No abstract

As an ecotoxicological test organism, Daphnia magna Straus has a long history and is now used extensively. Despite this, considerable variation in interlaboratory bioassays using the same reference toxicant has been reported. Using a standard quantitative genetics approach, the relative tolerance of different genotypes of Daphnia magna to two toxicants (sodium bromide and 3,4‐dichloroaniline) was assessed. As expected, the environmental component of variability dominated the chronic response with a significant component of interaction. Differences between genotypes, although significant, were not large. It was concluded that genotype‐environment interactions played a key role in determining chronic responses of Daphnia magna to both compounds. Some suggestions are given to improve the level of repeatability in Daphnia magna bioassays.

Due to the advancing agricultural frontier in the Brazilian Amazon, the present rate of deforestation engenders a pessimistic scenario for vertebrate diversity in the area. Protected areas are an essential conservation tool to limit biodiversity loss, but their efficiency have yet to be proven. Here, we used camera-trap data on the presence of medium and large-size vertebrates in a protected area (Cantão State Park) and a neighbouring private forest reserve (Santa Fé Ranch) to evaluate their effectiveness in protecting biodiversity. We also gathered information on seasonality and activity patterns. A total sampling effort of 7929 trap-nights revealed a diverse vertebrate fauna in the region. A total of 34 mammal species, belonging to 8 different orders was detected in the study area, some of which have a high level of conservation interest and value. The photographic index showed that diversity was more abundant outside the protected area of Cantão State Park, where seasonality could play a major role in vertebrate occurrence. Overall, the influence of seasonality on distribution appears to be species-specific. During the wet season around 40% of the common species were not detected inside the park, whereas in Santa Fé Ranch most species (62.5%) suffered only a slight decrease in relative abundance probably due to changes in the availability of food resources. Our results highlight the importance of private land for vertebrate conservation in the Amazon and alert to the need for increased law enforcement in these areas to secure biodiversity preservation.

A short-term, sublethal, and cost-effective in situ sediment toxicity assay for routine assessments with the midge Chironomus riparius Meigen, based on postexposure feeding, was developed and evaluated. An inexpensive and easy-to-use assay chamber was designed. A sediment toxicity assay was successfully performed at a lentic system impacted by acid mine drainage, at sites with different types of sediment. It consisted of a 48-h exposure period followed by a 1-h postexposure feeding during which the larvae were fed on Artemia franciscana nauplii. Methodologies for feeding quantification of fourth-instar larvae (10-d old) were first developed and optimized under laboratory conditions. A. franciscana nauplii were shown to be more suited than fish flake food for postexposure feeding quantification, allowing higher precision and cost-effectiveness. It also required a shorter postexposure feeding period, thus minimizing the chances for an eventual organism physiological recovery from toxicant exposure. The influence of several environmental conditions during exposure on postexposure feeding was also evaluated: temperature, dissolved oxygen, pH, salinity, hardness, substrate, humic acids, light, and food availability. Only temperature was found to significantly influence postexposure feeding rates; exposure at 5 degrees C led to reduced feeding activity compared to 30 degrees C. Recovery rates of 87% were obtained after the 48-h field exposure at all sites (except site R2). A statistically significant postexposure feeding depression was observed at the three sites impacted by acid mine drainage. Therefore, the proposed short-term in situ assay is a potentially useful tool to assess sediment sublethal toxicity on a routine basis.

Life table response experiments (LTRE) were performed to investigate effects of food supply on density-dependent effects on life history and population responses of the tropical cladoceran Moinodaphnia macleayi to cadmium. Its short life cycle and relatively constant age-specific birth and mortality rates allowed population growth rates () to be accurately estimated from short life table experiments and by using a simplified twostage demographic model. Decomposition and regression analyses of showed that densitydependent effects on population responses to cadmium were modified by food availability through density-dependent effects on mortality and reproductive rate. At moderate food levels (1.8 g C/mL of Chorella vulgaris) and low densities (Ͻ125 animals/L), the effects of cadmium on decreased with increasing population density, due to antagonistic effects between the contributions of age at first reproduction and daily reproduction on . At high densities (Ͼ125 animals/L), the negative effects of cadmium on daily reproduction rates increased with density; hence density promoted the negative effects of cadmium on . At low food levels (0.4 g C/mL of Chorella vulgaris), increasing population density reduced juvenile survival, increasing food per head. Thus adverse effects of cadmium on reproduction, which had the greatest contribution to , were buffered by increasing population density. Regression analysis performed on population responses across increasing population density levels and cadmium concentrations showed that at high densities and low food levels ecological compensation will prevent populations at the steady-state equilibrium size from being driven to extinction by toxicity effects at the individual level. Alternatively, at low densities, when food availability is not limiting, exposure to toxic substances can increase extinction probability. These results indicate that risk assessment procedures based on demographic analysis performed at low densities and high food levels may overestimate the ecological risk posed by toxic substances.