Role of sulfhydryl groups in catalytic activity of purified cholesterol 7α-hydroxylase system from rabbit and rat liver microsomes

Electrophoretically homogeneous preparations of cytochrome P-450 LM₄ from cholestyramine-treated rabbits catalyzed 7α-hydroxylation of cholesterol, 12α-hydroxylation of 5β-cholestane-3α,7α-diol and 25-hydroxylation of 5β-cholestane-3α,7α,12α-triol. Dithiothreitol, a disulfide reducing agent, specifically stimulated the cholesterol 7α-hydroxylase activity severalfold. The 7α-hydroxylase activity was much more sensitive to the sulfhydryl reagents p-chloromercuribenzoate, N-ethylmaleimide and iodoacetamide than the 12α- and 25-hydroxylase activities. Cholesterol 7α-hydroxylase activity, inactivated by these reagents, could be reactivated by treatment with dithiothreitol. Similar results were obtained with purified cytochrome P-450 from rat liver microsomes.The results indicate that sulfhydryl groups are more important for cholesterol 7α-hydroxylation than for other C₂₇-steroid hydroxylations.     

Can species distribution modelling provide estimates of population densities? A case study with jaguars in the Neotropics

Aim To test the prediction that environmental suitability derived from species distribution modelling (SDM) could be a surrogate for jaguar local population density estimates. Location Americas. Methods We used 1409 occurrence records of jaguars to model the distribution of the species using 11 SDM methods. We tested whether models’ suitability is linearly correlated with jaguar population densities estimated from 37 different locations. We evaluated whether the relationship between density and suitability forms a constraint envelope, in which higher densities are found mainly in regions with high suitability, whereas low densities can occur in regions with variable suitability. We tested this using heteroscedasticity test and quantile regressions. Results A positive linear relationship between suitability and jaguar density was found only for four methods [bioclimatic envelope (BIOCLIM), genetic algorithm for rule set production (GARP), maximum entropy (Maxent) and generalized boosting models (GBM)], but with weak explanatory power. BIOCLIM showed the strongest relationship. Variance of suitability for lower densities values was larger than for higher values for many of the SDM models used, but the quantile regression was significantly positive only for BIOCLIM and random forests (RF). RF and GBM provided the most accurate models when measured with the standard SDM evaluation metrics, but possess poor relationship with local density estimates. Main conclusions Results indicate that the relationship between density and suitability could be better described as a triangular constraint envelope than by a straight positive relationship, and some of the SDM methods tested here were able to discriminate regions with high or low local population densities. Low jaguar densities can occur in areas with low or high suitability, whereas high values are restricted to areas where the suitability is greater. In high suitability areas but with low jaguar density estimates, we discuss how extrinsic factors driving abundance could act at local scales and then prevent higher densities that would be expected by the favourable regional environmental conditions.     

Thinking with relations in nature conservation? A case study of the Etosha National Park and Haiǁom

The area of the Etosha National Park in Namibia has been inhabited for many centuries by Haiǁom, a group of (now former) hunter-gatherers. In 1907, Etosha was proclaimed as a game reserve, although Haiǁom were still allowed to live in the area until they were expelled in the 1950s due to then-dominant ideas of fortress conservation. In recent years, Haiǁom have been provided with several resettlement farms by the Namibian government as a reaction to the colonial land dispossession. In this article, I explore the onto-epistemology of Haiǁom (i.e. their being in and knowing the Etosha area), focusing on their relations with the land and with human and beyond-the-human beings before their eviction. I argue that the eviction implies not only economic marginalization but also social deprivation, which is inadequately addressed with resettlement. I suggest that thinking with relations, illustrated with the Haiǁom case, would call for other solutions in the context of measures taken for past land dispossessions and would open new paths for Namibia's nature conservation initiatives.     

Why are Dormice rare? A case study in conservation biology

In the last 100 years, the Dormouse Muscardinus avellcmarius has disappeared from about half its geographical range in Britain. Evidence is presented which indicates that declining range and numbers are due to a complex interplay of factors which include fragmentation, deterioration and loss of specialized habitat. The Dormouse is unusual in being a relatively A-selected small mammal, with exacting ecological requirements which render it very vulnerable, particularly to habitat fragmentation. The Dormouse is also sensitive to climate, both directly and probably indirectly through the effects of weather on the timing and abundance of food (insects, flowers and fruits). Combined with low population density and low intrinsic rate of population increase, this makes the Dormouse highly vulnerable, not just to absolute climatic measures (e.g. temperature, rainfall), but especially to climatic stochasticity, particularly at the edge of its range. There are strong associations between the distribution and changing status of the Dormouse and various climatic parameters, and clear parallels with other climate-sensitive taxa, notably bats and butterflies.
The Dormouse is a very specialized species, highly sensitive to environmental change, resulting in its piecemeal, progressive extinction, particularly in northern counties. It is likely to be a very sensitive indicator species for monitoring future changing environments and an excellent model for studying the effects of habitat fragmentation, climatic shifts and climatic stochasticity.     

