Path analysis of natural selection via survival and fecundity across contrasting environments in Avena barbata.

We employed path analysis to analyse natural selection through two major fitness components in each of three contrasting environments. Using a randomized block design, 188 Recombinant Inbred Lines (RILs) derived from a cross between contrasting ecotypes of Avena barbata were planted in common gardens in the greenhouse, and in two field sites typical of each ecotype's native habitat. Individuals were monitored for germination phenology, early growth, survival, final size, flowering phenology, reproductive allocation, fecundity and lifetime reproductive success. The variance/covariance matrix of the RIL (genotype) means was fit to a path model in which total fitness was made up of survival and fecundity (of survivors) components. In the greenhouse, all fitness variation was determined by fecundity variation (with no mortality), which was itself primarily determined by reproductive allocation mediated by date of first flowering. By contrast, in the field, early growth was the major determinant of survival, and final size was the major determinant of fecundity. Both components of fitness affected lifetime reproductive success equally in the field. Thus the major difference between greenhouse and field seems to be a shift from selection on allocation patterns in adults, to selection on resource acquisition, especially at earlier life stages. The pattern of selection was similar in the two field sites, despite the contrasting environments.

Heritable variation and genetic correlation of quantitative traits within and between ecotypes of Avena barbata.

We examined heritable variation for quantitative traits within and between naturally occurring mesic and xeric ecotypes of the slender wild oat (Avena barbata), and in 188 recombinant inbred lines derived from a cross between the ecotypes. We measured a suite of seedling and adult traits in the greenhouse, as well as performance-related traits in field sites native to the two ecotypes. Although the ecotypes were genetically diverged for most traits, few traits showed significant heritable variation within either ecotype. In contrast, considerable heritable variation was released in the recombinant progeny of the cross, and transgressive segregation was apparent in all traits. Heritabilities were substantially greater in the greenhouse than in the field, and this was associated with an increase in environmental variance in the field, rather than a decrease in genetic variance. Strong genetic correlations were evident among the recombinants, such that 22 measured traits could be well represented by only seven underlying factors, which accounted for 80% of the total variation. The primary axis of variation in the greenhouse described a trade-off between vegetative and reproductive allocation, mediated by the date of first flowering, and fitness was strongly correlated with this trade-off. Other factors in the greenhouse described variation in size and in seedling traits. Lack of correlation among these factors represents the release of multivariate trait variation through recombination. In the field, a separate axis of variation in overall performance was found for each year/site combination. Performance was significantly correlated across field environments, but not significantly correlated between greenhouse and field.

Fitness consequences of hybridization between ecotypes of Avena barbata: hybrid breakdown, hybrid vigor, and transgressive segregation.

Hybridization is an important factor in the evolution of plants; however, many of the studies that have examined hybrid fitness have been concerned with the study of early generation hybrids. We examined the early- and late-generation fitness consequences of hybridization between two ecotypes of the selfing annual Avena barbata in a greenhouse environment as well as in two natural environments. Fitness of early generation (F2) hybrids reflects both the action of dominance effects (hybrid vigor) and recombination (hybrid breakdown) and was not significantly different from that of the midparent in any environment. Fitness of later generation (F6) recombinant inbred lines (RILS) derived from the cross reflect both the loss of early generation heterozygosity as well as disruption of any coadapted gene complexes present in the parents. In all environments, F6 RILs were on average significantly less fit than the (equally homozygous) midparent, indicating hybrid breakdown through the disruption of epistatic interactions. However, the inbred F6 were also less fit than the heterozygous F2, indicating that hybrid vigor also occurs in A. barbata, and counteracts hybrid breakdown in early generation hybrids. Also, although the F6 generation mean is lower than the midparent mean, there are individual genotypes within the F6 generation that are capable of outperforming the parental ecotypes in the greenhouse. Fewer hybrid genotypes are capable of outperforming the parental ecotypes in the field. Overall, these experiments demonstrate how a single hybridization event can result in a number of outcomes including hybrid vigor, hybrid breakdown, and transgressive segregation, which interact to determine long-term hybrid fitness.

Mitochondrial haplotype distribution, seed dispersal and patterns of postglacial expansion of ponderosa pine.

Maternally inherited mtDNA in a secondary contact zone of ponderosa pine revealed a cline less than 10 km wide - much narrower than previously described. A survey of 76 populations gave no evidence either of intermixing or of a mosaic contact zone. Such sharp contact zones are consistent with diffusive range expansion, rather than long distance colonization. However, evidence for long distance seed dispersal events was found in two populations where haplotypes were observed far from their main area of occurrence. The results suggest a small number of long distance colonists with diffusive dispersal from these centres.

