ectothermic species more than endothermic taxa. We tested the effect of three fixed temperatures (20, 25 and 30 °C) and a 24 h variable (20-30 °C) on the population growth and fatty acid profiles of the common rotifer Brachionus calyciflorus. Depending on the temperature treatment, the peak population abundances of B. calyciflorus varied from 65 to 80 ind./ml, the lowest being on variable temperature range. The rate of population increase varied from 0.31 to 0.52 per day, highest being at 30 °C. There was a curvilinear relationship between the population density and the egg ratio (number of eggs/female) in all the tested temperature regimes. The egg ratio was higher (>0.6) for treatments involving fixed temperatures, but for variable temperature regime, the egg ratios were lower (<0.5). Temperature also induced changes in the fatty acid content of B. calyciflorus. While the total saturated fatty acids increased, both mono-unsaturated and poly-unsaturated fatty acids decreased with increasing temperature regime. These results have been interpreted in relation to the role of temperature (both intensity and mode of exposure) on the population growth characteristics of rotifers., (Copyright © 2020. Published by Elsevier Ltd.)

Several abiotic factors influence the ecological responses of aquatic invertebrates to metal toxicity. We examined the effect of salinity (10, 20, and 30 psu) and temperature (25 and 32 °C) on acute and chronic arsenic (As) toxicity to the euryhaline rotifers, Proales similis and Brachionus ibericus. In general, higher salinities and low temperature resulted in lower arsenic toxicity. The population growth studies indicated that P. similis was more sensitive than B. ibericus to As. Arsenic toxicity intensified the vulnerability of P. similis to B. ibericus competition. Life table parameters decreased with increasing As levels in the medium. Chronic toxicity bioassays were more sensitive than acute toxicity tests for determining the adverse effect of As to rotifers. Our findings provide useful insights on the effect of arsenic on rotifer populations exposed to different temperature and salinity scenarios. Proales similis could be an important complement to brachionid rotifers for marine toxicity bioassays., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Organisms are usually exposed to mixtures of emerging pollutants in aquatic environments. Due to their widespread use and environmental relevance, the individual and combined effects of the drugs azithromycin (AZT) and ivermectin (IVM) on the freshwater rotifer Lecane papuana and the euryhaline rotifer Proales similis were investigated. Rotifers showed greater sensitivity to IVM compared to AZT. The LC 50 values of IVM and AZT for L. papuana and P. similis were 0.163 and 0.172 mg/L, and 13.52 and 20.00 mg/L, respectively. Population growth rates, assessed in chronic toxicity assays, responded negatively to increasing concentrations of both toxicants, either individually or in combination. Our results revealed two distinct combined toxicity responses: a strong synergistic effect in the freshwater rotifer and a marked antagonistic impact of the AZT-IVM mixtures in the euryhaline rotifer., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Proliferating cyanobacterial blooms due eutrophication in reservoirs is a major global problem. The production of cyanotoxins often increases with grazing pressure and temperature while the sensitivity of zooplankton to cyanotoxins is directly related to temperature. Here we evaluate the effect of different concentrations of the crude extract of cyanobacteria from Valle de Bravo reservoir during dry (January) and rainy (September) seasons at 20 and 25 °C on the rotifer Brachionus calyciflorus based on acute and chronic toxicity tests. We filtered 20 or 150 l of lake water, depending on the intensity of the bloom, and estimated the density and diversity of the cyanobacteria. The crude extracts, after 5 cycles of freezing, thawing and sonication at 14 MHz, were filtered and the microcystin concentration quantified based on ELISA. The extracts were used to conduct the acute and chronic toxicity tests, all in quadruplicate. Acute toxicity tests were based on 24 h mortality. Chronic toxicity tests (population growth and life table experiments) were conducted at 5 and 10% of the median lethal concentration. The field samples were dominated by Microcystis sp. (January) or Woronichinia naegeliana (September). The microcystin concentration in lake water was 9.57 μg/l and 0.097 μg/l and the median lethal concentration was 5.34 μg microcystin/L and 0.35 μg microcystin/L in January and September, respectively. Survival and reproduction of B. calyciflorus were lower in the presence of the cyanobacteria crude extract, more so at 20° than at 25 °C. Our results highlight the urgency of regular monitoring based on zooplankton assays for reservoirs in tropical and temperate regions, subject to frequent and dominant cyanobacterial blooms, often as a result of climate change., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The demographic response of the brackish-water rotifers Proales similis and Brachionus plicatilis to mercury (0.5, 2, 8 and 32 μg L -1 of HgCl 2 ) at different salinity levels (10 and 20‰) and two temperature (25 °C and 32 °C) regimes were evaluated. Median lethal concentration (LC 50 ) for P. similis and B. plicatilis was 10 and 16 μg L -1 , respectively, showing that Proales similis was more sensitive to mercury than B. plicatilis. The rate of population increase (r) for both species was greater at 10‰ salinity and 32 °C (ranged from 0.6 to 0.95 d -1 ). The r-value decreased as the concentration of mercury in the medium increased. Regardless of the temperature, at lower salinity and higher mercury concentration (32 μg L -1 ), P. similis died within six days. The survivorship of P. similis and B. plicatilis was higher at 25 °C than at 32 °C (ranged from 5 to 8 and 7-13 d, respectively). Fecundity was higher at 32 °C than at 25 °C for both rotifers species. There was a significant effect of the interaction among salinity, temperature, and mercury in both species on the reproductive variables such as net and gross reproductive rates, generation time and the rate of population increase. Considering the sensitivity of P. similis, we suggest that this species be included in the list of marine bioassay organisms., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Chloroquine (CQ) has been widely used for many years against malaria and various viral diseases. Its important use and high potential to being persistent make it of particular concern for ecotoxicological studies. Here, we evaluated the toxicity of CQ alone and in combination with copper (Cu) to the euryhaline rotifer Proales similis. All experiments were carried out using chronic toxicity reproductive five-day tests and an application factor (AF) of 0.05, 0.1, 0.3, and 0.5 by multiplying the 24-h LC 50 values of CQ (4250 µg/L) and Cu (68 µg/L), which were administered in solution. The rate of population increase (r, d -1 ) ranged from 0.50 to 52 (controls); 0.20 to 0.40 (CQ); 0.09 to 0.43 (Cu); and -0.03 to 0.30 (CQ-Cu) and showed significant decrease as the concentration of both chemicals in the medium increased. Almost all tested mixtures induced synergistic effects, mainly as the AF increased. We found that the presence of Cu intensifies the vulnerability of organisms to CQ and vice versa. These results stress the potential hazard that these combined chemicals may have on the aquatic systems. This research suggests that P. similis is sensitive to CQ as other standardized zooplankton species and may serve as a potential test species in the risk assessment of emerging pollutants in marine environments., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Triclosan is a personal care product widely used in North America, Europe and Asia as antimicrobial ingredient in many consumer chemical products. In Mexico concentrations of triclosan have been reported in aquatic systems. However, there is no law regulating the presence of chemicals such as triclosan, in aquatic systems. The scarce data about this chemical has increased concern among ecotoxicologists regarding possible effects on aquatic organisms. Moreover, multigenerational studies are rarely studied and the results vary depending on the contaminant. Rotifers, are a dominant group of zooplankton, and have been used in aquatic risk assessments of personal care products due to their sensitivity and high reproductive rates. Plationus patulus and Brachionus havanaensis are common rotifers distributed in aquatic ecosystems of Mexico and have been used in ecotoxicological bioassays. In this study, the median lethal concentration (LC50, 24h) of P. patulus and B. havanaensis exposed to triclosan was determined. Based on the LC50, we tested three sublethal concentrations of triclosan to quantify the demographic responses of both rotifers for two successive generations (F0, and F1). The 24h LC50 of triclosan for P. patulus and B. havanaensis were 300 and 500µgL -1 respectively. Despite the concentration, triclosan had an adverse effect on both Plationus patulus and Brachionus havanaensis in both generations exposed. Experiments show that P. patulus was more sensitive than B. havanaensis when exposed to triclosan. When exposed to triclosan the parental generation (F0) of P. patulus was far more affected than F1., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Unlike temperate regions, tropical ecosystems are characterized by high temperatures (>18 °C) all year, promoting blooms of cyanobacteria which often produce secondary metabolites toxic to zooplankton. Nabor Carillo and the Recreational Lake are part of the saline, Lake Texcoco, in Central Mexico which is filled nowadays with treated waste water. Both water bodies are dominated by Planktothrix, Anabaenopsis, Spirulina and Microcystis. In this study we present the concentration of microcystins in these waterbodies over an annual cycle. We also evaluated the chronic effects of cyanobacterial crude extracts from both lakes on two clones of the rotifer Brachionus calyciflorus, one from Nabor Carrillo Lake and the other from a canal in the shallow, Lake Xochimilco. The experiments on population growth were performed, beginning with 10 individuals per container for each of the following treatments: control (no crude extract), concentrated crude extract, and diluted crude extract (50:50) with moderately hard water and Chlorella vulgaris in a concentration of 0.5 × 10 6  cells ml -1 . The cyanotoxin levels were measured using an ELISA test and ranged between 0.20 and 2.4 μg L -1 in the lake water. The results showed that the Recreational Lake extracts were more toxic, killing the rotifers in less than five days. The r values ranged from -1.74 to 0.48 in the presence of the crude extracts and 0.16 and 0.24 in the controls. The results have been discussed with emphasis on the importance of conducting regular studies to test ecotoxicological impacts of cyanobacterial blooms in tropical waters., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

