Resilience of rotifers and cladocerans communities in four reservoirs with eutrophication pollution and lead concentrations in Aguascalientes, Mexico.

Pollution in aquatic ecosystems has been increasing drastically worldwide changing their water quality. Therefore, species must be adapted to these new scenarios. In Aguascalientes City, four representative urban reservoirs contain lead in the water column and extremely high concentrations of sediments. Therefore, an analysis was conducted to evaluate the resilience of zooplankton species to lead exposure in each reservoir using dormant and organisms. Results demonstrated a decrease range from 57.5 to 22.5% in overall diapausing egg hatching rate, while survivorship rate also decreased from 98 to 54% when organisms were exposed to the water of the four reservoirs and increasing lead concentrations. When Pb exposure increased, results showed a global negative effect on both hatching rate (decreasing from 58 to 30% at 0.09 mg L-1) and survivorship levels (decreasing from 100% to 0.07% at 0.09 mg L-1). We provide Species Sensitivity Distribution for both water reservoir dilutions and lead concentration to analyze diapausing eggs hatching and survivorship of offspring in the presence of same polluted conditions or lead of the autochthonous species found in reservoirs. Furthermore, specific analysis with two populations of the cladoceran Moina macrocopa showed clear dissimilar hatching patterns that suggested a different adaptive mechanism. Niagara population shows a hatching rate of approximately 25% in the first two days of reservoir water exposure, while UAA population drastically increased hatching rate to 75% on exposure at day seven. We provide the first record of bioaccumulation in ephippia of M. macrocopa.

Toxicity of binary-metal mixtures (As, Cd, Cu, Fe, Hg, Pb and Zn) in the euryhaline rotifer Proales similis: Antagonistic and synergistic effects.

Data regarding the effects of binary metal mixtures in marine zooplankton are scarce, particularly for rotifers. We examined the toxicity of 21 binary equitoxic mixtures of As, Cd, Cu, Fe, Hg, Pb, and Zn on the euryhaline rotifer Proales similis. The toxic units (TU50) revealed that 20 of these binary mixtures exhibited synergistic effects (TU50 < 1.00). The AsHg mixture showed a strong antagonistic effect (TU50 = 2.39), whereas the HgCu interaction exhibited a significant synergistic effect (TU50 = 0.29) on P. similis. TU50 values were <0.60 in all cases that showed synergism (80 %). Regarding the MIXTOX analysis, 13 binary mixtures presented some level of synergism, while two mixtures presented only additivity. Results emphasize the need for environmental agencies to revise and readjust protection guidelines for marine biota in response to the evident synergistic effects occurring at metal mixtures concentrations below the current permissible limits.

Integral Study of Paramecium caudatum Acute and Chronic Toxicity, Sites of Entry and Distribution, Bioconcentration and Body Burdens of Five Metals.

An integral analysis of the acute and chronic toxicity, bioaccumulation, sites of entry, and distribution of four trace metals: copper, iron, lead, and nickel, and the non-trace metal mercury were performed in the ciliate Paramecium caudatum. Mercury was the fastest metal accumulated, and the most toxic. The sensitivity of Paramecium caudatum to the five metals tested (Cu, Fe, Hg, Ni, and Zn) falls in the range of other ciliate species. We observed similarities between the toxicity of the five metals to the ciliate P. caudatum with the rotifer Euchlanis dilatata: (a) Mercury was the most toxic metal in terms of acute and body burdens. (b) Acute values were very similar in both species, Hg as the most toxic and Fe as the less toxic, (c) the vacuole/ingestion chronic tests were more sensitive than growth inhibition chronic tests. These analyses would ideally help generate safer guidelines for protecting aquatic biota.

Multi-and transgenerational synergistic effects of glyphosate and chlorpyrifos at environmentally relevant concentrations in the estuarine rotifer Proales similis.

