Prenatal ultrasonographic diagnosis of radial-ray reduction malformations

Radial-ray reduction malformations (RRRMs) may occur isolated or in association with other anomalies. The data of seven fetuses born with RRRMs were collected. Six fetuses had associated lethal abnormalities of the central nervous system, urogenital system, and/or heart, detected by ultrasound. In five cases, it was possible to establish the precise diagnosis, enabling an informed prognosis and subsequent genetic counselling. The diagnoses were: Edwards syndrome (n=3), VACTERL association (n=1), and Poland-Moebius-like complex (n= 1). In two cases, a complete diagnosis was not possible because of inadequate evaluation of these fetuses before and/or after birth. A proposal is given for the diagnostic approach for infants with RRRMs detected in the antenatal period by means of ultrasonography.     

Economic aspects of appropriative water rights

In the and portion of the western U.S., economic development has been affected by the doctrine of appropriative water rights. This paper considers the efficiency aspects of the appropriative doctrine for the case of a stochastic and uncontrolled river, then, subsequently, extends the analysis to the case where the presence of an upstream storage facility provides some degree of flexibility in determining releases. Lastly, the effects of institutions which limit the degree of river use and the implicit release policies attendant are considered.     

Emissions Trading with Shares and Coupons when Control over Discharges Is Uncertain

Two important decisions in designing markets for tradable emissions permits are whether to allow banking of permits (coupons) and whether to allow trading in entitlements to future permits (shares). Banking is predicted to reduce price instability when firms trade in a reconciliation market after the quantity of emissions has been determined. Tradable shares are a common feature in proposals for emissions trading in Canada. We conduct a laboratory experiment to investigate how bankable coupons and tradable shares affect efficiency and prices under uncertainty. Cognitive demands on the subjects are reduced by computerized advice on the optimal allocation of coupons across periods and the implied marginal values of coupons and shares. Banking, share trading, and uncertainty conditions are introduced in a complete factorial design with three observations per cell. High efficiencies are observed across all treatments. Uncertainty in the control of emissions leads to substantial price instability when banking is not allowed. Banking virtually eliminates the instability, but reduces the efficiency of the market institution. Share trading reduces trading volumes, increases price stability, and improves efficiency.     

Processes controlling metal transport and retention as metal-contaminated groundwaters efflux through estuarine sediments

Factors affecting the transport and retention of Cd, Cr, Cu, Ni, Pb and Zn in acidic groundwaters as they pass through estuarine sediments were investigated using column experiments. Acidic groundwaters caused the rapid dissolution of iron sulfide (AVS) and other iron and manganese phases from sediments that are important for metal binding and buffering. Metal breakthrough to overlying water occurred in the order of Ni>Zn>Cd>Cu>Cr/Pb. Metal transport increased as the sediment permeability increased, reflecting the low resistance to flow caused by larger sand-sized particles and the decreased abundance of metal adsorption sites on these materials. Metal mobility increased as the groundwater pH decreased, as flow rate or metal concentrations increased, and as the exposure duration increased. Groundwater Cr and Pb were promptly attenuated by the sediments, the mobility of Cu was low and decreased rapidly as sediment pH increased above 4.5, while Cd, Ni and Zn were the most easily transported to the surface sediments and released to the overlying waters. For groundwaters of pH 3, metal migration velocities through sandy sediments were generally 0.5-2% (Cr, Pb), 1-6% (Cu) and 4-13% (Cd, Ni, Zn) of the total groundwater velocity (9-700 m/yr). The oxidative precipitation of Fe(II) and Mn(II) in the groundwaters did not affect metal mobility through the sediments. The results indicated that the efflux of acidic and metal-contaminated groundwater through estuarine sediments would affect organisms resident in sandy sediments more greatly than organisms resident in fine-grained, silty, sediments.     

Global change and the boreal forest: thresholds, shifting states or gradual change?

Changes in boreal climate of the magnitude projected for the 21st century have always caused vegetation changes large enough to be societally important. However, the rates and patterns of vegetation change are difficult to predict. We review evidence suggesting that these vegetation changes may be gradual at the northern forest limit or where seed dispersal limits species distribution. However, forest composition may be quite resilient to climate change in the central portions of a species range until some threshold is surpassed. At this point, changes can be rapid and unexpected, often causing a switch to very different ecosystem types. Many of these triggers for change are amenable to management, suggesting that our choice of policies in the coming decades will substantially influence the ecological and societal consequences of current climatic change.     

