Extrapolating the effects of toxicants with either the fixed application factor approach or one of the species sensitivity distribution models currently in widespread use presumes that toxicant effects on single, individual-level endpoints (e.g., survival, fecundity, and growth) reflect effects at the population level. Here, we consider if extrapolations derived on the basis of individual-level endpoints might be misleading with regard to risk assessment and, hence, risk management decisions for ecosystems. Both analytically and by simulation, we demonstrate that for populations with multiplication rates close to one, effects of toxicants at the population level likely are less than or equal to effects on individual life-cycle traits, suggesting that risk assessments based on the latter likely are protective of population-level impacts. We used Monte Carlo simulations to explore how both the frequency of different life-cycle types in a community as well as their relative sensitivity to toxicants influence the toxicant sensitivity distribution of the community as a whole. We compared the output of our simulations with predicted no-effect concentrations derived by an application factor approach and a log-normal distribution-based model, using no-observed-effect concentrations for juvenile survival as input variables in both cases. Our analyses suggest that current extrapolation approaches appear to be protective, and may often be very overprotective, but we have identified conditions in which this may not be the case. We recommend that additional consideration be given to the relative frequency of different life-cycle types, to the proportions of sensitive and insensitive taxonomic groups in communities, and to the role of density-dependent influences on population dynamics to ensure that we develop environmental quality criteria that are sufficiently--but not overly--protective.

Ecology↗

PubMed1993

Freeze-dried Chlorella vulgaris as food for Daphnia magna Straus in toxicity testing.

The continuous culture of fresh green algae for use as food for Daphnia magna in toxicity tests is labor intensive. The possibility of using freeze-dried Chlorella vulgaris as an off-the-shelf food was investigated. The performance of D. magna provided with freeze-dried food was investigated over several generations and was found to satisfy the current EC validity criteria. However, a number of life-history parameters, for example, fecundity and neonate size, were significantly reduced when compared to animals fed fresh algae. The effect of freeze drying on cell size and availability are investigated and discussed in relation to daphnid performance.

Animals↗

PubMed1993

Variation in the development of cadmium resistance in Daphnia magna straus; effect of temperature, nutrition, age and genotype.

The extent to which responses to toxicants can be modified by the environment and genotype of Daphnia magna is important for interpreting the results from ecotoxicity tests. Variation in the development of cadmium resistance and its relevance for survivorship has been investigated in two genetically distinct clones of D. magna. Cadmium resistance was induced by pre-exposing daphnids to a sublethal concentration of a Cd/Zn mixture and thereafter cadmium tolerance was assessed in standard acute tests. The results showed that the ability to develop cadmium resistance is affected by temperature, but there is no consistent pattern for maternal nutrition. The age of the daphnids had no apparent effect on the development of cadmium resistance. Differences in the induction of cadmium resistance between clones were seen only under resource depression.

Journal Article↗

PubMed1992

Frozen algae as food for Daphnia magna Straus in toxicity testing.

As EC validity criteria for the production of Daphnia magna neonates in standard toxicity tests set fecundity minima which must be attained, it is important that culture conditions provide an adequate ration of high quality food. Maintaining a steady supply of fresh algae can be problematical so the possibility of using frozen food was investigated. The performance of three generations of D. magna fed on diets of fresh or frozen Chlorella was compared. There were no significant effects on fecundity due to food type or generation. Cumulative fecundity (over 21 days) on fresh or frozen food exceeded 120 neonates per female and satisfied that EC validity criterion (60 neonates per female). In addition criteria relating to survival and variability were met. We conclude that frozen Chlorella are an acceptable substitute for fresh algae.

Animals↗

PubMed1992

Induction of cadmium tolerance in two clones of Daphnia magna straus.

1. The abilities of two different genotypes of Daphnia magna to develop cadmium resistance through physiological adaptation, after pre-exposure to sublethal concentrations of Cd, Zn and Cd/Zn mixtures, was investigated. 2. The induced elevation in cadmium tolerance was shown to be associated with an increase in the body concentration of metallothionein-like proteins. 3. The highly significant difference in acute responses to cadmium between the two clones reduced after pre-exposure. 4. Differences in cadmium tolerance were shown to be associated with differences in cadmium uptake.

Animals↗

PubMed1992

Effects of temperature on the anaesthetic potency of halothane, enflurane and ethanol in Daphnia magna (Cladocera: Crustacea).

1. The effects of temperature on the anesthetic potencies of halothane, enflurane and ethanol have been studied in the water flea Daphnia magna. 2. In the absence of anaesthetics, decreasing temperature resulted in decreased activity by the daphnids. 3. Potencies in the gas phase decreased with increasing temperature for all of the anaesthetics, while aqueous potency decreased for halothane and enflurane but increased for ethanol. 4. Enthalpy calculations suggest that the observed potency changes for the inhalational anaesthetics cannot be accounted for in terms of changing solubility in lipid bilayers but most likely reflect more specific interactions with animal target sites.

Animals↗

PubMed1991

Testing life-cycle theory by computer simulation--I. Introduction of genetical structure.