We evaluated the multi-and transgenerational effects of single and combined environmentally relevant concentrations of glyphosate (GLY) and chlorpyrifos (CPF) in the estuarine rotifer Proales similis. The acute and chronic toxicities of GLY and CPF were determined as individual compounds and as a mixture. Rotifers were exposed to environmental concentrations of GLY (1, 10, 100, and 1000 µg/L) and CPF (0.1, 1, 5, and 10 µg/L). The main findings were as follows: (i) the LC50 values were 33.91 mg/L (GLY) and 280 µg/L (CPF); (ii) the toxic unit (TU50) of the mixture was 0.30, corresponding to 10.17 mg/L GLY and 83 µg/L CPF; (iii) the multigenerational study indicated that the tested concentrations of GLY and CPF, both single and combined, significantly and consistently decreased the growth rates of P. similis from the F0 to F6 generations; (iv) in most cases, GLY and CPF mixtures induced a strong synergistic effect; and (v) transgenerational effects were detected in the F4 generation, especially GLY and CPF in higher equitoxic proportions. These effects seem to dissipate in F5. Across multigeneration, a slight recovery could indicate population resilience to pollution. Our findings suggest that a mixture of GLY and CPF at environmental concentrations is likely to occur under real field conditions, increasing the risk to marine and estuarine invertebrates such as rotifers.

Synergistic effect of chloroquine and copper to the euryhaline rotifer Proales similis.

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 LC50 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.

Feeding behavior of early life stages of the zebrafish Danio rerio is altered by exposure to glyphosate.

Glyphosate levels and the transfer of glyphosate across trophic levels have rarely been studied in zooplankton. The food preferences of zebrafish during the first-feeding stage (which is critical for the survival of organisms), were analyzed because of the requirement for live food. Larval survival begins to be affected when glyphosate intake exceeds 0.3666 µg/larvae/day, in the case that only the food is contaminated; if the medium is also contaminated, the effects on survival start from 0.2456 µg/larvae/day. It was shown that glyphosate was more likely to be incorporated through the medium than through the food (zooplankton), which supports the results of previous studies that have ruled out the potential for biomagnification. The bioconcentration factor (BCF) of glyphosate was determined using an ELISA tests specific to measure glyphosate in the fish D. rerio, the rotifers Brachionus calyciflorus and Lecane papuana, and the cladoceran Ceriodaphnia dubia. The experimental design consisted in exposing seven zebrafish adults per replica (four replicates) in three treatments 1, 5, and 10 mg/L of glyphosate for 96 h to obtain bioconcentration factors in the gills, liver, and muscle. These concentrations were selected as potential glyphosate concentrations right after application as double highest reported concentration. Glyphosate levels in zooplankton can represent up to 6.26% of the total weight of rotifers (BFC = 60.35) and in zebrafish adult organs were less than 8 µg/mg of tissue (BCF values < 6). Although glyphosate does not biomagnify, our results suggest that glyphosate affected the dynamics between zooplankton and zebrafish larvae, diminishing survival and feeding rates, given that zooplankton species bioconcentrate glyphosate in large quantities. The BCF values found in this contribution are higher than expected. Glyphosate exposure affected energy metabolism and feeding behavior of zebrafish larvae, which presented high mortality rates at environmentally relevant concentrations.

Toxicity tests, bioaccumulation and residuality of pyrethroid insecticides commonly used to control conifer bark beetles in Mexico.

Effectiveness of pyrethroid insecticides against pests including bark beetles (Dendroctonus spp.) is well known, but little is known about their (a) residuality and persistence in forests after application to control an outbreak and (b) ability to bioaccumulate in insects, which could cause adverse effects on the trophic chains. The 24 h lethal toxicity, bioaccumulation factors, and lethal body burdens of the pyrethroid insecticides bifenthrin, deltamethrin, and cypermethrin were evaluated in the bark beetle Dendroctonus mexicanus. The residuality and persistence of the insecticide bifenthrin in the forest ecosystem (soil, water, and sediment) was also monitored after its application in a region infested by bark beetles. We determined whether contamination of soil, water, and sediments occurred near the sanitation site. For D. mexicanus, the most toxic insecticide for adults was bifenthrin for topical application (LC50 = 0.94 mg/L) and cypermethrin for bark application (LC50 = 5.04 mg/L). The insecticide that bioaccumulated the most in the insect body was deltamethrin (622.41 µg g-1 dw) and the insecticide that bioaccumulated the least amount was cypermethrin (183.09 µg g-1 dw). However, cypermethrin was the active substance that presented the lowest body burdens, and therefore required a lower dose to cause death of D. mexicanus adults. Our results demonstrate that prolonged presence of bifenthrin in the forest ecosystem could lead to bioaccumulation in soil, sediment, and insects.