Do species converge during adaptation? A case study in Drosophila

Adaptation to novel environments is a crucial theme in evolutionary biology, particularly because ex situ conservation forces populations to adapt to captivity. Here we analyze the evolution of life-history traits in two closely related species, Drosophila subobscura Collin and Drosophila madeirensis Monclus, during adaptation to the laboratory. Drosophila madeirensis, an endemic species from Madeira, is here shown to have less ability to adapt to the laboratory. Early fecundity was the only trait where this species showed a significant improvement with time. By comparison, D. subobscura improved in most traits, and its early fecundity increased faster than that of D. madeirensis. Our findings suggest that different species, even closely related ones, may adapt at different rates to the same environment.     

Can human disturbance promote nestedness? A case study with breeding birds in urban habitat fragments

Several factors, singly or in combination, have proven relevant in promoting nestedness in animal communities (area, isolation, habitat structure, etc.); however, little empirical evidence exists about the role of human disturbance. The goal of this paper was to assess whether human disturbance (pedestrians) may affect bird species composition in such a way as to generate a nested distributional pattern. The study was conducted in an urban fragmented landscape, the city of Madrid, where wooded parks were suitable fragments for many bird species, and had different levels of human visitation. At the community level, the distribution of species was significantly nested in two consecutive breeding seasons. Using two different procedures ("temperature" and "departures" methods) to analyse causality in nestedness, I found that pedestrian rate, fragment size and the diversity of stems were significantly correlated to the nested pattern. When analysed simultaneously, and controlling for their independent effects, these factors still accounted for nestedness. Pedestrian rate was the only factor significantly associated with changes in species composition between years. At the individual species level, 74 and 41% of species were significantly nested in relation to pedestrian rate in 1997 and 1998, respectively; however, these percentages were independent of foraging substrate and body size. Besides the classic area and habitat diversity effects, human disturbance can also promote nestedness: locally, by restraining the time and space of foraging and breeding opportunities, thus reducing fragment suitability, and regionally, by increasing extinction and decreasing colonization probabilities in highly disturbed fragments.     

Can ecosystem services be integrated with conservation? A case study of breeding waders on grassland

We review published studies to show that changes in soil moisture levels have significant impacts on a range of wading bird species that use UK lowland grassland, including wet grassland, and obtain their food predominantly by probing the soil. We examine both the hydrological and the ecological literature and assess how management options could alter (1) ecosystem services (via water quality and flooding) and (2) habitat quality for wading birds. The combination of biodiversity goals with broader ecosystem services has been widely advocated and we suggest that appropriate management at multiple scales (e.g. small‐scale: ponds; large‐scale: integrated washlands) could potentially provide both ecosystem services and habitat for wading grassland birds. However, there is only a limited base of evidence on which to assess the potential linkage between these two areas, particularly for non‐wading bird species. Future work should be directed at identifying (1) how crop yield, ecosystem services and biodiversity relate to each other, (2) the extent of land needed to be managed to benefit these multiple purposes and bring about measurable gain (e.g. one or two ponds may make significant inroads in reducing run‐off and pollution but make little difference to wading birds) and (3) solutions to the challenges of setting up management options at large spatial scales (e.g. catchments).     

Is acetylcholinesterase a pertinent biomarker to detect exposure of pyrethroids? A study case with deltamethrin

The possibility to use acetylcholinesterase as biomarker of exposure to deltamethrin insecticide in the honeybee, Apis mellifera were considered. Joined actions of deltamethrin and pirimicarb (carbamate), alone or in association (dual treatment), were investigated on AChE activity in surviving and dead honeybees in order to test its reliability as biomarker. All treatments induced a reduction in tissue AChE activity in dead bees. In surviving bees, deltamethrin treatment induced an important increase of AChE activity that is not abolished by pirimicarb treatment. The analysis of AChE forms revealed an increase in the soluble form in surviving and dead bees and an increase of the membrane form in surviving bees. No direct effect of deltamethrin on soluble and membrane AChE was observed in vitro. The important increase in AChE activity in response to deltamethrin, not altered by pirimicarb treatment, suggests that AChE activity could represent a robust biomarker specific to deltamethrin exposure in living bees.     