Computer simulation was used to relax assumptions of analytical life-cycle theory about the eventual outcome of evolution in a constant environment. The computer simulation models, of diploid one-locus genetic systems, are described in detail. Good agreement was obtained between the analytical and simulation outcomes, except in some cases of discrepancy between the male and female life cycles.

Animals↗

PubMed1991

Testing life-cycle theory by computer simulation--II. Bet-hedging revisited.

Analytical and computer models were used to reexamine bet-hedging, the reduction in fecundity that is evolutionarily advantageous in conditions of greater variation in juvenile survivorship or less variation in adult survivorship. The computer simulation models represent diploid one-locus genetic systems with semidominance. Schaffer's (1974) predictions proved remarkably robust when variations were symmetrical, and a simple modification allowed successful prediction for the asymmetries that occurred in the computer simulations when variations were large.

Animals↗

PubMed1991

An early life-stage test with Daphnia magna Straus: an alternative to the 21-day chronic test?

Chronic life-cycle tests using the freshwater cladoceran Daphnia magna aim to measure the effect of toxic chemicals on adult reproduction, in terms of the number of viable offspring produced. A tacit assumption is made that the primary effect of toxicants in these tests is a sublethal effect on the parent, reducing egg production and hence fecundity. The authors' observations on two chemicals, sodium bromide and 3,4-dichloroaniline, demonstrate that this assumption is at least partly false. In these experiments, the primary toxic effect of these compounds was to kill developing eggs in the brood chamber. Total egg output was unaffected, whereas output of viable eggs was severely impaired--an acute lethal effect. A further experiment demonstrated that the effect was limited to those eggs developing in the brood chamber, with eggs in the ovary remaining unaffected. It was suggested that these observations may provide the basis for the development of a short, sensitive early life-stage test with this species.

Aniline Compounds↗

PubMed1991

A comparative study of genotype sensitivity to acute toxic stress using clones of Daphnia magna straus.

The genetic typing of laboratory strains of Daphnia magna revealed that although there are genetic differences between different testing laboratory strains, most laboratories culture single genotypes as clones. A comparative study was made of the performance of five of the more common clones in terms of neonate mortality under acute exposure to nine toxic chemicals. The range in clonal EC50 response was from less than one to more than two orders of magnitude in terms of concentration. Surprisingly, there was little pattern in rank order of response of clones exposed to different toxicants, thus suggesting that genotype-environment interactions were predominating. Nevertheless, it was suggested that specifying the genotype used in D. magna toxicity tests will result in increased test repeatability. Evidence indicating that culture environment may also significantly affect the performance of neonates in acute toxicity tests was also presented.

Animals↗

PubMed1991

Physiological costs of combating chemical toxicants: ecological implications.

1. Evidence is presented that combating the poisoning effects of toxic chemicals is metabolically costly. 2. This has implications for relating physiological stress responses observed at the level of individual organisms to population effects, and needs to be incorporated explicitly into models making this link. 3. The cost hypothesis also has implication for the evolution of stress resistance either as a fixed or facultative (inducible) response. Optimization models incorporating these ideas are reviewed and discussed.

Animals↗

PubMed1990

Effect of stress on a freshwater benthic detritivore: scope for growth in Gammarus pulex.

Scope for growth (SfG), a measure of energy balance (between food intake and metabolic output) within animals, has been used as an indicator of pollution stress in marine systems. However, it has not been used commonly in freshwater systems and here we investigate the sensitivity of SfG in Gammarus pulex, a benthic freshwater crustacean, under conditions often associated with pollution. The effects of four specific substances were investigated; a metal (zinc), an organic (3,4-dichloroaniline), and two dissolved gases (oxygen and ammonia). In all cases SfG was reduced by the stress, primarily due to a depression in energy intake. Only with ammonia was energy output (respiration) significantly affected.

Ammonia↗

PubMed1990

Field deployment of a scope for growth assay involving Gammarus pulex, a freshwater benthic invertebrate.

Scope for growth (SfG) is a measure of the energy balance of an animal (i.e., the difference between energy intake and metabolic output). The SfG of marine invertebrates, particularly the mussel Mytilus edulis, has been successfully used as the basis of a field bioassay to detect a range of stresses both natural (temperature, food, salinity) and anthropogenic (hydrocarbons, sewage sludge). SfG of the freshwater amphipod Gammarus pulex was found to be a sensitive indicator of stress under laboratory conditions and here we describe the field deployment of this technique and present data from three field trials. In every case, SfG was reduced at the downstream polluted site compared with that at an upstream reference site. This reduction in SfG was the result of a decrease in energy intake (absorption) rather than an increase in energy expenditure (respiration).

Animals↗

PubMed1989

A model to test the potency of inhalation anaesthetics.

The water flea Daphnia magna was studied as a potential model of the potency of inhalation anaesthetics in humans. Anaesthesia was defined as lack of movement to a noxious stimulus (strong light). Effective concentrations which produced anaesthesia of 50% of the individuals (EC50) for halothane, isoflurane and enflurane were 1.006, 1.156 and 1.415, respectively. Anaesthesia was reversible rapidly. It is suggested that Daphnia should replace vertebrates in early studies of inhalation anaesthetic potency.

Anesthesia, Inhalation↗