Ecotoxicity of pesticides and semiochemicals used for control and prevention of conifer bark beetle (Dendroctonus spp.) outbreaks.

Application of pyrethroid pesticides and semiochemicals are two treatments used worldwide to control conifer bark beetles (Dendroctonus spp.); their residues can reach water reservoirs and water currents through run off and affect non-target organisms such as freshwater invertebrates. Therefore, we assessed the 48-h lethal toxicity, chronic toxicity (reproduction inhibition), and bioaccumulation of three pyrethroid pesticides (bifenthrin, cypermethrin, and deltamethrin) and two semiochemicals (verbenone and 3-methyl-2-cyclohexen-1-one) in two freshwater invertebrates: the cladoceran Alona guttata and the rotifer Lecane papuana. Bifenthrin was the most toxic of the five chemical compounds tested followed by deltamethrin and then cypermethrin, which was the least toxic pyrethroid for both species. Semiochemicals were far less toxic than pyrethroids and verbenone was most toxic than 3-methyl-2-cyclohexen-1-one for both species. For the rotifer Lecane papuana, the pyrethroid with the highest Bioconcentration Factor was bifenthrin, and for the semiochemicals it was 3-methyl-2-cyclohexen-1-one. For the cladoceran Alona guttata, the pyrethroid with the highest bioconcentration factor was cypermethrin and for the semiochemicals it was verbenone. The pyrethroid with highest body burdens both lethal and chronic was cypermethrin. Semiochemicals showed lethal and chronic body burdens 12-fold higher than pyrethroids and were therefore less toxic than pyrethroids. These results showed that the semiochemicals verbenone and 3-methyl-2-cyclohexen-1-one are a safe tool for the freshwater invertebrates tested when compared with pyrethroid pesticides. Cypermethrin was the least toxic of the pyrethroids tested and therefore could be considered as a good candidate to control outbreaks of the conifer bark beetle.

Evaluation of bioconcentration and toxicity of five metals in the freshwater rotifer Euchlanis dilatata Ehrenberg, 1832.

Metals are widely used in modern society harming the environment; their toxicity cause environmental adverse effects to many organisms including zooplankton. This contribution employed: (a) acute and chronic toxicity tests, (b) epifluorescence image analysis, and (c) atomic absorption techniques, to analyze toxicity of four trace (copper, iron, nickel, and zinc), and one non-trace metals (mercury) on the freshwater rotifer Euchlanis dilatata. This work integrated results of Bioconcentration Factors (BCF's), sites of entry and accumulation and to determine mechanisms of uptake and toxicity of these five metals of the freshwater rotifer Euchlanis dilatata. This integral analysis enhanced our understanding of knowledge on: (a) the toxicity mechanisms, (b) sites of metal entry and concentration inside the rotifer, (c) bioconcentration and body burdens. As expected, Hg the non-trace metal used here, was the most toxic. Our results suggest that the toxicity is ameliorated in the rotifer by selecting feeding avoiding the most toxic particles and reducing adverse effects on reproduction, until mortality per se reduces reproduction. The chronic effect on ingestion rate was quite sensitive for all metals whereas reproduction was slightly affected. The combination of acute and chronic tests and determination of BCF's for each metal allowed calculation of the acute and chronic body burdens. Body burdens again confirmed that mercury was the most toxic metal of the five employed here.

