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Proportional Decrease (proportional + decrease)
Selected AbstractsStress Resistance and Environmental Dependency of Inbreeding Depression in Drosophila melanogasterCONSERVATION BIOLOGY, Issue 4 2000Jesper Dahlgaard Two important issues are whether stress and inbreeding effects are independent as opposed to synergistic, and whether inbreeding effects are general across stresses as opposed to stress-specific. We found that inbreeding reduced resistance to acetone and desiccation in adult Drosophila melanogaster, whereas resistance to knockdown heat stress was not affected. Inbred flies, however, experienced a greater proportional decrease in productivity than outbreds following heat stress. Correlations using line means indicated that all resistance traits were uncorrelated in the inbred as well as in the outbred flies. Recessive, deleterious alleles therefore did not appear to have any general deleterious effects on stress resistance. Inbreeding within a specific environment and selection for resistant genotypes may therefore purge a population of deleterious genes specific to only one environmental stress. Resumen: Tanto la endogamia como el estrés ambiental pueden tener efectos adversos sobre la adaptabilidad afectando la conservación de especies en peligro de extinción. Dos temas importantes son determinar si los efectos del estrés y la endogamia son independientes en lugar de ser sinérgicos, y determinar si los efectos de la endogamia son generales para distintos tipos de estrés o si son específicos para un tipo determinado de estrés. Encontramos que la endogamia reduce la resistencia a la acetona y la desecación en adultos de Drosophila melanogaster, mientras que la resistencia al efecto demoledor del estrés por calor no fue afectada. Sin embargo, las moscas endogámicas experimentaron una disminución proporcionalmente mayor en la productividad que aquellas moscas sin endogamia después de experimentar un estrés por calor. Las correlaciones obtenidas usando líneas medias indicaron que las características de resistencia no estuvieron correlacionadas ni en moscas con endogamia, ni en moscas sin ella. Aparentemente los alelos nocivos recesivos no tuvieron ningún efecto nocivo general en la resistencia al estrés. La endogamia dentro de un ambiente específico y la selección por genotipos resistentes podrían, por lo tanto, eliminar una población de genes nocivos específicos a un solo estrés ambiental. [source] EFFECTS OF GENETIC DRIFT ON VARIANCE COMPONENTS UNDER A GENERAL MODEL OF EPISTASISEVOLUTION, Issue 10 2004N.H. Barton Abstract We analyze the changes in the mean and variance components of a quantitative trait caused by changes in allele frequencies, concentrating on the effects of genetic drift. We use a general representation of epistasis and dominance that allows an arbitrary relation between genotype and phenotype for any number of diallelic loci. We assume initial and final Hardy-Weinberg and linkage equilibrium in our analyses of drift-induced changes. Random drift generates transient linkage disequilibria that cause correlations between allele frequency fluctuations at different loci. However, we show that these have negligible effects, at least for interactions among small numbers of loci. Our analyses are based on diffusion approximations that summarize the effects of drift in terms of F, the inbreeding coefficient, interpreted as the expected proportional decrease in heterozygosity at each locus. For haploids, the variance of the trait mean after a population bottleneck is var(,z,) =where n is the number of loci contributing to the trait variance, VA(1)=VA is the additive genetic variance, and VA(k) is the kth-order additive epistatic variance. The expected additive genetic variance after the bottleneck, denoted (V*A), is closely related to var(,z,); (V*A) (1 ,F)Thus, epistasis inflates the expected additive variance above VA(1 ,F), the expectation under additivity. For haploids (and diploids without dominance), the expected value of every variance component is inflated by the existence of higher order interactions (e.g., third-order epistasis inflates (V*AA)). This is not true in general with diploidy, because dominance alone can reduce (V*A) below VA(1 ,F) (e.g., when dominant alleles are rare). Without dominance, diploidy produces simple expressions: var(,z,)==1 (2F) kVA(k) and (V*A) = (1 ,F)k(2F)k-1VA(k) With dominance (and even without epistasis), var(,z,)and (V*A) no longer depend solely on the variance components in the base population. For small F, the expected additive variance simplifies to (V*A)(1 ,F) VA+ 4FVAA+2FVD+2FCAD, where CAD is a sum of two terms describing covariances between additive effects and dominance and additive × dominance interactions. Whether population bottlenecks lead to expected increases in additive variance depends primarily on the ratio of nonadditive to additive genetic variance in the base population, but dominance precludes simple predictions based solely on variance components. We illustrate these results using a model in which genotypic values are drawn at random, allowing extreme and erratic epistatic interactions. Although our analyses clarify the conditions under which drift is expected to increase VA, we question the evolutionary importance of such increases. [source] Probing the role of oligomerization in the high thermal stability of Pyrococcus furiosus ornithine carbamoyltransferase by site-specific mutantsFEBS JOURNAL, Issue 14 2001Bernard Clantin The Pyrococcus furiosus ornithine carbamoyltransferase (OTCase) is extremely heat stable and maintains 50% of its catalytic activity after 60 min at 100 °C. The enzyme has an