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., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Brachionus plicatilis is a cosmopolitan rotifer used as a model organism in several research areas and as live food in aquaculture. Being a species complex, responses to stressors vary even among strains of the same species and, thus, the responses of one species are not representative of the whole complex. This study aimed to address the effects of extreme salinity ranges, and different concentrations of hydrogen peroxide, copper, cadmium, and chloramphenicol, in two strains of B. koreanus (MRS10 and IBA3) from B. plicatilis species complex, by assessing effects on their survival and swimming capacity. Neonates (0-4 h old) were exposed to the stressors in 48 well-microplates, for 24 and 6 h, to evaluate lethal and behavioural effects, respectively. Tested conditions of chloramphenicol did not show any effects on rotifers. The behavioural endpoint showed to be particularly sensitive to assess the effects of high salinity, hydrogen peroxide, and copper sulfate, as swimming capacity impairment was observed for both strains in the lowest concentrations used in lethal tests. Overall, results showed that IBA3 was more tolerant to the majority of stressors, comparing to MRS10, which may be due to differences in physiological characteristics, highlighting the importance of performing multiclonal experiments. Also, swimming capacity inhibition proved to be a good alternative to the classical lethality tests, being sensitive to lower concentrations and with shorter exposure periods., (© 2023. The Author(s).)

With the continuous accumulation of nanoplastics (NPs) in the ocean, it becomes urgent to explore their potential effects on filter-feeding zooplankton. This study exposed marine rotifer (Brachionus plicatilis) to 0, 20, 200, and 2000 μg/L of 70-nm polystyrene NPs (PS NPs) for two generations (F0 - F1), followed by two-generation (F2 - F3) culture in clean seawater, to investigate the impacts on life-history traits. The results showed that NPs were ingested by the rotifers within 10 min and reached a maximum level after 12 h of exposure. NPs were also observed in the feces of F0 and F1 generation rotifers and on the surface of F1 generation eggs. The intake of NPs inhibited microalgae ingestion, decreased body volume, delayed the first spawning time, reduced the total number of eggs and offspring of F0 and F1 generation. Moreover, 2000 μg/L NPs postponed the first hatching time of F0 generation eggs by 2.5 h, and the hatching time of F1 generation eggs was delayed by 7.3 h and 6.8 h under 200 and 2000 μg/L NPs exposure. The first spawning time and the first hatching time of rotifers were still significantly prolonged in the F2 generation, but other life-history traits returned to normal. After being cultured in clean seawater for two generations, all these indicators were recovered to the normal level. Overall, this study demonstrates that the life-history traits of marine rotifers could be flexibly changed with/without PS NPs exposure., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The aim of this study is to examine the trophic state of three reservoirs located in the northwest of Algeria based on the physicochemistry of water and the community of rotifers. The measurements of the physicochemical variables were carried out monthly over a 2-year period from December 2015 to November 2017. The rotifers were sampled simultaneously. Abiotic and biotic indices such as the Carlson index, Q B/T , and TSI ROT were determined in order to classify the three reservoirs according to their trophic state. Thus, the diversity indices of Shannon-Wiener (H'), Margalef richness index (D), Pielou evenness (J'), and the density were calculated in order to study the structure of the rotifers. The Kruskal-Wallis test confirmed the heterogeneity of the physicochemical quality (P value < 0.05) among the three reservoirs. A total of 71 species were identified during this study. The result of the various indices affirms this heterogeneity and indicates a trophic state hypereutrophic for the Hammam Boughrara reservoir, eutrophic for the Bakhadda reservoir and meso-oligotrophic for Sidi Yacoub. The use of canonical correspondence analysis (CCA) has shown that the structure of rotifers is influenced by local environmental factors. Some species such as the genus Brachionus species have shown their preference for extreme conditions. The use of biotic indices is highly recommended for the trophic state evaluation of reservoirs for a better water resources management., (© 2020. Springer-Verlag GmbH Germany, part of Springer Nature.)

