Genic capture and the genetic basis of sexually selected traits in the zebra finch

Abstract The lek paradox, in which female choice erodes genetic variation in male sexually selected traits, is a fundamental issue in sexual selection. If females gain only genetic benefits from preferentially having their ova fertilized by males with particular traits, what maintains variation in these traits? Under strong directional selection mediated through mate choice, the alleles for beneficial male traits are expected to go to fixation and exhibit little variation. A theoretical solution to the lek paradox is the genic capture hypothesis which states that: costly male traits subject to female choice are condition dependent, that male condition is dependent on genes at many loci and exhibits additive genetic variance, and that positive genetic correlations exist between sexually selected traits and condition. Using a captive population of the zebra finch Taeniopygia guttata, we tested two key predictions from this model: (1) that genetic variance exists in beak color which is a sexually selected trait, but also in condition and immune function, and (2) that positive genetic correlations exist between condition and beak color, and between beak color, condition, and immune function. Genetic parameters were estimated from a large breeding experiment involving 81 sires, 972 offspring, a pedigree of 1526 individuals, using the animal model. We employed the following index of body condition: residuals from a log‐log plot of body mass on tarsus length following a standardized and extended period of exercise, in which residual mass is known to reflect fat and protein reserves. Our results were broadly consistent with the genic capture hypothesis because we found (1) additive genetic variation in beak color and immune function and condition, and (2) positive genetic correlations between condition and beak color, and between condition, beak color, and several assays of immune responsiveness. However, both of these results need qualification. In the first case we identified an important general problem in estimating the coefficient of additive genetic variance (CV_A) in body condition. In the second case, although most of the genetic correlations were positive as predicted, only some were statistically significant, possibly due to our relatively small sample sizes, because genetic correlations typically have large standard errors and therefore require very large samples to be statistically significant. The statistically significant, positive genetic correlations included those between beak color and immune function (response to tetanus), and between immune function (response to tetanus) and condition, both of which indicate that females gain good genes from mating with males in good condition and/or with a redder beak color. We discuss the implications of our results for devising more rigorous but pragmatic tests of the genic capture hypothesis.     

Assessing the impact of denitrifier-produced nitric oxide on other bacteria

A series of experiments was undertaken to learn more about the impact on other bacteria of nitric oxide (NO) produced during denitrification. The denitrifier Rhodobacter sphaeroides 2.4.3 was chosen as a denitrifier for these experiments. To learn more about NO production by this bacterium, NO levels during denitrification were measured by using differential mass spectrometry. This revealed that NO levels produced during nitrate respiration by this bacterium were in the low muM range. This concentration of NO is higher than that previously measured in denitrifiers, including Achromobacter cycloclastes and Paracoccus denitrificans. Therefore, both 2.4.3 and A. cycloclastes were used in this work to compare the effects of various NO levels on nondenitrifying bacteria. By use of bacterial overlays, it was found that the NO generated by A. cycloclastes and 2.4.3 cells during denitrification inhibited the growth of both Bacillus subtilis and R. sphaeroides 2.4.1 but that R. sphaeroides 2.4.3 caused larger zones of inhibition in the overlays than A. cycloclastes. Both R. sphaeroides 2.4.3 and A. cycloclastes induced the expression of the NO stress response gene hmp in B. subtilis. Taken together, these results indicate that there is variability in the NO concentrations produced by denitrifiers, but, irrespective of the NO levels produced, microbes in the surrounding environment were responsive to the NO produced during denitrification.     

In adult onset myositis, the presence of interstitial lung disease and myositis specific/associated antibodies are governed by HLA class II haplotype, rather than by myositis subtype

The Fcγ receptors play important roles in the initiation and regulation of many immunological and inflammatory processes, and genetic variants (FCGR) have been associated with numerous autoimmune and infectious diseases. The data in rheumatoid arthritis (RA) are conflicting and we previously demonstrated an association between FCGR3A and RA. In view of the close molecular proximity with FCGR2A, FCGR2B and FCGR3B, additional polymorphisms within these genes and FCGR haplotypes were examined to refine the extent of association with RA. Biallelic polymorphisms in FCGR2A, FCGR2B and FCGR3B were examined for association with RA in two well characterized UK Caucasian and North Indian/Pakistani cohorts, in which FCGR3A genotyping had previously been undertaken. Haplotype frequencies and linkage disequilibrium were estimated across the FCGR locus and a model-free analysis was performed to determine association with RA. This was followed by regression analysis, allowing for phase uncertainty, to identify the particular haplotype(s) that influences disease risk. Our results reveal that FCGR2A, FCGR2B and FCGR3B were not associated with RA. The haplotype with the strongest association with RA susceptibility was the FCGR3A–FCGR3B 158V-NA2 haplotype (odds ratio 3.18, 95% confidence interval 1.13–8.92 [P = 0.03] for homozygotes compared with all genotypes). The association was stronger in the presence of nodules (odds ratio 5.03, 95% confidence interval 1.44–17.56; P = 0.01). This haplotype was also more common in North Indian/Pakistani RA patients than in control individuals, but not significantly so. Logistic regression analyses suggested that FCGR3A remained the most significant gene at this locus. The increased association with an FCGR3A–FCGR3B haplotype suggests that other polymorphic variants within FCGR3A or FCGR3B, or in linkage disequilibrium with this haplotype, may additionally contribute to disease pathogenesis.     

