Age effect on the antioxidant activity of Daphnia magna (Anomopoda: Daphniidae): does younger mean more sensitivity?

It has been accepted that for most species newborns and senescent organisms are more sensitive than other ages to environmental stressors. Nevertheless, it must be considered that there are several biochemical and physiological compensatory processes which are not expressed with the same magnitude during the whole life cycle. With this aim, Daphnia magna individuals of different age were exposed to hexavalent chromium, Cr (VI), at two different sublethal concentrations (0.032 and 0.0064 mg l(-1)), and the activity of some antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR) and glutathione peroxidase (GPx) were evaluated during most of the life cycle of this cladoceran. The antioxidant enzymatic activity showed an inverse relationship with respect to age. The activity of CAT, GR and GPx were increased in the two treated groups, at all life stages tested. On the other hand, the activity of SOD decreased in the same groups. Both, increase and decrease in the antioxidant enzymatic activities, showed significant differences with respect to the control group, being higher for the 0.032 mg l(-1) group. The Cr (VI) LC50 was also estimated for these age groups, finding statistical differences among them. Even though adults exhibited higher responses, these enzymatic activity changes should not be interpreted as higher sensitivity, since the daphnids acute chromium toxicity followed a different pattern, with increasing LC50 values according to age.     

Using information theory as a substitute for stepwise regression in ecology and behavior

In ecological and behavioral research, drawing reliable conclusions from statistical models with multiple predictors is usually difficult if all predictors are simultaneously in the model. The traditional way of handling multiple predictors has been the use of threshold-based removal-introduction algorithms, that is, stepwise regression, which currently receives considerable criticism. A more recent and increasingly propagated modelling method for multiple predictors is the information theoretic (IT) approach that quantifies the relative suitability of multiple, potentially non-nested models based on a balance of model fit and the accuracy of estimates. Here, we examine three shortcomings of stepwise regression, subjective critical values, model uncertainty, and parameter estimation bias, which have been suggested to be avoided by applying information theory. We argue that, in certain circumstances, the IT approach may be sensitive to these issues as well. We point to areas where further testing and development could enhance the performance of IT methods and ultimately lead to robust inferences in behavioral ecology.     

Fiscal spending and the environment: Theory and empirics

During economic crises, governments often increase fiscal spending to stimulate the economy. While the fiscal spending surge may be temporary, spending composition is often altered in favor of expenditures on social programs and other public goods which may persist over time. We model and measure the impact of fiscal spending patterns on the environment. The model predicts that a reallocation of government spending composition towards social and public goods reduces pollution. However, increasing total government spending without altering its composition does not reduce pollution. We empirically test these predictions for air and water pollutants showing that they are fully supported.     

Intra- and interannual variability in the larval fish assemblage off Gran Canaria (Canary Islands) over 2005–2007

The present study provides the longest and most intensive plankton and larval fish seasonal variability analysis in the Canary Islands and forms a basis for understanding life cycle scheduling and interactions among species, as well as the potential variability in transport processes of early life stages. Larval fish assemblages were studied weekly at Gran Canaria Island, Canary Islands, from January 2005 to June 2007, which represented two contrasting hydrological and biological periods. The former year was characterized by lower temperature and salinity that increased through 2006 and 2007. In contrast, chlorophyll concentration and mesozooplankton biomass decreased through the same period, especially when only the late winter bloom period was evaluated. However, ichthyoplankton abundance did not exhibit any clear pattern, as larger values were observed during 2006. The larval fish community of this oceanic island, located near the NW African upwelling, was composed of both neritic and oceanic taxa. Two families accounted for almost half of the collected larvae: Clupeidae (21.9%) and Myctophidae (20.5%). Although total larval concentration did not exhibit any seasonal peak linked to changes in zooplankton, the ichthyoplankton composition gradually changed during the year due to the high diversity and extended spawning periods of the fish species represented in samples. “Winter” and “summer” larval assemblages were identified, corresponding to the mixing and stratification periods of the water column, respectively. These assemblages were characterized by changes in the contribution of the most abundant annual taxa (Sardinella aurita, Cyclothone braueri, Ceratoscopelus spp. and Gobids) and by the presence of larvae of winter (Pagellus bogaraveo, Pomacentridae sp1) or summer spawners (Pomacentridae sp2, Trachinus draco, Arnoglossus thori, Tetraodontidae sp1). Upwelling filaments shed from the NW African coast reached the sampling area three times during this study, but changes in the local larval community were only detected in August 2005.     

