Temporal Distribution Patterns of Cryptic Brachionus calyciflorus (Rotifera) Species in Relation to Biogeographical Gradient Associated with Latitude.

Sympatric distribution and temporal overlap of cryptic zooplankton species pose a challenge to the framework of the niche differentiation theory and the mechanisms allowing competitor coexistence. We applied the methods of phylogenetic analysis, DNA taxonomy, and statistical analysis to study the temporal distribution patterns of the cryptic B. calyciflorus species, an excellent model, in three lakes, and to explore the putative mechanisms for their seasonal succession and temporal overlap. The results showed that in the warm-temperate Lake Yunlong, B. fernandoi and B. calyciflorus s.s. underwent a seasonal succession, which was largely attributed to their differential adaptation to water temperature. In the subtropical Lake Jinghu, B. fernandoi, B. calyciflorus s.s., and B. dorcas exhibited both seasonal succession and temporal overlap. Seasonal successions were largely attributed to their differential adaptation to temperature, and temporal overlap resulted from their differential responses to algal food concentration. In the tropical Lake Jinniu, B. calyciflorus s.s. persisted throughout the year and overlapped with B. dorcas for 5 months. The temporal overlap resulted from their differential responses to copepod predation. These results indicated that the temporal distribution pattern of the cryptic B. calyciforus species and the mechanism that allows competitor coexistence vary with different climate zones.

Evolution Under Dietary Restriction Increases Reproduction at the Cost of Decreased Somatic Growth.

Dietary restriction (DR) is cited as the most reliable means of extending life span in a wide range of taxa, yet the evolutionary basis of the DR effect on life span remains unclear. The resource reallocation hypothesis proposes that the longevity-extending response of DR is adaptive and stems from the reallocation of resources from reproduction to somatic maintenance under food-limited conditions. However, if DR continues for multiple generations, such a response becomes maladaptive, and genotypes with higher fecundity should be selectively favored over genotypes with longer longevity. To test this prediction, we exposed replicate populations of the rotifer Brachionus dorcas, a model organism for aging and experimental evolution studies, to DR and ad-libitum (AL) diets for 100 days. During the selection experiment, AL-selected populations showed higher growth rates and mictic ratios than DR-selected populations. After approximately 27 asexual generations of selection, populations with a DR selection history had a higher net reproductive rate but lower body volume and ingestion rate in the absence of survival costs than populations with an AL selection history when they were assayed on an AL diet. Our results are inconsistent with the prediction that evolution on sustained DR increases reproduction and reduces life span, and show for the first time that sustained DR selects for clones with higher energy investment in reproduction but lower investment in somatic growth.

Combined Effects of Warming and Imidacloprid on Survival, Reproduction and Population Growth of Brachionus calyciflorus (Rotifera).

Global warming and pesticide contamination are two stressors of high concern, but their combined effects on freshwater biota are controversial. This study investigated the combined effects of warming and imidacloprid (IMI) on survival (measured as life expectancy at hatching), reproduction (net reproductive rate), population growth (intrinsic rate of population increase) and sexual reproduction (proportion of sexual offspring) of Brachionus calyciflorus using a life table experiment. The results showed that compared with controls, treatments with IMI at 50-100 mg/L significantly decreased survival, reproduction and population growth of the rotifers at 20℃. The inhibiting effect at higher IMI concentrations on survival increased with increasing temperatures, but those on reproduction and population growth increased only when the temperature increased from 25℃ to 30℃. The proportion of sexual offspring decreased with increasing temperatures. When monitoring the ecological effects of pollutants, environmental temperature and the possible adaptation of rotifers to it should be taken into consideration.

Effect of chloramphenicol on the life table demography of Brachionus calyciflorus (Rotifera): A multigenerational study.

During the last two decades, there has been increasing concerns about the presence of antibiotics in aquatic environments. Phenicol antibiotics, such as chloramphenicol (CMP), commonly used in the veterinary and aquaculture fields to treat infections, have been often detected in aquatic environments, but scarce ecotoxicity information regarding the effects of CMP on non-target aquatic organisms is available, and multigenerational studies are seldom studied. Here we quantified the demographic responses of Brachionus calyciflorus exposed to sublethal concentrations (0, 5, 10, 30, 50, 70 and 90 mg L-1) of CMP for three successive generations (P0, F1, and F2). Our results showed that compared to the control, higher concentrations of CMP significantly decreased the life expectancy at hatching, generation time, net reproductive rate and intrinsic rate of population increase in all three generations, and the proportion of mictic offspring in the F1 generation of B. calyciflorus. With increasing generations, higher concentrations of CMP showed increased toxic effects on life expectancy at hatching and net reproductive rate, but irregular negative effects on generation time, intrinsic rate of population increase, and proportion of mictic offspring of the rotifers. These results indicate that multigenerational studies are necessary to prevent insufficient assessments of the impact of antibiotics in aquatic ecosystems.