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]

Intensive interspecific competition for limited resource often can result in the exclusion of inferior competitors, decrease the species diversity and alter the structure of the zooplankton community. Competitive experiments between Brachionus calyciflorus and Brachionus angularis were conducted at three Scenedesmus densities (0.5 × 106, 1.0 × 106 and 2.0 × 106 cells ml−1) and four initial inoculation densities (numerically, 100% B. calyciflorus, 75% B. calyciflorus and 25% B. angularis, 50% each of the two species, 25% B. calyciflorus and 75% B. angularis, and 100% B. angularis). The results showed that at the low food level, B. angularis outcompeted B. calyciflorus and vice versa at the high food levels. At the intermediate food level, B. angularis was displaced by B. calyciflorus at nearly all the initial inoculation densities except for 75% B. angularis, at which both species coexisted until the termination of the experiment. When grown alone at 0.5 × 106, 1.0 × 106 and 2.0 × 106 cells ml−1 of Scenedesmus, B. calyciflorus reached the peak abundance values of 34 ± 4, 69 ± 5 and 101 ± 9 individuals ml−1 and had population growth rates of 0.608 ± 0.032, 0.654 ± 0.033 and 0.518 ± 0.039 d−1, respectively. The corresponding values for B. angularis were 265 ± 8, 330 ± 30 and 802 ± 87 individuals ml−1 and 0.623 ± 0.020, 0.770 ± 0.036 and 0.871 ± 0.013 d−1. The results suggest that the outcome of competition depends not only on the size of the competing species and food availability but also on their colonizing density. At the low food level, Brachionus angularis outcompeted B. calyciflorus and vice versa at the high food level. At the intermediate food level, B. angularis was displaced by B. calyciflorus at nearly all the initial inoculation densities except for 75% B. angularis at which both species coexisted. [ABSTRACT FROM AUTHOR]

We tested the effect of different food (Chlorella vulgaris) concentrations on the population growth and demographic variables of Dipleuchlanis propatula. In addition, we also tested the effect of competition from two other zooplankton species (a rotifer Plationus patulus and a ciliate Paramecium sp.). The parthenogenetic eggs of D. propatula carry a gelatinous matrix with a thickness of about 20 µm. Population growth of D. propatula increased with increase in the algal density. Depending on the food availability, the peak abundances of D. propatula varied from 9 to 50 ind. ml−1. The rate of population increase, r, varied from 0.18 to 0.23 per day. Food density had a significant effect (p < 0.05, Tukey test) on this variable too. In spite of higher peak densities observed at high food levels, the r values were not very different; this was due to the long lag phase before the population increased. Dipleuchlanis propatula growth was lower due to competition from ciliates. Food density had no significant effect on the average life span, which varied from 5 to 7 days. However, both gross and net reproductive rates increased with increase in algal food. These results show that D. propatula had growth patterns similar to other members of the family Euchlanidae. [ABSTRACT FROM AUTHOR]

To understand the population growth potential of different species of rotifers in nature, field collections through seasons are essential. We sampled zooplankton (and measured selected physicochemical variables) from the Madín reservoir, a high altitude eutrophic urban waterbody from Mexico, every month for a year. Qualitative analysis of zooplankton revealed 28 rotifer species and four cladoceran crustaceans plus one unidentified copepod. Cephalodella catellina (1400 ind L-1), Horaella thomassoni (550 ind L-1), Conochilus dossuarius (380 ind L-1) and Filinia longiseta (25 ind L-1) had higher peak density than other rotifers. Based on the concentrations of nitrates and phosphates, chlorophyll a levels or different diversity indices (e.g., Carlson, Shannon-Wiener, Pantle and Buck, Ejsmont-Karabin's TSIRot), the waterbody is eutrophic to hypertrophic, depending on the season. In this waterbody we observed high densities of Aphanothece sp. which is a toxic picocyanobacterium. During the blooms of Aphanothece, we also recorded higher densities of H. thomassoni and C. catellina. Based on the gut contents we found that both these rotifer species feed on Aphanothece in this waterbody. This study thus suggests the potential growth of Horaella, Cephalodella, Conochilus and Filinia in this eutrophic reservoir containing blooms of Aphanothece. [ABSTRACT FROM AUTHOR]

Aquatic organisms are constantly exposed to effluents which often contain microplastics. Microplastics adversely affect aquatic organisms as a result of mechanical damage during ingestion or intoxication by chemicals adsorbed on the microplastics. Sub-optimal temperatures may acerbate the adverse effects of microplastics on aquatic biota. Brachionid rotifers, such as Brachionus havanaensis and Brachionus calyciflorus, are common in tropical freshwaters. They are generalist filter feeders capable of consuming microplastic particles of a wide size range 0.05 to 40 µm, which can eventually affect growth and competitive interactions among species. Here, we evaluated the effect of 30 µm beads of polystyrene microplastics at 10 and 20 mg l−1 on the population growth and competition of B. havanaensis and B. calyciflorus at 20 and 25 °C using 0.5 × 106 cells ml−1Chlorella vulgaris as food. Population growth decreased in treatments with microplastics at both temperatures as compared to the controls. The population growth rates ranged between 0.21 and 0.38 d−1 for B. calyciflorus, and between 0.27 and 0.48 d−1 for B. havanaensis. The presence of the competing species significantly lowered the population growth rate for B. calyciflorus but not for B. havanaensis. On the other hand, while the presence of the microplastics had little impact on the population growth rate of B. calyciflorus in the presence of the competitor, the reverse was true for B. havanaensis, especially at 20 °C. Our results show that the presence of microplastics may affect rotifer community structure in natural water bodies. [ABSTRACT FROM AUTHOR]

We quantified the population growth of the predatory heliozoan Actinosphaerium eichhornii fed separately four rotifer prey (Anuraeopsis fissa, Brachionus calyciflorus, Brachionus havanaensis and Plationus patulus) at three densities (0.5, 1 and 2 ind. ml−1 per day). All the four prey rotifer species were consumed by A. eichhornii. Regardless of the prey species, increasing rotifer prey density resulted in an increased population growth of the heliozoans. Higher cyst production in A. eichhornii occurred at higher prey densities on all prey species. A. fissa offered at the lower densities of 0.5–1.0 ind. ml−1 day−1 did not lead to cyst production by A. eichhornii. The predator did not survive beyond 2 days on Chlorella vulgaris alone. When cultured together with heliozoans, A. fissa, B. calyciflorus and B. havanaensis were eliminated within 4 days. However, the prey rotifer Plationus patulus continued to survive for about 10 days with heliozoans. The highest rate of population increase of heliozoans (0.91 day−1) was recorded when fed B. calyciflorus at a density of 2 ind. ml−1 day−1, while of those of prey varied from 0.30 to 0.41 day−1 when fed Chlorella vulgaris at 1 × 106 cells ml−1 day−1. We have analyzed the impact of heliozoan predation on rotifers. [ABSTRACT FROM AUTHOR]

Predation is a well-known factor that structures rotifer communities. However, the role of protists as predators is relatively understudied. Here, we investigated predatory behavior of Actinosphaerium sp., a freshwater heliozoan, on seven rotifer species. Predators and prey were collected from a local playa; except for Brachionus calyciflorus that served as a naive prey control. Prey included large species (≥ 175 µm mean length: Asplanchna sieboldii, B. calyciflorus, Platyias quadricornis, and Lacinularia flosculosa) and small species (< 175 µm: Cephalodella gibba, Euchlanis dilatata, and Lepadella patella). Four experiments were conducted. (1) Single prey items of varying size and motility. Larger prey types were ~ 1.7 to 3.0 times more likely to be ingested than small prey. No L. flosculosa were ingested, contrary to field observations. No correlation was found between swimming speed and predation risk. (2) Preference tests. Asplanchna sieboldii and B. calyciflorus were favored prey. (3) Growth rate of Actinosphaerium on mixed diets, with and without Asplanchna. Highest population growth of Actinosphaerium was observed in presence of A. sieboldii. (4) Prey defenses. Susceptibility of spined versus unspined B. calyciflorus resulted in no significant difference in predation risk. Thus, size and being mobile (compared to sessility) are the primary risk factors influencing rotifer predation vulnerability. [ABSTRACT FROM AUTHOR]

