EVOLUTION, Issue 7 2007
Christopher R. Herlihy
The mating system of flowering plant populations evolves through selection on genetically based phenotypic variation in floral traits. The physical separation of anthers and stigmas within flowers (herkogamy) is expected to be an important target of selection to limit self-fertilization. We investigated the pattern of phenotypic and genetic variation in herkogamy and its effect of self-fertilization in a broad sample of natural populations of Aquilegia canadensis, a species that is highly selfing despite strong inbreeding depression. Within natural populations, plants exhibit substantial phenotypic variation in herkogamy caused primarily by variation in pistil length rather than stamen length. Compared to other floral traits, herkogamy is much more variable and a greater proportion of variation is distributed among rather than within individuals. We tested for a genetic component of this marked phenotypic variation by growing naturally pollinated seed families from five populations in a common greenhouse environment. For three populations, we detected a significant variation in herkogamy among families, and a positive regression between parental herkogamy measured in the field and progeny herkogamy in the greenhouse, suggesting that there is often genetic variation in herkogamy within natural populations. We estimated levels of self-fertilization for groups of flowers that differed in herkogamy and show that, as expected, herkogamy was associated with reduced selfing in 13 of 19 populations. In six of these populations, we performed floral emasculations to show that this decrease in selfing is due to decreased autogamy (within-flower selfing), the mode of selfing that herkogamy should most directly influence. Taken together, these results suggest that increased herkogamy should be selected to reduce the production of low-quality selfed seed. The combination of high selfing and substantial genetic variation for herkogamy in A. canadensis is enigmatic, and reconciling this observation will require a more integrated analysis of how herkogamy influences not only self-fertilization, but also patterns of outcross pollen import and export. [source]

WHY DOES A TRAIT EVOLVE MULTIPLE TIMES WITHIN A CLADE?

EVOLUTION, Issue 1 2006
REPEATED EVOLUTION OF SNAKELINE BODY FORM IN SQUAMATE REPTILES
Abstract Why does a trait evolve repeatedly within a clade? When examining the evolution of a trait, evolutionary biologists typically focus on the selective advantages it may confer and the genetic and developmental mechanisms that allow it to vary. Although these factors may be necessary to explain why a trait evolves in a particular instance, they may not be sufficient to explain phylogenetic patterns of repeated evolution or conservatism. Instead, other factors may also be important, such as biogeography and competitive interactions. In squamate reptiles (lizards and snakes) a dramatic transition in body form has occurred repeatedly, from a fully limbed, lizardlike body form to a limbreduced, elongate, snakelike body form. We analyze this trait in a phylogenetic and biogeographic context to address why this transition occurred so frequently. We included 261 species for which morphometric data and molecular phylogenetic information were available. Among the included species, snakelike body form has evolved about 25 times. Most lineages of snakelike squamates belong to one of two ecomorphs, either short-tailed burrowers or long-tailed surface dwellers. The repeated origins of snakelike squamates appear to be associated with the in situ evolution of these two ecomorphs on different continental regions (including multiple origins of the burrowing morph within most continents), with very little dispersal of most limb-reduced lineages between continental regions. Overall, the number of repeated origins of snakelike morphology seems to depend on large-scale biogeographic patterns and community ecology, in addition to more traditional explanations (e.g., selection, development). [source]

AN EXACT FORM OF THE BREEDER'S EQUATION FOR THE EVOLUTION OF A QUANTITATIVE TRAIT UNDER NATURAL SELECTION

EVOLUTION, Issue 11 2005
John S. Heywood
Abstract Starting with the Price equation, I show that the total evolutionary change in mean phenotype that occurs in the presence of fitness variation can be partitioned exactly into five components representing logically distinct processes. One component is the linear response to selection, as represented by the breeder's equation of quantitative genetics, but with heritability defined as the linear regression coefficient of mean offspring phenotype on parent phenotype. The other components are identified as constitutive transmission bias, two types of induced transmission bias, and a spurious response to selection caused by a covariance between parental fitness and offspring phenotype that cannot be predicted from parental phenotypes. The partitioning can be accomplished in two ways, one with heritability measured before (in the absence of) selection, and the other with heritability measured after (in the presence of) selection. Measuring heritability after selection, though unconventional, yields a representation for the linear response to selection that is most consistent with Darwinian evolution by natural selection because the response to selection is determined by the reproductive features of the selected group, not of the parent population as a whole. The analysis of an explicitly Mendelian model shows that the relative contributions of the five terms to the total evolutionary change depends on the level of organization (gene, individual, or mated pair) at which the parent population is divided into phenotypes, with each frame of reference providing unique insight. It is shown that all five components of phenotypic evolution will generally have nonzero values as a result of various combinations of the normal features of Mendelian populations, including biparental sex, allelic dominance, inbreeding, epistasis, linkage disequilibrium, and environmental covariances between traits. Additive genetic variance can be a poor predictor of the adaptive response to selection in these models. The narrow-sense heritability s,2A/s,2P should be viewed as an approximation to the offspring-parent linear regression rather than the other way around. [source]

