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This paper reports results obtained from microsatellite DNA analysis of genetic structure for populations of the native fungus Cronartium quercuum f. sp fusiforme infecting loblolly pine (Pinus taeda L.) over much of this host's natural range. Mostly all fusiform rust galls formed under field conditions are produced as a result of infection and colonization by haploid mycelium originating from a single basidiospore of C. quercuum fusiforme. If multiple infections do occur, then only a single haplotype must ultimately dominate and be responsible for gall formation. High levels of microsatellite variability exist in C. quercuum fusiforme and most of this variation occurs within local populations (average 88.4%). A statistically significant proportion, however, is found among populations, and the magnitude of this differentiation is closely associated with geographic distance between populations. Unweighted pair-group mean analysis and principal components analysis both indicate that at least four genetically distinct regional groups of C. quercuum fusiforme exist in the south Atlantic and Gulf coastal plains. In summary, the distribution of genetic variability in C. quercuum fusiforme is consistent with a hypothesis of at least four metapopulations with gene flow occurring less among regions than among populations within regions, and where overall levels of gene migration are related to geographic distance between populations.

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A system of non-linear difference equations is used to model the effects of density-dependent selection and migration in a population characterized by two alleles at a single gene locus. Results for the existence and stability of polymorphic equilibria are established. Properties for a genetically important class of equilibria associated with complete dominance in fitness are described. The birth of an unusual chaotic attractor is also illustrated. This attractor is produced when migration causes chaotic dynamics on a boundary of phase space to bifurcate into the interior of phase space, resulting in bistable genetic polymorphic behavior.

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The effects of population density on the survival and growth of an individual species are modeled by assuming that the species per capita growth rate (i.e., fitness) is a function of a weighted total density. A species is called a pioneer population if it thrives at low density but its fitness decreases monotonically with increasing density. A species is called a climax population if its fitness increases up to a maximum value and then decreases as a function of its total density. Hopf bifurcations for deterministic models of the interaction of pioneer and climax populations are discussed. Stability properties for the Hopf invariant curves in the discrete models are compared to the stability properties of the Hopf periodic orbits in the corresponding continuous models. Examples illustrate that stability may be more common in the discrete models.

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A method for quantifying mating behavior in clonal seed orchards of forest tree species is presented. It involves the estimation of effective numbers of pollen parents from seed samples collected from individual ramets in such orchards. These effective numbers are variance effective numbers for populations of male gametes that are successful in uniting with ovules to produce viable seed. Three such effective numbers are defined for clonal seed orchards:N p (a) for male gamete populations for ramets within clones,N p (b) for male gamete populations for clones, andN p (c) for male gamete populations for entire orchards. Estimators for these effective numbers and for standardized variances of allele frequencies in the male gametic populations are presented. Expressions are also given for the confidence intervals for each of the three effective numbers. Estimates of these parameters and the corresponding confidence intervals for two seed orchards are presented and interpreted.

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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.

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The effect of the rate of partial self-fertilization and viability selection on the magnitude of inbreeding depression was investigated for the overdominance genetic model. The influence of these factors was determined for populations with equilibrium genotypic frequencies. Inbreeding depression was measured as the normalized disadvantage in mean viability of selfed progeny as compared to outcrossed progeny. When caused by symmetric homozygous disadvantage at a single locus it is shown always to be less than one-third. Moreover, for fixed rates of self-fertilization, its maximum value is found at intermediate levels of homozygous disadvantage. As the rate of self-fertilization increases, inbreeding depression increases and the homozygote viability that results in maximum depression tends toward one-half the heterozygote viability. Symmetric selection against homozygotes at multiple loci can lead to substantially higher values than selection at a single-locus. As the number of independent loci involved increases, inbreeding depression can reach high levels even though the selfing rate is low. Viability distributions for progenies produced from both random mating and self-fertilization were derived for the case of symmetric selection at independently assorting multiple loci. Distributions of viabilities in progenies resulting from mixtures of selfing and outcrossing were shown to be bimodal when inbreeding depression is high.

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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.

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The basis for measuring differentiation among subpopulations is discussed and a number of conditions formulated that are desirable for an appropriate measure. These conditions imply that each subpopulation is characterized by the difference in genetic composition between it and its complement. A direct method of determining this difference is described and shown to result from a known measure of genetic distance between populations. The weighted average of the genetic distances between subpopulations and their complements constitutes a measure of differentiation among subpopulations which fulfills all of the desirable conditions and has the additional advantage that its values are directly interpretable. This measure (δ) is equally applicable to gene (δ ge ), gametic (δ ga ) or genotypic (δ go ) frequencies, which guarantees an unequivocal multilocus treatment, provided that the sets of genetic entities to which the frequencies refer are properly defined. The general relationship δ ge ≤ δ ga ≤ δ go is consistent with the principle that increasing complexity of organization of genetic material results in increased opportunity for differentiation. It is demonstrated that Wright's F st (G ST in Nei's notation), which is often used to measure subpopulation differentiation, meets some but not all of the conditions formulated for a desirable measure.

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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.

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The effects of competition on the growth of families of loblolly pine (Pinus taeda, L.) seedlings were investigated. The experimental design made it possible to evaluate the effects of crowding on growth and to determine the types and magnitudes of intergenotypic interactions among pairs of families. The results showed that intergenotypic interactions were both highly variable and pronounced in their effect on early growth. Evidence was also found for precompetition cooperating interactions occurring among seedlings surrounded by neighbors of the same family.