Brachionus paranguensis sp. nov. (Rotifera, Monogononta), a member of the L group of the Brachionus plicatilis complex.

The Brachionus plicatilis complex represents the most studied group of rotifers, although the systematics of the species complex has not been completely clarified. Many studies have been conducted trying to explore the diversity within the complex, leading to the recognition of three major morphotypes: large (L), small-medium (SM), and small (SS). Currently six species have been described and classified under these types and another nine taxa have been identified but not formally described. Within the L group, three species have been officially described [B. plicatilis s.s. (L1), B. manjavacas (L2), and B. asplanchnoidis (L3)], while a formal description of L4, unofficially known as B. 'Nevada', is still lacking. In the present study, a new species, Brachionus paranguensis sp. nov., is formally described and presented as a representative of the L4 clade. The species has been named after a high altitude saline crater lake from Central Mexico, where the specimens were collected. An integrated approach using DNA taxonomy through COI and ITS1 markers, morphology, and ecology was used to confirm the identity of the new species.

Energy budget in Alona guttata (Chydoridae: Aloninae) and toxicant-induced alterations.

Although chydorids are the most diverse cladocerans in the world, there is still little information available related to their biology and even less with respect to their susceptibility to toxicants. Therefore, this work aimed to implement protocols with Alona guttata for acute, chronic, and sublethal toxicity tests, using the environmental concern toxicants deltamethrin (DM) and lead (Pb2+), which are commonly used due to agriculture and vector control or for the automotive industry, respectively. Once the results of LC50 (0.1160 ± 0.0107 µg/L for DM and 1.5797 ± 0.1605 mg/L for Pb2+) were obtained, sublethal concentrations (0.01 to 0.2 LC50) were used for the evaluation of biomarkers and chronic toxicity. Concentrations as low as 0.01 LC50 reduced Alona's survival and fecundity, negatively affecting demographic parameters, and decreased the energy reserves. A significant correlation was found between the natural rate of population increase and the caloric content, which demonstrates the suitability of these biomarkers as endpoints of early warning that allow inferring alterations at higher biological levels. Subsequently, this work could constitute the first report on the evaluation of the energy budget in a non-daphnid species, its alterations due to exposure to toxic substances and the correlation with demographic responses.

Toxicity evaluation of cypermethrin, glyphosate, and malathion, on two indigenous zooplanktonic species.

In Aguascalientes, Mexico, there is a special concern about pesticides because of their intensive use on guava production areas, which are located in the vicinity of water reservoirs; thus, non-target organisms could be exposed. Thereafter, the aim of this work was to assess the effect of cypermethrin, Faena® (glyphosate), and malathion, which are the most used pesticides in Aguascalientes' guava production, on the indigenous freshwater species Alona guttata (cladoceran) and Lecane papuana (rotifer). Acute 48-h toxicity tests were carried out, and LC50 values were calculated. Then, five sublethal concentrations (1/80, 1/40, 1/20, 1/10, and 1/5 of the respective LC50) were selected for the chronic assays: (a) intrinsic growth rate analysis in the rotifer and (b) partial life table analysis in the cladoceran. The results of the acute toxicity tests showed that A. guttata was more sensitive to malathion (LC50 = 5.26 × 10-3 mg/L) at concentrations found in natural environments with continuous application on guava fields, whereas L. papuana was more sensitive to Faena® (LC50 = 19.89 mg/L). The somatic growth of A. guttata was inhibited for the chronic exposure to cypermethrin. In addition, cypermethrin and Faena® seemed to exert endocrine disruptive effects on A. guttata. Moreover, malathion chronic exposure significantly decreased the survival of A. guttata. Moreover, L. papuana was affected chronically for the three pesticides.

Adverse effects and bioconcentration of chromium in two freshwater rotifer species.

