Variance For Characters Research Articles

Fruiting and Fitness in Crataeugs Monogyna: The Effects of Frugivores and Seed Predators

The factors influencing variation in the rates of loss of fruit from Crataegus monogyna individuals are examined for one population near Liverpool, England. In contrast to the expectations from optimal foraging theory, there appears to be no simple relationship between fruit abundance and the activities of frugivores. A number of factors may influence rates of fruit loss including: bush width; inter-bush distance; the damage caused by seed predators. Because of correlation between fruiting characters there is a weak relationship between numbers of fruit and their consumption by frugivores. Fruit on larger, more fecund bushes also suffer high rates of seed predation. The outcome of opposing selective influences may be that fruit on smaller bushes have higher fitness. Fluctuations in frugivore and predator abundance may help maintain the observed high variance in fruit characters.

Efficient Estimators for the verianoe of a Finite Population

AbstractFor the estimation of finite population variance of a character, DAS and TRIPATHI (1978) proposed some efficient estimators when population mean of variance of some other character (associated with main character) is known. We propose here some estimators for population variance using same information and compare with those given by DAS and TRIPATHI (1978). Some examples are given for illustration.

Quantitative characters under assortative mating: Gametic model

The gametic model introduced by Gimelfarb (1982, Theor. Pop. Biol. 22, 324–366) is applied to investigating the dynamics, represented in the model by a second-order recurrence equation, the the variance of sex-independent and sex-controlled characters under assortative mating. It is shown that, for any additive character, there always exists a unique equilibrium for the variance, which is stable. Dynamical properties of the variance under positive and negative matings are considered, and numerical evaluations of the equilibrium values as well as of the dynamical changes of the variance are presented. Comparisons with results from a biological experiment are made.

QUANTITATIVE GENETIC ANALYSIS OF TEMPERATURE REGULATION IN MUS MUSCULUS. II. DIALLEL ANALYSIS OF INDIVIDUAL TRAITS.

Because the adaptation of animals to the physical environment typically involves simultaneous modification of several characters, studies of complexes of traits should yield more information about the nature of evolutionary change than separate analyses of single traits. Temperature regulation in small mammals is a convenient model system for such investigations because it is accomplished with a well defined set of traits that allow adaptation to a specific environmental variable. Mechanisms exploited by homeotherms for cold weather survival have been described, and several reviews are available (Hart, 1957, 1971; Irving, 1964). In rodents these mechanisms include morphological, behavioral, and physiological characters influenced by variation at multiple loci and suitable for quantitative genetic analysis. In the application of quantitative genetic methods to evolutionary questions, we assume that description of the genetic influences on traits in randomly mating populations near genetic equilibria reflect their importance to the fitness of individuals. Traits that have been closely and consistently associated with fitness will have been subjected to natural selection in the past and, as a result, are expected to exhibit low heritabilities (Lemer, 1954; Fisher, 1958; Falconer, 1981). Potential exceptions to this rule are traits selected for intermediate optima. Remaining genetic variance in characters closely associated with fitness will be largely non-

THE LIMITS TO LIFE HISTORY EVOLUTION IN DAPHNIA.

Although evolutionary ecologists have studied variation within and between populations for some time, the variation reported in nearly all ecological investigations is restricted to the phenotypic level. In many cases this type of information is entirely adequate for solving ecological problems. However, because the phenotypic variance for characters can often be largely or even entirely attributed to environmental effects, a comparison of phenotypes is often an inappropriate evolutionary analysis. The concoction of evolutionary explanations from ecological data with little regard for genetic constraints has attracted some rather severe criticism (Gould and Lewontin, 1979) that is well supported on theoretical grounds (Lande, 1979, 1980, 1982; Templeton, 1981). If we are to understand the adaptiveness of morphological and behavioral characters and their potential for evolutionary change, it is imperative that we begin to evaluate the relative contribution of genetic effects to the variance of characters as well as the mechanistic and quantitative relations of characters to fitness and to each other via linkage disequilibrium and pleiotropy. Data of this type have been slow in coming for natural populations (Istock et al., 1976; Derr, 1980; Giesel and Zettler, 1980; Arnold, 1981; Dingle and Hegmann, 1982) and, for practical reasons, may be nearly unattainable for many of the organisms upon which evolutionary ecologists have focused research. One organism that is particularly suitable for genetic as well as ecological analysis and that may help shed some light on the limits to phenotypic evolution is the planktonic cladoceran, Daphnia pulex. This small (1-3 mm) crustacean reproduces by a non-recombinational mode of parthenogenesis during most of the year. Daphnia populations are often annually initiated by resting eggs produced sexually in previous years, and almost always consist of a multitude of genetically unique clones that differentially expand depending upon their fitness attributes. As parthenogenesis may proceed without disturbance for > 10-25 generations and generation times are short (1020 days), an excellent opportunity is provided for examining the operation of selection on a group of constant genotypes. Here I examine the genetic basis of fitness characters in a Daphnia pulex population inhabiting an intermittent wood-