Brood parasitism disproportionately increases nest provisioning and helper recruitment in a cooperatively breeding bird

Obligate avian brood parasites lay their eggs in nests of other species (hosts), which raise parasitic young. Parasitic nestlings are likely to influence host’s parental behaviours as they typically beg for food more vigorously than young host for a given hunger level. However, few studies have tested this idea, with conflicting results. These prior studies were largely limited to biparental hosts, but little is known about the effect of brood parasitism on parental behaviours in hosts that breed cooperatively. We followed a multimodel approach to examine the effect of brood parasitism on nest provisioning and helper recruitment in the baywing (Agelaioides badius), a cooperative breeder parasitised by screaming (Molothrus rufoaxillaris) and shiny (Molothrus bonariensis) cowbirds. Multimodel inference results indicated that feeding visits increased with nestling age, cooperative group size and number of cowbird nestlings in the brood. Brood size had little influence on feeding visits, which further suggests that baywings adjusted their provisioning effort in response to cowbird parasitism. In addition, nests parasitised artificially with shiny cowbird eggs or hatchlings recruited more helpers than unmanipulated nests having only host or screaming cowbird young. Our results provide novel evidence that brood parasitism and cooperative breeding interact in determining the levels of nest provisioning.     

Information-theoretic approaches to statistical analysis in behavioural ecology: an introduction

Scientific thinking may require the consideration of multiple hypotheses, which often call for complex statistical models at the level of data analysis. The aim of this introduction is to provide a brief overview on how competing hypotheses are evaluated statistically in behavioural ecological studies and to offer potentially fruitful avenues for future methodological developments. Complex models have traditionally been treated by model selection approaches using threshold-based removal of terms, i.e. stepwise selection. A recently introduced method for model selection applies an information-theoretic (IT) approach, which simultaneously evaluates hypotheses by balancing between model complexity and goodness of fit. The IT method has been increasingly propagated in the field of ecology, while a literature survey shows that its spread in behavioural ecology has been much slower, and model simplification using stepwise selection is still more widespread than IT-based model selection. Why has the use of IT methods in behavioural ecology lagged behind other disciplines? This special issue examines the suitability of the IT method for analysing data with multiple predictors, which researchers encounter in our field. The volume brings together different viewpoints to aid behavioural ecologists in understanding the method, with the hope of enhancing the statistical integration of our discipline.     

Leaf ontogeny interacts with Bt modification to affect innate resistance in GM aspens

Bioassays with a non-target slug (Deroceras spp.) and chemical analyses were conducted using leaf tissue from already existing genetically modified insect-resistant aspen trees to examine whether genetic modifications to produce Bacillus thuringiensis (Bt) toxins could affect plant phytochemistry, which in turn might influence plant–herbivore interactions. Three major patterns emerged. First, two independent modifications for Bt resistance affected the phytochemical profiles of leaves such that both were different from the isogenic wild-type (Wt) control leaves, but also different from each other. Among the contributors to these differences are substances with a presumed involvement in resistance, such as salicortin and soluble condensed tannins. Second, bioassays with one Bt line suggest that the modification somehow affected innate resistance (“Innate” is used here in opposition to the “acquired” Bt resistance) in ways such that slugs preferred Bt over Wt leaves. Third, the preference test suggests that the innate resistance in Bt relative to Wt plants may not be uniformly expressed throughout the whole plant and that leaf ontogeny interacts with the modification to affect resistance. This was manifested through an ontogenetic determined increase in leaf consumption that was more than four times higher in Bt compared to Wt leaves. Our result are of principal importance, as these indicate that genetic modifications can affect innate resistance and thus non-target herbivores in ways that may have commercial and/or environmental consequences. The finding of a modification–ontogeny interaction effect on innate resistance may be especially important in assessments of GM plants with a long lifespan such as trees.     

