Showing papers on "Selection (genetic algorithm) published in 1985"

Genotype-environment interaction and the evolution of phenotypic plasticity.

Abstract: Studies of spatial variation in the environment have primarily focused on how genetic variation can be maintained. Many one-locus genetic models have addressed this issue, but, for several reasons, these models are not directly applicable to quantitative (polygenic) traits. One reason is that for continuously varying characters, the evolution of the mean phenotype expressed in different environments (the norm of reaction) is also of interest. Our quantitative genetic models describe the evolution of phenotypic response to the environment, also known as phenotypic plasticity (Gause, 1947), and illustrate how the norm of reaction (Schmalhausen, 1949) can be shaped by selection. These models utilize the statistical relationship which exists between genotype-environment interaction and genetic correlation to describe evolution of the mean phenotype under soft and hard selection in coarse-grained environments. Just as genetic correlations among characters within a single environment can constrain the response to simultaneous selection, so can a genetic correlation between states of a character which are expressed in two environments. Unless the genetic correlation across environments is ± 1, polygenic variation is exhausted, or there is a cost to plasticity, panmictic populations under a bivariate fitness function will eventually attain the optimum mean phenotype for a given character in each environment. However, very high positive or negative correlations can substantially slow the rate of evolution and may produce temporary maladaptation in one environment before the optimum joint phenotype is finally attained. Evolutionary trajectories under hard and soft selection can differ: in hard selection, the environments with the highest initial mean fitness contribute most individuals to the mating pool. In both hard and soft selection, evolution toward the optimum in a rare environment is much slower than it is in a common one. A subdivided population model reveals that migration restriction can facilitate local adaptation. However, unless there is no migration or one of the special cases discussed for panmictic populations holds, no geographical variation in the norm of reaction will be maintained at equilibrium. Implications of these results for the interpretation of spatial patterns of phenotypic variation in natural populations are discussed.

Selecting Software Test Data Using Data Flow Information

Abstract: This paper defines a family of program test data selection criteria derived from data flow analysis techniques similar to those used in compiler optimization It is argued that currently used path selection criteria, which examine only the control flow of a program, are inadequate quate Our procedure associates with each point in a program at which a variable is defined, those points at which the value is used Several test data selection criteria, differing in the type and number of these associations, are defined and compared

Moment-preserving thresolding: A new approach

Abstract: A new approach to automatic threshold selection using the moment-preserving principle is proposed. The threshold values are computed deterministically in such a way that the moments of an input picture is preserved in the output picture. Experimental results show that the approach can be employed to threshold a given picture into meaningful gray-level classes. The approach is described for global thresholding, but it is applicable to local thresholding as well.

An Application of Clustering for Strategic Group Analysis

Abstract: Summary Taxonomies, factor analysis and clustering are discussed as tools to investigate the structure of competitors within an industry (strategic groups'). An example using cluster analysis is presented as one means of operationalizing this concept. Careful definition and selection of the dimensions used to identify the boundaries between strategic groups (their mobility barriers) are particularly crucial in the effective application of analytical tools.

