Quantitative Tests (quantitative + test)

Distribution by Scientific Domains

Selected Abstracts


EVOLUTION, Issue 7 2004
Devi M. Stuart-Fox
Abstract Many animal species display striking color differences with respect to geographic location, sex, and body region. Traditional adaptive explanations for such complex patterns invoke an interaction between selection for conspicuous signals and natural selection for crypsis. Although there is now a substantial body of evidence supporting the role of sexual selection for signaling functions, quantitative studies of crypsis remain comparatively rare. Here, we combine objective measures of coloration with information on predator visual sensitivities to study the role of crypsis in the evolution of color variation in an Australian lizard species complex (Ctenophorus decresii). We apply a model that allows us to quantify crypsis in terms of the visual contrast of the lizards against their natural backgrounds, as perceived by potential avian predators. We then use these quantitative estimates of crypsis to answer the following questions. Are there significant differences in crypsis conspicuousness among populations? Are there significant differences in crypsis conspicuousness between the sexes? Are body regions "exposed" to visual predators more cryptic than "hidden" body regions? Is there evidence for local adaptation with respect to crypsis against different substrates? In general, our results confirmed that there are real differences in crypsis conspicuousness both between populations and between sexes; that exposed body regions were significantly more cryptic than hidden ones, particularly in females; and that females, but not males, are more cryptic against their own local background than against the background of other populations. Body regions that varied most in contrast between the sexes and between populations were also most conspicuous and are emphasized by males during social and sexual signaling. However, results varied with respect to the aspect of coloration studied. Results based on chromatic contrast ("hue' of color) provided better support for the crypsis hypothesis than did results based on achromatic contrast ("brightness' of color). Taken together, these results support the view that crypsis plays a substantial role in the evolution of color variation and that color patterns represent a balance between the need for conspicuousness for signaling and the need for crypsis to avoid predation. [source]

Quantitative tests for stratigraphic cyclicity

R. J. Bailey
Abstract Periodic Milankovitch (M-) orbital forcing provides an explanation for subjectively recognized short-term repetition of lithofacies-,cycles'-in the stratigraphic record. Tests of this explanation often find no order in the lithofacies and/or no regularity in the recurrence of lithofacies. This does not disprove the influence of M-forcing, but a sedimentary response in terms of irregular M-forced ,cycles' is indistinguishable from one in which repetition of facies is not M-forced. Use of such cycles in time calibration is correspondingly suspect. Stricter, dimensional cyclicity invokes Sander's Rule, which suggests periodicity in sedimentation, for which M-forcing provides an obvious explanation. Time calibration on the basis of strict cyclicity thus appears more dependable. Objective tests for regular M-forced stratigraphic cyclicity commonly depend upon spectral analyses. Such tests are not unambiguous. Bilogarithmic thickness/frequency plots derived from objective layer thickness inventories (LTI) provide an alternative. Commonly, such plots show power-law relationships that preclude dimensional M-cyclicities. By contrast, a model data series that perfectly encodes the M-cyclic fluctuations in terrestrial insolation generates a strongly inflected, non-power-law LTI plot. Power-law plots result where the model data series is decimated by random hiatuses, with numbers and durations tuned to M-cycle frequencies. It seems improbable that natural data series record such tuning. The general absence of strict cyclicity in the M-frequency range is more likely to reflect the nonlinear response of sedimentary systems to cyclic M-forcing of insolation. Interestingly, when applied to the classically cyclic lacustrine Triassic sediments of the Newark Basin, USA, the LTI test suggests a decimated record, preserving some evidence of M-cyclicity. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Quantitative tests of liver function measure hepatic improvement after sustained virological response: results from the HALT-C trial