We quantified the feeding behavior (encounter, attack, capture and ingestion) and demographic parameters (survival and reproduction) of the predatory rotifer Asplanchna sieboldii fed on the prey Plationus patulus previously exposed to microplastics (MPs), Cd or their combination. As compared to controls, capture and ingestion rates of P. patulus by A. sieboldii decreased by 71 and 61%, respectively, with prey previously exposed to mixed MPs and Cd treatment. Life table data showed that the predator died earlier in controls than when fed on prey exposed to both Cd and microplastics. Regardless of the prey treatment, the offspring production by A. sieboldii increased as the available prey numbers increased (from 1 to 4 ind. ml−1). Compared to controls, the fecundity rate of the predator decreased when contaminated prey was offered as food. [ABSTRACT FROM AUTHOR]

The River Nile is the artery of Egypt, as it presents more than 96% of the municipal, industrial, and irrigation necessities of Egypt. This study was dedicated to providing data about the effect of pollution at six stations on the River Nile at the Rosetta branch during the period from August 2019 to April 2020, using heavy metals analysis and zooplankton as biological indicators. It was found that the average of heavy metals concentration follows the descending order Al > Fe > Mn > Zn > Ni > Co. Most of the heavy metals recorded its highest values at El-Rahawy station. Zooplankton community was represented by 32 species in addition to 4 Meroplanktons. Five groups of zooplankton were recorded, viz. Rotifera (1717 org./L), Protozoa (552 org./L), Cladocera (54 org./L), Nematoda (46 org./L), and other Meroplankton (44 org./L), dominated by Rotifera followed by Protozoa, Cladocera, Nematoda, and other Meroplanktons contributing 71%, 23%, 2%, 2%, and 2%, respectively. The highest average density of total zooplankton was recorded during spring while the lowest was recorded during summer. The highest similarity of (79.12%) was observed between (Site 1) and (Site 5). Almost all diversity indices were conducted and showed its highest values in site 6. The principal component analysis conducted between heavy metals, and zooplankton showed a significant negative correlation was shown for the dominant zooplankton with the heavy metals except with cobalt. Nematoda and the rotifer Brachionus angularis recorded a positive correlation with heavy metals except cobalt. [ABSTRACT FROM AUTHOR]

In hypertrophic waterbodies, seston may be an important food for planktonic rotifers. Therefore, we hypothesized that seston in the hypertrophic waterbody (Lake Xochimilco, State of Mexico) supports high diversity and density of rotifers. To test this, we conducted growth experiments using six rotifer species (Brachionus bidentatus, Brachionus budapestinensis, Brachionus calyciflorus, Brachionus caudatus, Brachionus havanaensis and Plationus patulus) cultured on three seston size fractions (< 3, 3–15 and < 15 µm) for 15 days. The three fractions of seston contained 3.15, 6.30, and 9.45 μg C ml−1, respectively. The physical and chemical variables of the waterbody were fairly stable during the study period. Brachionus budapestinensis, B. calyciflorus and B. caudatus showed negative growth rates when cultured on seston size of 3–15 or < 15 µm, while B. bidentatus had negative r on < 3 µm particle size. Brachionus havanaensis and P. patulus were well adapted to feed on different sizes of seston, while B. budapestinensis and B. caudatus had higher growth on < 3 µm particle size. These results explain the high diversity and density of brachionid rotifers in this waterbody where they coexist by partitioning the available seston. [ABSTRACT FROM AUTHOR]

Rotifers and cladocerans compete for resources in freshwater ecosystems. Cladocerans, due to their large size, are competitively superior to rotifers. Cladocerans also release secondary metabolites into the medium which may be allelopathic to rotifers. However, in many eutrophic water bodies, rotifers are competitively dominant to cladocerans. We therefore hypothesize that allelochemicals released by competing species of Cladocera have weak or no adverse effects on rotifers. To test this, we conducted cohort life table demography experiments of the three rotifers Brachionus calyciflorus, Brachionus havanaensis, and Plationus patulus with cladoceran-conditioned medium (CM) derived from Moina macrocopa, Ceriodaphnia dubia, and Daphnia pulex. All six zooplankton species were isolated at the same time from a shallow eutrophic water body in Central Mexico. We found that the following demographic variables of B. calyciflorus cultured in CM did not differ from controls: life expectancy at birth, gross and net reproductive rates, generation time and the rate of population increase. We further showed that B. havanaensis was most sensitive to the cladoceran-mediated chemicals and that M. macrocopa-CM caused varied demographic responses in rotifers. We conclude that cladoceran-conditioned medium had weak allelopathic effects on rotifers unlike the negative experience from direct physical contact with Cladocera. [ABSTRACT FROM AUTHOR]

Diapausing embryos of invertebrates represent investments in future populations. Thus, they must be capable of withstanding a variety of environmental assaults. Consequently, their eggshells should be adapted to resist injuries from predators, sediments, or excessive shrinkage if desiccated. To date, there have been no direct nanomechanical measurements of the eggshells of most invertebrates that produce diapausing eggs. Here, we used three approaches to understand how the eggshells of two rotifers, a freshwater species (Brachionus calyciflorus) and a brackish-water species (B. plicatilis), tolerate harsh conditions: (1) atomic force microscopy to measure elasticity and hardness; (2) transmission electron microscopy to study ultrastructure; (3) scanning electron microscopy to examine surface features. We compared these values to measurements of brine shrimp (Artemia salina) cysts and mosquito (Aedes aegypti) overwintering eggs. Our results revealed that rotifer eggshells are structurally similar and have comparable nanomechanical values. While rotifer eggshells had lower Young's moduli (ca 13–16 MPa) and hardness values (1.84–1.85 × 10−2 GPa) than eggshells of Artemia and Aedes, eggshells of all species were relatively elastic and not particularly resistant to deformation. Pliancy of shells that form egg banks (ie Artemia, Brachionus) may be an adaptation to resist cracking under the physical forces associated with burial in sediments. Although there are no obvious relationships among eggshell thickness, ultrastructure, ornamentation, or nanomechanical values in rotifer eggshells, we hypothesise that eggshell composition may play an important role in determining elasticity and hardness. Future studies should consider an integrative approach to understand the importance of eggshell structure, chemistry, and mechanics in protecting diapausing embryos. [ABSTRACT FROM AUTHOR]

The advent of molecular techniques has resulted in the discovery of previously unknown cryptic species in many organisms, including rotifers, allowing researchers to perform detailed tests on reproductive barriers between closely related taxa. Here, we review the available literature about molecular techniques implemented for detecting cryptic diversity in rotifers and delimiting species, and discuss the potential mechanisms of reproductive isolation among rotifer cryptic species. Half of the evaluated studies used quantitative statistical approaches for species delimitation. Species boundaries defined by molecular approaches were also examined by conducting mating experiments. Those mating experiments were used to test various reproductive barriers. Most (75%) studies that identified reproductive isolation mechanisms provided evidence of prezygotic barriers. The available literatures suggest that behavioral reproductive isolation may have a more important role than other prezygotic barriers in facilitating reproductive isolation. Postzygotic barriers such as hybrid unviability or sterility and female mortality also contribute to reproductive isolation among rotifer cryptic species. The prevalence of prezygotic barriers in our assessment may stem from the difficulty of studying postzygotic barriers, which can require long-term maintaining and monitoring of rotifer populations. Sequencing tools, including whole genome sequencing, could be implemented to investigate the molecular basis of reproductive isolation in rotifers. [ABSTRACT FROM AUTHOR]