Cytonuclear disequilibrium and genetic drift in a natural population of ponderosa pine.

We measured the cytonuclear disequilibrium between 11 nuclear allozyme loci and both mitochondrial and chloroplast DNA haplotypes in a natural population of ponderosa pine (Pinus ponderosa, Laws). Three allozyme loci showed significant associations with mtDNA variation, while two other loci showed significant association with cpDNA. However, the absolute number of individuals involved in any of the associations was small, such that in none of the nuclear-organellar combinations was the difference between observed and expected numbers >11 individuals. Patterns of association were not consistent across loci or organellar genomes, suggesting that they are not the result of mating patterns, which would act uniformly on all loci. This pattern of disequilibria is consistent with the action of genetic drift and with existing knowledge of the structure of this population and thus does not imply the action of other evolutionary processes. The overall magnitude (normalized disequilibrium) of associations was greater for maternally inherited mtDNA than for paternally inherited cpDNA, though this difference was neither large nor significant. Such significant disequilibria involving the paternally inherited organelle indicate that not only are there a limited number of seed parents, but the effective number of pollen parents is also limited.

Galectin-3-mediated adherence of Proteus mirabilis to Madin-Darby canine kidney cells.

Proteus mirabilis is an important cause of urinary tract infections (UTIs) and can result in acute pyelonephritis. Proteus mirabilis expresses several, morphologically distinct, fimbrial species, and previous studies have shown that the nonagglutinating fimbriae (NAF) mediate bacterial adherence to a number of cell lines, including Madin-Darby canine kidney (MDCK) cells. Immunoblot overlay analysis of the plasma membrane fraction from MDCK cells with purified NAF revealed a 34-kDa band, which has been analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Database search identified galectin-3 as a potential protein candidate. Immunocytochemical assay of MDCK cells with a galectin-3-specific monoclonal antibody, anti-Mac-2, confirmed its presence on the plasma membrane extracellular surface. Preincubation of P. mirabilis with anti-Mac-2 monoclonal antibodies, specific for galectin-3, resulted in the inhibition of bacterial binding to MDCK cells. These data suggest a role for galectin-3, interacting with appropriately glycosylated surface receptors and P. mirabilis fimbriae, as a mediator of bacterial adherence in vitro.

The binding of Proteus mirabilis nonagglutinating fimbriae to ganglio-series asialoglycolipids and lactosyl ceramide.

Proteus mirabilis is a common opportunistic Gram-negative uropathogen that infects the upper urinary tract. We have examined the role of the nonagglutinating fimbriae (NAF) of P. mirabilis in mediating bacterial adhesion to cell surface receptors. Purified NAF of P. mirabilis were demonstrated to bind to a number of glycolipids, including asialo-GM1, asialo-GM2, and lactosyl ceramide (LacCer) in solid-phase binding assays and in thin layer chromatography (TLC) overlay assays. Furthermore, preincubation of the biotinylated NAF (Bt-NAF) with anti-NAF monoclonal antibodies resulted in inhibition of NAF binding to immobilized asialo-GM1, asialo-GM2, and LacCer. In adherence assays, P. mirabilis binding to Madin-Darby canine kidney (MDCK) cells was inhibited by murine anti-asialo-GM1 monoclonal antibodies H2G10 to about 50% of the binding level in the absence of the antibody, specific for the terminal beta-galactopyranosyl residue of asialo-GM1 (Harrison et al. 1998). The results of this study suggest that NAF of P. mirabilis recognize a GalNAc beta 1-4Gal moiety present in the ganglio-series of asialoglycolipids, and that the terminal beta-galactopyranosyl-containing glycoconjugates play a role in NAF-mediated adherence of P. mirabilis to MDCK cells. Similarly to other bacteria, P. mirabilis NAF was also shown to express the LacCer specificity.

Glacial refugia of limber pine (Pinus flexilis James) inferred from the population structure of mitochondrial DNA.

To make inferences about the glacial refugia that harboured the limber pine, Pinus flexilis James, we examined the range-wide population structure of mitochondrial DNA (mtDNA) with eight size variants in the second intron of nad1. The data consisted of haplotypes from 704 trees collected from 40 localities. The value of FST for these populations was 0.80, which is a much larger value than has been reported for allozymes and chloroplast DNA (cpDNA) in limber pine, and it suggests that the number of seeds moving among localities per generation is approximately 0.12. Gene flow of this magnitude would allow mutation and subsequent genetic drift to have a substantial impact on the population structure of mtDNA. The majority of the mtDNA haplotypes are restricted to minor portions of the geographical range. The data are consistent with mtDNA differentiation in seven glacial refugia, followed by dispersal out of those refugia.