Which components of plant diversity are most correlated with ecosystem properties? A case study in a restored wetland in northern China

The relationship between plant diversity and ecosystem services is a controversial topic in ecology that may be due, at least in part, to the variety of methods used to define and quantify diversity. This study examined the relationship between plant diversity and 11 ecosystem properties of a restored wetland in northern China by considering four primary components of diversity (dominance, richness, evenness, and divergence). Each diversity component was expressed by eight taxonomic and functional diversity indices respectively. Results showed that trait-based functional diversity had a stronger correlation with ecosystem processes than non-trait taxonomic diversity did. Among the four components of diversity, dominance (in terms of mean trait value index) was the best in explaining the variation in ecosystem processing. Richness and divergence also had significant correlations with ecosystem properties in some instances. By contrast, evenness had no significant correlation with most of the studied ecosystem properties. Our results indicated that wetland ecosystem properties are significantly related to certain traits of the dominant species. Thus, the dominant species and functional traits should be considered before the number of species in managing diversity and enhancing certain ecosystem functions of wetlands, especially in the case of conservation.     

The effect of sulfhydryl groups and disulphide linkage in the thermal aggregation of Z19 α-zein

Zeins are the major storage proteins in corn seeds organized in protein bodies located in the endosperm. They are soluble in alcoholic solution and depict a high tendency to aggregation. The Z19 α-zein aggregates obtained by heating show a particular and interesting temperature-dependent behavior. This work was aimed at determining not only the effect of temperature on the aggregation behavior, but also the effect of the sulfhydryl groups and disulphide bonds on the thermal aggregation process under non-aqueous conditions. Z19 α-zein was chemically modified to obtain different sulfhydryl groups and disulphide-bonds content. Far-UV CD, ANS emission fluorescence, and dynamic light scattering, as well as differential scanning calorimetry, were performed to characterize this protein. Removal of these disulphide-bonds and alkylation of all the sulfhydryl groups in the protein promoted the lowest T_m of 57.36 °C, eliminated aggregation, enhanced protein flexibility, and diminished thermal stability. These results suggest that the disulphide linkage could be the driving force for the Z19 α-zein aggregation.     

Do flowers wave to attract pollinators? A case study with Silene maritima

To answer the question whether flowers wave to attract pollinators, we determine: (1) the heritability of floral mobility; (2) whether wavy flowers attract more insects; (3) does the duration of pollination affect seed set; and (4) the relationship between seed set and floral mobility. The pollination ecology of Silene maritima was investigated. Flowers on stalks of different waviness were used to investigate the effect of floral movement on pollinator visits. There is heritable variation in both direct and indirect estimates of floral mobility. The highest insect total visitation times were associated with medium length thin stalks that were visited more frequently and by more insect species. Although mean individual visit durations were less than those of less mobile flowers, this was compensated for by increased visits. Observations of controlled pollinations show that when the visit times are low, so is seed set and therefore low and high mobility flowers might suffer from reduced fitness. Combining these observations provides a mechanism that could be driving stabilizing selection for flower stalk traits, with a trade-off applying between waving to attract pollinators and not being too mobile as to prevent effective pollination. Further evidence for stabilizing selection is provided by the relationship observed in the field between seed set and floral mobility where the highest levels of fitness was associated with intermediate levels of floral waving.     

Reed die-back in southern Europe? A case study from Central Italy

Common reed die-back is a widely investigated phenomenon in Central Europe, not frequently recorded in S-European areas and almost unknown in the Mediterranean Basin. Symptoms of reed decline recently observed in the Italian Peninsula provided the starting point for a detailed investigation on a reed population in one of the largest freshwater ecosystems in Central Italy. The analyses were conducted over two vegetative seasons in 19 plots at seven locations. A set of 13 morphologic and phenologic reed traits were screened, monitored and statistically analysed. The data indicated the presence of the reed die-back syndrome in a wet Mediterranean ecosystem and enabled us to highlight a set of usable traits to detect the condition of decline. Among them, the stem height and diameter, the number of nodes, the relative growth rate and the lateral root diameter resulted the most significant factors highlighting the declining condition. Some environmental characteristics of the reed stands were also taken into account. The period of submersion and the presence of standing litter emerged as important features of the stands, strictly related to the degree of decline in the population. The results draw attention to the risk, in southern Europe too, of the loss of an ecosystem which plays an important role in biodiversity conservation.     

The sulfhydryl groups of ferredoxin-NADP+ oxidoreductases: is a disulfide bond really present?

The sulfhydryl groups of three ferredoxin-NADP+ oxidoreductases [EC 1.18.1.2] (FNR) two from blue-green algae, Spirulina sp. and Synechococcus sp., respectively, and one from spinach, were analyzed by carboxymethylation and titration with sulfhydryl reagents under different conditions. Five sulfhydryl groups in Spirulina and spinach enzymes and four in Synechococcus enzyme were found to be in reduced forms. There was no disulfide bond in any FNR tested. The results in the present experiment contradict those reported by Karplus et al. [Biochemistry 23, 6576-6583 (1984)].     

