Selection for Annual Growth Curves in NICOTIANA TABACUM L.

The cumulative growth of a plant is the result of interrelated processes, and response to selection for changes in the annual growth curve requires many physiological adjustments. Selection to modify the entire annual growth curve may therefore not be as effective as linear models may predict. Periodic growth of a population of Nicotiana tabacum L. was estimated to have heritabilities increasing from 7% up to 31% for successive heights, with positive genetic and phenotypic correlations among all periods. Two selection experiments on this population indicate the difficulties of using simple index selection to raise the entire growth curve. A selection index of eight periodic heights resulted in a gain in all periods for the first cycle of selection but mixed losses and gains in subsequent cycles for a small net gain after four cycles of selection. A selection index of three parameters of a nonlinear height growth function resulted in a consistent change in the growth curves over the four cycles of selection but a net loss in early growth and a large net gain in late-season growth.

The influence of composite traits on genotype by environment relations.

In breeding for multiple trait value functions, the existence of genotype-by-environment interaction effects can vastly complicate the designation of optimum sets of genotype-environment pairings into Target Populations of Environments. In this paper it is shown that even in the absence of any changes in genotypic ranking over environments on a trait-by-trait basis, it is possible to generate changes in genotypic ranking in value in different environments. This is shown to be true even for linear value functions in a case example in pine breeding.

The question is not, "can they talk"?

An argument for denying moral rights to nonhuman species is that beliefs, desires, and interests are inherent in the normal human capacity for speech and, since only humans are linguistically capable, only humans can have rights. We argue that linguistics and many conceptual abilities are ontogenetically independent in humans and that various morally relevant mental capacities can exist independently. We also then argue that phylogenetic independence is also possible and hence, that the concept of an inherent dependence of moral standing on having linguistic capabilities is insufficient for denying rights to nonhumans.

Limits of artificial selection under unbalanced mating systems.

The influence of unbalanced mating systems - factorial mating (FM) and random loss of families after a full diallel crossing (RS) - on the ultimate probability of gene fixation (u(Π)) and the time required to fix or lose a gene (t(Π)) are investigated. The average u(Π) of these systems is smaller than that of random mating, and the range of u(Π) for a given initial parental genotype combination is very large (close to one for most initial genotypic combinations). The average u(Π) of different parental genotypic combinations of a given gene frequency are different. These systems accelerate the t(Π).

Examples of the effect of genetic variation on competing species.

An ordinary differential equation model for two competing populations with genetic variation in one population is presented. The degree of frequency dependence needed to produce various configurations of stable equilibria is discussed. For example, if the fitnesses are frequency independent then there may exist stable polymorphism although the genetically varying population becomes extinct in each fixation plane. Stable polymorphism where the genetically invariant population becomes extinct in each fixation plane requires frequency dependence in the fitness of the genetically invariant population.

Frequency-dependent selection in logistic growth models.

This paper describes the dynamics of a continuously reproducing diploid population with two alleles at one locus. The dependent variables are allele frequency and population density. We modify the basic density-dependent logistic growth model by inserting three possible types of frequency dependence in the fitness functions. These models are analyzed and contrasted with the purely density-dependent situation. Examples are given of periodic fluctuations in allele frequency and population density, which would be impossible for purely density-dependent fitness functions.

Joint analysis of genotypic and environmental effects.

A definition of jointly contributing genotypic and environmental effects is introduced, from which a new concept of genotype × environment interactions is derived. Interaction is defined to be the failure of genotypic or environmental response functions to be separable. For separable response functions, the contributions of the genotypic and environmental effects must be related in terms of an operator which can describe their joint actions. A scale-free method of determining the simplest operator is developed in terms of comparative norms of reaction and a characteristic of the operator is given for several operators. With a defined operator, the genetic and environmental contributions can be derived, and biologically interpreted. These methods are applied to published data on Pinus caribaea.

Genetic variation in nutrient response functions.

Genetic differences in the non-linear growth response function of Pinus sylvestris seedlings to five nutrient levels are analyzed to estimate the causes of variation. Analyses of genotypic differences as quadratic response functions, as stability coefficients, and as separable functions indicate that the estimation of genetic effects can vary widely depending on the analytical model assumed. The existence of different reaction norms is demonstrated.

Population selection to maximize value in an environmental gradient.

A theory for determining optimum planting and breeding zones is described. The theory is based on a model consisting of Gaussian response functions for traits that vary in a gradient for a single environmental variable. Environments are assumed to be normally distributed with known mean and variance. Methods are presented for determining parameters of response functions that maximize the expected value for such a trait when two, three and four populations are selected for breeding or as sources of propagules. Expected value is maximized only when the populations selected have response functions symmetrically arrayed about the mean of the environmental variable. Maximum expected value was shown to increase with increasing number of selected populations at a rate that depends upon the ratio of homostasis to environmental variability. The methods presented are illustrated with data on performance of Scots pine provenances in Sweden.

Genetic analysis of risk in clonal populations of forest trees.