Rapid adaptation of Brachionus dorcas (Rotifera) to tetracycline antibiotic stress.

Although natural populations can rapidly adapt to selection pressures, the fitness consequences of selection are controversial. In this study, a selection experiment was conducted with replicate populations of Brachionus dorcas that were exposed to two sublethal concentrations (26.8 and 78.3 mg/L) of oxytetracycline (OTC), followed by two common garden experiments (population growth and life table experiments). During the 102-day (approximately 36 asexual generations) selection experiment, a markedly increased growth rate but a significantly decreased mictic ratio over time in the populations exposed to OTC when compared to the control populations suggested that the former adapted to the selection pressures and that a trade-off exists between asexual and sexual reproduction. The high and stable population growth rates after 90 days of OTC selection illustrate an example of evolutionary rescue. After 102 days of selection, OTC-selected populations showed higher population growth rates than the control populations when exposed to OTC, indicating significantly increased tolerance. OTC-selected populations showed a lower average growth rate, longer average generation time and life expectancy at hatching, and higher average net reproduction rate and proportion of mictic offspring than the control populations in the absence of OTC, which indicate that OTC selection results in two fitness costs and three fitness gains and that the effect of OTC selection on fitness differs with the measured fitness variables. Both the evolutionary potential of populations under the stress of higher concentrations of OTC and the fitness costs and gains of selection in the absence of OTC indicate that past exposures to pollutants cannot be neglected when evaluating the effects of current stressors on natural populations.

Effects of bromate on life history parameters, swimming speed and antioxidant biomarkers in Brachionus calyciflorus.

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

[Effects of ibuprofen concentration on life table demography of Moina macrocopa under different densities of Scenedesmus obliquus]. / 不同斜生æ è—»å¯†åº¦ä¸‹å¸ƒæ´›èŠ¬æµ“åº¦å¯¹å¤šåˆºè£¸è ¹æºžç”Ÿå‘½è¡¨ç»Ÿè®¡å­¦å‚æ•°çš„å½±å“.

The cladoceran Moina macrocopa was used as test animal to investigate the effects of ibuprofen concentrations (0, 0.45, 0.9, 1.8, 3.6, 7.2 and 14.4 mg·L-1) on its life table demographic parameters under low (0.5×106 cells·mL-1), medium (1.0×106 cells·mL-1), and high (2.0×106 cells·mL-1) densities of Scenedesmus obliquus. The results showed that at low and high food levels, ibuprofen concentration significantly affected the intrinsic rate of population increase and the life expectancy of M. macrocopa, respectively. At all the three food levels, however, ibuprofen concentration did not significantly affect the generation time, net and gross reproduction rate of M. macrocopa. Compared with the controls, the intrinsic rate of population increase of M. macrocopaexposed to ibuprofen at 0.45, 0.9, 3.6 and 14.4 mg·L-1 was significantly decreased at low food level. At high food level, the life expectancy at hatching of M. macrocopa exposed to ibuprofen at 3.6 and 14.4 mg·L-1 was significantly increased. The results indicated that at low food level, certain concentrations of ibuprofen had negative effect on the population growth of M. macrocopa, which disappeared at medium and high food levels. At high food level, ibuprofen had positive effect on the survival of M. macrocopa, which disappeared at low and medium food levels. The effects of ibuprofen concentration on demographic parameters of M. macrocopa were dependent on food levels.

Comparison of the life-history parameters and competition outcome with Moina macrocopa between two morphs of Brachionus forficula.

