Parental care and sexual size dimorphism in wasps and bees

Sexual size dimorphism, in which one sex is larger than the other, occurs when body size has differential effects on the fitness of males and females. Mammals and birds usually have male-biased size dimorphism, probably because of strong sexual competition among males. Invertebrates usually have female-biased size dimorphism, perhaps because their inflexible exoskeletons limit ovary size, leading to a strong correlation between female body size and fecundity. In this paper, we test whether an additional factor, the type of parental care provided, affects the degree of sexual size dimorphism. Among wasps and bees, there is a contrast between provisioning taxa, in which females must gather and transport heavy loads of provisions to nests they have constructed, and non-provisioning taxa, in which females lay eggs but do not construct nests or transport provisions. Males have no role in parental care in either case. An analysis of British wasps and bees shows that provisioning taxa have significantly more female-biased size dimorphism than non-provisioning taxa. This is true for simple cross‑species comparisons and after controlling for phylogeny. Our data imply that the demands of carrying provision loads are at least part of the explanation for this pattern. Thus, sexual size dimorphism is greatest in pompilid wasps, which carry the heaviest prey items. Bees, which transport minute pollen grains, exhibit the least dimorphism. We also find that cavity‑nesting species, in which nest construction costs may be minimized, exhibit reduced dimorphism, but this was not significant after controlling for phylogeny.     

Toxicity of TiO2, ZrO2, Fe,Fe2O3, and Mn2O3 nanoparticles to the yeast, Saccharomyces cerevisiae

The growing application of engineered nanomaterials is leading to an increased occurrence of nanoparticles (NPs) in the environment. Thus, there is a need to better understand their potential impact on the environment. This study evaluated the toxicity of nanosized TiO₂, ZrO₂, Fe⁰, Fe₂O₃, and Mn₂O₃ towards the yeast Saccharomyces cerevisiae based on O₂ consumption and cell membrane integrity. In addition, the state of dispersion of the nanoparticles in the bioassay medium was characterized.     

Toxicity of copper to acetoclastic and hydrogenotrophic activities of methanogens and sulfate reducers in anaerobic sludge

Heavy metals could potentially negatively impact microorganisms in anaerobic sulfate reducing bioreactors. The objective of this is study was to evaluate the inhibitory effect of copper to acetoclastic and hydrogenotrophic activities of methanogens and sulfate reducers in sludge obtained from a full-scale sulfate reducing bioreactor. The 50% inhibiting concentration (50%IC) of Cu(2+) to acetoclastic and hydrogenotrophic methanogens was 20.7 and 8.9 mg l(-1), respectively. The 50%IC of Cu(2+) to acetoclastic sulfate reduction was 32.3 mg l(-1). The hydrogenotrophic sulfate reducers were only inhibited by 27% at the highest concentration of Cu(2+) tested, 200 mg l(-1), indicating a high level of tolerance. The soluble Cu(2+) was observed to decrease rapidly in both the methanogenic and sulfate reducing assays. The highest level of decrease was observed in the hydrogenotrophic sulfate reducing assay which was over 99% in 5h. The results of this study indicate that sulfate reducing biotechnologies would be robust at relatively high inlet concentrations of Cu(2+).     

AN OVERVIEW OF POROUS PAVEMENT RESEARCH1

ABSTRACT: This paper discusses the economics, advantages, potential applications, and status and future research needs of porous pavements. Porous pavements are an available storm water management technique which can be used on parking lots and low volume roadways in order to reduce both storm water runoff volume and pollution. In addition, ground water recharge is enhanced. Also, cost reductions result due to elimination of curbs, drains, and small sized storm sewers. Porous asphalt pavements consist of a relatively thin course of open graded asphalt mix over a deep base of large size crushed stones. Water can be stored in the crushed stone base until it can percolate into the subbase or drain laterally. Other porous pavement types include concrete lattice blocks and a porous concrete mix.     