Many zooplankton organisms facing harsh environmental conditions producing resting eggs. Resting eggs accumulate in the sediment and create a resting egg bank. Knowledge on the egg bank structure, morphology and morphometry of the eggs as well as the effect of cues on hatching, contributes to the understanding zooplankton dynamics in lakes. Here we described the composition and structure of zooplankton egg bank from a shallow tropical lake and analyzed the effect of some biotic factors on hatching rates. In order to describe the structure and composition of the resting egg bank, we determined the richness, density, morphology and morphometry of the resting eggs isolated by the sugar flotation method. Diapausing eggs were measured and their external features studied by microphotography under optical microscope and SEM. To analyze the effect of biotic factors on hatching rates, we exposed the resting structures and the entire sediment to three biotic factors: a chlorophyte (Scenedesmus acutus), a cyanobacteria (Microcystis sp.) and a predatory rotifer (Asplanchna girodi). A total of 25 zooplankton species hatched from the sediments. Our results show that the medium density of the healthy-looking diapausing eggs was of 7.6 ± 2 diapausing eggs · cm−3 and that rotifers are the predominant group in the egg bank. Medium conditioned with the chlorophyte and the cyanobacteria resulted in a higher hatching rate. The ornamentations of rotifer diapausing eggs present different features, such as wrinkles and spines, which can help to taxonomic identification without the need of promoting hatching. This study provides information on the structure and composition of the egg bank of a shallow lake and the effect of biotic factors on hatching rates. The results show the dominance of rotifers over cladocerans and copepods and a positive effect of certain biotic factors on hatching. [ABSTRACT FROM AUTHOR]

We report a dataset of known and published occurrence records of Italian taxa from species (and subspecies) to family rank of the phylum Rotifera; we considered only Bdelloidea, Monogononta, and Seisonacea, and did not include Acanthocephala. The dataset includes 15,525 records (12,015 of which with georeferenced coordinates) of 584 valid species and subspecies names and other taxa at family level, gathered from 332 published papers. The published literature spans the period from 1838 to 2022, with the lowest number of papers published during the first half of the twentieth century, followed by an increasing number of papers, from 20 to more than 60 in each decade. The Italian regions with the highest number of records and species are Emilia-Romagna, Lombardy, and Piedmont, whereas no records are known for Molise. The number of species known from each region mostly mirrors sampling efforts, measured as the number of publications per region. The dataset is available through the Open Science Framework (OSF), and all the georeferenced occurrence data have been uploaded to the Global Biodiversity Information Facility (GBIF). [ABSTRACT FROM AUTHOR]

We report a dataset of all known and published occurrence records of animals of the phylum Rotifera, including Bdelloidea, Monogononta, and Seisonacea (with the exclusion of Acanthocephala) for Africa and surrounding islands and archipelagos. The dataset includes 27,455 records of 957 taxa (subspecies: 39; species: 819; species group: 1; genus: 81; family: 17), gathered from 706 published papers. The published literature spans from 1854 to 2022, with the highest number of records in the decades 1990-1999 and 2010-2019. The African countries with the highest number of taxa are Nigeria, Algeria, South Africa, and the Democratic Republic of the Congo, whereas no records are yet available for a dozen countries. The number of species known from each country can be explained mostly by sampling efforts, measured as the number of papers published for each country up to now. The dataset is available through the Open Science Framework (OSF) and in the Global Biodiversity Information Facility (GBIF). [ABSTRACT FROM AUTHOR]

Plasticity of spine morphology is a universal phenomenon in rotifers. Some Brachionus calyciflorus clones consistently develop two posterolateral spines (PS) with similar length (Type A), but others (Type B) not. The underlying mechanisms remain unknown. In the present study, the resting eggs were collected from the same B. calyciflorus strain, their hatchlings (stem rotifers) were categorized into types A and B, and then, clonally cultured for eight generations at different algal densities or temperatures. The results showed that the PS varied in length among different temperatures and food levels, but inherent differences between types A and B were always observed, indicating that differentiation between types A and B might not associate with temperature or food availability. Next, we compared the population growth and PS length between types A and B at the general condition (control), in responses to Asplanchna kairomone, Keratella tropica and Moina macrocopa. The results showed that type B had higher population growth rate than type A, suggesting the higher adaptability of type B in the general condition. In response to Asplanchna kairomone, the PS length of both types A and B was significantly induced, and their PS length was similar, but type B showed higher population growth rate than type A. Coculture with M. macrocopa significantly lengthened the PS of type B but not type A, and types A and B showed similar population growth curves. Coculture with K. tropica did not affect significantly the PS length of types A and B. However, type A showed significantly and greatly higher population density and population growth rate than type B, indicating a much stronger competition ability of type A than type B against K. tropica. Overall, these results indicated that consistent development of PS might facilitate B. calyciflorus to defend against small competitors. [ABSTRACT FROM AUTHOR]

We studied temporal variations in phenolic compounds from the hydrophyte Myriophyllum aquaticum collected from a shallow lake. The effects of macrophyte-conditioned medium containing phenols with other compounds and phenols only as well as plant tissue extracts were tested on the survival and reproduction of the rotifer Plationus patulus. Apical tissue of the hydrophyte had the highest levels of total phenols. Rotifers in controls, and those exposed to phenols from the macrophyte-conditioned medium grew rapidly within two weeks, but cultures exposed to phenols extracted from the apical region took longer. Age-specific survival of P. patulus showed a rapid decline within one week when exposed to plant extracts compared to conditioned medium. The average lifespan of P. patulus was longer in the macrophyte-conditioned medium as compared to the controls, but shorter in the aqueous plant extract. Gross and net reproductive rates showed similar trends, wherein the controls had significantly higher values than those exposed to plant extracts, but increased with the conditioned medium only at the two lower concentrations tested. The demographic response of rotifers exposed to phenols only from the macrophyte-conditioned medium differed from those of the macrophyte-conditioned medium containing both phenolic and non-phenolic compounds. Macrophyte phenolic compounds influenced the survival and reproduction of P. patulus but depended on the other chemicals released into the medium. [ABSTRACT FROM AUTHOR]