A major concern arising from the culture of clonally propagated crops of forest trees is risk of catastrophic loss due to an agent or event not anticipated at the time of population establishment. Since danger of such a catastrophe depends to some degree on the genetic variability within clonal mixtures, attention has been focused on the number of clones needed to keep the risk of catastrophic loss below specified levels. In this paper, we describe a genetical analysis of susceptibility to a destructive agent and the effect that frequency of genes for susceptibility have on the number of clones needed to effectively manage this risk. As a part of the analysis, parameters representing the minimum unacceptable mortality rates in plantations (ß) and acceptable levels of risk (α) are defined, and their effects on the number of single-pair matings needed for the production of clonal stock are evaluated. Dominance and recessive gene action models for a single two-allele genetic locus are investigated. Probabilities for plantation failure are functions of the gene frequency for the allele conferring susceptibility. These functions converge to zero for allele frequencies less than ß but to one for frequencies greater than or equal to ß. This convergence is periodic rather than monotonie, since probabilities for plantation failure increase rather than decrease over restricted ranges of increasing numbers of clones. Recessive and dominance gene actions are found to have different effects on the minimum number of clones needed to attain acceptable risk levels. For conditions in which substantial numbers of clones are required, selecting multiple clones per mating is an effective method for reducing the number of matings necessary to achieve acceptable risks.

Age-related variation in genetic control of height growth in Douglas-fir.

The development of genetic variances in height growth of Douglas-fir over a 53-year period is analyzed and found to fall into three periods. In the juvenile period, variances in environmental error increase logarithmically, genetic variance within populations exists at moderate levels, and variance among populations is low but increasing. In the early reproductive period, the response to environmental sources of error variance is restricted, genetic variance within populations disappears, and populational differences strongly emerge but do not increase as expected. In the later period, environmental error again increases rapidly, but genetic variance within populations does not reappear and population differences are maintained at about the same level as established in the early reproductive period. The change between the juvenile and early reproductive periods is perhaps associated with the onset of ecological dominance and significant allocations of energy to reproduction.

Point estimation and graphical inference of marginal dominance for two viability loci controlling inbreeding depression.

A deterministic analysis is conducted to examine marginal dominance for two linked viability loci influencing inbreeding depression and its graphical inferences. Four estimators of marginal dominance are derived, assuming a biallelic marker locus completely linked to one of the viability loci, and the biases in expected estimates due to the other deleterious locus are discussed. Three conditions under which apparent partial dominance or underdominance could occur are found, i.e. when two multiplicative, partially recessive loci are linked in coupling phase and when two synergistic, highly overdominant loci are linked in coupling or repulsion phases. Expected frequencies of the three marker genotypes in selfed progeny are derived, considering two linkage phases, two types of marker locus position with respect to the viability loci, and the multiplicative and synergistic fitness models. Segregation ratios are generated for the marker locus linked to either two overdominant or partially recessive loci and plotted in gene action graphs to examine the robustness of the graphical inferences of gene action due to the presence of an additional linked viability locus. Under a multiplicative fitness model, the presence of an additional partially recessive or overdominant locus in the vicinity of the marker locus does not greatly affect the graphical inferences of the relative role of partially recessive or overdominant genes in expression of inbreeding depression. A marker linked to two synergistic, highly overdominant loci can behave as though linked to a partially recessive, partially dominant or underdominant locus, even with relatively weak synergism.

A comparison of planned unbalanced designs for estimating heritability in perennial tree crops.

One hundred families of average size 10 are allocated in single-tree plots to 20 blocks in several planned unbalanced designs. Based on the variance of the estimate of heritability from the Minimum Variance Quadratic Unbiased Estimates and 100% survival, the three partially balanced designs are equally efficient. A design with variable family size is more efficient for heritabilities (h(2)) generally less than 0.25; an equal family size design is more efficient for h(2) generally greater than 0.25. A design with a large number of small families is more efficient at high h(2) than that with a small number of large families; a design with fewer families of larger size is more efficient at low h(2). Two-tree plot designs are never more efficient than single-tree plot designs and are also shown to be sensitive to the magnitude of the variance components that generate a given h(2), whereas the single-tree plot designs are not.

Population genetic structure of Nantucket pine tip moth.

Variation at polymorphic isozyme loci was analyzed in Nantucket pine tip moth (NPTM) populations from 5 geographic locations. At the North Carolina location, populations representing 3 generations at 3 local sites were also studied. Four of the loci investigated (LAP, MDH, α-GPDH and AK), although variable, had few alleles per locus (3-5) and few differences among populations in allele frequencies. At each locus, all populations had the same allele at a high frequency.At the PGM locus, fifteen alleles were identified and allelic frequencies varied among populations. At least eight alleles were present within a population and, in most populations, two or more alleles had high frequencies that differed among populations. An excess of homozygotes over Hardy-Weinberg expectations was found for 7 out of the 10 populations studied, indicating the probable existence of some form of inbreeding structure or populational subdivision within sampled stands.Joint consideration of the results observed for PGM and the other four loci is counterindicative of neutrality at all loci and strongly indicative of genetic differentiation among locally disjunct populations.