ABDOMINAL PIGMENTATION VARIATION IN DROSOPHILA POLYMORPHA: GEOGRAPHIC VARIATION IN THE TRAIT, AND UNDERLYING PHYLOGEOGRAPHY

EVOLUTION, Issue 5 2005
Jennifer A. Brisson
AbstractDrosophila polymorpha is a widespread species that exhibits abdominal pigmentation variation throughout its range. To gain insight into this variation we combined phenotypic and genotypic data to test a series of nested hypotheses. First, we tested the null hypothesis that geographic variation in pigmentation is due to neutral factors. We used nested clade analysis to examine the distribution of haplotypes from a nuclear and a mitochrondrial locus. Restricted gene flow via isolation by distance, the primary inference of this phylogeographic analysis, was then used to generate and test the hypothesis of increasing average abdominal pigmentation difference with increasing geographic distance. We found no correlation between geographic distance and phenotypic distance. We then tested the hypothesis that pigmentation is affected by environmental differences among localities. We found a significant effect of habitat type on the average abdominal pigmentation phenotype of different localities. Finally, we tested the hypothesis that pigmentation in D. polymorpha is associated with desiccation resistance. We found that dark individuals of both sexes survived significantly longer in a desiccating environment than light individuals. These patterns combined lead us to hypothesize that abdominal pigmentation variation in D. polymorpha is important in mediating the organism's interactions with local ecological factors. [source]

"FLEXIBILITY" AS A TRAIT AND METHODOLOGICAL ISSUES IN SPECIES DIVERSITY VARIATION AMONG ANGIOSPERM FAMILIES

EVOLUTION, Issue 3 2000
Jonathan Silvertown
No abstract is available for this article. [source]

STRAIN, PERSONALITY TRAITS, AND DELINQUENCY: EXTENDING GENERAL STRAIN THEORY

CRIMINOLOGY, Issue 1 2002
ROBERT AGNEW
Although Agnew's (1992) general strain theory (GST) has secured a fair degree of support since its introduction, researchers have had trouble explaining why some individuals are more likely than others to react to strain with delinquency. This study uses data from the National Survey of Children to address this issue. Drawing on Agnew (1997) and the psychological research on personality traits, it is predicted that juveniles high in negative emotionality and low in constraint will be more likely to react to strain with delinquency. Data support this prediction. [source]

RELATIVE ROLE OF GENETIC DETERMINATION AND PLASTIC RESPONSE DURING ONTOGENY FOR SHELL-SHAPE TRAITS SUBJECTED TO DIVERSIFYING SELECTION

EVOLUTION, Issue 5 2009
Paula Conde-Padín
We studied the relative role of genetic determination versus plastic response for traits involved in ecological adaptation of two ecotypes of Littorina saxatilis living at different shore levels. To investigate the magnitude of the plastic response across ontogeny, we compared morphological data from individuals grown in the laboratory and taken from the wild at three developmental stages: shelled embryos, juveniles, and adults. The results indicate that most shell shape variation (72,99%) in adaptive traits (globosity and aperture of the shell) is explained by the ecotype irrespective of the growth environment, suggesting that direct genetic determination is the main factor responsible for the process of adaptation in the wild. There was a tendency for the contribution of plasticity to increase over ontogeny but, in general, the direction of the plastic response did not suggest that this was adaptive. [source]

WATER STRESS ALTERS THE GENETIC ARCHITECTURE OF FUNCTIONAL TRAITS ASSOCIATED WITH DROUGHT ADAPTATION IN AVENA BARBATA

EVOLUTION, Issue 3 2009
Mark E. Sherrard
Environmental stress can alter genetic variation and covariation underlying functional traits, and thus affect adaptive evolution in response to natural selection. However, the genetic basis of functional traits is rarely examined in contrasting resource environments, and consequently, there is no consensus regarding whether environmental stress constrains or facilitates adaptive evolution. We tested whether resource availability affects genetic variation for and covariation among seven physiological traits and seven morphological/performance traits by growing the annual grass Avena barbata in dry and well-watered treatments. We found that differences in the overall genetic variance,covariance (G) matrix between environments were driven by physiological traits rather than morphology and performance traits. More physiological traits were heritable in the dry treatment than the well-watered treatment and many of the genetic correlations among physiological traits were environment dependent. In contrast, genetic variation and covariation among the morphological and performance traits did not differ across treatments. Furthermore, genetic correlations between physiology and performance were stronger in the dry treatment, which contributed to differences in the overall G -matrix. Our results therefore suggest that physiological adaptation would be constrained by low heritable variation in resource-rich environments, but facilitated by higher heritable variation and stronger genetic correlations with performance traits in resource-poor environments. [source]