Differential expression of nonagglutinating fimbriae and MR/P pili in swarming colonies of Proteus mirabilis.

The expression of nonagglutinating fimbriae (NAF) and mannose-resistant/Proteus-like (MR/P) pili in swarming colonies of Proteus mirabilis was investigated. Elongated swarmer cells do not express pili, and the relative number of bacteria expressing NAF during swarming and early consolidation phases was very low (<5%). Relative expression of NAF in a terrace increased to approximately 30% at 48 h. We also determined the expression of NAF and MR/P pili in two phenotypically distinguishable regions of each terrace. The expression of both NAF and MR/P pili was always higher in the region closer (proximal) to the middle of the colony than in the distal region of the terrace. The relative numbers of bacteria expressing NAF or MR/P pili in the proximal region were between 39.1 and 63% and between 5.9 and 7.7%, respectively. In the distal region, expression levels were between 20.8 and 27.3% and between 3.7 and 5. 6%, respectively. A time course experiment testing NAF expression in both the proximal and distal regions of a terrace indicated that NAF expression in the proximal regions was always higher than in the distal regions and increased to a plateau 40 to 50 h after the start of the swarming phase for any given terrace. These results indicate that expression of NAF or MR/P pili in swarming colonies of P. mirabilis is highly organized, spatially and temporally. The significance of this controlled differentiation remains to be uncovered.

Phosphatidyl choline-mediated inhibition of Streptococcus pneumoniae adherence to type II pneumocytes in vitro.

Nearly 80% of the adherence of several strains of Streptococcus pneumoniae to A549 lung cells was inhibited by dimyristoylphosphatidylcholine (DMPC), as well as by the following mixtures of lipids: DMPC/globoside, DMPC/asialo GM-1 and DMPC/asialo GM-1/globoside liposomes. Control phosphatidylserine liposomes were ineffective at inhibiting bacterial adherence demonstrating the specificity of the interaction between bacteria and liposomes. FITC-labelled bacteria were shown to adhere directly to silica beads coated with DMPC. The proportion of S. pneumoniae bacteria binding to DMPC-coated beads did not exceed 20% of the bacterial population as shown by the binding isotherm. This clearly demonstrates that only a fraction of the bacterial population (a subpopulation) was capable of binding to the beads. The specificity of bacterial binding to DMPC was further demonstrated by surface plasmon resonance. By this latter technique, the affinity between DMPC and bacteria was shown to be high and substantially non-reversible. Finally, we established that in order to be efficient at inhibiting bacterial binding to A549 cells the average liposome diameter must be greater than approximately 200 nm suggesting that a multivalent attachment of the bacterium to a liposome is required for high affinity binding.

The effect of growth conditions on in vitro adherence, invasion, and NAF expression by Proteus mirabilis 7570.

Proteus mirabilis is a common cause of upper urinary tract infections. Fimbriae-mediated adherence of this organism to urinary tract epithelium and invasion of host cells are factors thought to be important in its pathogenesis. We have assessed the effect of growth in serum, blood, and urine on the ability of P. mirabilis 7570 to adhere to and invade in vitro the cell line EJ/28, derived from a human urinary tract tumour, and to express nonagglutinating fimbriae (NAF). Proteus mirabilis was capable of adhering to EJ/28 cells to varying degrees depending upon the growth conditions used. It was invasive under all conditions, except when grown in urine, and was found to be particularly so when serum or blood was present in the media. Expression of NAF occurred under all growth conditions examined and was limited only by a decrease in temperature.

A decision analysis of mandatory compared with voluntary HIV testing in pregnant women.

BACKGROUND: The benefit of antiretroviral therapy in reducing maternal-fetal transmission of HIV during pregnancy has caused a public policy debate about the relative benefits of mandatory HIV screening and voluntary HIV screening in pregnant women. OBJECTIVE: To evaluate the benefits and risks of mandatory compared with voluntary HIV testing of pregnant women to help guide research and policy. DESIGN: A decision analysis that incorporated the following variables: acceptance and benefit of prenatal care, acceptance and benefit of zidovudine therapy in HIV-infected women, prevalence of HIV infection, and mandatory compared with voluntary HIV testing. MEASUREMENTS: The threshold deterrence rate (defined as the percentage of women who, if deterred from seeking prenatal care because of a mandatory HIV testing policy, would offset the benefit of zidovudine in reducing vertical HIV transmission) and the difference between a policy of mandatory testing and a policy of voluntary testing in the absolute number of HIV-infected infants or dead infants. RESULTS: Voluntary HIV testing was preferred over a broad range of values in the model. At baseline, the threshold deterrence rate was 0.4%. At a deterrence rate of 0.5%, the number of infants (n = 167) spared HIV infection annually in the United States under a mandatory HIV testing policy would be lower than the number of perinatal deaths (n = 189) caused by lack of prenatal care. CONCLUSIONS: The most important variables in the model were voluntary HIV testing, the deterrence rate associated with mandatory testing compared with voluntary testing, and the prevalence of HIV infection in women of child-bearing age. At high levels of acceptance of voluntary HIV testing, the benefits of a policy of mandatory testing are minimal and may create the potential harms of avoiding prenatal care to avoid mandatory testing.