Bioaccumulation of trivalent (CrIII) and hexavalent chromium (CrVI), and its adverse effects were studied in two rotifer species: Brachionus calyciflorus (two different strains), and Lecane quadridentata. Median Lethal Concentration (LC50) at 24 h of both species showed that CrVI is highly toxic: LC50 ranges from 4.7 × 10(-5) to 4 × 10(-6) mg L(-1)), compared with CrIII: LC50 ranges from 0.64 to 1.279 mg L(-1). Using the LC50 as an exposure concentration, and using atomic absorption, the bioconcentration factor (BCF) was obtained and BCFs of rotifers exposed to CrIII are four orders of magnitude lower than BCFs of rotifers exposed to CrVI. The effect of Cr on the elemental composition of the two species of rotifers in their structures by X-ray microanalysis by energy dispersion showed that Cr is found in intoxicated rotifers, but not in control rotifers. The basal immunoreactivity to metallothioneins is greater in B. calyciflorus than L. quadridentata. The immunoreactivity to metallothioneins decreases in B. calyciflorus when is exposed to CrIII, in contrast in L. quadridentata the immunoreactivity to metallothioneins increase when is exposed to CrIII, and the immunoreactivity to CrVI in L. quadridentata decrease. A mechanism is proposed in which the harder lorica of L. quadridentata acts as a barrier and accumulator of CrVI, and allows for attenuating responses like metallothionein production in L. quadridentata. Instead, in B. calyciflorus the lack of a harder lorica allows for deeper penetration of CrVI, and no time to produce attenuating measures.

Morphological alterations in the freshwater rotifer Brachionus calyciflorus Pallas 1766 (Rotifera: Monogononta) caused by vinclozolin chronic exposure.

Vinclozolin (VZ) is a dicarboximide fungicide widely used on fruits, vegetables and wines, effective against fungi plagues. In this study we characterized the effects of VZ using a 4-day reproductive chronic assay with the freshwater rotifer Brachionus calyciflorus. The assay included observations of several features of asexual and sexual reproduction. Our results indicate that VZ: (a) increased asexual and sexual reproduction, (b) caused severe abnormality in females and (c) these abnormalities were inherited by sexual and asexual reproduction. At 1.2 mg/L three abnormal females were found out of 457 total females (0.66 %). This low percentage is consistent and reproducible according to further analysis, where we increased the number of replicates and total females exposed to 1.2 mg/L of VZ, and found 18 abnormal females out of 2868 total females (0.63 % abnormality). Interestingly, abnormal females found at 5.6 mg/L VZ exposure, were able to show mating behavior. Our results suggest that VZ behaves as a strong endocrine disruptor whose effects show the characteristic inverted-U-shape exposure concentration response curve regarding the intrinsic population increase and the percentage of abnormalities as endpoints.

Morphology and ultrastructure of the freshwater rotifer Brachionus bidentatus (Monogononta: Brachionidae) using scanning and transmission electron microscopy / Morfología y ultraestructura del rotífero de agua dulce Brachionus bidentatus (Monogononta: Brachionidae), utilizando microscopía electrónica de barrido y transmisión

