Somatic deleterious mutation rate in a woody plant: estimation from phenotypic data.

We conducted controlled crosses in populations of the long-lived clonal shrub, Vaccinium angustifolium (lowbush blueberry) to estimate inbreeding depression and mutation parameters associated with somatic deleterious mutation. Inbreeding depression level was high, with many plants failing to set fruit after self-pollination. We also compared fruit set from autogamous pollinations (pollen collected from within the same inflorescence) with fruit set from geitonogamous pollinations (pollen collected from the same plant but from inflorescences separated by several meters of branch growth). The difference between geitonogamous versus autogamous fitness within single plants is referred to as 'autogamy depression' (AD). AD can be caused by somatic deleterious mutation. AD was significantly different from zero for fruit set. We developed a maximum-likelihood procedure to estimate somatic mutation parameters from AD, and applied it to geitonogamous and autogamous fruit set data from this experiment. We infer that, on average, approximately three sublethal, partially dominant somatic mutations exist within the crowns of the plants studied. We conclude that somatic mutation in this woody plant results in an overall genomic deleterious mutation rate that exceeds the rate measured to date for annual plants. Some implications of this result for evolutionary biology and agriculture are discussed.

Impact of selective logging on inbreeding and gene dispersal in an Amazonian tree population of Carapa guianensis Aubl.

Selective logging may impact patterns of genetic diversity within populations of harvested forest tree species by increasing distances separating conspecific trees, and modifying physical and biotic features of the forest habitat. We measured levels of gene diversity, inbreeding, pollen dispersal and spatial genetic structure (SGS) of an Amazonian insect-pollinated Carapa guianensis population before and after commercial selective logging. Similar levels of gene diversity and allelic richness were found before and after logging in both the adult and the seed generations. Pre- and post-harvest outcrossing rates were high, and not significantly different from one another. We found no significant levels of biparental inbreeding either before or after logging. Low levels of pollen pool differentiation were found, and the pre- vs. post-harvest difference was not significant. Pollen dispersal distance estimates averaged between 75 m and 265 m before logging, and between 76 m and 268 m after logging, depending on the value of tree density and the dispersal model used. There were weak and similar levels of differentiation of allele frequencies in the adults and in the pollen pool, before and after logging occurred, as well as weak and similar pre- and post-harvest levels of SGS among adult trees. The large neighbourhood sizes estimated suggest high historical levels of gene flow. Overall our results indicate that there is no clear short-term genetic impact of selective logging on this population of C. guianensis.

Somatic stability of microsatellite loci in Eastern white pine, Pinus strobus L.

Variation at nuclear- and chloroplast-encoded microsatellite loci was studied among and within clonally propagated individuals of Eastern white pine. Total DNA was extracted and assayed from gamete-bearing tissue (megagametophytes) located on six different branch positions on each of 12 individual genets. No within-individual variation was observed among 12 loci studied. Estimates of numbers of mitotic cell divisions required to produce the tissue used as the source of genomic DNA were obtained by combining tree growth and anatomical data. This allowed for the calculation of upper bound estimates of numbers of mutations per locus per somatic cell division. The estimated somatic mutation rate was found to be substantially lower than those published for genomic microsatellite mutation rates in other plant species.

Population dynamics of an Ac-like transposable element in self- and cross-pollinating arabidopsis.

Theoretical models predict that the mating system should be an important factor driving the dynamics of transposable elements in natural populations due to differences in selective pressure on both element and host. We used a PCR-based approach to examine the abundance and levels of insertion polymorphism of Ac-III, a recently identified Ac-like transposon family, in natural populations of the selfing plant Arabidopsis thaliana and its close outcrossing relative, Arabidopsis lyrata. Although several insertions appeared to be ancient and shared between species, there is strong evidence for recent activity of this element family in both species. Sequences of the regions flanking insertions indicate that all Ac-III transposons segregating in natural populations are in noncoding regions and provide no evidence for local transposition events. Transposon display analysis suggests the presence of slightly higher numbers of insertion sites per individual but fewer total polymorphic insertions in the self-pollinating A. thaliana than A. lyrata. Element insertions appear to be segregating at significantly lower frequencies in A. lyrata than A. thaliana, which is consistent with a reduction in transposition rate, reduction in effective population size, or reduced efficacy of natural selection against element insertions in selfing populations.