The joint evolution of seed dormancy and flowering time in annual plants living in variable environments

In annual plants, both seed germination (as opposed to dormancy) and delayed flowering are assumed to confer both greater and more variable reproduction. With this assumption, a simple model of these two characters, together with a reparameterization of survival and reproductive rates and a general approximation, leads to several predictions based on maximizing geometric growth rates. Each character optimum is a ratio of mean to variance of future reproduction, and the two optimums are interdependent, with compensation by one favored if the other changes. Optimal character variances, possible with prediction of future reproduction, are roughly squared correlations of characters with future reproduction, divided by variances of future reproduction. The optimal mean of each character is more sensitive to the other character's variance than to its own variance, and the optimal variance of each character is more sensitive to the other character's mean than to its own mean. Optimal germination is increased with better correlation between flowering time and future reproduction. A diffusion approximation for the single locus, single character genetic analog of the phenotypic model showed fluctuating natural selection to favor, in expectation and under suitable conditions, the allele frequency maximizing the geometric population growth rate. Conditions for a protected polymorphism at a second locus, controlling the other character, show genetic variation at the first locus favors alleles at the second locus adapted to greater environmental variability. Computer simulations check some results, and the general predictions should be relevant for studies of correlated life history characters.

Accuracy and Precision in Anuran Morphometrics: Artifacts of Preservation

Lee,J. C. (Department of Biology, University of Miami, Coral Gables, Florida 33124) 1982. Accuracy and precision in anuran morphometrics: artifacts of preservation. Syst. Zool., 31: 266-281.-Univariate comparisons of twenty morphometric characters of sixty adult Bufo marinus recorded before preservation and six and 14 months after preservation reveal a statistically significant heterogeneity among group means of fourteen characters. After six months in preservative, the means of six of these 14 characters are significantly larger, and eight are significantly smaller, than for the same individuals prior to preservation. After eight. additional months in preservative, the means of five of these 14 characters differ significantly in the opposite direction of that initially detected. Linear regressions and analyses of covariance suggest that over the range of sizes considered here, preservation effects the elevations but not the slopes of the regressions between pairs of morphometric characters. Sexual size dimorphism in six characters is documented for the fresh material; certain of these intersexual differences are reduced or are undetectable in the preserved material, and in one instance a new, marginally significant, difference is apparent after 14 months in preservative. Not all characters are measurable with equal precision, and there is a highly significant rank correlation between precision and inter-individual character variance. Principal component analyses confirm and extend the univariate findings, and discriminant function analysis reveals differences between fresh and preserved specimens of roughly the same magnitude as those commonly used to justify taxonomic decisions. The assumption that preservation induces tolerably little morphological distortion in frogs appears to be substantially violated, but an unknown proportion of among-group character variation may be attributable to measurer bias. [Bufo marinus; univariate analysis; discriminant function analysis; principal component analysis; morphometrics; accuracy; precision.]

Genetics of life history in Drosophila melanogaster. I. Sib analysis of adult females.

A sib analysis of adult life-history characters was performed on about twelve hundred females from a laboratory Drosophila melanogaster population that had been sampled from nature and cultured so as to preserve its genetic variability. The following results were found. There was no detectable trend with age in additive or dominance genetic variances for age-specific fecundity. Environmental variance for age-specific fecundity increased with age. The genetic variance for fecundity characters was primarily additive. The genetic variance for longevity was primarily dominance variance. There were negative genetic correlations between early fecundity and lifespan, as well as between mean egg-laying rate and longevity.

Phylogenetic Differentiation of Cultivated Rice, XXII. Numerical Evaluation of the Indica-Japonica Differentiation

Principal component analysis of the data for 11 characters of 89 cultivars sampled at random from a large collection of Asian origin has reconfirmed the previous assertion by the junior author that the Indica-Japonica diferentiation of rice cultivars is recogni-zable on the basis of character-association patterns, although there is no key character discriminating between the two types. The probability of misclassification by a single character ranged from about 3 percent by the potassium chlorate resistance of seedling to about 40 percent by the length/width ratio of spikelets. Discriminant functions combining 3 or 4 character values gave lower probabilities of misclassification, although there still remained a few intermediate forms having recombined characteristics. The F1 sterility relationships were almost useless for the purpose of classification. About a half of the total character variance among the cultivars was attributable to Indica-Japonica differenti-ation. The normalized genetic identity between the two types was estimated to be 0.62 from data for 28 alleles at 12 Ioci. A great number of genic differences seem to be involved in the Indica-Japonica differentiation.