The study of sexual reproductive behavior supported by ultrastructural evidence is important in rotifers to describe differences among potential cryptic species. In this research, the morphology of the rotifer Brachionus bidentatus is described at the ultrastructural level, using electronic microscopy, together with a brief description and discussion of its sexual reproductive behavior. The characteristics of the (a) male,(b) the female, (c) the sexual egg or cyst, (d) the partenogenic egg, (e) the no-fecundated sexual egg (male egg), and (f) the trophi, were described. Another part of this research is dedicated to the ultrastructure of the sex cells of the male rotifer B. bidentatus. Samples were obtained from La Punta pond in Cosio, Aguascalientes, Mexico (22°08’ N - 102°24’ W), and a culture was maintained in the laboratory. Fifty organisms, from different stages of the rotifer Brachionus bidentatus, were fixed in Formol at 4% and then prepared; besides, for the trophi, 25 female rotifer Brachionus bidentatus were prepared for observation in a JEOL 5900 LV scanning electronic microscope. In addition, for the observation of male sex cells, 500 males of Brachionus bidentatus were isolated, fixed and observed in a JEOL 1010 transmission microscope. Females of B. bidentatus in laboratory cultures had a lifespan of five days (mean±one SD=4.69±0.48; N=13), and produced 4.5+3.67 (N=6) parthenogenetic eggs during such lifespan. In the case of non-fertilized sexual eggs, they produced up to 18 eggs (mean±one SD=13±4.93; N=7). Sexual females produced a single cyst on average (mean±one SD=1±0; N=20). For the sexual cycle, the time of copulation between male and female ranged from 10 to 40 seconds (mean±one SD=17.33±10.55, N=7). The spermatozoa are composed of a celular body and a flagellum, the size of the body is of 300nm while the flagellum measures 1 700nm. The rods have a double membrane. Their mean length is almost 2.45µm±0.74, N=6; and their mean wide is 0.773µm±0.241, N=11. The evidence on the specific ultrastructural characteristics of the rotifer B. bidentatus is notorious, even more in the male and in the cyst cell. Regarding the ultrastructure of the spermatozoa and the rods, compared to other species they only differ in size, despite their structural resemblance. Our study of the ultraestructure of this species adds useful information that along with molecular data will help clarify the taxonomy of brachionid rotifers. Rev. Biol. Trop. 61 (4): 1737-1745. Epub 2013 December 01.

El estudio del comportamiento reproductivo sexual apoyado en evidencias ultraestructurales en rotíferos, es importante para describir diferencias entre especies potencialmente crípticas. En este trabajo se describe a nivel ultraestructural la morfología del rotífero Brachionus bidentatus, usando microscopía electrónica, junto con una breve descripción y discusión de su comportamiento sexual reproductivo. Se presentan las características del: (a) macho, (b) hembra, (c) huevo partenogenético, (d) huevo sexual no fecundado, (e) trofos. También se muestra un apartado sobre la ultra estructura de las células sexuales de rotíferos macho B. bidentatus. Para el estudio se utilizó una cepa proveniente del bordo La Punta (22°08’ N - 102°24’ W), ubicado en Cosió, estado de Aguascalientes, México y se cultivaron en el laboratorio. Para el procesamiento de las muestras se tomaron 50 organismos fijados en Formol al 4%, de los diferentes estadios del rotífero Brachionus bidentatus, mientras que para el trofos se tomaron 25 organismos hembra del rotífero Brachionis bidentatus y se prepararon para observarse en un microscopio electrónico de barrido JEOL 5900 LV, mientras que para las observaciones de las células sexuales del macho se aislaron 500 organismos machos del rotífero Brachionus bidentatus, se fijaron e incluyeron en resina epóxica (EPON) para su observación en un microscopio electrónico de transmisión JEOL 1010 operado a 80kv. Los análisis obtenidos de hembras de B. bidentatus en cultivos de laboratorio demuestran un ciclo de vida de cinco días (4.69±0.48; N=13), y una producción de 4.5±3.67 (N=6) huevos partenogenéticos. En el caso de los huevos no fertilizados, la hembra produce más de 18 huevos (13±4.93; N=7). Para los huevos sexuales solo se produce uno solo por hembra (1±0; N=20). En el ciclo sexual, los tiempos de copula entre el macho y la hembra están en el rango de 10 a 40 segundos (17.33±10.55, N=7). Los espermatozoides se componen de un cuerpo celular y un flagelo, el tamaño del cuerpo celular es de 300nm mientras que el flagelo mide 1 700nm. Los bastones presentan una doble membrana y su tamaño a lo largo va de 2.45µm±0.74; N=6 mientras que el ancho es de 0.773µm±0.241; N=11. La evidencia sobre las características específicas ultraestructurales del rotífero B. bidentatus son notorias, más aun en el macho y en el quiste. En cuanto a la ultraestructura de los espermatozoides y los bastones respecto a otras especies sólo difieren en su tamaño, a pesar de las similitudes estructurales las estructuras de los bastones se evidencian con mayor claridad y dan más evidencias sobre su funcionalidad. Nuestro estudio de la ultraesturctura de esta especie añade información útil que junto con un análisis molecular ayudarán a clarificar la taxonomía de rotíferos brachionidos.