The expression of nonagglutinating fimbriae and its role in Proteus mirabilis adherence to epithelial cells.

Proteus mirabilis is a common causative agent of human urinary tract infections, especially in catheterized patients and in those patients with structural abnormalities of the urinary tract. In addition to the production of hemolysin and urease, fimbriae-mediated adherence to uroepithelial cells and kidney epithelium may be essential for virulence of P. mirabilis. A single P. mirabilis strain is capable of expressing several morphologically distinct fimbrial species, which can each be favoured by specific in vitro growth conditions. The fimbrial species reported to date include mannose-resistant/Proteus-like fimbriae, ambient temperature fimbriae, P. mirabilis fimbriae, and nonagglutinating fimbriae (NAF). Here, using intact bacteria or purified NAF as immunogens, we have generated the first reported NAF-specific monoclonal antibodies (mAbs). Bacteria expressing NAF as their only fimbrial species adhered strongly to a number of cell lines in vitro, including uroepithelial cell lines. Binding of P. mirabilis was markedly reduced following preincubation with NAF-specific mAbs and Fab fragments. The presence of NAF with highly conserved N-terminal sequences on all P. mirabilis strains so far examined, combined with the ability of both anti-NAF mAbs and purified NAF molecules to inhibit P. mirabilis adherence in vitro, suggests that NAF may contribute to the pathogenesis of P. mirabilis.

Skin carcinogenicity of condensed asphalt roofing fumes and their fractions following dermal application to mice.

Condensed roofing asphalt fumes, generated at 316 degrees C, were collected by cold trap condensation and fractionated by preparative high performance liquid chromatography. Chemical classes in each of the fractions (A-E) were identified by gas chromatography/mass spectroscopy. The fractions, various combinations of fractions, the raw and heated asphalt, the neat asphalt fume and the reconstituted asphalt were tested for carcinogenicity, and three fractions were tested for cocarcinogenicity and tumor promotion with benzo[a]pyrene (BaP). The skin application carcinogenesis bioassay was conducted by twice weekly application of test materials in 0.05 ml of acetone/cyclohexane (1:1) for 104 weeks to 40 groups of male C3H/HeJ mice (30/group). Fractions were applied at a mass in proportion to their amount in the neat asphalt fumes. In addition, the neat asphalt fume was tested on Sencar mice to determine if this strain was more susceptible to the carcinogenic effects of the fumes. Condensed neat asphalt fumes produced similar and statistically significant increased tumor yields of papillomas and carcinomas in both strains as compared to respective vehicle controls. Recombination of all fractions resulted in a tumor response similar to neat asphalt fumes. Among individual fractions, C was most potent, followed by B. The other single fractions were without significant tumorigenic activity. Combinations containing fractions B and C were most active among the mixtures that were assayed and no evidence of enhancement of tumorigenesis in the mixtures was found. No significant cocarcinogenic or tumor promoting activity was observed with fractions A, D, or E and BaP. Raw unheated asphalt produced a few tumors in C3H mice, but no tumors were seen when raw asphalt heated to 316 degrees C, with the fumes permitted to escape, was applied.

A comparison of population differentiation across four classes of gene marker in limber pine (Pinus flexilis James).

We examined genetic differentiation among seven populations of limber pine using four classes of gene marker. Among-population differentiation was much higher for maternally inherited mitochondrial DNA polymorphisms than for paternally inherited chloroplast DNA, indicating that wind-dispersed pollen is the main agent of gene flow. Chloroplast DNA differentiation is consistent with gene flow estimated in a prior paternity analysis. Using the estimates of seed and pollen flow derived from mtDNA and cpDNA differentiation, we predicted the value of Fst expected at nuclear loci. Allelic frequency differentiation at seven allozyme loci was relatively homogeneous across loci and consistent with the level of differentiation predicted from the organellar haplotypes. By contrast four of the nine randomly applied polymorphic DNA (RAPD) markers we examined were more strongly differentiated than this prediction, suggesting the action of diversifying selection. However, the differentiated RAPDs and mtDNA were concordant in dividing the populations into two groups, suggesting some historical division. Simulations show that such historical division can increase the interlocus variance in Fst, but neither a historical nor an equilibrium model could account for the joint distribution of Fst estimates across both allozyme and RAPD loci. Thus at least one group of loci appears to be experiencing natural selection.