PLASTICITY IN REPRODUCTIVE PHENOTYPES REVEALS STATUS-SPECIFIC CORRELATIONS BETWEEN BEHAVIORAL, MORPHOLOGICAL, AND PHYSIOLOGICAL SEXUAL TRAITS

EVOLUTION, Issue 5 2008
Charlie K. Cornwallis
Reproductive success is determined by a complex interplay between multiple sexual traits that promote mate acquisition and, following copulation, provide control over paternity. The intensity of sexual competition that individuals experience often fluctuates, and here we investigate how this influences the expression of reproductive traits and their relationships. We show in the fowl, Gallus gallus, that males of different social status, which experience different intensities of sexual competition, before and after copulation, have different reproductive phenotypes. Dominant males are more vigilant, feed less, and have larger sexual ornaments than subordinate males. Experimentally manipulating social status revealed that these differences were phenotypically plastic, indicating multiple sexual traits were dependent on the social environment. We integrated these data with previous published findings on changes in sperm numbers and velocity to show that relationships between traits were different for males when they were dominant and when they were subordinate. Furthermore, when males switched status a complex array of negative and positive correlations between the degree traits changed was observed. Our results suggest that variation in the intensity of sexual competition generates reversible plasticity in reproductive phenotypes and that relationships between sexual traits may be variable and influence the evolution of reproductive strategies. [source]

ADAPTIVE POPULATION DIFFERENTIATION IN PHENOLOGY ACROSS A LATITUDINAL GRADIENT IN EUROPEAN ASPEN (POPULUS TREMULA, L.): A COMPARISON OF NEUTRAL MARKERS, CANDIDATE GENES AND PHENOTYPIC TRAITS

EVOLUTION, Issue 12 2007
David Hall
A correct timing of growth cessation and dormancy induction represents a critical ecological and evolutionary trade-off between survival and growth in most forest trees (Rehfeldt et al. 1999; Horvath et al. 2003; Howe et al. 2003). We have studied the deciduous tree European Aspen (Populus tremula) across a latitudinal gradient and compared genetic differentiation in phenology traits with molecular markers. Trees from 12 different areas covering 10 latitudinal degrees were cloned and planted in two common gardens. Several phenology traits showed strong genetic differentiation and clinal variation across the latitudinal gradient, with QST values generally exceeding 0.5. This is in stark contrast to genetic differentiation at several classes of genetic markers (18 neutral SSRs, 7 SSRs located close to phenology candidate genes and 50 SNPs from five phenology candidate genes) that all showed FST values around 0.015. We thus find strong evidence for adaptive divergence in phenology traits across the latitudinal gradient. However, the strong population structure seen at the quantitative traits is not reflected in underlying candidate genes. This result fit theoretical expectations that suggest that genetic differentiation at candidate loci is better described by FST at neutral loci rather than by QST at the quantitative traits themselves. [source]

EPISTASIS AND DOMINANCE: EVIDENCE FOR DIFFERENTIAL EFFECTS IN LIFE-HISTORY VERSUS MORPHOLOGICAL TRAITS

EVOLUTION, Issue 10 2006
Derek A. Roff
Abstract Dominance and epistatic effects are predicted to be larger in life-history than in morphological traits. We test these predictions using published results from line cross analyses. We find that dominance is found in more than 95% of traits, regardless of the type of trait, but that the magnitude of the effect in relation to the additive effect is much greater in life-history than in morphological traits. Epistatic effects were detected more often in life-history than in morphological traits (79% and 67%, respectively). We also test for a difference in the magnitude of the effects by comparing the ratio of the nonadditive components separately to the additive component. For both dominance and epistatic components, the ratio of the nonadditive component to additive effects in life-history traits is approximately twice as large as that for morphological traits. [source]