ELEVATED ATMOSPHERIC CO2 INCREASES WATER AVAILABILITY IN A WATER-LIMITED GRASSLAND ECOSYSTEM1

ABSTRACT: Californian annual grassland on sandstone (moderately fertile) and serpentine (very infertile) soils at the Jasper Ridge Biological Preserve, Stanford, California, were exposed to ambient or elevated (ambient + 36 Pa CO₂) atmospheric CO₂ in open-top chambers since December 1991. We measured ecosystem evapotranspiration with open gas-exchange systems, and soil moisture with time-domain reflectometry (TDR) over 0–15 cm (serpentine) and 0–30 cm (sandstone) depths, at times of peak above ground physiological activity. Evapotranspiration decreased by 12 to 63 percent under elevated CO₂ in three consecutive years in the sandstone ecosystem (p = 0.053, p = 0.162, p = 0.082 in 1992, 1993, and 1994, respectively). In correspondence with decreased evapotranspiration, late-season soil moisture reserves in the sandstone were extended temporally by 10 ± 3 days in 1993 and by 28 ± 11 days in 1994. The effect of elevated CO₂ on soil moisture was greater in the drier spring of 1994 (419 mm annual rainfall) than in 1993 (905 mm annual rainfall). In the serpentine ecosystem, evapotranspiration and soil moisture reserves were not clearly affected by elevated CO₂. Soil water may be conserved in drought-affected ecosystems exposed to elevated CO₂, but the amount of conservation appears to depend on the relative importance of transpiration and soil evaporation in controlling water flux.     

Constructive controversy,the Vroom-Yetton model,and managerial decision-making

Empirical tests have indicated that following the Vroom-Yetton Normative Model of leadership predicts reliably to successful managerial decision-making. However, it does not consider the kind of social interaction among decision makers. Recent experiments have demonstrated that controversy constructively discussed can facilitate decision-making. To see whether constructive controversy can supplement the Vroom-Yetton model, 58 managers enrolled in an executive-level MBA programme described a successful and unsuccessful decision-making experience by answering the Vroom-Yetton questions and by indicating the extent those involved in making the decision experienced constructive controversy. Results indicate that both the Vroom-Yetton model and constructive controversy are significantly related to successful decision-making. A regression analysis indicated that constructive controversy accounted for 45 per cent of the variance of decision success whereas the Vroom-Yetton model accounted for 5 per cent. While the Vroom-Yetton model is useful at the preplanning stage for choosing a decision style, much greater contribution is provided by constructive discussions of opposing opinions when actually generating the decision.     

Some observations on work‐sharing

The background to this paper is the substantial and prolonged rise in the measured rate of unemployment which appears to have continued, more or less unabated, since 1968. A number of commentators have recently questioned the effectiveness and desirability of remedial policy measures designed to expand labour demand, and there appears to be increasing support for the idea that a return to full employment can only be achieved by limiting the supply of labour, with work‐sharing apparently offering the greatest scope for success. The author questions the validity of such a policy, given the current legislative and operational environment in which labour market decisions are taken.     

Molecular approaches to microbiological monitoring: fecal source detection

Molecular methods are useful both to monitor natural communities of bacteria, and to track specific bacterial markers in complex environments. Length-heterogeneity polymerase chain reaction (LH-PCR) and terminal restriction fragment length polymorphism (T-RFLP) of 16S rDNAs discriminate among 16S rRNA genes based on length polymorphisms of their PCR products. With these methods, we developed an alternative indicator that distinguishes the source of fecal pollution in water. We amplify 16S rRNA gene fragments from the fecal anaerobic genus Bacteroides with specific primers. Because Bacteroides normally resides in gut habitats, its presence in water indicates fecal pollution. Molecular detection circumvents the complexities of growing anaerobic bacteria. We identified Bacteroides LH-PCR and T-RFLP ribosomal DNA markers unique to either ruminant or human feces. The same unique fecal markers were recovered from polluted natural waters. We cloned and sequenced the unique markers; marker sequences were used to design specific PCR primers that reliably distinguish human from ruminant sources of fecal contamination. Primers for more species are under development. This approach is more sensitive than fecal coliform assays, is comparable in complexity to standard food safety and public health diagnostic tests, and lends itself to automation and high-throughput. Thus molecular genetic markers for fecal anaerobic bacteria hold promise for monitoring bacterial pollution and water quality.     

冷拔无缝钢管爆裂分析

在无缝钢管的冷拔过程中,存在着冷作硬化和氢脆现象,它们是造成钢管爆裂的主要原因。此文对两个现象进行了分析,提出了一些防止钢管爆裂的措施。