Parahebe catarractae(Scrophulariaceae): intraspecific taxonomy

Abstract Seventeen morphological characters (both binary and continuous) were recorded in thirty-five population samples of Parahebe catarractae grown under uniform conditions. Interpopulation variation was shown to be present in all characters by inspection for binary characters and by analysis of variance for continuous characters. For all continuous and most binary characters individually, this variation was not invariably associated with geography. Two multivariate techniques, clustering by the unweighted pair-group method of arithmetic averages and principal component analysis using character correlations, both revealed four groups with allopatric distributions, a classification supported by discriminant analysis. These groups are recognised as P. catarractae ssp. catarractae from Fiordland ssp. diffusa from east and central North Island and Nelson, ssp. lanceolata from Taranaki and Coromandel (and one population in north-west Nelson) and ssp. martinii from Marlborough, the last previously undescribe...

Monodromy Structure of Solutions of Holonomic Systems of Linear Differential Equations is Invariant under the Deformation of the System

Inspired by some physical problems, Sato has recently proposed to investigate the deformation of systems of (micro-) differential equations with the emphasis on the in variance of global character of solutions. (Sato et al. [4]) Especially, he has observed that the classical result of Schlesinger [5] is most neatly explained from this point of view. The purpose of this note is to show that the monodromy structure of solutions of holonomic systems of linear differential equations is invariant under the deformation of the system specified below (Definition 1) on the condition that related topological structure does not change. (See Corollary 1 for the precise statement.) We first list up some notations used in this note. We refer the reader to S-K-K [3] for notations not listed here. X: a complex maniford. A point in X shall be denoted by x. 7t: the projection map from T*X to X. U: a connected Stein open set in CN. A point in CN shall be denoted by *=(*i, —,**)• Xc={c}xXc:UxX for c^U. The natural injection from Xc to UxX shall be denoted by cc. We sometimes identify Xc with X.

Morphological variance and enzyme heterozygpsity in the monarch butterfly

IT was shown several decades ago that the reduction in genetic heterozygosity produced by inbreeding in domesticated plants and animals is accompanied by an increase in morphological variability1,2. While studies of laboratory populations and results of plant and animal breeding have been instrumental in identifying the relationship between genetic heterozygosity and morphological variability, such investigations often involved substantial changes in genetic heterozygosity, such as are produced when entire chromosomes are made homozygous. For this reason their relevance to the levels of heterozygosity in natural populations is unclear. Until recently attempts to examine this relationship in natural populations were hindered by the inability to routinely estimate levels of genetic heterozygosity in nature. However, determinations of genetic heterozygosity at specific enzyme-loci can now be made by electrophoresis. Recently Mitton3 found that heterozygotes for a set of five enzyme-loci had reduced multivariate variances for a set of morphological characters when compared to homozygotes at the same loci in populations of the killifish, Fundulus heteroclitus. It is very important to determine the generality of this observation for other species populations. I have now examined the relationship between genetic heterozygosity, as identified by electrophoresis, and the variance of morphological characters in the monarch butterfly, Danaus plexippus. Study of six polymorphic enzyme-loci in the monarch shows that once again heterozygotes have smaller variances for morphological characters when compared to homozygotes at the same locus.

Line × tester analysis of combining-ability and heterosis for some economic characters in okra

In okra ( Abelmoschus esculentus (L) Moensch), heterosis over the mid-parental values was manifested in all the characters studied. However, overdominance was observed only for days to first flowering, fruit length, plant height, fruit weight and yield per plant. Among the testers, ‘Pusa Sawani’ was found to be the best general combiner for yield and most other characters, whereas ‘Pusa Sawani’ (Bangalore lot-NSC) and ‘Crimson Spineless’ were observed to be high general combiners for yield and other desirable attributes amongst the females. Gene action based on the general and specific combining ability variances for various characters was found to be mainly non-additive. ‘Pusa Sawani’ (Bangalore lot-NSC) × ‘Smooth Long Green’ was found to be a good cross combination for number of fruits per plant and fruit yield. Another good combination for plant height and fruit yield was ‘American Seven Dhari’ × ‘Pusa Sawani’.

Variance Partitioning and Nongeographic Variation

The variability of characters within populations is generally measured as a function of the character variance, although questions of nongeographic variation are addressed as tests of mean differences between subgroups within populations. Presented here is an alternative approach based upon partitioning the variance of a character into components due to the presence of such subgroups within the population. The relative magnitude of these variance components is used to determine the relative importance of sources of variation within populations and to examine patterns of variability across taxonomic groups. The method is flexible enough to utilize data with unequal sample sizes and provides estimates which are directly comparable across characters and taxa.