Molecular markers in management of ex situ PGR – A case study

Worldwide germplasm collections contain about 7.4 million accessions of plant genetic resources for food and agriculture. One of the 10 largest ex situ genebanks of our globe is located at the Leibniz Institute of Plant Genetics and Crop Plant Research in Gatersleben, Germany. Molecular tools have been used for various gene bank management practices including characterization and utilization of the germplasm. The results on genetic integrity of long-term-stored gene bank accessions of wheat (self-pollinating) and rye (open-pollinating) cereal crops revealed a high degree of identity for wheat. In contrast, the out-pollinating accessions of rye exhibited shifts in allele frequencies. The genetic diversity of wheat and barley germplasm collected at intervals of 40 to 50?years in comparable geographical regions showed qualitative rather than a quantitative change in diversity. The inter- and intraspecific variation of seed longevity was analysed and differences were detected. Genetic studies in barley, wheat and oilseed rape revealed numerous QTL, indicating the complex and quantitative nature of seed longevity. Some of the loci identified were in genomic regions that co-localize with genes determining agronomic traits such as spike architecture or biotic and abiotic stress response. Finally, a genome-wide association mapping analysis of a core collection of wheat for flowering time was performed using diversity array technology (DArT) markers. Maker trait associations were detected in genomic regions where major genes or QTL have been described earlier. In addition, new loci were also detected, providing opportunities to monitor genetic variation for crop improvement.     

Are wives and daughters disadvantaged in polygynous households? A case study of the Arsi Oromo of Ethiopia

Whether polygyny is harmful for women and their children is a long-standing question in anthropology. Few studies, however, have explored whether the effect of polygyny varies for women of different wife order, and whether there are different outcomes for their sons and daughters. Because males have higher reproductive variance, especially when they are allowed to take multiple wives, parents may have higher fitness returns from investing in sons over daughters in polygynous households. Moreover, previous studies have found that first wives and their children are advantaged over monogamous and second order wives (who marry into unions later). Here we test the predictions that children of first wives will have an advantage over children to monogamous or second wives, and that sex-biased investment will be strongest among first wives. Using data from the Arsi Oromo of Ethiopia (n ~ 6200 children) we test whether associations with mother's wife order extend beyond childhood into adulthood by examining simultaneously child survival, education and age at marriage. We find that polygynous first wives have no child survival disadvantage, first wives' sons benefit in terms of longer education and daughters have an earlier age at marriage than daughters of monogamous women. Second wives have lower child survival than monogamous women, but surviving children experience advantages in later life outcomes, particularly marriage. These findings challenge the view that polygynous women are always doing the ‘best of a bad job’. Rather, our results suggest that via their surviving sons and daughters there may be long-term benefits for some polygynous women.     

Does diversity beget diversity? A case study of crops and weeds

Abstract. The ecological literature is ambiguous as to whether the initial diversity of a plant community facilitates or deters the diversity of colonizing species. We experimentally planted annual crop species in monoculture and polyculture, and examined the resulting weed communities. The species composition of weeds was similar among treatments, but the species richness of weeds was significantly higher in the polycultures than in the monocultures. This supports the ‘diversity begets diversity’ hypothesis. Environmental microheterogeneity, diversity promoters, and ecological equivalency do not seem able to explain the observed patterns.     

Role of angiopoietin-2 in infection – A double-edged sword?

The endothelial angiopoietin (Angpt)/Tie2 ligand receptor system maintains vascular quiescence and modulates the response to injury. Angpt-1 is considered the natural Tie2 agonist and receptor ligation leads to its phosphorylation inducing various protective downstream pathways. The natural antagonist – Angpt-2 – appears to inhibit these protective effects. In sepsis, the balance between both ligands is shifted in favor for Angpt-2 and the vasculature is highly dysfunctional, activated and leaky. Circulating levels of Angpt-2 strongly predict mortality in septic patients. Consistently, experimental strategies that target Angpt-2 (e.g. antibody, RNAi, etc.) can protect the vascular barrier and improve survival. However, in vitro is has also been shown that Angpt-2 can act as a dose-dependent Tie2 agonist/antagonist. Based on this, people have wondered if Angpt-2 is per se injurious or if it might have protective effects dependent on the scenario. A recent paper by Safioleas and colleagues showed survival benefits after a therapeutic injection of recombinant Angpt-2 in experimental pyelonephritis. Here, we discuss their counter-intuitive but interesting findings and put them into a global context with respect to the existent literature in the angiopoietin/Tie2 sepsis field.