Method of delivery of the nonvertex second twin: a community hospital experience.

The purpose of this study is to examine the incidence of cesarean section and fetal distress complicating the delivery of the second twin in vertex-nonvertex twin gestations in which the second twin underwent either breech extraction or external version. The intrapartum courses of 510 twin gestations delivered at a community hospital over a 10-year period were retrospectively analyzed. All vertex-nonvertex twin gestations were identified in which the second twin underwent attempted breech extraction or external version. Exclusion criteria included birthweight < or = 1,500 g, fetal anomaly, intrauterine demise, and monoamniotic twins. Of the 76 twin sets that met inclusion criteria, 33 underwent external version and 43 underwent primary breech extraction. The two groups had similar demographic characteristics. External version compared to breech extraction was associated with a significantly greater incidence of cesarean section (8/33 vs. 1/43, P = .008) and fetal distress (8/33 vs. 1/43, P = .008). There was no difference between groups in neonatal outcome for the second twin as measured by length of stay, 5-minute Apgar < 7, intensive care unit admissions, hyaline membrane disease, intraventricular hemorrhage, and traumatic birth injury. In conclusion, the increased incidence of cesarean section and fetal distress in patients undergoing attempted external version suggests that breech extraction may be the preferable route of delivery for the nonvertex second twin weighing more than 1,500 g.

Path analysis of natural selection on plant chemistry: the xylem resin of ponderosa pine.

We analyzed the pattern of correlations among fitness components, herbivory, and resin characteristics in a natural all-aged stand of ponderosa pine, to infer the strength and mechanism of natural selection on plant chemistry. Male and female cone production were monitored yearly for 15 years, and levels of herbivory for 9 years in 165 trees. Resin flow rate and monoterpene composition were determined for these same trees. Multiple regression of fitness components on resin characteristics showed significant associations consistent with directional selection for increased resin flow rates and increased proportions of α- and ß-pinene, myrcene and terpinolene. However, negative correlations among monoterpene fractions of the resin constrained the overall selection. Selective herbivory by aphids approached statistical significance and monoterpenes showed some (non-significant) effect as deterrents against deer browse. Resin characteristics were not correlated with attack by cone insects or porcupines. However, the association between resin characteristics and fitness is significantly different from that predicted by the path coefficients involving herbivores. Therefore the hypothesis that these herbivores mediate selection on the resin is not supported by the observed pattern of correlations among resin characteristics, herbivory, growth and fecundity. In this population, most of the association between resin characteristics and fitness appears to be mediated by some other factor independent of attack by herbivore species present.

Emergent cervical cerclage: predictors of success or failure.

Emergent cervical cerclage is a procedure not commonly performed in general clinical practice. The outcome of pregnancies requiring emergent cerclage is based on limited information. The factors that predict success are not well known. Previous studies have suggested that advanced cervical dilation, significant cervical effacement, and the presence of prolapsed membranes are correlated with cerclage failure. We present a retrospective review of maternal characteristics predictive of perinatal survival. Analysis showed the presence of membrane prolapse to be the strongest predictor of poor outcome. Analysis also reveals a significant association between initial white blood cell count and perinatal outcome. This information may be helpful in decision making regarding adjunctive procedures such as amniocentesis and counseling patients regarding the likely outcome.

Treatment of recurrent eczema herpeticum in pregnancy with acyclovir.

BACKGROUND: Eczema herpeticum is an uncommon manifestation of an infection with herpes simplex virus (HSV). The disease is primarily seen in patients with histories of atopic eczema. Eczema herpeticum may be a life-threatening illness, but the mortality is felt to be <10% with modern antiviral and antibacterial agents. The use of acyclovir for other viral infections secondary to herpesvirus in pregnancy has been well documented. The authors now present a case report of eczema herpeticum treated with acyclovir during pregnancy. CASE: A patient with a history of eczema herpeticum presented in pregnancy with a recurrence. She was successfully treated with intravenous (IV) acyclovir with good maternal and fetal outcome. CONCLUSION: Acyclovir may be utilized in pregnancy for several manifestations of HSV including eczema herpeticum.