Soft Selection, Hard Selection, Kin Selection, and Group Selection

Abstract: In this paper I illustrate the theoretical relationship among several different models of selection in structured populations, soft selection, hard selection, kin selection, and group selection, by using the covariance formulations ofLi (1967) and Price (1970, 1972) to partition the operation of selection into withinand between-group components. This partitioning ofcovariance can be directly extended from the single-locus population genetic models derived in this paper to the description of selection within and between groups for continuously distributed, quantitative traits of the type presently under investigation i several research programs of kin and group selection. In addition, because of the algebraic relationship between the covariance and the coefficient of linear regression, regression coefficients can be used to evaluate the relative importance of selection within and between groups in these models of subdivided populations. Price (1970, 1972) was the first o apply the covariance approach to the mathematics of group selection but only for \"the limiting case of reproductively isolated groups with no intergroup migration\" (Price 1972, p. 487). Because of this assumption concerning the complete isolation of groups, his major result (eq. [A17] of Price [1972]) did \"not depend upon any assumptions about mechanisms of heredity or anything else of that sort\" (Price 1972, p. 487). I will show that Price's equations for gene-frequency hange represent a special case of a general partitioning of covariance into withinand between-group components and, in addition, that it can be applied to cases with intergroup migration. Furthermore, the algebraic relationship between the covariance and the coefficient of linear regression will be used to illustrate how assumptions concerning hereditary mechanisms are implicit in the covariance formulations. In particular, the equations of Price (1970, 1972) completely describe selection in terms of the change in the mean value of a trait within a generation, but they require a hereditary mechanism in order to predict how much of this within-generation change is transmitted across generations ( ee below and also Arnold and Wade 1984a). The covariance formulation completely describes selection but it does not necessarily describe the response to selection. In the derivation presented below individuals will be assigned character values in such a way that the average value of the character is the

Threshold selection based on a simple image statistic

Abstract: The problem of automatic threshold selection is considered. After a brief review of available techniques, a novel method is proposed. It is based on image statistics which can be computed without histogramming the grey level values of the image. A detailed analysis of the properties of the algorithm is then carried out. The effectiveness of the method is shown on a number of practical examples.

Selection for life span in Drosophila melanogaster.

Abstract: Selection for reproduction at an early or a late age in life was applied to populations of D. melanogaster for 21 to 29 generations, with two experimental treatments of larval density. Populations with high and uncontrolled numbers of competing larvae responded strongly to selection for late-reproduction with the length of adult life increasing by as much as 50 per cent. In this treatment, selection produced true breeding long- and short-lived lines. When populations of developing larvae were held low, however, longevity fluctuated wildly during selection, showing little overall response, as several previous tests of senescence theory have also found. These experiments suggest that life span is either physiologically limited in that environment, or populations are unable to respond because either phenotype/genotype correlations are reversed, or genetic variation is suppressed. The inability of former studies to obtain a response to selection appears to have resulted from the artifactual introduction of strong gene-environment interactions through the use of a competition-free environment.

Breeding crop varieties for stress environments

Abstract: Plant stress is a major limitation to crop yield. The amelioration of crop environments is either impossible or costly. The breeding of crop varieties resistant to environmental stress is the most effective economical means to improve and stabilize yield under conditions of stress. Crop resistance to various environmental stresses is being improved by traditional and costly breeding methods that involve the stability of yield performance over different environments as a major criterion. Recent advances in stress physiology allow embarkation upon breeding programs that employ distinct physiological selection indices for stress tolerance. Using physiological selection indices in breeding work requires the definition of the importance and effectiveness of given physiological attributes under stress conditions, the design of a proper selection scheme within the logistic framework of the breeding program and the development of rapid and effective selection techniques. These requirements, the progress made and ...

The mathematical theory of quantitative genetics.

Abstract: The theory of quantitative genetics bridges the gap between observable statistical properties of a character and the genetic and environmental factors which are thought to determine its expression. This book covers a wide range of genetic topics from Mendelian genetics to selection theory in breeding. It looks at the decomposition of the genotypic value into components representing various types of gene action; estimation of the components of variance and other quantities generated by this decomposition, and stochastic effects of finite population size.

Group selection, altruism, and structured-deme models

Abstract: Group selection is defined as a process by which traits advantageous to the group are favored because of the positive association of individuals exhibiting the traits. In addition, group selection acts to protect this positive association against cheats. This definition, unlike those in current use, incorporates the essential features of the traditional verbal arguments by excluding the effects of individual selection and incorporating the problem of cheating. Kin selection is considered an example of group selection in which the "groups" are associations of relatives and in which special mechanisms, such as individual recognition, maintain the integrity of the associations. The "groups" of group selection are quite different from the trait groups of structured-deme models, so that structured-deme models can be used to demonstrate individual or group selection. By analyzing the models in terms of group neighbors, it has been shown that whenever trait groups are formed at random only individual selection c...