GEOGRAPHIC VARIATION OF GENETIC AND BEHAVIORAL TRAITS IN NORTHERN AND SOUTHERN TÚNGARA FROGS

EVOLUTION, Issue 8 2006
Heike Pröhl
Abstract We use a combination of microsatellite marker analysis and mate-choice behavior experiments to assess patterns of reproductive isolation of the túngara frog Physalaemus pustulosus along a 550-km transect of 25 populations in Costa Rica and Panama. Earlier studies using allozymes and mitochondrial DNA defined two genetic groups of túngara frogs, one ranging from Mexico to northern Costa Rica (northern group), the second ranging from Panama to northern South America (southern group). Our more fine-scale survey also shows that the northern and southern túngara frogs are genetically different and geographically separated by a gap in the distribution in central Pacific Costa Rica. Genetic differences among populations are highly correlated with geographic distances. Temporal call parameters differed among populations as well as between genetic groups. Differences in calls were explained better by geographic distance than by genetic distance. Phonotaxis experiments showed that females preferred calls of males from their own populations over calls of males from other populations in about two-thirds to three-fourths of the contrasts tested. In mating experiments, females and males from the same group and females from the north with males from the south produced nests and tadpoles. In contrast, females from the south did not produce nests or tadpoles with males from the north. Thus, northern and southern túngara frogs have diverged both genetically and bioacoustically. There is evidence for some prezygotic isolation due to differences in mate recognition and fertilization success, but such isolation is hardly complete. Our results support the general observation that significant differences in sexual signals are often not correlated with strong genetic differentiation. [source]

MULTILOCUS GENETICS AND THE COEVOLUTION OF QUANTITATIVE TRAITS

EVOLUTION, Issue 7 2006
Michael Kopp
Abstract We develop and analyze an explicit multilocus genetic model of coevolution. We assume that interactions between two species (mutualists, competitors, or victim and exploiter) are mediated by a pair of additive quantitative traits that are also subject to direct stabilizing selection toward intermediate optima. Using a weak-selection approximation, we derive analytical results for a symmetric case with equal locus effects and no mutation, and we complement these results by numerical simulations of more general cases. We show that mutualistic and competitive interactions always result in coevolution toward a stable equilibrium with no more than one polymorphic locus per species. Victimexploiter interactions can lead to different dynamic regimes including evolution toward stable equilibria, cycles, and chaos. At equilibrium, the victim is often characterized by a very large genetic variance, whereas the exploiter is polymorphic in no more than one locus. Compared to related one-locus or quantitative genetic models, the multilocus model exhibits two major new properties. First, the equilibrium structure is considerably more complex. We derive detailed conditions for the existence and stability of various classes of equilibria and demonstrate the possibility of multiple simultaneously stable states. Second, the genetic variances change dynamically, which in turn significantly affects the dynamics of the mean trait values. In particular, the dynamics tend to be destabilized by an increase in the number of loci. [source]

THE PHENOTYPIC VARIANCE WITHIN PLASTIC TRAITS UNDER MIGRATION-MUTATION-SELECTION BALANCE

EVOLUTION, Issue 6 2006
Xu-Sheng Zhang
Abstract How phenotypic variances of quantitative traits are influenced by the heterogeneity in environment is an important problem in evolutionary biology. In this study, both genetic and environmental variances in a plastic trait under migration-mutation-stabilizing selection are investigated. For this, a linear reaction norm is used to approximate the mapping from genotype to phenotype, and a population of clonal inheritance is assumed to live in a habitat consisting of many patches in which environmental conditions vary among patches and generations. The life cycle is assumed to be selection-reproduction-mutation-migration. Analysis shows that phenotypic plasticity is adaptive if correlations between the optimal phenotype and environment have become established in both space and/or time, and it is thus possible to maintain environmental variance (VE) in the plastic trait. Under the special situation of no mutation but maximum migration such that separate patches form an effective single-site habitat, the genotype that maximizes the geometric mean fitness will come to fixation and thus genetic variance (VG) cannot be maintained. With mutation and/or restricted migration, VG can be maintained and it increases with mutation rate but decreases with migration rate; whereas VE is little affected by them. Temporal variation in environmental quality increases VG while its spatial variance decreases VG. Variation in environmental conditions may decrease the environmental variance in the plastic trait. [source]

ADAPTIVE CHANGE IN THE RESOURCE-EXPLOITATION TRAITS OF A GENERALIST CONSUMER: THE CEOLUTION AND COEXISTENCE OF GENERALISTS AND SPECIALISTS