In rotifers, the costs of morphological defenses, especially the development of long spines, have been investigated for several decades. However, the obtained results were inconsistent and the underlying reasons were complicated. Investigations on more species might be helpful to find out the reasons. In the present study, Brachionus forficula was selected as the model organism. The differences in developmental durations, life-table demography, starvation resistant time and the competitive ability with Moina macrocopa were compared between B. forficula with long (LPS) and short (SPS) posterior spines. The results showed that LPS showed relatively longer durations of juvenile stage at 1.0 × 106, 2.0 × 106 and 4.0 × 106 cells/ml Scenedesmus obliquus, and longer embryo stage at 2.0 × 106 cells/ml S. obliquus than SPS. The intrinsic rate of population increase and net reproduction rate were lower in LPS than SPS, suggesting the energy input to reproduction decreased. The starvation resistant time was also reduced in LPS, in comparison to SPS, further supporting that LPS consumed more energy, which might be directed to the development of long spines. All these results revealed that LPS spent more energy for individual growth than SPS, which might be used to develop long spines. Moreover, the maximum population density and population growth rate of LPS were always lower than those of SPS, suggesting that LPS might have a weaker competition ability with M. macrocope than SPS.

Morphological differentiation of Brachionus calyciflorus caused by predation and coal ash pollution.

Different rotifer stains exhibited remarkably morphological differences which could not be eliminated under laboratory conditions. In the present study, we hypothesized that predation pressure and pollution might be two forces driving morphological differentiation of rotifer. To test this hypothesis, rotifers (Brachionus calyciflorus) belonging to two sibling species were collected from three special lakes (with coal ash pollution, high predation pressure or neither) and cultured for more than three months to investigate their potential differentiation in morphology. Twelve morphological parameters were measured and compared among three lakes at four food density (Scenedesmus obliquus). The results showed that most of the tested morphological parameters changed in response to food level and differed among three habitats. Rotifers from the habitat with high predation pressure evolved stable long posterior lateral spine and relatively small body size. Rotifers collected from the polluted habitat was of smaller body size, compared with those from ordinary habitat. Bigger eggs were laid by rotifers from polluted area or lake with high predation pressure, enabling newborns more resistant to pollution or predation, and thus ensuring the survival rate of newborns. Finally, we concluded that both predation and pollution could affect the morphological differentiation and evolution of rotifers.

Combined Effects of Temperature and the Microcystin MC-LR on the Feeding Behavior of the Rotifer Brachionus calyciflorus.

The aim of this study was to investigate the responses in filtration and grazing rates of five rotifer strains of the species Brachionus calyciflorus under different temperatures and MC-LR concentrations. The results showed that strain identity, MC-LR concentration, temperature, and the interactions of these factors significantly affected both response variables, with the exception of the interaction of strain and MC-LR on the grazing rates. At low MC-LR concentrations and for the control group, the filtration and grazing rates increased with increasing temperature. The filtering and grazing rates of B. calyciflorus exposed to higher MC-LR concentrations, however, showed no evident enhancement with increasing of temperature. At high temperatures, the filtration and grazing rates of all rotifer strains decreased significantly with increasing concentration of MC-LR, however B. calyciflorus exhibited a refractory stability in the presence of increased MC-LR levels at lower temperatures.

Interactive effects of algal level and predator density (Asplanchna sieboldi) on the life-history strategy and morphology of Brachionus calyciflorus.

Predation plays an important role in mediating the coexistence and the community structure of rotifera. In response to predation stresses, prey rotifers develop morphological defenses and change their life-history strategy for the reallocation of energy investment. Yet, how these changes respond to different total energy ingestion remains largely unknown. In the present study, we investigated the life-table demographic, population growth and morphological parameters of Brachionus calyciflorus in response to various densities of Asplanchna sieboldi at two food levels (1.0  ×  106 and 2.0  ×  106 cells per ml of Scenedesmus obliquus). To resist predators, B. calyciflorus developed long postero-lateral spines. The life-table demographic results showed that predation only significantly shortened the generation time of B. calyciflorus at the algal level of 2.0  ×  106 cells per ml, but not affect other demographic parameters. The population growth tests revealed that predator density, algal level and their interactions all significantly influenced the population growth rate of prey rotifers. At 1.0  ×  106 cells per ml of S. obliquus, treatments with two, four, and eight A. sieboldi individuals per 50 ml significantly reduced the population growth rate of B. calyciflorus. In contrast, the population growth rate was not affected in response to two A. sieboldi individuals per 50 ml at 2.0  ×  106 cells per ml of S. obliquus. These results suggested that algal level probably affected the inhibitory effects of predation on the population growth of prey rotifers, and the underlying mechanisms should be further investigated.