Life history strategies of rotifers vary in relation to their habitats. We compared the demography of Hexarthra jenkinae (de Beauchamp, 1932) from ephemeral pools and the large, permanent Nabor Carrillo Lake, both parts of the saline Lake Texcoco in Mexico. Population growth tests were conducted at salinities of 10, 12.5 and 15 g l−1 (1:1 ratio of NaCl and NaHCO3), at 22 ± 1 °C with two algal food concentrations (0.25 × 106 and 1.0 × 106 cells ml−1 of Nannochloropsis oculata). The population growth experiments were initiated with ten individuals per jar, whereas for the cohort life table study we used ten neonates. Observations were taken once (population growth) or twice (life table) a day; experiments continued until the populations declined or the last individual of each cohort in the life table study died. Survivorship and growth rates increased with increasing food availability. From the population growth studies, we found that the clone established from the ephemeral pools had higher growth rates (0.23–0.55 day−1) than those from the permanent lake (0.12–0.34 day−1). Growth rates were lower in the lifetable experiments than in the population growth studies. Our results are discussed in relation to habitat and life history strategies exhibited by rotifers in shallow saline waterbodies. [ABSTRACT FROM AUTHOR]

We investigated the taxonomic and functional diversity of rotifers in the littoral, intermediate, and pelagic zones of a tropical lake. Rotifers were collected at 10 sampling stations located in the three distinct zones. Taxonomic diversity was determined by species richness, abundance, and Shannon–Wiener diversity, while functional diversity was calculated using functional richness (FRic), functional evenness (FEve), and the community-weighted mean of functional traits (CWM). Redundancy analysis (RDA) were applied to ordinate the taxonomic and functional composition between the zones of the lake. The taxonomic diversity, represented by the abundance of organisms, was higher in the ecotone (i.e., intermediate zone). The RDA showed a difference between the three zones, with the occurrence of epiphytic rotifers in the littoral zone and semi-planktonic and planktonic species in the intermediate and pelagic zones. Regarding functional diversity, values of FRic and FEve did not differ between the zones. In contrast, CWM showed a distinct response between the zones of the lake. Illoricate species with raptorial characteristics, virgate trophi, and corona of the Asplanchna-type dominated in the littoral zone. In turn, microphagous rotifers, loricate species with spines, malleate trophi, and corona of the Brachionus/Euchlanis-type occurred in the intermediate and pelagic zones of the lake. The ecotone (intermediate zone) was taxonomically more diverse for the abundance of organisms compared to other two zones of the lake. For functional diversity, the three zones of the lake presented distinct functional traits. [ABSTRACT FROM AUTHOR]

In this study we evaluated the toxicological effects of crude extracts of Dolichospermum planctonicum on Plationus patulus (Rotifera) and Ceriodaphnia cornuta (Cladocera). The active compound from the laboratory-cultured cyanobacteria was extracted by lyophilizing it at −70 °C for 48 h, after which the sample was thawed. The cycle was repeated five times, and between each cycle the cells were sonicated to lyse them. Using the extract of Anabaena, experiments of population growth and life table demography of the two zooplankton species were compared in media with and without (controls) the cyanotoxins. In both experiments two toxic concentrations diluted in US EPA medium were used, one in a 5:15 proportion, and the other in a 2.5:17.5. We found that the rotifers were more resistant to the toxicants than the cladocerans. Their population growth rates ranged from 0.11 d in controls to 0.08 d in the presence of the crude extracts for P. patulus and from 0.18 in controls to −0.27 in the presence of the crude extracts for C. cornuta. The crude extract also had a significant negative impact on the demographic parameters, adversely affecting reproduction more than survival. The data have been discussed with emphasis on the importance of further research using cyanobacterial crude extracts. [ABSTRACT FROM AUTHOR]

Bdelloids are commonly found in freshwaters or limno-terrestrial habitats. No formal attempt has yet been performed to define bdelloid niche and to identify whether species respond in a clear, consistent, and quantifiable fashion to environmental parameters. Therefore, we analysed the correlation between the occurrence of common Rotaria species in Thailand and environmental variables, including limnological, climatic, and biotic features. We followed two approaches to determine the niche of the investigated species: performing regression models for each species and reconstructing the niche spaces occupied by each species using n-dimensional hypervolumes. The effect of local-scale limnological and large-scale climatic variables was almost negligible at explaining the occurrence and distribution of Rotaria species. Surprisingly, primary productivity, known in temperate areas to be a major positive correlate of the occurrence of R. neptunia, appeared to have no effect on this species when measured as chlorophyll a, and a negative effect when measured as cyanobacterial productivity. Biotic variables revealed that different Rotaria species have a similar response to environmental variables. Two main messages are supported: (i) no clear environmental features unambiguously affected bdelloids species; (ii) features that are relevant for limnological processes at temperate latitudes may not be applicable for explaining processes in tropical latitudes. [ABSTRACT FROM AUTHOR]

A first study of the rotifers of the Niger River in Niger is reported here. Two surveys took place under contrasting hydrological conditions: low-water level (16 April to 8 May 2018) and high-water level (1 to 15 February 2019). Zooplankton and physico-chemical parameters were sampled at eight stations spread over 520 km from Ayorou to Gaya. In total, 32 taxa were identified, including 26 at species level. During the low-water sampling, Polyarthra sp. (31%), Brachionus caudatus (23%), Synchaeta longipes (11%), Keratella tropica (7%) and Filinia longiseta (5%) were the most abundant, whereas Brachionus quadridentatu s (26%), Lecane hastata (25%), Keratella cochlearis (9%), Keratella lunaris (5%), Hexarthra sp. (3%) were dominant during the high-water sampling. The mean abundance of rotifers ranged between 14 × 103 ind. m−3 during the high-water sampling and 244 × 103 ind. m−3 during the low-water sampling. The highest diversity was observed in the three stations located upstream from the city of Niamey. The results reflect the difference in environmental parameters between the downstream and upstream Niamey stations. RDA analyses showed that the main environmental factors explaining the distribution of rotifers were dissolved oxygen, orthophosphate and nitrate concentrations. [ABSTRACT FROM AUTHOR]

Background: Seisonidea (also Seisonacea or Seisonidae) is a group of small animals living on marine crustaceans (Nebalia spec.) with only four species described so far. Its monophyletic origin with mostly free-living wheel animals (Monogononta, Bdelloidea) and endoparasitic thorny-headed worms (Acanthocephala) is widely accepted. However, the phylogenetic relationships inside the Rotifera-Acanthocephala clade (Rotifera sensulato or Syndermata) are subject to ongoing debate, with consequences for our understanding of how genomes and lifestyles might have evolved. To gain new insights, we analyzed first drafts of the genome and transcriptome of the key taxon Seisonidea. Results: Analyses of gDNA-Seq and mRNA-Seq data uncovered two genetically distinct lineages in Seison nebaliae Grube, 1861 off the French Channel coast. Their mitochondrial haplotypes shared only 82% sequence identity despite identical gene order. In the nuclear genome, distinct linages were reflected in different gene compactness, GC content and codon usage. The haploid nuclear genome spans ca. 46 Mb, of which 96% were reconstructed. According to ~ 23,000 SuperTranscripts, gene number in S. nebaliae should be within the range published for other members of Rotifera-Acanthocephala. Consistent with this, numbers of metazoan core orthologues and ANTP-type transcriptional regulatory genes in the S. nebaliae genome assembly were between the corresponding numbers in the other assemblies analyzed. We additionally provide evidence that a basal branching of Seisonidea within Rotifera-Acanthocephala could reflect attraction to the outgroup. Accordingly, rooting via a reconstructed ancestral sequence led to monophyletic Pararotatoria (Seisonidea+Acanthocephala) within Hemirotifera (Bdelloidea+Pararotatoria). Conclusion: Matching genome/transcriptome metrics with the above phylogenetic hypothesis suggests that a haploid nuclear genome of about 50 Mb represents the plesiomorphic state for Rotifera-Acanthocephala. Smaller genome size in S. nebaliae probably results from subsequent reduction. In contrast, genome size should have increased independently in monogononts as well as bdelloid and acanthocephalan stem lines. The present data additionally indicate a decrease in gene repertoire from free-living to epizoic and endoparasitic lifestyles. Potentially, this reflects corresponding steps from the root of Rotifera-Acanthocephala via the last common ancestors of Hemirotifera and Pararotatoria to the one of Acanthocephala. Lastly, rooting via a reconstructed ancestral sequence may prove useful in phylogenetic analyses of other deep splits. [ABSTRACT FROM AUTHOR]