EVOLUTION, Issue 3 2006
Peter A. Abrams
Abstract Mathematical models of consumer-resource systems are used to explore the evolution of traits related to resource acquisition in a generalist consumer species that is capable of exploiting two resources. The analysis focuses on whether evolution of traits determining the capture rates of two resources by a consumer species produce one generalist, two specialists, or all three types, when all types are characterized by a common fitness function. In systems with a stable equilibrium, evolution produces one generalist or two specialists, depending on the second derivative of the trade-off relationship. When there are sustained population fluctuations, the nature of the trade-off between the consumer's capture rates of the two resources still plays a key role in determining the evolutionary outcome. If the trade-off is described by a choice variable between zero and one that is raised to a power n, polymorphic states are possible when n > 1, which implies a positive second derivative of the curve. These states are either dimorphism, with two relatively specialized consumer types, or trimorphism, with a single generalist type and two specialists. Both endogenously driven consumer-resource cycles, and fluctuations driven by an environmental variable affecting resource growth are considered. Trimorphic evolutionary outcomes are relatively common in the case of endogenous cycles. In contrast to a previous study, these trimorphisms can often evolve even when new lineages are constrained to have phenotypes very similar to existing lineages. Exogenous cycles driven by environmental variation in resource growth rates appear to be much less likely to produce a mixture of generalists and specialists than are endogenous consumer-resource cycles. [source]

THE COEVOLUTIONARY DYNAMICS OF ANTAGONISTIC INTERACTIONS MEDIATED BY QUANTITATIVE TRAITS WITH EVOLVING VARIANCES

EVOLUTION, Issue 10 2005
Scott L. Nuismer
Abstract Quantitative traits frequently mediate coevolutionary interactions between predator and prey or parasite and host. Previous efforts to understand and predict the coevolutionary dynamics of these interactions have generally assumed that standing genetic variation is fixed or absent altogether. We develop a genetically explicit model of coevolution that bridges the gap between these approaches by allowing genetic variation itself to evolve. Analysis of this model shows that the evolution of genetic variance has improtant consequences for the dyanmics and outcome of coevolution. Of particular importance is our demonstration that coevolutionary cycles can emerge in the absence of stabilizing selection, and outcome not possible in previous models of coevolution mediated by quantitative traits. whether coevolutionary cycles evolve depends upon the strength of selection, the number of loci, and the rate of mutation in each of the interacting species. Our results also generate novel predictions for the expected sign and magnitude of linkage disequilibria in each species. [source]

STATISTICAL ANALYSIS OF DIVERSIFICATION WITH SPECIES TRAITS

EVOLUTION, Issue 1 2005
Emmanuel Paradis
Abstract Testing whether some species traits have a significant effect on diversification rates is central in the assessment of macroevolutionary theories. However, we still lack a powerful method to tackle this objective. I present a new method for the statistical analysis of diversification with species traits. The required data are observations of the traits on recent species, the phylogenetic tree of these species, and reconstructions of ancestral values of the traits. Several traits, either continuous or discrete, and in some cases their interactions, can be analyzed simultaneously. The parameters are estimated by the method of maximum likelihood. The statistical significance of the effects in a model can be tested with likelihood ratio tests. A simulation study showed that past random extinction events do not affect the Type I error rate of the tests, whereas statistical power is decreased, though some power is still kept if the effect of the simulated trait on speciation is strong. The use of the method is illustrated by the analysis of published data on primates. The analysis of these data showed that the apparent overall positive relationship between body mass and species diversity is actually an artifact due to a clade-specific effect. Within each clade the effect of body mass on speciation rate was in fact negative. The present method allows to take both effects (clade and body mass) into account simultaneously. [source]

MULTIVARIATE QUANTITATIVE GENETICS AND THE LEK PARADOX: GENETIC VARIANCE IN MALE SEXUALLY SELECTED TRAITS OF DROSOPHILA SERRATA UNDER FIELD CONDITIONS

EVOLUTION, Issue 12 2004
Emma Hine
Abstract Single male sexually selected traits have been found to exhibit substantial genetic variance, even though natural and sexual selection are predicted to deplete genetic variance in these traits. We tested whether genetic variance in multiple male display traits of Drosophila serrata was maintained under field conditions. A breeding design involving 300 field-reared males and their laboratory-reared offspring allowed the estimation of the genetic variance-covariance matrix for six male cuticular hydrocarbons (CHCs) under field conditions. Despite individual CHCs displaying substantial genetic variance under field conditions, the vast majority of genetic variance in CHCs was not closely associated with the direction of sexual selection measured on field phenotypes. Relative concentrations of three CHCs correlated positively with body size in the field, but not under laboratory conditions, suggesting condition-dependent expression of CHCs under field conditions. Therefore condition dependence may not maintain genetic variance in preferred combinations of male CHCs under field conditions, suggesting that the large mutational target supplied by the evolution of condition dependence may not provide a solution to the lek paradox in this species. Sustained sexual selection may be adequate to deplete genetic variance in the direction of selection, perhaps as a consequence of the low rate of favorable mutations expected in multiple trait systems. [source]

