Useful Descriptor (useful + descriptor)

Distribution by Scientific Domains

Selected Abstracts


EVOLUTION, Issue 5 2007
Derek A. Roff
Quantitative genetics is at or is fast approaching its centennial. In this perspective I consider five current issues pertinent to the application of quantitative genetics to evolutionary theory. First, I discuss the utility of a quantitative genetic perspective in describing genetic variation at two very different levels of resolution, (1) in natural, free-ranging populations and (2) to describe variation at the level of DNA transcription. Whereas quantitative genetics can serve as a very useful descriptor of genetic variation, its greater usefulness is in predicting evolutionary change, particularly when used in the first instance (wild populations). Second, I review the contributions of Quantitative trait loci (QLT) analysis in determining the number of loci and distribution of their genetic effects, the possible importance of identifying specific genes, and the ability of the multivariate breeder's equation to predict the results of bivariate selection experiments. QLT analyses appear to indicate that genetic effects are skewed, that at least 20 loci are generally involved, with an unknown number of alleles, and that a few loci have major effects. However, epistatic effects are common, which means that such loci might not have population-wide major effects: this question waits upon (QTL) analyses conducted on more than a few inbred lines. Third, I examine the importance of research into the action of specific genes on traits. Although great progress has been made in identifying specific genes contributing to trait variation, the high level of gene interactions underlying quantitative traits makes it unlikely that in the near future we will have mechanistic models for such traits, or that these would have greater predictive power than quantitative genetic models. In the fourth section I present evidence that the results of bivariate selection experiments when selection is antagonistic to the genetic covariance are frequently not well predicted by the multivariate breeder's equation. Bivariate experiments that combine both selection and functional analyses are urgently needed. Finally, I discuss the importance of gaining more insight, both theoretical and empirical, on the evolution of the G and P matrices. [source]

Connectivity and patch area in a coastal marine landscape: Disentangling their influence on local species richness and composition

Abstract Landscape ecology emerged as a terrestrial discipline to evaluate the effect of spatial configuration of natural systems on ecological patterns. The advances in marine systems have been comparatively scarce perhaps as a consequence of a long-standing view about the greater dispersal potential of marine species and its effect on the spatial homogenization of marine landscapes. Herein we used an intertidal rocky system as a model to analyse the effect of landscape attributes on local species richness and composition. We evaluated the effect of patch area, landscape connectivity and salinity gradient on local species richness of macro-invertebrates, and the effect of geographic distance on species similarity. We sampled 19 rocky patches along the Uruguayan Atlantic coast one time during the spring of 2003. The relative contribution of the variables assessed on specific richness of sessile, mobile and total macrofauna was analysed with a stepwise multiple linear regression. For the mobile macrofaunal richness, we also incorporated the sessile macrofaunal richness as another independent variable. The effect of geographic distance on biological similarity was assessed by a Mantel test. We showed that landscape connectivity, as a descriptor of the average physical isolation of a biological community in the landscape, is an important factor explaining the community species richness for sessile macrofauna, what indirectly increases the mobile macrofaunal richness. The geographic distance between sites was negatively related to species similarity. We suggest that at the landscape scale, connectivity among sites can be important to understand the local structure of marine communities, particularly in rocky intertidal systems. Also the distance-decay of similarity in community composition provides a useful descriptor of how biological composition varies along a physical gradient. Our results contribute to reinforce the view that mesoscale connectivity (101,2 km) in coastal marine landscapes plays a more important role in local community structure than previously assumed. [source]


ABSTRACT A trained panel developed rating scales for crispness, crunchiness and crackliness for dry and wet foods based on the auditory perception of selected foods. The newly developed scales were then evaluated by 40 untrained panelists and the sound perception of standard foods was assessed through the analysis of the root mean square (RMS) of the 5-s audio waveforms and multidimensional scaling (MDS). The RMS was highly correlated to auditory sensory perception of crispness (r = 0.83 and 0.96), crunchiness (r = 0.99 and 0.99) and crackliness (r = 0.88 and 0.96) for dry and wet foods, respectively. MDS technique applied for the 40 untrained panelists was instructive in assessing auditory textural differences of naïve panelists and a useful statistical instrument to graphically validate selected scales. Auditory perception of the selected foods were rated similarly using standard auditory texture scales for crispness, crunchiness and crackliness developed by the trained panel (oral evaluation) and MDS results from the untrained panel (recordings). PRACTICAL APPLICATIONS Crispness, crunchiness and crackliness are not only important and useful descriptors of food texture, but are also desirable textural qualities in many foods. The lack of consistency in the procedures used for the evaluation of crunchy, crispy and crackly in sensory studies often results in confusion when training expert panels. Research will benefit textural studies through an improvement of consistent textural definitions and development of standard scales and evaluation techniques. The crispness, crunchiness and crackliness scales developed and applied in the current study represent a new potential standard frame of reference that may be used for training panelists in texture parameters related to food auditory perception. The scales may be considered illustrations demonstrating full and practical ranges for each texture attribute with regard to analyzing auditory parameters of foods and effective objective tools for assessing panelists in descriptive analysis. [source]

Surface texture characterization of injection-molded pigmented plastics

Ingrid Ariño
An appropriate description of the surface textures deliberately created on injection-molded plastic parts of interior car components is presented. A spatial wavelength-dependent analysis is used as an interesting alternative to the traditional roughness parameters. Auto-correlation functions and power spectral densities are examples of such spectral functions that include parameters both in amplitude and profile directions. Even fractal concepts can be useful descriptors. As an illustration, it is also shown how the effects on the surface topography of the plastic part of after-etching the mold can be assessed by suitable descriptors. An experimental evaluation of injection-molded plaques containing three different surface patterns was carried out using an optical profilometer, supplemented by contact stylus measurements. The ability to assess the topography of these plaques by means of a new fast photometric stereo-technique, denoted OptiTopo, was also evaluated. In its present form, however, this technique does not provide a detailed description of the topography of a pigmented plastic. Reasons for this and possible improvements are discussed. Polym. Eng. Sci. 44:1615,1626, 2004. © 2004 Society of Plastics Engineers. [source]