Species richness, temporal variability and resistance of biomass production in a Mediterranean grassland

We studied the temporal variability and resistance to perturbation of the biomass production of grassland communities from an experimental diversity gradient (the Portuguese BIODEPTH project site). With increasing species richness relative temporal variability (CV) of plant populations increased but that of communities decreased, supporting the insurance hypothesis and related theory. Species‐rich communities were more productive than species‐poor communities in all three years although a natural climatic perturbation in the third year (frequent frost and low precipitation) caused an overall decrease in biomass production. Resistance to this perturbation was constant across the experimental species richness gradient in relative terms, supporting a similar response from the Swiss BIODEPTH experiment. The positive biomass response was generated by different combinations of the complementarity and selection effects in different years. Complementarity effects were positive across mixtures on average in all three years and positively related to diversity in one season. The complementarity effect declined following perturbation in line with total biomass but, counter to predictions, in relative terms overyielding was maintained in all years. Selection effects were positively related to diversity in one year and negative overall in the other two years. The response to perturbation varied among species and for the same species growing in monoculture and mixture, but following the frost communities were more strongly dominated by species with lower monoculture biomass and the selection effect was more negative. In total, our results support previous findings of a positive relationship between diversity and productivity and between diversity and the temporal stability of production, but of no effect of diversity on the resistance to perturbation. We demonstrate for the first time that the relative strength of overyielding remained constant during an exceptional natural environmental perturbation.     

Endothelial cells of the meningeal capillaries in the rainbow trout: A freeze-fracture study

Meningeal capillaries are unfenestrated. They are made up of endothelial cells that have a pinocytotic caveolae density of 41 ± 11/μm² and 89 ± 21/μm² on the abluminal and luminal sides respectively. The total density of intramembrane particles is not significantly different between the luminal and the abluminal membranes; however, the coefficients of partition are significantly different (P< 0.001). One or two strands of tight junctions occur between adjacent cells but no gap junctions nor desmosomes exist. The density of nuclear pores is less than 3.2/μm². An abundance of intermediate filaments and free vesicles, some of which are seriated, characterize the cytoplasm. The functional significance of these findings is discussed.     

Secretion of an Aeromonas hydrophila aerolysin by a mutant strain of Escherichia coli

Abstract Expression of the Aeromonas hydrophila AH2 aerolysin was analysed in 2 mutant derivatives of Escherichia coli 5K that overproduce E. coli haemolysin, encoded by the multicopy plasmid pANN202–312. When plasmid pHPC3–700 carrying the A. hydrophila aerolysin genes was transformed into one of the mutants, Hha-2T, the transformants produced external aerolysin. Neither the parental 5K strain or the other mutant, Hha-1T, showed extracellular aerolysin activity. For strain Hha-2T, the kinetics of external aerolysin production was similar to that previously reported for A. hydrophila AH2. No cell lysis or release of other proteins to the culture medium could be detected for the period of time that strain Hha-2T exported aerolysin into the external medium.     

Use of phenotypic suppression for direct selection of loss of aminoglycoside antibiotic resistance determinants

Summary A strain of Escherichia coli containing a conditional drug dependent arginine auxotrophy was used to select for the loss of plasmid and/or transposon encoded kanamycin (Km) or streptomycin (Sm) resistance determinants. Because these determinants inactivate the corresponding drug thus elminating drug suppression, loss of the drug-resistance determinants was selected directly by growth on minimal media plates containing sub-lethal dosages of the drug. This method was used to select loss of Km or Sm resistance determinants due to loss of plasmids, transposition from plasmid to chromosome, and eduction of transposons from the chromosome. Drug suppression was compared to phage PRD1 resistance in selecting for loss of plasmid vehicles during transposition and was found to be 10-1,000 times more efficient. Eighty percent of the eductant clones had undergone imprecise eductions suggesting that this method may be useful in selecting stable deletion mutants. An antibiotic suppressible strain of Pseudomonas stutzeri was obtained implying a broad utility of this selection procedure.     

Gender in atrial fibrillation: Ten years later

Background: Atrial fibrillation (AF) is the most common arrhythmia encountered in both male and female patients.Objective: This evidence-based update attempts to address the advances in the science of AF management in light of key gender issues.Methods: In October 2009, 2 investigators (H.I.M. and B.D.P.) independently searched MEDLINE (PubMed [1950–2009] and Ovid [2000–2009]) for all publication types in the English language, using database-specific controlled vocabulary describing the concepts of AF and gender (atrial fibrillation, gender, women, and men for PubMed; atrial fibrillation and gender for Ovid). The reference sections from the identified publications were also used. The methodologic quality of publications, their content relevance, and the authors' expert opinions guided publication inclusion in this evidence-based narrative review. Articles relevant to gender differences in pathophysiology, outcomes, and treatment of AF are summarized and discussed.Results: Based on current available data, mortality is greater for women with AF than for men with AF. Women with AF have a higher risk of stroke compared with their male counterparts. Women derive the greatest benefit from anticoagulation in AF. There are no significant sex differences in major bleeding risk from warfarin. Women tend to be more symptomatic from AF than are men, but fare worse than men when a rhythm-control strategy is utilized with antiarrhythmic medications. Women have an increased risk for torsades de pointes when taking sotalol or dofetilide, and have a higher risk of bradyarrhythmias when taking antiarrhythmics. AF catheter ablation is successful and beneficial for selected patients of both sexes, although women may incur higher procedural bleeding complications. Women tend to be referred for AF ablation less and later than are men.Conclusions: The past decade has witnessed significant progress in the understanding and management of AF. Awareness of key sex-specific differences in AF allows for a more safe, effective, and personalized approach to the management of this disorder.