SEXUAL SELECTION DRIVES RAPID DIVERGENCE IN BOWERBIRD DISPLAY TRAITS

EVOLUTION, Issue 1 2000
J. Albert C. Uy
Abstract., Sexual selection driving display trait divergence has been suggested as a cause of rapid speciation, but there is limited supporting evidence for this from natural populations. Where speciation by sexual selection has occurred in newly diverged populations, we expect that there will be significant differences in female preferences and corresponding male display traits in the absence of substantial genetic and other morphological differentiation. Two allopatric populations of the Vogelkop bowerbird, Amblyornis inornatus, show large, qualitative differences in a suite of display traits including bower structure and decorations. We experimentally demonstrate distinct male decoration color preferences within each population, provide direct evidence of female preferences for divergent decoration and bower traits in the population with more elaborate display, and show that there is minimal genetic differentiation between these populations. These results support the speciation by sexual selection hypothesis and are most consistent with the hypothesis that changes in male display have been driven by divergent female choice. [source]

EFFECT OF PACKAGING AND STORAGE TIME ON BEEF QUALITATIVE AND MICROBIAL TRAITS

JOURNAL OF FOOD QUALITY, Issue 2010
MARIA D'AGATA
ABSTRACT The effect of polyvinyl chloride packaging (PP), vacuum packaging (VP) and modified atmosphere packaging (MAP) (60% O2, 30% CO2, 10% N2) on some quality parameters and microbiological profile of beef was studied. Longissimus dorsi samples were examined at 7-day intervals during storage at 4C ± 2C, until 21 days. pH of PP beef increased during storage, whereas in VP and MAP beef remained stable. Superficial color darkened for PP samples, remaining stable until 7 and 21 days for VP and MAP samples, respectively; internal color was not significantly influenced by either storage time and packaging methods. Water-holding capacity was not affected by packaging methods, increasing from 7 to 21 days. VP showed lower lipid oxidation than MAP until 21 days and than PP until 14 days. Total mesophilic counts reached the threshold of 107 ufc/g after 7 days in PP and after 14 and 21 days in MAP and VP, respectively. PRACTICAL APPLICATIONS The results of this study confirmed that meat packaged in polyvinyl chloride packaging (PP) must be stored for few days to not fall into pH, color and microbiological alterations; meat packaged in modified atmosphere packaging (MAP), even though maintained appreciable superficial colorimetric characteristics, showed a high microbiological growth from 14 days of storage; meat vacuum packaged (VP), although the worst colorimetric appearance, showed the best keeping properties in terms of microbiological profile and lipid oxidation lower than MAP until 21 days of storage. Nevertheless, the fact that the internal color of meat is similar among different packaging systems, independently from time of storage, may suggest that VP system may be useful for prolonged storage of big pieces of meat. [source]

KERNEL MORPHOLOGY VARIATION IN A POPULATION DERIVED FROM A SOFT BY HARD WHEAT CROSS AND ASSOCIATIONS WITH END-USE QUALITY TRAITS,

JOURNAL OF FOOD QUALITY, Issue 4 2000
CHRISTINE J. BERGMAN
ABSTRACT Physical attributes, including kernel morphology, are used to grade wheat, and indicate wheat milling and baking quality (MBQ). Using a recombinant inbred population derived from a soft by hard wheat cross, this study quantified kernel traits' sources of variation, studied their heritability, and relationships between morphological and MBQ traits. Transgressive segregation occurred for all traits. Thousand-kernel weight (TKW) and kernel texture (NIR-T) were primarily [source]

PREFERENCE FOR ONE OF TWO IDENTICAL STIMULI: EXPECTATIONS, EXPLICIT INSTRUCTIONS AND PERSONAL TRAITS

JOURNAL OF SENSORY STUDIES, Issue 2010
KATHRYN W. CHAPMAN
ABSTRACT Most consumers, given two identical food samples, express a preference for one, rather than choosing a no-preference option. The stability and potential causes of this seemingly irrational preference were examined across three trials under different conditions, specifically, when the first test pair was identical or different, and when participants were explicitly told that the pairs would often be identical. Choice of no preference typically increased from the first to second trial, especially for groups who saw a pair of different samples on the first trial. The explicit instruction that samples might be the same failed to reduce expressing a preference on the initial trial although it had some effect on later trials. Analysis, by individuals, of sequences of preference or no-preference responses across trials support independence of sequential responses and argue against stable personal traits as a predictor of preference choice. PRACTICAL APPLICATIONS More research needs to be done to understand the origins and operation of biases in preference tests. When tested under conditions in which the samples differ only slightly, participants tend to avoid the no-preference option. This is potentially important when interpreting the results of preference tests and assigning practical significance to their outcomes. Also, single trial testing may produce somewhat different results from multi-trial testing, the latter allowing for examination of effects of variation in recent experience. [source]