Whether bdelloid rotifers can detect and respond to the chemical cues of predators has not been studied, and research on their behaviour is scarce in general. To test for such response, we observed the behaviour of Philodina megalotrocha rotifers in either control or copepod-conditioned water. We then introduced a mechanical disturbance to test if predator odour sensitises rotifers to subsequent cues. We found intensified swimming in P. megalotrocha exposed to Macrocyclops fuscus-conditioned water, i.e. the larger and more predatory of the tested copepods. Such response may be adaptive, depending on the predominant hunting mode of the predator in the particular habitat. [ABSTRACT FROM AUTHOR]

Because every species has unique attributes relevant to understanding specific aspects of aging, using a diversity of study systems and a comparative biology approach for aging research has the potential to lead to novel discoveries applicable to human health. Monogonont rotifers, a standard model for studies of aquatic ecology, evolutionary biology, and ecotoxicology, have also been used to study lifespan and healthspan for nearly a century. However, because much of this work has been published in the ecology and evolutionary biology literature, it may not be known to the biomedical research community. In this review, we provide an overview of Brachionus rotifers as a model to investigate nutritional and metabolic regulators of aging, with a focus on recent studies of dietary and metabolic pathway manipulation. Rotifers are microscopic, aquatic invertebrates with many advantages as a system for studying aging, including a two-week lifespan, easy laboratory culture, direct development without a larval stage, sexual and asexual reproduction, easy delivery of pharmaceuticals in liquid culture, and transparency allowing imaging of cellular morphology and processes. Rotifers have greater gene homology with humans than do established invertebrate models for aging, and thus rotifers may be used to investigate novel genetic mechanisms relevant to human lifespan and healthspan. The research on caloric restriction; dietary, pharmaceutical, and genetic interventions; and transcriptomics of aging using rotifers provide insights into the metabolic regulators of lifespan and health and suggest future directions for aging research. Capitalizing on the unique biology of Brachionus rotifers, referencing the vast existing literature about the influence of diet and drugs on rotifer lifespan and health, continuing the development of genetic tools for rotifers, and growing the rotifer research community will lead to new discoveries a better understanding of the biology of aging. [ABSTRACT FROM AUTHOR]

There are two types of movement pattern in the Brachionidae (rotifers), swimming and attachment, although the factors that induce a shift between them have not been adequately clarified. This study investigated the effects of five external factors—food limitation, temperature, salinity, predator, and un-ionized ammonia—on movement in females of the euryhaline rotifer Brachionus plicatilis sensu stricto. Rotifers under periodic starvation showed increased swimming frequency (percentage of swimming rotifers) to about 50% on feeding compared to controls under continuous feeding (21%). Starved rotifers were further exposed to the following conditions for 2 days: a range of water temperature (15–25 °C), salinity (17–34 practical salinity units), a predator (or other rotifers)-conditioned medium, and un-ionized ammonia (NH3-N; 5–20 mg/l). Neither temperature nor predator conditioning significantly affected rotifer swimming frequency. However, rotifers transferred to a higher salinity or to a rotifer-conditioned medium ceased to exhibit swimming. All the tested ammonia levels caused vigorous swimming of rotifers during the initial experimental period. The results indicate that swimming in female rotifers can be classified as (1) an escape behavior induced by environmental stress, and (2) a response to higher viability under certain favorable environmental conditions. [ABSTRACT FROM AUTHOR]

Assessing zooplankton biodiversity is essential to support freshwater management/conservation programs. Here, we investigated the zooplankton community structure from 180 shallow lakes in northeastern Brazil and analyzed them according to biome (Atlantic Forest or Caatinga), the origin of ecosystems (natural or man-made lakes), and habitat type (pelagic or littoral). Additionally, we provided an updated list of zooplankton species. We registered 227 species (137 Rotifera, 65 Cladocera, 25 Copepoda). The most common species of each major group among all lakes were the cladoceran Ceriodaphina cornuta, the rotifers Brachionus havanaensis and Lecane bulla, and the copepod Termocyclops decipiens. Species related to aquatic vegetation, as the Lecanidae rotifers and phytophilous cladocerans, were more frequent along Atlantic Forest biome and natural lakes. On the other hand, species that are bioindicators of eutrophic waters were more common at the Caatinga biome and man-made lakes. Atlantic Forest and Caatinga biomes had similar species richness, but different community compositions for all zooplankton groups, reinforcing the Caatinga significance for the Brazilian aquatic biodiversity. The type of habitat was the most important factor structuring species richness, with higher richness in the littoral region when compared to the pelagic. A result of many unique species of Cladocera and Rotifera associated with the aquatic vegetation were observed. The findings demonstrated that conservation/management plans cannot generalize zooplankton species distribution across different biomes, origins and even within a single lake, between the pelagic and littoral zones. This study provided a zooplankton species list from 180 lakes in northeastern Brazil and showed that species distribution, richness and composition vary according to biome (Atlantic Forest or Caatinga), the lake origin (natural or man-made lakes), and the lake habitat (pelagic or littoral). [ABSTRACT FROM AUTHOR]

To test the hypothesis that Brachionus angularis can rapidly develop local adaptation to invasion by other monogonont rotifers, replicate populations of B. angularis were exposed to two environments invaded by B. calyciflorus at different inoculation densities and an environment free from invaders. During the selection experiment, the density of each population was reduced to starting conditions every 3 days, and the changes in population growth rate and mictic ratio of B. angularis were continuously tracked. During the 81-day (69 asexual generations) period of selection, the B. angularis populations in the environments with invaders showed a significant increase in growth rate but a non-significant change in mictic ratio over time when compared with those in the environment without invaders. A common garden experiment revealed that when exposed to the environments with invaders, the B. angularis populations evolved in the environments with invaders had higher growth rates than those evolved in the environment without invaders, and the opposite was also true, indicating that local adaptation was rapidly formed. Info-chemicals released by invaders to the environment might increase the heritability of higher growth rates, and thus facilitate the local adaptation of B. angularis populations to invasion by B. calyciflorus. [ABSTRACT FROM AUTHOR]