Summary Backgroud, The impact of virologic response on hepatic function has not been previously defined. Aim, To determine the relationships of quantitative liver function tests (QLFTs) with virological responses to peginterferon (PEG) ± ribavirin (RBV) in patients with chronic hepatitis C and to use serial QLFTs to define the spectrum of hepatic improvement after sustained virological response (SVR). Methods, Participants (n = 232) were enrolled in the Hepatitis C Antiviral Long-term Treatment against Cirrhosis (HALT-C) Trial, had failed prior therapy, had bridging fibrosis or cirrhosis and were retreated with PEG/RBV. All 232 patients had baseline QLFTs; 24 patients with SVR and 68 nonresponders had serial QLFTs. Lidocaine, [24- 13C]cholate, galactose and 99mTc-sulfur colloid were administered intravenously; [2,2,4,2- 2H]cholate, [1- 13C]methionine, caffeine and antipyrine were administered orally. Clearances (Cl), breath 13CO2, monoethylglycylxylidide (MEGX), perfused hepatic mass (PHM) and liver volume were measured. Results, Rates of SVR were 18,26% in patients with good function by QLFTs, but ,6% in patients with poor function. Hepatic metabolism, measured by caffeine kelim (P = 0.02), antipyrine kelim (P = 0.05) and antipyrine Cl (P = 0.02) and the portal circulation, measured by cholate Cloral (P = 0.0002) and cholate shunt (P = 0.0003) and PHM (P = 0.03) improved after SVR. Conclusion, Hepatic dysfunction impairs the virological response to PEG/RBV. SVR improves hepatic metabolism, the portal circulation and PHM. [source]

Evidence for selection on coloration in a Panamanian poison frog: a coalescent-based approach

Jason L. Brown
Abstract Aim, The strawberry poison frog, Oophaga pumilio, has undergone a remarkable radiation of colour morphs in the Bocas del Toro archipelago in Panama. This species shows extreme variation in colour and pattern between populations that have been geographically isolated for < 10,000 years. While previous research has suggested the involvement of divergent selection, to date no quantitative test has examined this hypothesis. Location, Bocas del Toro archipelago, Panama. Methods, We use a combination of population genetics, phylogeography and phenotypic analyses to test for divergent selection in coloration in O. pumilio. Tissue samples of 88 individuals from 15 distinct populations were collected. Using these data, we developed a gene tree using the mitochondrial DNA (mtDNA) d-loop region. Using parameters derived from our mtDNA phylogeny, we predicted the coalescence of a hypothetical nuclear gene underlying coloration. We collected spectral reflectance and body size measurements on 94 individuals from four of the populations and performed a quantitative analysis of phenotypic divergence. Results, The mtDNA d-loop tree revealed considerable polyphyly across populations. Coalescent reconstructions of gene trees within population trees revealed incomplete genotypic sorting among populations. The quantitative analysis of phenotypic divergence revealed complete lineage sorting by colour, but not by body size: populations showed non-overlapping variation in spectral reflectance measures of body coloration, while variation in body size did not separate populations. Simulations of the coalescent using parameter values derived from our empirical analyses demonstrated that the level of sorting among populations seen in colour cannot reasonably be attributed to drift. Main conclusions, These results imply that divergence in colour, but not body size, is occurring at a faster rate than expected under neutral processes. Our study provides the first quantitative support for the claim that strong diversifying selection underlies colour variation in the strawberry poison frog. [source]

Dust emission in the far-infrared as a star formation tracer at z= 0: systematic trends with luminosity