A comparison of periodontal disease in HIV-infected children and household peers: a two year report.

PURPOSE: The purpose of this study was to compare the incidence and progression of periodontal disease in HIV-infected children to HIV-negative household peers. This paper reports the findings after two years. METHODS: Children diagnosed as HIV-infected and their household peers were recruited from the Children's Hospital AIDS Program in Newark NJ. A periodontal examination was performed at baseline and at six-month intervals for two years. A total of 121 subjects were examined two years after baseline (68 HIV-infected and 53 controls). These children ranged in age from 2-15 years at baseline. RESULTS: Plaque assessment (PHP-M) in HIV-infected cases showed a seven-fold increase over controls for the period. However, there were no significant differences between the two groups in changes over the two years for Bleeding on Probing, Gingival Index or Pocket Depths. There was virtually no recession or pathologic mobility in either group. One-fourth of the HIV-infected group exhibited Linear Gingival Erythema at both baseline and year two. Although the number of subjects with LGE did not increase, there was an increase in the severity of LGE at year 2. CONCLUSION: This study suggests that in a medically well-controlled HIV-infected population, with the exception of the prevalence of Linear Gingival Erythema, the periodontal findings are similar to their HIV-negative household peers and to the general pediatric population.

Comparative genomics, marker density and statistical analysis of chromosome rearrangements.

Estimates of the number of chromosomal breakpoints that have arisen (e.g., by translocation and inversion) in the evolutionary past between two species and their common ancestor can be made by comparing map positions of marker loci. Statistical methods for doing so are based on a random-breakage model of chromosomal rearrangement. The model treats all modes of chromosome rearrangement alike, and it assumes that chromosome boundaries and breakpoints are distributed randomly along a single genomic interval. Here we use simulation and numerical analysis to test the validity of these model assumptions. Mean estimates of numbers of breakpoints are close to those expected under the random-breakage model when marker density is high relative to the amount of chromosomal rearrangement and when rearrangements occur by translocation alone. But when marker density is low relative to the number of chromosomes, and when rearrangements occur by both translocation and inversion, the number of breakpoints is underestimated. The underestimate arises because rearranged segments may contain markers, yet the rearranged segments may, nevertheless, be undetected. Variances of the estimate of numbers of breakpoints decrease rapidly as markers are added to the comparative maps, but are less influenced by the number or type of chromosomal rearrangement separating the species. Variances obtained with simulated genomes comprised of chromosomes of equal length are substantially lower than those obtained when chromosome size is unconstrained. Statistical power for detecting heterogeneity in the rate of chromosomal rearrangement is also investigated. Results are interpreted with respect to the amount of marker information required to make accurate inferences about chromosomal evolution.

NAON: the second decade. A leader among specialty nursing organizations.

The new millennium coincides with the 20th Anniversary of NAON, and provides an occasion to look back and reflect on our past. The first decade of NAON was well described by Mary Rodts in her 1990 article in Orthopaedic Nursing, "NAON: The First Decade, A Firm Foundation for a Successful Future" (Orthopaedic Nursing 9(3), 15-26). This article is an attempt to look at the highlights of the second decade of NAON, 1990-2000.

Transposon dynamics and the breeding system.

The selfish DNA hypothesis predicts that natural selection is responsible for preventing the unregulated build up of transposable elements in organismal genomes. Accordingly, between-species differences in the strength and effectiveness of selection against transposons should be important in driving the evolution of transposon activity and abundance. We used a modeling approach to investigate how the rate of self-fertilization influences the population dynamics of transposable elements. Contrasting effects of the breeding system were observed under selection based on transposon disruption of gene function versus selection based on element-mediated ectopic exchange. This suggests that the comparison of TE copy number in organisms with different breeding systems may provide a test of the relative importance of these forces in regulating transposon multiplication. The effects of breeding system also interacted with population size, particularly when there was no element excision. The strength and effectiveness of selection against transposons was reflected not only in their equilibrium abundance, but also in the per-site element frequency of individual insertions and the coefficient of variation in copy number. These results are discussed in relation to evidence on transposon abundance available from the literature, and suggestions for future data collection.

Profiling the commission for environmental cooperation.

