Genetic Demography of Plant Populations

Clegg, Michael T.; Kahler, A. L.; Allard, R. W.

doi:10.1007/978-1-4612-6330-2_10

Cited by 22 publications

(17 citation statements)

References 27 publications

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“…After a data set was generated, the maximum likelihood procedure of Clegg et al (12) was used to compute estimates of the maternal parent frequencies (Mjs), the frequency of allele Al in the pollen pool (p), and the outcrossing rate (t).…”

Section: Failure Of the Mixed-mating Modelmentioning

confidence: 99%

“…Plant population biologists have instead relied on methods to infer the mating system retrospectively from progeny genotypes. These methods use marker loci and statistical estimation (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). A common practice in mating system studies that use allozymic markers is to assay several progeny from single maternal (seed) parents and estimate the maternal parent frequencies from the progeny genotype distributions using, as a basis, some underlying statistical model of the mating process.…”

mentioning

confidence: 99%

“…In plant population genetics, one model of mating, the mixed-mating model, has held a central position in both theoretical and experimental investigations (7,12). There are several reasons for choosing the mixed-mating model rather than assuming random mating to describe the pattern of gene transmission in plant populations.…”

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Estimation of mating system parameters when outcrossing events are correlated

Schoen

Clegg

1984

Proc. Natl. Acad. Sci. U.S.A.

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Many plant species have mating systems characterized by a mixture of self-fertilization and outcrossing. Statistical estimation of the outcrossing rate has relied on a model of the mating process that assumes that successive outcross events within a family arise from independent draws of pollen from the total population of male plants. Although this assumption is likely to be most appropriate for wind-pollinated plants, it is not appropriate in certain insect-pollinated plants. An alternative model is developed that assumes that successive outcross events within a family involve pollen drawn front a single male parent. The estimation of the parameters that index this model is outlined and a procedure for calculating the variances of the parameter estimates is presented. Monte Carlo simulations of the sampling processes assumed by each model are also presented. The simulations show that application of the incorrect estimation model to data can lead to a large bias in parameter estimates.The mating system of a population determines how genetic information is transferred from one generation to the next (1). Moreover, the recombinational potential of the population may be strongly influenced by the mating system (2). Accurate information on the mating system in plant populations cannot be obtained through direct observation. This is due, in part, to difficulties inherent in tracing the flow of pollen among and within individuals. Plant population biologists have instead relied on methods to infer the mating system retrospectively from progeny genotypes. These methods use marker loci and statistical estimation (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). A common practice in mating system studies that use allozymic markers is to assay several progeny from single maternal (seed) parents and estimate the maternal parent frequencies from the progeny genotype distributions using, as a basis, some underlying statistical model of the mating process. This logistically simple method of sampling the population avoids problems associated with age-and/or tissue-specific expression of allozyme phenotypes.In plant population genetics, one model of mating, the mixed-mating model, has held a central position in both theoretical and experimental investigations (7, 12). There are several reasons for choosing the mixed-mating model rather than assuming random mating to describe the pattern of gene transmission in plant populations. First, inbreeding is common in many plant species and the random-mating model is, therefore, inappropriate. Second, the mixed-mating model is simple and requires the estimation of only one additional parameter, the outcrossing rate. Third, the assumptions of the mixed-mating model are reasonable descriptions of the reproductive biology of many species. Despite the wide utility of the mixed-mating model, it may fail to properly describe the reproductive biology of certain insect-pollinated plants.Below we document this failure and then propose an alternative to the mixed-mating model th...

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Section: Failure Of the Mixed-mating Modelmentioning

confidence: 99%

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confidence: 99%

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Estimation of mating system parameters when outcrossing events are correlated

Schoen

Clegg

1984

Proc. Natl. Acad. Sci. U.S.A.

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“…Most theoretical studies on demographic genetics have analyzed rather simplified models, and most empirical work has been on ecosystems and species that represent only a subset of the diversity of life histories and population structures that exist among plant species. Previous demographic-genetic studies of plants have been conducted mainly for annual or perennial herbs, emphasizing the role of natural selection (Clegg and Allard 1973;Schaal and Levin 1976;Allard et al 1977;Clegg et al 1978;Tonsor et al 1993). Very few studies have examined genetic changes through the entire life cycle of tree species (but see Linhart et al 1981;Hamrick et al 1993).…”

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confidence: 99%

“…Seed banks, which are characteristic of early colonizing species, can slow down the rate of genetic change (Clegg et al 1978;Templeton and Levin 1979;Hairston and De Stasio 1988), but they could also be a "prime source of novel genetic variation" (Levin 1990:563) if mutation rates in seeds aged in the field are as high as those of seeds aged in the laboratory. Differences in the genetic structure of the seed bank and established individuals can depend on a variety of processes, including variation in the breeding structure, seed dispersal pattern, temporal and spatial patterns of selection, variance in survival and fecundity, seed longevity in the soil, and the proportion of seedlings germinating from the persistent seed bank versus those germinating from the previous season's reproductive output (Tonsor et al 1993).…”

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Demographic Genetics of a Pioneer Tropical Tree Species: Patch Dynamics, Seed Dispersal, and Seed Banks

et al. 1996

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Abstract.-We consider whether changes in population-genetic structure through the life cycle of Cecropia obtusifolia, a tropical pioneer tree, reflect its gap-dependent demography and the role of evolutionary processes that are important for this species. We asked whether the spatial scale at which population-genetic subdivision occurs corresponds to the scale of habitat patchiness created by gap dynamics; whether patterns of seed dispersal and storage in the soil affect spatial genetic patterns; and whether spatial genetic patterns change through the species life cycle. We estimated Wright's F-statistics for six successive life-history stages for individuals grouped into subpopulations according to occurrence in natural gaps, physical proximity, or occurrence within large quadrats. For each life stage, Fsrstatistics were significantly higher when individuals were grouped by gaps, although concordant patterns across life stages for the three grouping methods were obtained. This supports the hypothesis that patchy recruitment in gaps or amonggap heterogeneity influences the species' genetic structure. F-statistics of seeds collected from females before dispersal (tree seeds), seed-rain seeds, soil seeds, seedlings, juveniles, and adults grouped by gaps, were, respectively: 002. Spatial genetic differentiation in rain seeds was not significantly lower than that of tree seeds. The loss of genetic structure in the soil seed bank, relative to that found in the seed rain may be due to sampling artifacts, but alternative explanations, such as microsite selection or temporal Wahlund effect are also discussed. If structure among soil seeds is unbiased, the peak in seedling F ST may be due to microsite selection. F IS of seeds in the rain and soil were significantly greater than zero. A Wahlund effect is the most likely cause of these positive F IS values. Such fine-scale substructuring could be caused by correlated seed deposition by frugivores. The decrease in F IS from seedlings to adults could result from loss of fine-scale genetic structure during stand thinning or from selection.

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Dedication: Robert W. Allard, Population Geneticist and Agronomist

Clegg

1994

Plant Breeding Reviews

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Genetic Demography of Plant Populations

Cited by 22 publications

References 27 publications

Estimation of mating system parameters when outcrossing events are correlated

Estimation of mating system parameters when outcrossing events are correlated

Demographic Genetics of a Pioneer Tropical Tree Species: Patch Dynamics, Seed Dispersal, and Seed Banks

Dedication: Robert W. Allard, Population Geneticist and Agronomist

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