D. Pierini
ABSTRACT We investigate whether dust emission in the far-infrared (far-IR) continuum provides a robust estimate of the star formation rate (SFR) for a nearby, normal late-type galaxy. We focus on the ratio of the 40,1000 ,m luminosity (Ldust) to the far-ultraviolet (far-UV) (0.165 ,m) luminosity, which is connected to recent episodes of star formation. Available total photometry at 0.165, 60, 100 and 170 ,m limits the statistics to 30 galaxies, which, however, span a large range in observed (and, thus, attenuated by dust) K -band (2.2 ,m) luminosity, morphology and inclination (i). This sample shows that the ratio of Ldust to the observed far-UV luminosity depends not only on i, as expected, but also on morphology and, in a tighter way, on observed K -band luminosity. We find that Ldust/LFUV, eLK0.62, where LFUV and LK are the unattenuated stellar luminosities in far-UV and K, respectively, and , is the ratio of the attenuation optical depths at 0.165 ,m (,FUV) and 2.2 ,m (,K). This relation is to zeroth order independent of i and morphology. It may be further expressed as Ldust/LFUV,L,K, where ,= 0.61 , 0.02,, under the observationally motivated assumption that, for an average inclination, e,L,0.02K. We adopt calculations of two different models of attenuation of stellar light by internal dust to derive solid-angle-averaged values of ,. We find that , is positive and decreases towards 0 from the more luminous to the less luminous galaxies. This means that there is no universal ratio of far-IR luminosity to unattenuated far-UV luminosity for nearby, normal late-type galaxies. The far-IR luminosity systematically overestimates SFR in more luminous, earlier-type spirals, owing to the increased fractional contribution to dust heating of optical/near-IR photons in these objects. Conversely, it systematically underestimates SFR in fainter, later-type galaxies, the ,FUV of which is reduced. The limited statistics and the uncertainty affecting the previous scaling relations do not allow us to establish quantitative conclusions, but an analogous analysis making use of larger data sets, available in the near future (e.g. from GALEX, ASTRO-F and SIRTF), and of more advanced models will allow a quantitative test of our conclusions. [source]

Prenatal diagnosis for risk of spinal muscular atrophy

I. Cuscó
Objectives Prenatal diagnosis of spinal muscular atrophy is usually performed in high risk couples by detection of a homozygous deletion in the survival motor neurone gene (SMN1). However, other relatives at risk of being carriers very often request genetic counselling and the possibility of prenatal diagnosis. The aim of this study was to validate a SMN1 gene quantitative test to help the couples formed by one spinal muscular atrophy carrier and a partner of the general population (1/200 potential risk) to achieve a less ambiguous risk result for the pregnancy. Design Spinal muscular atrophy carrier studies in at-risk individuals. Setting Department of Genetics and Gynaecology and Obstetrics in a large university hospital. Population Seventy-nine obligate carriers (more than one affected child with deletion in the offspring) and 58 non-carriers (relatives of spinal muscular atrophy families defined by marker studies) were tested to set up a quantitative analysis. The method was applied in different situations in 126 members from 34 families with spinal muscular atrophy patients. Methods DNA studies of the SMN1 gene by marker analysis and quantitative assay. Main outcome measures To determine double (non-carrier) or single dose (carrier) of exon 7 of the SMN1 gene in relatives of spinal muscular atrophy patients. Bayesian calculation of risk. Results The sensitivity and specificity of the method were 96% and 100%, respectively. Studies on different couples with an a priori risk of 1/200 allowed us to reduce the final risk to 1/5000 or to increase it to 1/4. Conclusions The quantitative method can be used to achieve a less ambiguous risk in pregnancies with a 1/200 risk and in families where no sample is available to study the index case. Screening of gamete donors when the recipient is a known carrier should also be considered. [source]

Aneusomy of chromosomes 7 and 17 predicts the recurrence of transitional cell carcinoma of the urinary bladder

A.D. Watters
Objective,To determine if changes in chromosome 7 and 17 copy number can be used to predict recurrence in patients with primary noninvasive (pTa) or superficially invasive (pT1) transitional cell carcinoma (TCC) of the urinary bladder. Patients and methods,Tissue specimens for 129 tumours from 52 patients (38 men and 14 women) with pTa/pT1 TCC at first diagnosis were retrieved from pathology archives. All patient notes were accessed and disease outcome documented for superficial (pTa/pT1) recurrence or progression to detrusor muscle invasion ( pT2). The tumours were examined for chromosomal copy number of chromosomes 7 and 17 using fluorescence in situ hybridization (FISH) with chromosome-specific probes. The copy number of chromosomes 7 and 17 was determined in interphase nuclei on intact 6 µm tissue sections. Results,Aneusomy of chromosomes 7 and 17 was detected in the index primary tumours of 10 of 32 (31%) patients with subsequent recurrent disease. No aneusomy for these chromosomes was detected in primary tumours from 20 patients with no detect-able recurrence (P = 0.0082). The relative risk of recurrence was 3.62 times greater (95% confi-dence interval 1.6,8.1, Cox's multiple regression P = 0.0019) for patients with chromosomal aneusomy in primary TCC. Neither stage nor grade of the primary tumours was associated with recurrence in these patients, nor was there a significant association with increased grade (G2/3) or stage ( pT2) at recurrence. Conclusion,These results suggest that the measurement of aneusomy by FISH, using markers for chromosomes 7 and 17, predict recurrence in a subgroup of patients with pTa/pT1 tumours at presentation. This finding may offer a new objective and quantitative test for patients destined to recur. [source]