Selection, follow-up, and analysis in the American Cancer Society prospective studies.

Abstract: The organization and selection characteristics of the American Cancer Society's prospective studies are reviewed, and problems connected with the follow-up procedures are discussed. Also included are descriptions of some of the features of analysis in cohort studies.

The selection mutation equation.

Abstract: Fisher's Fundamental Theorem of Natural Selection is extended to the selection mutation model with mutation rates epsilon ij = epsilon i, i.e. depending only on the target gene, by constructing a simple Lyapunov function. For other mutation rates stable limit cycles are possible.

The influence of environmental variation on group and individual selection in a cress.

Abstract: An experimental study of group and individual selection for leaf area under different patterns of environmental variation is presented. This study, which uses the cress Arabidopsis thaliana, demonstrates that group selection can occur in plants. The response to group selection was always in the expected direction, but surprisingly, the response to individual selection was not. Furthermore the interaction between group and individual selection was significant. Individual selection interfered with the response to group selection whether the two forces were acting in concert or were opposed. The effects of the environmental variation treatments were detected mainly as three-way interactions with group and individual selection. Group selection was more effective in environments that interfered with individual selection, as well as in environments that did not interfere with group selection. These results suggest that the ability of a character to respond to group selection, individual selection, or both will depend on a great many factors and that the relative importance of the different levels of selection can only be determined empirically.

Compendium of recurrent selection methods and their application

Abstract: Recurrent selection is a breeding method that has been used for the genetic improvement of germplasm. Although recurrent selection methods were suggested over 40 years ago, there use has not been as extensive as the other classical plant breeding methods. Recurrent selection is used for the improvement of traits inherited in a quantitative manner, and the primary objective of the method is to gradually increase the frequency of favorable alieles and maintain genetic variability for future selection. Different methods of recurrent selection have been suggested, depending on the types of gene action considered important in the inheritance of the traits under selection, relative efficiency of selection, and the complexity of the trait under selection. Most methods of recurrent selection include three phases conducted in a repetitive manner; development of progenies, evaluation of progenies in replicated trials, and recombination of the superior progenies based on the evaluation trials. Most information sugge...

Selection for iteroparity in a variable environment.

Abstract: Charnov and Schaffer's (1973) model for annual versus perennial reproduction in plants has been extended to include both density dependence and environmental variability. Two models of density dependence were investigated, and the method of invasibility analysis (Turelli 1978) was used to study their behavior. The results are interpreted in terms of bet-hedging theory; it is shown that the criticisms of this interpretation by Hastings and Caswell (1979) are unfounded.

Selection on bill characters in a population of darwin's finches: geospiza conirostris on isla genovesa, galápagos.

Abstract: Lande and Arnold's (1983) technique for measuring selection on correlated quantitative traits was used to identify the targets of selection and to reveal the direction of selection on three bill dimensions, during different stages of the life cycle in a population of Darwin's finches, Geospiza conirostris, on Isla Genovesa, Galapagos. There was a tendency towards disruptive selection during dry conditions, arising from differential survival. In terms of longevity and breeding success of females, the direction of selection was to increase bill length. For males competing for territories, selection acted to increase bill depth and bill length. The effects of male-male interactions were separated from those of female choice. Male-male interactions selected for deep and long bills, whereas females chose their mates on the basis of a male's territory position and plumage coloration. The results reveal three factors constraining changes in bill dimensions: a tendency for the mean of a dimension to shift in one direction is counteracted by selection in the opposite direction on 1) another, positively correlated, bill dimension, 2) the same dimension in the other sex, and 3) the same dimension at another stage of the life cycle. If these factors are overcome by strong directional selection at one stage of the life cycle and relaxation at another, there can be an evolutionary response because the bill dimensions in this population are known to be heritable. The results complement those found in studies of G. fortis on another island and strengthen the view that these populations of Darwin's finches are frequently subjected to natural selection.