A coupled numerical model to investigate the air–sea interaction at the coastal upwelling area of Cabo Frio,Brazil

This work investigates the capability of an oceanic numerical model dynamic and thermodynamically coupled to a three-dimensional mesoscale atmospheric numerical model to simulate the basic features of the air–sea interaction in the coastal upwelling area of Cabo Frio (RJ, Brazil). The upwelling/downwelling regime is an important feature in the oceanic circulation of Cabo Frio and determines the sustainability of local ecosystems. This regime is predominantly driven by the atmospheric circulation and is well documented, being suitable to be used as test reference for atmospheric and oceanic coupled and uncoupled models. The oceanic boundary conditions, coastline shape and coupling effect have been tested. The uncoupled oceanic model forced by a NE (SW) wind field generates a realistic upwelling (downwelling) phenomenon regardless of the proximity of the lateral boundary and how realistic is the shape of the coastline. The atmospheric-oceanic coupled model generates an upwelling location and intensity similar to the uncoupled simulation, but the upwelling is gradually enhanced by the sea-breeze circulation. It also generates vertical profiles of mixing ratio that compare better to the observations than the uncoupled simulation and air potential temperature and wind vertical profiles that represent particular features of the atmospheric circulation at Cabo Frio.     

When conservation management becomes contraindicated: impact of food supplementation on health of endangered wildlife

Understanding the conditions that force the implementation of management actions and their efficiency is crucial for conservation of endangered species. Wildlife managers are widely and increasingly using food supplementation for such species because the potentially immediate benefits may translate into rapid conservation improvements. Supplementary feeding can also pose risks eventually promoting undesired, unexpected, subtle, or indirect, and often unnoticed, effects that are generally poorly understood. For two decades, intensive food supplementation has been used in attempting to improve the breeding productivity of the Spanish Imperial Eagle, Aquila adalberti, one of the most endangered birds of prey in the world. Here, we examined the impact of this intensive management action on nestling health, including contamination, immunodepression, and acquisition of disease agents derived from supplementation techniques and provisioned food. Contrary to management expectations, we found that fed individuals were often inadvertently "medicated" with pharmaceuticals (antibiotics and antiparasitics) contained in supplementary food (domestic rabbits). Individuals fed with medicated rabbits showed a depressed immune system and a high prevalence and richness of pathogens compared with those with no or safe supplementary feeding using non-medicated wild rabbits. A higher presence of antibiotics (fluoroquinolones) was found in sick as opposed to healthy individuals among eaglets with supplementary feeding, which points directly toward a causal effect of these drugs in disease and other health impairments. This study represents a telling example of well-meaning management strategies not based on sound scientific evidence becoming a "contraindicated" action with detrimental repercussions undermining possible beneficial effects by increasing the impact of stochastic factors on extinction risk of endangered wildlife.     

Element determination in environmental samples using Z-GFAAS with variable magnetic field

Electrothermal atomic absorption spectrometry methods with Zeeman effect background correction (Z-GFAAS) for determination of As, Sb, Se, Ag, Cd, Pb, Cu, Fe, Zn, Cr, and Ni in water and sludge samples were developed. The measurements using Z-GFAAS and variable magnetic field at the three-field dynamic mode permit the sensitivity adaptation for higher analytical concentrations. Calibration ranges were expanded over two orders of magnitude within one measurement run by the applying three-field dynamic mode of this correction system. There are presented calibration data, furnace programs, modifiers, and microwave digestion programs of the obviously monitored elements in the environmental samples. Very low detection limits (3σ criterion) were obtained. Quality assurance was checked by the suitable CRM. The study brings simultaneous determination of the samples with different element concentration range and different sample matrixes, as an important application information for an analyst working in the area of the eco-analytical research.