Agreement between clinical examination and quantitative tests of neurologic function among 384 subjects,

Kyle Steenland
Abstract Background Quantitative neurological tests are often cheaper and easier than clinical examinations, and provide continuous data which may discriminate between exposed and nonexposed groups with more sensitivity than dichotomous (normal/abnormal) examination data. Methods We compare clinical examinations and analogous quantitative tests for arm tremor, postural sway, and vibrotactile sensitivity (finger and toe), for 384 subjects. Results The "abnormal" clinical outcomes studied were relatively common (range, 3,36%), and did not result in impairment of daily activity for affected subjects. All the quantitative tests were reasonably good predictors of the corresponding clinical outcome. The most predictive test was for toe vibrotactile sensitivity. The probability of an abnormal clinical result for those in the worst quartile for the toe test was 0.63, compared with 0.36 for all subjects. Conclusions Our results suggest that certain quantitative tests might be used in epidemiologic studies instead of a physical examination. Am. J. Ind. Med. 39:361,368, 2001. Published 2001 Wiley-Liss, Inc. [source]

Comparison of PDQuest and Progenesis software packages in the analysis of two-dimensional electrophoresis gels

Arsi T. Rosengren
Abstract Efficient analysis of protein expression by using two-dimensional electrophoresis (2-DE) data relies on the use of automated image processing techniques. The overall success of this research depends critically on the accuracy and the reliability of the analysis software. In addition, the software has a profound effect on the interpretation of the results obtained, and the amount of user intervention demanded during the analysis. The choice of analysis software that best meets specific needs is therefore of interest to the research laboratory. In this paper we compare two advanced analysis software packages, PDQuest and Progenesis. Their evaluation is based on quantitative tests at three different levels of standard 2-DE analysis: spot detection, gel matching and spot quantitation. As test materials we use three gel sets previously used in a similar comparison of Z3 and Melanie, and three sets of gels from our own research. It was observed that the quality of the test gels critically influences the spot detection and gel matching results. Both packages were sensitive to the parameter or filter settings with respect to the tendency of finding true positive and false positive spots. Quantitation results were very accurate for both analysis software packages. [source]

Measuring and interpreting genetic structure to minimize the genetic risks of translocations

M S. Johnson
Genetic subdivision of a species indicates the potential for local adaptation, and the genetic differences among populations are a key component of genetic diversity. Molecular genetic markers are generally used to assess the extent and pattern of subdivision. These traits provide an abundance of simple genetic markers, and they allow comparisons across studies. However, the connection of molecular genetic variation to local adaptation and, hence, to possible genetic problems of translocation, is weak. In the extreme case of no genetic subdivision, there is no reason to expect genetic problems with translocation. Where there is deep genetic structure, indicating substantial evolutionary independence of sets of populations, translocations may threaten basic components of genetic diversity. Between these extremes, however, predicting genetic problems of translocations is extremely difficult. The molecular markers used to measure genetic structure indicate where there has been opportunity for local adaptation, but they are not directly related to such adaptation. The relationship of the level of genetic divergence to genetic incompatibilities is very loose, although quantitative tests are scarce. However, studies of reproductive isolation between species illustrate the fundamental inadequacy of using measures of genetic divergence to predict interactions between populations. Although it is tempting to use simple measures as predictors, such use may provide a false sense of scientific rigour. There is no substitute for direct tests for variation in ecologically relevant traits and possible genetic incompatibilities among populations. [source]