unusual quaternary structure when compared to anabolic OTCases from mesophilic organisms. It is built up of four trimers arranged in a tetrahedral manner, while other anabolic enzymes are single trimers. Residues Trp21, Glu25, Met29 and Trp33 are located in the main interfaces that occur between the catalytic trimers within the dodecamer. They participate in either hydrophobic clusters or ionic interactions. In order to elucidate the role played by the oligomerization in the enzyme stability at very high temperatures, we performed mutagenesis studies of these residues. All the variants show similar catalytic activities and kinetic properties when compared to the wild-type enzyme, allowing the interpretation of the mutations solely on heat stability and quaternary structure. The W21A variant has only a slight decrease in its stability, and is a dodecamer. The variants E25Q, M29A, W33A, W21A/W33A and E25Q/W33A show that altering more drastically the interfaces results in a proportional decrease in heat stability, correlated with a gradual dissociation of dodecamers into trimers. Finally, the E25Q/M29A/W33A variant shows a very large decrease in heat stability and is a trimer. These results suggest that extreme thermal stabilization of this OTCase is achieved in part through oligomerization. [source] Titration methodologies for monitoring of anaerobic digestion in developing countries,a reviewJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 12 2004O Lahav Abstract An increase in volatile fatty acids (VFA) concentration (or the proportional decrease in carbonate alkalinity concentration) is the first practical measurable indication that an anaerobic treatment system is in a state of stress. If the system is not rectified at this early stage, failure is likely. Current methods for VFA measurement include distillation, colorimetry, gas chromatography and various titration techniques. In terms of simplicity, speed and cost-effectiveness it is generally accepted that titration methods are superior for the purpose of on-site routine monitoring and control, particularly in developing countries. This paper reviews the methods published in the last four decades concerning on-site titration measurement of VFA and carbonate alkalinity concentrations. The review encompasses the following: aquatic chemistry related to the theory on which most of the methods are based, and a detailed description of each of the principal methods published followed by critical and comparative evaluation. Copyright © 2004 Society of Chemical Industry [source] Transaction tax and market quality of the Taiwan stock index futuresTHE JOURNAL OF FUTURES MARKETS, Issue 12 2006Robin K. Chou On May 1, 2000, the Taiwan government reduced the tax levied on futures transactions on the Taiwan Futures Exchange from 5 to 2.5 basis points. This event provides a unique opportunity to test empirically the impact of a tax rate reduction on trading volume, bid-ask spreads, and price volatility. Intraday and daily time series data from May 1, 1999, through April 30, 2001, are tested in a three-equation structural model. Findings show that transaction taxes have a negative impact on trading volume and bid-ask spreads, as trading volume increased and bid-ask spreads decreased in the period following the reduction in the transaction tax. This study's analysis is not consistent with the argument that the imposition of a transaction tax may reduce price volatility because there are no significant changes in price volatility after the tax reduction. Further, it was found that although the reduction in the transaction tax did reduce tax revenues, the proportional decrease in tax revenues is less than the 50% reduction in the tax rate. Finally, tax revenues in the second and third year after the tax reduction increased, as compared to the year before the tax reduction. © 2006 Wiley Periodicals, Inc. Jrl Fut Mark 26:1195,1216, 2006 [source] On the Weight-bearing Function of the Medial Coronoid Process in DogsANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 1 2006S. Breit Summary The shape of and proportions between the surface areas of the medial coronoid process (MCP) and the fovea of the radial head were determined in 88 juvenile dogs and 146 adult dogs grouped as giant, large, mid-sized, chondrodystrophic, or small dogs. Thereby, the longitudinal (length) and transverse (width) extension of the MCP and fovea of the radial head have been measured. Original values were used to describe changes of the parameters attributed to growth. Normalized values (i.e. values expected in case of a width of the fovea of the radial head of 20 mm) were used to determine potential differences between constitutional types. All original values increased during growth (P < 0.05) except for the width and length of the MCP in chondrodystrophic and small breeds. Normalized values revealed a proportional decrease in width and length of the MCP during growth (P < 0.05) compared with the radial head. In adults, the normalized MCP was widest in giant dogs followed by large, mid-sized, small, and chondrodystrophic breeds. The MCP was also longest in giant dogs but shortest in large and chondrodystrophic dogs with those of large dogs being significantly (P < 0.05) shorter than those in giant, mid-sized and small dogs. Present results suggest that a deficiency in length-growth of the MCP , which has been present especially in large dogs , results in smaller humeral contact areas and decreased weight-bearing capacity of the MCP. Because loading forces acting on the MCP increase with body weight, the condition noted in large dogs might increase the risk of fragmentation of the MCP in these. [source] | |||||||||||||