Effects of Multi-metal (Cu, Zn, Cd, Cr, and Mn) Mixtures on the Reproduction of Freshwater Rotifer Brachionus calyciflorus.

In the field, organisms are usually exposed to mixtures of various metals. However, the effects of multi-metal mixtures on growth and reproduction of rotifers remain unknown. In the present study, effects of multi-metal mixtures (Cu, Zn, Cd, Cr, and Mn) on reproduction of the freshwater rotifer Brachionus calyciflorus were assessed by determining various endpoints, including the ratio of ovigerous females to nonovigerous females, the ratio of mictic to amictic females, the mictic rate, the fertilization rate, the population growth rate, and the resting eggs production. The results demonstrated that reproduction of rotifers was significantly affected by all multi-metal mixtures assessed. Moreover, the ratio of mictic to amictic females was the most sensitive endpoint and might be suitable to evaluate effects of multi-metal mixtures to rotifers.

[Effects of mercury concentration on life table demography of Moina macrocopa under different Scenedesmus obliquus densities].

In order to compare the chronic toxicity of pollutants to organisms in an aquatic environment under different food densities, the cladoceran Moina macrocopa was used as test animal to investigate the effects of Hg²âº concentrations (0, 0.4, 1.1, 1.8, 2.5, 3.2 and 3.9 µg · L⁻¹) on its life table demography under low (0.5 x 106 cells · mL⁻¹), medium (1.0 x 106 cells · mL⁻¹) and high (2.0 x 106 cells · mL⁻¹) densities of Scenedesmus obliquus. The results showed that at low and high food levels, certain concentrations of Hg²âº had inhibitory effects on survival, reproduction and population growth of M. macrocopa. However, at the medium food level, the inhibitory effects disappeared. Compared with the control, at the low food level, Hg²âº at 0.4-2.5 and 3.9 µg · L⁻¹ significantly decreased the life expectancy at hatching, Hg²âº at 0.4, 1.1, 2.5 and 3.9 µg · L⁻¹ decreased the generation time, Hg²âº at 1.1, 2.5 and 3.9 µg · L⁻¹ decreased the net reproduction rate, and Hg²âº at 3.9 µg · L⁻¹ decreased the gross reproduction rate of M. macrocopa. At the high food level, Hg²âº at 1.1 µg · L⁻¹ decreased the intrinsic rate of population increase, and Hg²âº at 3.9 µg · L⁻¹ decreased the life expectancy at hatching and the net reproduction rate of M. macrocopa. However, at the medium food level, Hg²âº at 3.2 µg · L⁻¹ increased the life expectancy at hatching of M. macrocopa. When S. obliquus density was 0.5 x 106 cells · mL⁻¹, there were significant dose-effect relationships between Hg²âº concentration and the life expectancy at hatching, the generation time as well as the cross reproduction rate of M. macrocopa. However, when S. obliquus density was 1.0 x 106 or 2.0 x 106 cells · mL⁻¹, there were no any significant dose-effect relationships between Hg²âº concentration and each of the life table demographic parameters of M. macrocopa.

Coal fly ash effluent affects the distributions of Brachionus calyciflorus sibling species.

Fly ash, a coal combustion residue of thermal power plants and a source of multiple pollutants, has been recognized as an environmental hazard all over the world. Although it is known that fly ash effluent affects density, diversity and distribution of rotifers in drainage systems and receiving water bodies, the effect of fly ash effluent on the distributions of highly similar rotifer species remains unknown. In this study, the mtDNA COI genes of 90 individuals in Brachionus calyciflorus complex from Lake Hui (as a fly ash discharge water pond) and other two neighboring lakes (Lake Fengming and Lake Tingtang) were sequenced and analyzed, and the responses in selected life table demographic parameters (life expectancy at hatching, net reproductive rate, intrinsic rate of population increase and proportion of sexual offspring) of different rotifer populations to fly ash effluent were investigated. Overall, 72 mtDNA haplotypes were defined, and were split into two clades by the phylogenetic trees. The divergence of COI gene sequences between the two clades ranged from 11.8% to17.8%, indicating the occurrence of two sibling species (sibling species I and sibling species II). Sibling species I distributed in all the three lakes, showing strong capabilities for dispersal and colonization, which were supported by its higher level of gene flow (2.60-4.04) between the populations from Lake Hui and each of the other two lakes, longer life expectancy at hatching (101.6-148.2 h), and higher net reproductive rate (4.4-16.4 offspring/female) and intrinsic rate of population increase (0.60-0.98/d) when cultured in aerated tap water and fly ash effluent. Sibling species II distributed in both Lake Tingtang and Lake Fengming, showing that its dispersal existed between the two lakes. Considering that the distance between Lake Hui and Lake Fengming is shorter than that between Lake Tingtang and Lake Fengming, sibling species II is able to disperse at least from Lake Fengming to Lake Hui. The restricted distribution of sibling species II in Lake Hui might be attributed to its lower intrinsic rate of population increase (0.34-0.39/d) when cultured in aerated tap water and fiy ash effluent, which might be further lowered by the lower algal food level and quality in Lake Hui.