Estimating the toxicity of ambient fine aerosols using freshwater rotifer Brachionus calyciflorus (Rotifera: Monogononta).

The toxicity of atmospheric fine particulate matter (PM2.5) in Atlanta is assessed using freshwater rotifers (Brachionus calyciflorus). The PM-laden quartz filters were extracted in both water and methanol. Aerosol extracts were passed through a C-18 column to separate the PM components into hydrophobic and hydrophilic fractions. Toxicity data reported in the units of LC50 (concentration that kills 50% of the test population in 24 h) shows that ambient particles are toxic to the rotifers with LC50 values ranging from 5 to 400 µg of PM. The methanol extract of the aerosols was substantially more toxic (8 ± 6 times) to the rotifers compared to the water extracts. A sizeable fraction (>70%) of toxicity was found to be associated with the hydrophobic fraction of PM. However, none of the bulk aerosol species was strongly correlated with the LC50 values suggesting a complicated mechanism of toxicity probably involving synergistic interactions of various PM components.

Morphology and ultrastructure of the freshwater rotifer Brachionus bidentatus (Monogononta: Brachionidae) using scanning and transmission electron microscopy.

The study of sexual reproductive behavior supported by ultrastructural evidence is important in rotifers to describe differences among potential cryptic species. In this research, the morphology of the rotifer Brachionus bidentatus is described at the ultrastructural level, using electronic microscopy, together with a brief description and discussion of its sexual reproductive behavior. The characteristics of the (a) male, (b) the female, (c) the sexual egg or cyst, (d) the partenogenic egg, (e) the no-fecundated sexual egg (male egg), and (f) the trophi, were described. Another part of this research is dedicated to the ultrastructure of the sex cells of the male rotifer B. bidentatus. Samples were obtained from La Punta pond in Cosio, Aguascalientes, Mexico (22 degrees 08' N - 102 degrees 24' W), and a culture was maintained in the laboratory. Fifty organisms, from different stages of the rotifer Brachionus bidentatus, were fixed in Formol at 4% and then prepared; besides, for the trophi, 25 female rotifer Brachionus bidentatus were prepared for observation in a JEOL 5900 LV scanning electronic microscope. In addition, for the observation of male sex cells, 500 males of Brachionus bidentatus were isolated, fixed and observed in a JEOL 1010 transmission microscope. Females of B. bidentatus in laboratory cultures had a lifespan of five days (mean+one SD = 4.69 +/- 0.48; N=13), and produced 4.5 +/- 3.67 (N=6) parthenogenetic eggs during such lifespan. In the case of non-fertilized sexual eggs, they produced up to 18 eggs (mean+one SD = 13 +/- 4.93; N=7). Sexual females produced a single cyst on average (mean +/- one SD = I +/- 0; N=20). For the sexual cycle, the time of copulation between male and female ranged from 10 to 40 seconds (mean +/- one SD = 17.33 +/- 10.55, N=7). The spermatozoa are composed of a celular body and a flagellum, the size of the body is of 300 nm while the flagellum measures 1 700nm. The rods have a double membrane. Their mean length is almost 2.45 microm +/- 0.74, N=6; and their mean wide is 0.773 microm +/- 0.241, N=11. The evidence on the specific ultrastructural characteristics of the rotifer B. bidentatus is notorious, even more in the male and in the cyst cell. Regarding the ultrastructure of the spermatozoa and the rods, compared to other species they only differ in size, despite their structural resemblance. Our study of the ultraestructure of this species adds useful information that along with molecular data will help clarify the taxonomy of brachionid rotifers.

Sexual Reproductive Biology of a Colonial Rotifer Sinantherina socialis (Rotifera: Monogononta): Do mating strategies vary between colonial and solitary rotifer species?