Due to the expanding world aquaculture production, the demand for high quality and quantity of fish larvae has also increased. Up to date, the bottleneck in larviculture is the stable and ample production of appropriate live food such as rotifers and copepods. Among rotifers, Brachionus plicatilis species complex, which encompasses 15 species with varied sizes ranging from 100 to 400 µm, is commonly used in most hatcheries. The use of B. plicatilis species complex (B. plicatilis, B. koreanus, and B. rotundiformis) in larviculture is reported in several review papers. In this review, we first described rotifer species not classified under B. plicatilis species complex, some of which are already used in larviculture, while some have high potential for use based on their characteristics, life history, and distribution. Rotifers, Brachionus angularis, Brachionus calyciflorus, and Proales similis, are described in detail in comparison with B. plicatilis species complex. Furthermore, we discussed some characteristics of rotifers which can affect their predation. [ABSTRACT FROM AUTHOR]

Although the theoretical underpinnings of habitat selection by marine invertebrate larvae have been well studied, this theory has been neglected for freshwater sessile rotifers. To study how substratum selection affects larval fitness, we developed a dynamic model to examine influences of three elements of larval life (survival, substratum acceptance, substratum encounter probability) and substratum-dependent reproductive success in adults. Monte Carlo simulation models were run using an initial cohort of larvae. Our Basic Model assessed fitness as simply settling on a substratum using only the larval elements and revealed statistically greatest fitness when swimming speed decreased with age and when substratum preference was constant or exhibited mid-age competence. The Reproductive Model assessed fitness (mean number of offspring adult−1) as a function of substratum. We compared reproduction on neutral substrata to substrata where quality varied and separately as a function of adult population density: coloniality (synergism) versus competition. The model showed fitness was statistically greatest when larval swimming speed decreased with age and when coloniality increased reproduction. We also explored conditions where populations of planktonic adults could survive. The model is applicable to sessile organisms and may be modified to examine other life history activities including selection of mates, prey, or territory. [ABSTRACT FROM AUTHOR]

A dynamic change in environmental conditions among floodplain habitats with different geomorphology might be a significant trigger in determining rotifer functional diversity. The aim of the study was to test the importance of environmental differences between several waterbody types, their positions within the floodplain and supporting microcrustacean communities in the structuring of rotifer functional feeding guilds. The study was conducted in Kopački rit floodplain during 2008 at five sites (two lakes, two channels and the main river). ANOSIM showed a significant difference in spatial distribution among rotifer feeding guilds. Redundancy analyses indicated biotic variables to significantly influence rotifer functional diversity in lake systems while in channel environments and the main riverbed guild representation was mainly influenced by limnological variables. Individual guild abundance changed relative to the site position within the floodplain as well, where the increased distance from the main riverbed resulted in increased rotifer numbers, and a different proportion of microfilter-feeders and macrofilter-feeders was recorded. The multiple linear regression showed a significant relation of macrofilter-feeder rotifers with microcrustaceans pointing to notable exploitative competition among these groups. The results highlight the ecological importance of all types of natural floodplain habitats necessary for preserving and maintaining the rotifer diversity. [ABSTRACT FROM AUTHOR]

The current study adds 23 new records to the previously described monogonot rotifers of Cozumel, increasing the number of reported species to 40; these species are grouped into two orders, 11 families and 18 genera. Littoral and limnetic samples from 17 aquatic systems were examined, including wet dolines, coastal lagoons, temporary pools and artificial systems (reservoirs). Of the 36 species found, the following organisms represent new findings for Cozumel: Anuraeopsis fissa, Brachionus angularis, B. rubens, B. plicatilis sensu lato, Beuchampiella eudactylota, Euchlanis dilatata, Mytilina bisulcata, Colurella adriatica, Lepadella ovalis, L. rhomboides, Squatinella mutica, Lecane aculeata, L. climacois, L. crepida, L. cornuta, L. grandis, L. obtusa, L. pyriformis, Cephalodella forficula, Scaridium bostjani, Trichocerca pusilla, Polyarthra cf. dolichoptera, P. vulgaris, Dicranophorus epicharis and Testudinella patina. Additional information is reported for these species. [ABSTRACT FROM AUTHOR]

There is a need to develop more animal species for assessing toxicity in marine environments. Cyst‐based toxicity tests using invertebrates are especially fast, technically simple, cost‐effective, and sensitive to a variety of toxicants. Over the past 30 years, a variety of toxicity endpoints have been measured using the marine rotifer Brachionus plicatilis hatched from cysts, including mortality, reproduction, ingestion, swimming, enzyme activity, and gene expression. A consensus has developed that the most ecologically relevant toxicity measurements should be made using more than one species. Furthermore, it has been noted that the rotifer species toxicant sensitivity distribution is much broader than which endpoint is measured. This implies that toxicity should be measured with the simplest, fastest, least expensive test available on as many species as feasible. If a battery of test species is to be used to estimate toxicity, diapause egg‐based toxicity tests that do not require culturing of test animals will be key. In this paper, we describe how diapause eggs of a new marine rotifer, Proales similis, can be produced, stored and hatched under controlled conditions to produce animals for toxicity tests. Methods are described for quantifying the toxicity of copper, mercury and cadmium based on mortality, ingestion, reproduction, and diapause egg hatching endpoints. We found that reproduction and ingestion endpoints were generally more sensitive to the metals than mortality or diapause egg hatching. When the copper sensitivity of P. similis was compared to Brachionus manjavacas and B. plicatilis using an ingestion test, similar EC50s were observed. In contrast, the B. rotundiformis ingestion EC50 for copper was about 4× more sensitive. Although diapause egg hatching was not the most sensitive endpoint, it is the most ecologically relevant for assessing sediment toxicity. Our discovery of diapausing eggs in the P. similis life cycle has created a conundrum. We have not observed males or sex in P. similis populations, which is a direct contradiction to the orthodox view of the monogonont rotifer life cycle. Work is needed to clarify how diapause egg production is accomplished by P. similis and whether sexual reproduction is involved. [ABSTRACT FROM AUTHOR]

We quantified the predation of Acanthocyclops americanus from the shallow Mediterranean lake Albufera, using gut contents from field collections and laboratory feeding tests. For functional response studies, we used Brachionus plicatilis (at 6 concentrations, 400-4000 ind. 40 ml−1) and Diaphanosoma mongolianum (at 2-20 ind. 40 ml−1). Copepod feeding rates were also estimated using different proportions of rotifer prey and lake seston (0-67.5% of seston + 40 individuals of B. plicatilis). Prey selection studies were conducted using five zooplankton species: Brachionus angularis, Brachionus plicatilis, Keratella tropica, Daphnia magna and Diaphanosoma mongolianum. Gut contents of field-collected adult Acanthocyclops contained filamentous algae and cyanobacteria and 16 zooplankton species (Keratella cochlearis, unspined and spined forms, K. tropica, Brachionus plicatilis, Brachionus calyciflorus, Brachionus angularis, Brachionus variabilis, Asplanchna girodi, Polyarthra vulgaris, Synchaeta pectinata, Lepadella rhomboides, unidentified bdelloids, Alona rectangula, Chydorus sphaericus, Bosmina longirostris, D. magna, Ceriodaphnia dubia and copepod nauplii). When fed B. plicatilis or D. mongolianum, female A. americanus had higher prey consumption rates than males. Increased proportion of lake seston caused reduced consumption of brachionid prey. Our data suggest that A. americanus is omnivorous in nature. [ABSTRACT FROM AUTHOR]