By facilitating cooperation and public participation, the organization is fostering conservation, protection, and enhancement of the North American environment.

Learning from polar ice core research.

An understanding of long-term climate changes, with some surprises, is emerging from analysis of ice core samples.

Deleterious mutation accumulation and the regeneration of genetic resources.

The accumulation of mildly deleterious mutations accompanying recurrent regeneration of plant germ plasm was modeled under regeneration conditions characterized by different amounts of selection and genetic drift. Under some regeneration conditions (sample sizes >/=75 individuals and bulk harvesting of seed) mutation accumulation was negligible, but under others (sample sizes <75 individuals or equalization of seed production by individual plants) mutation numbers per genome increased significantly during 25-50 cycles of regeneration. When mutations also are assumed to occur (at elevated rates) during seed storage, significant mutation accumulation and fitness decline occurred in 10 or fewer cycles of regeneration regardless of the regeneration conditions. Calculations also were performed to determine the numbers of deleterious mutations introduced and remaining in the genome of an existing variety after hybridization with a genetic resource and subsequent backcrossing. The results suggest that mutation accumulation has the potential to reduce the viability of materials held in germ plasm collections and to offset gains expected by the introduction of particular genes of interest from genetic resources.

A renaissance for genotoxicity testing?

Test results are driving a rebirth of interest in the use of the technique to evaluate pollution.

Interleukin-6 is not altered in cerebrospinal fluid of first-degree relatives and patients with Alzheimer's disease.

We investigated interleukin-6 (IL-6) levels in cerebrospinal fluid (CSF) of 25 patients with clinically diagnosed sporadic Alzheimer's disease (AD) and 19 healthy control subjects (HC). For comparison 19 clinically healthy subjects with at least one first-degree relative with clinical or autopsy confirmed AD (CF/AD) were examined. CSF levels of IL-6 did not show statistically significant differences between AD patients, CF/AD and HC subjects. There was no correlation between age, gender, age of onset, degree of cognitive impairment, blood-brain barrier dysfunction and IL-6 values. We could not demonstrate altered CSF concentrations of IL-6 that may indicate an inflammatory response or capability to support neuronal survival in the central nervous system (CNS) of first-degree relatives and patients with AD. We suggest that combined measurement of all parameters of the IL-6-receptor complex could yield more insight in a probably altered IL-6 function.

The evolution of self-fertilization in perennials.

Many plants are perennials, but studies of self-fertilization do not usually include features of perennial life histories. We therefore develop models that include selfing, a simple form of perenniality, adult inbreeding depression, and an adult survivorship cost to seed production. Our analysis shows that inbreeding depression in adults diminishes the genetic transmission advantage associated with selfing, especially in long-lived perennials that experience inbreeding depression over many seasons. Perennials also pay a cost when selfing increases total seed set at the expense of future survivorship and reproduction. Such life-history considerations shed new light on the generalization that annuals self-fertilize more than perennials. Past research suggested reproductive assurance as an explanation for this association, but common modes of selfing offer equal reproductive assurance to annuals and perennials. Instead, perennials may avoid selfing because of adult inbreeding depression and the cost to future survivorship and reproduction.

The role of theory in an emerging new plant reproductive biology.

Recent empirical studies hint at an end to the historical solitude between pollination and mating system approaches to plant reproductive character evolution. Now is an opportune time to distill theoretical results into comprehensible insight, and to integrate these findings into the emerging new plant reproductive biology. We outline four theoretical insights for understanding the evolution of reproductive characters, and show how these allow researchers to dissect complex ecological scenarios into clear and evolutionarily relevant components.

Annals of conflicting results: looking back on electromagnetic field research.

Few environmental health issues are as contentious as the question of whether exposure to electromagnetic fields (EMFs) from power lines increases cancer risk. Among the many actors in this controversy, epidemiologists have played the leading role in raising the question and motivating research. Epidemiologic studies of the effects of exposure to power-line EMFs include the investigation by Dr. Gilles Thériault and colleagues into incidence rates of cancer among electric-utility workers in Quebec, Ontario and France. With the development of personal dosimeters to measure exposure to electric, magnetic and pulsed EMFs, occupational studies in the 1990s have made an important methodologic advance. But, as Thériault explains, improvements in assessing exposure have not yet translated into clear and consistent findings.