In many aquatic invertebrates including monogonont rotifers, sex provides genetic variation and dormant stages that allows dispersal in time and space. While the reproductive biology of some solitary monogonont rotifer species is known, little is known concerning mating behaviors in colonial rotifers. Coloniality poses unique challenges to the typical mating behavior of solitary rotifers. For instance, most species engage in circling behavior, where the male swims in close proximity to the female. In colonial forms, access to a particular female may be hindered by nearby colony mates. Here we provide descriptions of (1) male morphology, (2) mating behavior, and (3) types of eggs of the widespread colonial rotifer Sinantherina socialis, and discuss modifications in mating strategies as a consequence of coloniality. Two important differences from mating patterns documented in solitary rotifers were found in S. socialis. First, duration of circling phase of mating is protracted for males encountering small colonies of females as compared to solitary females. Males encountering single females removed from their colonies behave similarly to those of solitary species. Second, duration of copulation in S. socialis is the shortest reported for any rotifer species. Endogamy might occur in this species as sons copulate with their sisters and mothers, at least under laboratory conditions. Examples of behaviour in linked video clips.

Synergistic toxicity of Macondo crude oil and dispersant Corexit 9500A(®) to the Brachionus plicatilis species complex (Rotifera).

Using the marine rotifer Brachionus plicatilis acute toxicity tests, we estimated the toxicity of Corexit 9500A(®), propylene glycol, and Macondo oil. Ratios of 1:10, 1:50 and 1:130 for Corexit 9500A(®):Macondo oil mixture represent: maximum exposure concentrations, recommended ratios for deploying Corexit (1:10-1:50), 1:130 the actual dispersant:oil ratio used in the Deep Water Horizon spill. Corexit 9500A(®) and oil are similar in their toxicity. However, when Corexit 9500A(®) and oil are mixed, toxicity to B. manjavacas increases up to 52-fold. Extrapolating these results to the oil released by the Macondo well, suggests underestimation of increased toxicity from Corexit application. We found small differences in sensitivity among species of the B. plicatilis species complex, likely reflecting phylogenetic similarity. Just 2.6% of the water-accommodated fraction of oil inhibited rotifer cyst hatching by 50%, an ecologically significant result because rotifer cyst in sediments are critical resources for the recolonization of populations each Spring.

Contribution of water-soluble and insoluble components and their hydrophobic/hydrophilic subfractions to the reactive oxygen species-generating potential of fine ambient aerosols.

Relative contributions of water- and methanol-soluble compounds and their hydrophobic/hydrophilic subfractions to the ROS (reactive oxygen species)-generating potential of ambient fine aerosols (D(p) < 2.5 µm) are assessed. ROS-generating (or oxidative) potential of the particulate matter (PM) was measured by the dithiothreitol (DTT) assay. Particles were collected on quartz filters (N = 8) at an urban site near central Atlanta during January-February 2012 using a PM(2.5) high-volume sampler. Filter punches were extracted separately in both water and methanol. Hydrophobic and hydrophilic fractions were then subsequently segregated via a C-18 solid phase extraction column. The DTT assay response was significantly higher for the methanol extract, and for both extracts a substantial fraction of PM oxidative potential was associated with the hydrophobic compounds as evident from a substantial attenuation in DTT response after passing PM extracts through the C-18 column (64% for water and 83% for methanol extract; both median values). The DTT activities of water and methanol extracts were correlated with the water-soluble (R = 0.86) and water-insoluble organic carbon (R = 0.94) contents of the PM, respectively. Brown carbon (BrC), which predominantly represents the hydrophobic organic fraction (referred to as humic-like substances, HULIS), was also correlated with DTT activity in both the water (R = 0.78) and methanol extracts (R = 0.83). Oxidative potential was not correlated with any metals measured in the extracts. These findings suggest that the hydrophobic components of both water-soluble and insoluble organic aerosols substantially contribute to the oxidative properties of ambient PM. Further investigation of these hydrophobic organic compounds could help identify sources of a significant fraction of ambient aerosol toxicity.