UNDERSTANDING THE IMPACT OF PERSONALITY TRAITS ON INDIVIDUALS' TURNOVER DECISIONS: A META-ANALYTIC PATH MODEL

PERSONNEL PSYCHOLOGY, Issue 2 2008
RYAN D. ZIMMERMAN
Historically, researchers have sought to identify environmental causes of employee turnover. This paradigm has led to the underemphasis of individual differences as being an important cause of individuals' turnover decisions. The results of the meta-analysis show that personality traits do have an impact on individuals' turnover intentions and behaviors. The trait of Emotional Stability best predicted (negatively) employees' intentions to quit, whereas the traits of Conscientiousness and Agreeableness best predicted (negatively) actual turnover decisions. A theoretically developed path model showed important direct effects from personality to intentions to quit and turnover behaviors that were not captured through job satisfaction or job performance. These direct effects indicate that employees who are low on Emotional Stability may intend to quit for reasons other than dissatisfaction with their jobs or not being able to perform their jobs well. The direct effects on turnover suggest that individuals who are low on Agreeableness or high on Openness may engage in unplanned quitting. Personality traits had stronger relationships with outcomes than did non-self-report measures of job complexity/job characteristics. [source]

AN EXPLORATION OF MEMBER ROLES AS A MULTILEVEL LINKING MECHANISM FOR INDIVIDUAL TRAITS AND TEAM OUTCOMES

PERSONNEL PSYCHOLOGY, Issue 2 2005
GREG L. STEWART
We use data from 220 individuals in 45 teams to examine team member roles as a cross-level linking mechanism between personality traits and team-level outcomes. At the individual level, peer ratings of task role behavior relate positively with Conscientiousness and negatively with Neuroticism and Extraversion. Peer ratings of social role behavior relate positively with Agreeableness and negatively with Openness to Experience. At the team level, a composition process of aggregation operates such that the mean for social roles corresponds with social cohesion. Compilation processes of aggregation also occur, as the variance of social roles corresponds negatively with task performance, and the variance of task roles corresponds negatively with cohesion. Skew of the distribution for social roles within each team,a measure of critical mass of members individually enacting the role,also correlates with social cohesion. [source]

ENDOGENOUS BUSINESS CYCLES: THE INFLUENCE OF CHARACTER TRAITS,

AUSTRALIAN ECONOMIC PAPERS, Issue 1 2009
FUJIO TAKATA
This article deals with how business cycles can occur, in light of character traits which influence individual behaviour in an economy. We assume an overlapping generations model in which every consumer has identical instantaneous utility which is additively separable with respect to time. The parameters of utility here include character traits which influence the choice between consumption and savings. In this situation, young individuals choose between current consumption and current savings which lead to future consumption in their old age. Individual character traits, which appear both in the shape of utility functions and in evaluations about utility in the future, affect these choices. And since these choices determine savings, individual character traits can eventually determine how our economy moves. Focusing on the relationship between individual character traits and savings formation, we demonstrate that endogenous business cycles with two periods can occur, in an economy comprised of individuals who opt for current consumption and who are careless in relation to future events, like Aesopian grasshoppers, and in other cases they do not. [source]

AUTONOMY AND AUTHENTICITY OF ENHANCED PERSONALITY TRAITS

BIOETHICS, Issue 6 2009
JAN CHRISTOPH BUBLITZ
ABSTRACT There is concern that the use of neuroenhancements to alter character traits undermines consumer's authenticity. But the meaning, scope and value of authenticity remain vague. However, the majority of contemporary autonomy accounts ground individual autonomy on a notion of authenticity. So if neuroenhancements diminish an agent's authenticity, they may undermine his autonomy. This paper clarifies the relation between autonomy, authenticity and possible threats by neuroenhancements. We present six neuroenhancement scenarios and analyse how autonomy accounts evaluate them. Some cases are considered differently by criminal courts; we demonstrate where academic autonomy theories and legal reasoning diverge and ascertain whether courts should reconsider their concept of autonomy. We argue that authenticity is not an appropriate condition for autonomy and that new enhancement technologies pose no unique threats to personal autonomy. [source]

Trait-based ecological risk assessment (TERA): The new frontier?

INTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT, Issue 1 2008
Donald J Baird
Traits describe the physical characteristics, ecological niche, and functional role of species within ecosystems, and trait-based approaches are now being introduced into the field of Ecological Risk Assessment (ERA). The costs and benefits arising from the adoption of these approaches in the assessment of risks from toxic substances are described, and the path forward for this new frontier in risk assessment science is presented. In particular, the necessity for more open collaboration and web-based data-sharing to facilitate the development of these exciting new tools is stressed, and the role of scientific organizations such as SETAC as promoters of this ambitious program is highlighted. [source]

The impact of anxiety on conversion from mild cognitive impairment to Alzheimer's disease

INTERNATIONAL JOURNAL OF GERIATRIC PSYCHIATRY, Issue 12 2009
Deidre J. Devier
Abstract Objective To compare state and trait anxiety in mild cognitive impairment (MCI) patients and matched control subjects, and to assess the impact of these variables in predicting conversion to Alzheimer's disease. Methods One hundred and forty-eight patients with MCI, broadly defined, were assessed and followed systematically. Baseline predictors for follow-up conversion to AD (entire sample: 39/148 converted to Alzheimer's disease (AD)) included the Spielberger State-Trait Anxiety Inventory (STAI). Results At baseline evaluation, MCI patients had higher levels of state and trait anxiety than controls, with no differences between future AD converters (n,=,39) and non-converters. In age-stratified Cox proportional hazards model analyses, STAI State was not a significant predictor of conversion to AD (STAI State ,30 vs.,>,30 risk ratio, 1.68; 95% CI, 0.75, 3.77; p,=,0.21), but higher Trait scores indicated a lower risk of conversion when STAI State, education, the Folstein Mini-Mental State Examination and HAM-D (depression score) were also included in the model (STAI Trait ,30 vs.,>,30 risk ratio, 0.36; 95% CI, 0.16, 0.82; p,=,0.015). Conclusions In contrast to two other recent studies that showed anxiety predicted cognitive decline or conversion to AD, in this clinic-based sample, state anxiety was not a significant predictor. However, higher Trait anxiety predicted a lower risk of future conversion to AD. Further research with systematic long-term follow-up in larger samples is needed to clarify the role of state and trait anxiety in predicting MCI conversion to AD. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Personality and Self-Regulation: Trait and Information-Processing Perspectives

JOURNAL OF PERSONALITY, Issue 6 2006
Rick H. Hoyle
ABSTRACT This article introduces the special issue of Journal of Personality on personality and self-regulation. The goal of the issue is to illustrate and inspire research that integrates personality and process-oriented accounts of self-regulation. The article begins by discussing the trait perspective on self-regulation,distinguishing between temperament and personality accounts,and the information-processing perspective. Three approaches to integrating these perspectives are then presented. These range from methodological approaches, in which constructs representing the two perspectives are examined in integrated statistical models, to conceptual approaches, in which the two perspectives are unified in a holistic theoretical model of self-regulation. The article concludes with an overview of the special issue contributions, which are organized in four sections: broad, integrative models of personality and self-regulation; models that examine the developmental origins of self-regulation and self-regulatory styles; focused programs of research that concern specific aspects or applications of self-regulation; and strategies for increasing the efficiency and effectiveness of self-regulation. [source]

Single-Nucleotide Polymorphisms in Corticotropin Releasing Hormone Receptor 1 Gene (CRHR1) Are Associated With Quantitative Trait of Event-Related Potential and Alcohol Dependence

ALCOHOLISM, Issue 6 2010
Andrew C. H. Chen
Background:, Endophenotypes reflect more proximal effects of genes than diagnostic categories, hence providing a more powerful strategy in searching for genes involved in complex psychiatric disorders. There is strong evidence suggesting the P3 amplitude of the event-related potential (ERP) as an endophenotype for the risk of alcoholism and other disinhibitory disorders. Recent studies demonstrated a crucial role of corticotropin releasing hormone receptor 1 (CRHR1) in the environmental stress response and ethanol self-administration in animal models. The aim of the present study was to test the potential associations between single-nucleotide polymorphisms (SNPs) in the CRHR1 gene and the quantitative trait, P3 amplitude during the processing of visual target signals in an oddball paradigm, as well as alcohol dependence diagnosis. Methods:, We analyzed a sample from the Collaborative Study on the Genetics of Alcoholism (COGA) comprising 1049 Caucasian subjects from 209 families (including 472 alcohol-dependent individuals). Quantitative transmission disequilibrium test (QTDT) and family-based association test (FBAT) were used to test the association, and false discovery rate (FDR) was applied to correct for multiple comparisons. Results:, Significant associations (p < 0.05) were found between the P3 amplitude and alcohol dependence with multiple SNPs in the CRHR1 gene. Conclusions:, Our results suggest that CRHR1 may be involved in modulating the P3 component of the ERP during information processing and in vulnerability to alcoholism. These findings underscore the utility of electrophysiology and the endophenotype approach in the genetic study of psychiatric disorders. [source]