Effects of DDT and dicofol on population growth of Brachionus calyciflorus under different algal (Scenedesmus obliquus) densities.

A number of organochlorine pesticides, including DDT and dicofol, used to be important in crop protection and management. Their residues may reach water bodies and eventually affect the non-target organisms such as rotifers. In the present study, we evaluated the effects of DDT (0.05, 0.1, 0.2 and 0.4 mg l(-1)) and dicofol (0.1, 0.2, 0.4 and 0.8 mg l(-1)) on the population growth of rotifer Brachionus calyciflorus under two levels of Scenedesmus obliquus (1.0 x 10(6) and 3.0 x 10(6) cell ml(-1)). Regardless of the food level, DDT was more toxic than dicofol to B. calyciflorus. Under low food level, DDT at 0.1 and 0.2 mg l(-1) decreased the population growth rate (r), and DDT at 0.05-0.4 mg l(-1) decreased the maximum population density (K). Dicofol at 0.4 and 0.8 mg l(-1) decreased r and K, but dicofol at 0.2 mg l(-1) increased K. Under high food level, DDT at 0.05-0.2 mg l(-1) increased K, whereas DDT at 0.4 mg l(-1) as well as dicofol at 0.4 and 0.8 mg l(-1) decreased r and K. Increase in food level increased r exposed to DDT at 0.05-0.2 mg l(-1) as well as dicofol at 0.8 mg l(-1), and Kexposed to DDTat 0.05-0.2 mg l(-1) as well as dicofol at 0.1 and 0.2 mg l(-1). DDT concentration, algal density and their interaction affected r and K of B. calyciflorus. Both dicofol concentration and algal density affected r. Dicofol concentration, algal density and their interaction affected K. Both r and K were suitable endpoints for assessing the effects of DDT and dicofol on the rotifers population dynamics under two algal densities, and the latter was more sensitive.

The life-table demographic response of freshwater rotifer Brachionus calyciflorus to multi-metal (Cu, Zn, Cd, Cr, and Mn) mixture interaction.

The effects of multi-metal mixtures on the life-table demography of rotifers are not well known. In this study, the freshwater rotifer Brachionus calyciflorus was exposed to mixture of Cu, Zn, Cd, Cr, and Mn, and the life-table demographic parameters including net reproductive rate, generation time, life expectancy at hatching, and intrinsic rate of population increase were calculated. The results showed that interactions between a given element concentration, except Mn, and the other four elements mixture concentration affected the intrinsic rate of population increase (p < 0.01). Interactions between Zn concentration, as well as Mn, and the other four elements mixture concentration affected the net reproductive rate and the life expectancy at hatching, respectively (p < 0.05). The variation of parameters with the rise of the other four elements mixture concentrations from 0 to high was mainly attributed to the difference of interaction among the five metals mixture with different ratio of concentrations.

[Rapid change in structure of Brachionus calyciflorus complex collected from Jiulian Pond and its ecological mechanism].