Sexual selection on alleles that determine body size in the swordtail Xiphophorus nigrensis

Summary In a natural population, we document changes in the frequencies of alleles influencing body size and size-correlated alternative male reproductive tactics, and we examine the possible role of sexual selection in producing these changes. Male swordtails (Xiphophorus nigrensis, Rio Choy) exhibit three body size classes (small, intermediate, and large) that primarily derive from allelic variation (s, I, L) at the Y-linked pituitary (P) locus. Some XX individuals are male. They are small and can be fathered either by XX or XY males. We compared the frequencies of Y-linked P alleles across two generations in a natural population. There was a significant decrease in the Y-s genotype relative to Y-I and Y-L genotypes. Laboratory experiments suggest that the disadvantage of Y-s resulted, at least in part, from female preference for larger courting males relative to small chasing males. All larger courting males are of the Y-I or Y-L genotypes. Although the frequency of Y-linked P alleles changed across generations, there was no change in the distribution of male body size classes. The stability of the phenotypic distribution across generations, despite changes in P allele frequencies, was maintained by the production of small XX sons by Y-I and Y-L males. Offprint requests to: M.J. Ryan     

Renormalized numerical simulation of flow over planar and non-planar fractal trees

We review the fundamentals of a new numerical modeling technique called Renormalized Numerical Simulation (RNS). The goal of RNS is to model the drag force produced by high Reynolds-number turbulent flow over objects that display scale-invariant properties, objects such as tree-like fractals. The hallmark of RNS in this application is that the drag of the unresolved tree branches is modeled using drag coefficients measured from the resolved branches and unresolved branches (as modeled in previous iterations of the procedure). In the present paper, RNS is used to study the effects of branch orientation on the drag force generated by highly idealized trees in which trunk and branches have square cross-section, and the branches all lie in a plane perpendicular to the incoming flow. Then, the procedure is generalized to the more general case of non-planar branch arrangements. Results illustrate that RNS may enable numerical modeling of environmental flow processes associated with fractal geometries using affordable computational resolution.     

Asymmetric larval competition in the parasitoid wasp <Emphasis Type="Italic">Nasonia vitripennis</Emphasis>: a role in sex allocation?

Sex allocation theory offers excellent opportunities for testing how animals adjust their behaviour in response to environmental conditions. A major focus has been on instances of local mate competition (LMC), where female-biased broods are produced to maximise mating opportunities for sons. However, the predictions of LMC theory can be altered if there is both local competition for resources during development and an asymmetry between the competitive abilities of the sexes, as has been seen in animals ranging from wasps to birds. In this paper, we test the extent to which asymmetric larval competition alters the predictions of LMC theory in the parasitoid wasp Nasonia vitripennis. We found that the body size of both sexes was negatively correlated with the number of offspring developing within the host. Further, we found that when faced with high levels of competition, the body size of females, but not males, was influenced by the sex ratio of the competing offspring; females were smaller when a higher proportion of the brood was female. This asymmetric competition should favour less biased sex ratios than are predicted by standard LMC theory. We then develop a theoretical model that can be parameterised with our data, allowing us to determine the quantitative consequences of the observed level of asymmetric larval competition for sex allocation. We found that although asymmetric competition selects for less biased sex ratios, this effect is negligible compared to LMC. Furthermore, a similar conclusion is reached when we re-analyse existing data from another parasitoid species where asymmetric larval competition has been observed; Bracon hebetor. Consequently, we suspect that asymmetric larval competition will have its greatest influence on sex ratio evolution in species that have smaller clutches and where local mate competition is not an issue, such as birds and mammals.     

How <Emphasis Type="Italic">Doratomyces stemonitis</Emphasis> copes with Benzoxazolin-2(3<Emphasis Type="Italic">H</Emphasis>)-one (BOA), its derivatives and detoxification products

Summary. Doratomyces stemonitis (Hyphomycetales, Dematiaceae) is a saprotrophic fungus belonging to the mycobiota of the cereal rhizosphere. The fungus is able to metabolize benzoxazolin-2-(3H)-one and a variety of its derivatives including higher plant detoxification products, microbial degradation products and the chemically rather stable 2-amino-(3H)-phenoxazin-3-one. D. stemonitis can use all of these compounds as sole C-sources but their utilization, especially that of microbial degradation products and 2-amino-(3H)-phenoxazin-3-one, seems to be highly energy consuming, resulting in slow mycelium growth and a change of colony morphology. Benzoxazolin-2-(3H)-one derived compounds induce the synthesis of different isoforms of a glycosylated protein with sequence homologies to the endo-1,3-β-glucanase Asp f2, an allergen from Aspergillus fumigatus and other Asp f2-like proteins e.g., from Verticillium dahliae or PRA1 antigen from Candida albicans. The induction of the protein is regarded as a stress response.