Spatial patterns in the distributions of polygenic characters

The spatial patterns in the mean and variance of a quantitative character that result from the interaction of spatially varying, optimizing selection and gene flow are considered. The model analyzed is an extension of those of Kimura (1965) and Lande (1976) for the distribution of a quantitative character maintained in a population by independent mutations. For weak selection, it is shown that there is only a small effect of gene flow on the variance of the character and that the mean value changes on a length scale that is large compared to the average dispersal distance. As in models of clines in allele frequencies, it is possible to define a “characteristic length” in terms of the average dispersal distance and strength of selection. The characteristic length is the smallest length scale environmental change to which the mean value of the character can significantly respond. It is also shown that, for weak selection, an asymmetry in dispersal can result in a significant shift in location of a cline. By considering an infinite linear cline in optimal values, it is shown that gene flow can increase the variance only when there is sufficient mixing in each generation of individuals from locations with different means. A model of selection in different niches is also considered. There is an increase in variance due to the effective weakening of the intensity of selection because of the differences in optimal values in different niches. The implications of the different models for maintenance of genetic polymorphism are discussed. Under some conditions gene flow can produce a significant increase in heterozygosity. It is also argued that spatial variation in selection on a polygenic character can be much more effective in increasing heterozygosity than temporal variation because of the potentially greater increase in phenotypic variance. The difference between some of the results for polygenic characters from those of similar models of one and two locus systems is accounted for by the fact that for normally distributed polygenic characters, changes in the variance are effectively decoupled from changes in the mean.

Morphological composition of the people of India

The paper provides an overview of the spatial and temporal aspects of human morphological variation in India. Four morphological types—Australoids, Negritos, Mongoloids and Caucasoids—have been discerned in the contemporary Indian population. The Australoids appear to be the oldest and have evolved in India. The Caucasoids are physically heterogeneous and suggests incorporation of more than one physical type involving more than one migration. The within-type variance compared to between-type variance for characters studied is smaller. The paper further discusses the observed variability in terms of Indian social organization as well as in terms of endogamy, small numerical strength of the groups and varying ecological conditions prevalent in India.

THE INFLUENCE OF THE MATING SYSTEM ON THE MAINTENANCE OF GENETIC VARIABILITY IN POLYGENIC CHARACTERS

The traditional models of the effect of assortative mating and inbreeding on the genetic variance of polygenic characters (FISHER 1918; WRIGHT 1921) presume that there is no natural selection or mutation. In a large population, the genetic variance determined by additive genes may then increase by up to a factor of two with local inbreeding, and even more with assortative mating. The classical models are still used to interpret data from natural populations. But contrary to their assumptions, most metrical characters in natural populations are usually thought to be under a type of selection which depletes polygenic variation. Mutation is then necessary to maintain genetic variation. The present models show that with the additional features of mutation and selection, in a large population, the mating system has no influence on the amount of genetic variability maintained by additive genes.

Chiasmata and variability in Lolium and Festuca populations

There are significant differences in mean pollen mother cell chiasma frequencies between populations within Lolium perenne, L. multiflorum and Festuca pratensis. The differences are genotypically controlled. With low chiasma frequencies the chiasmata are distally located. With increasing chiasma frequency the frequency of chiasmata in interstitial segments increases. Shorter lived populations have higher chiasma frequencies than the more perennial. — The higher the chiasma frequency of a population the lower the phenotypic and genetic variance for characters under polygenic control, such as flowering time, and the less effective also is the response to selection for such characters. These observations are interpreted on the premise that high chiasma frequencies are instrumental in the breaking up of supergene sequences in interstitial chromosome segments.

Quantitative inheritance studies in sugar-cane. I. Estimation of variance components

Two experiments in quantitative genetics were conducted, one based on a nested design in lattice squares and the other on a factorial design in a balanced lattice. Lattice designs were found to be suitable for genetic experiments if a large number of crosses was involved, but posed some problems in partitioning the sum of squares for treatments. The factorial design was considered preferable to the nested design, although neither design permitted estimation of epistatic variances which, therefore, were assumed to be negligible. Additive genetic variance was found to be more important than dominance genetic variance for most characters. However, most estimates of genetic variance lacked precision in spite of the use of large, precise experiments, which illustrated the difficulty in obtaining estimates of variance components with adequate precision. The validity of assumptions made for these analyses is discussed. The effect of competition was studied and estimates of heritability and degree of genetic determination were determined.

Morphometric and Allometric Variations of Trichodorus Christiei

Variations existed within geographical isolates, populations, and strains of Trichodorus christiei Allen. Host species, host variety, host physiology, and geographical origin of a population influenced the extent of variation of morphometric and allometric characters. Stylet length was the least variable morphometric character. Ratios formed from the body length, stylet length and position of the vulva were the least variable allometric characters. It was shown that the variance of morphometric characters and the allometry of pairs of characters used to form ratios should be studied before they are used for taxonomic purposes. Ten morphometric and allometric characters of 1,371 specimens of T. christiei from 22 populations were evaluated with numerical analyses. Numerical affinities were shown between intraspecific groups and among the populations within each group.