In order to investigate the rapid variation in the structure of Brachionus calyciflorus complex and the fitness traits of the two sibling species, the rotifers were collected once a week from Jiulian Pond during 16 July and 6 August, their COI genes were sequenced and analyzed, and their fitness parameters (average lifespan, net reproductive rate, intrinsic rate of population increase and proportion of sexual offspring) were calculated at 28 degrees C and 32 degrees C with 1.0 x 10(6), 3.0 x 10(6) and 5.0 x 10(6) cells x mL(-1) of Scenedesmus obliquus as food. In total of 35 samples, 22 haplotypes were defined, among which two distinct lineages (Lineage I and II) were revealed by phylogenetic analysis. Sequence divergence was 14.8%-15.6% between the two lineages, indicating the occurrence of two sibling species (sibling species I and II). Sibling species II occurred only in the second event of sample collection, and its relative abundance in the density of the species complex was lower (1/35). In the population of sibling species I, the clones of three shared haplotypes showed overlap, while the others showed displacement. Three-way ANOVA indicated that temperature affected the net reproductive rate, the intrinsic rate of population increase and the proportion of sexual offspring, food level affected the average lifespan, the net reproductive rate and the intrinsic rate of population increase, sibling species affected the average lifespan, the intrinsic rate of population increase and the proportion of sexual offspring. The interaction between temperature and sibling species affected the net reproductive rate and the intrinsic rate of population increase (P < 0.05), the interaction between temperature and food level affected the proportion of sexual offspring (P < 0.01), and the interaction between food level and sibling species affected the intrinsic rate of population increase of the rotifers (P < 0.05). Sibling species I had a higher intrinsic rate of population increase, a shorter average lifespan and a lower proportion of sexual offspring than sibling species II.

[Combined toxicity of copper and cadmium to cladoceran Moina marocopa].

In this paper, the 48 h LC50 values of Cu2+, Cd2+ and CU(2+)+Cd2+ (CU2+:Cd2+ = 1:1) to Moina macrocopa were determined by acute toxicity tests, and the effects of different concentrations of Cu2+, Cd2+ and Cu(2+)+Cd2+ on the life table demography of M. macrocopa were studied by life table demography. The 48 h LC50 of Cu2+, Cd2+ and Cu(2+)+Cd2+ to M. macrocopa was 0.106, 0.117 and 0.212 mg x L(-1), respectively, and the acute toxicity of Cu(2+)+Cd2+ mixture to M. macrocopa showed an antagonistic effect. Cu2+ had no significant effects on the life expectancy at hatching, gross reproductive rate, net reproductive rate, generation time, and intrinsic rate of population increase of M. macrocopa, whereas Cd2+ and Cu(2+)+Cd2+ had significant effects on the life expectancy at hatching, gross reproductive rate, net reproductive rate and generation time, but no significant effects on the intrinsic rate of population increase of M. macrocopa. Compared with the control, the 0.004 and 0.005 mg x L(-1) of Cd2+ and the 0.006-0.010 mg x L(-1) of Cu(2+)+Cd2+ decreased the life expectancy at hatching and the gross reproductive rate of M. macrocopa significantly, and the 0.004 and 0.005 mg x L(-1) of Cd2+ and the 0.008-0.010 mg x L(-1) of Cu(2+)+Cd2+ reduced the net reproductive rate and the generation time of M. macrocopa significantly. The chronic toxicity of Cu(2+)+Cd2+ mixture to M. macrocopa showed a synergistic effect. There existed significant dose-effect relationships between the concentrations of Cd2+ and Cu(2+)+Cd2+ and the life expectancy at hatching, gross reproductive rate, net reproductive rate, and generation time of M. macrocopa.

Effect of butyl benzyl phthalate on life table-demography of two successive generations of cladoceran Moina macrocopa Straus.

In this study, the acute toxicity of butyl benzyl phthalate (BBP) to freshwater cladoceran Moina macrocopa was tested, and its chronic effects on survival and reproduction of two successive generations of the cladoceran were studied using life-table demographic method. The results showed that the 48-hr LC50 of BBP for M. macrocopa was 3.69 mg l(-1). Compared to the blank controls, BBP at 125, 500, 1000 and 2000 microg l(-1) significantly shortened the life expectancy at birth, BBP at 125-2000 microg l(-1) decreased the net reproductive rate, and BBP at 500 and 1000 microg I(-1) shortened the generation time but increased the intrinsic rate of population increase of the parental M. macrocopa. BBP at 62.5,125, 500,1000 and 2000 microg l(-1) increased the intrinsic rate of population increase of the F1 generation. A significant dose-effect relationship existed between BBP concentration and life expectancy at birth, net reproductive rate as well as intrinsic rate of population increase of the parental M. macrocopa. The parental M. macrocopa were more sensitive in survival, development and reproduction to BBP than the F1 generation, but the reverse was also true in the population growth. Extending chronic toxicity tests to the second generation of M. macrocopa increased the cost-effectiveness of the assays.