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T Giraud

Publications and source records attributed to T Giraud.

At least 19 recordsLinked to original sources
PubMed2006

Antagonistic pleiotropy may help population-level selection in maintaining genetic polymorphism for transmission rate in a model phytopathogenic fungus.

It has been shown theoretically that the conditions for the maintenance of polymorphism at pleiotropic loci with antagonistic effects on fitness components are rather restrictive. Here, we use a metapopulation model to investigate whether antagonistic pleiotropy could help maintain polymorphism involving common deleterious alleles in the phytopathogenic fungus Microbotryum violaceum. This fungus causes anther smut disease of the Caryophyllaceae. A previous model has shown that the sex-linked deleterious alleles can be maintained under a metapopulation structure, when intra-tetrad selfing (mating between products of the same meiosis) is high, due to founder effects and selection at the population level. Here, we add two types of pleiotropic advantages to the metapopulation model. A competitive advantage for strains carrying the sex-linked deleterious alleles did not facilitate their maintenance because competitive situations were too rare. In contrast, higher spore production did facilitate the maintenance of the deleterious alleles at low intra-tetrad mating rates and with a large advantage for spore production. These results show that antagonistic pleiotropy may promote the persistence of genetic variation, in combination with other selective forces.

Basidiomycota↗
PubMed2006

Pathogen relatedness affects the prevalence of within-host competition.

Although the evolutionary consequences of within-host competition among pathogens have been examined extensively, there exists a critical gap in our understanding of factors determining the prevalence of multiple infections. Here we examine the effects of relatedness among strains of the anther-smut pathogen Microbotryum violaceum on the probability of multiple infection in its host, Silene latifolia, after sequential inoculations. We found a significantly higher probability of multiple infection when interacting strains were more closely related, suggesting mechanisms of competitive exclusion that are conditional on genotypic characteristics of the strains involved. Pathogen relatedness therefore determines the prevalence of multiple infection in addition to its outcome, with important consequences for our understanding of virulence evolution and pathogen population structure and diversity.

Basidiomycota↗
PubMed2006

Common sex-linked deleterious alleles in a plant parasitic fungus alter infection success but show no pleiotropic advantage.

Microbotryum violaceum is a fungus that causes the sterilizing anther smut disease in Caryophyllaceae. Its diploid teliospores normally produce equal proportions of haploid sporidia of its two mating types. However natural populations contain high frequencies of individuals producing sporidia of only one mating type ('biased strains'). This mating type-ratio bias is caused by deleterious alleles at haploid phase ('haplo-lethals') linked to the mating type locus that can be transmitted only by intra-tetrad selfing. We used experimental inoculations to test some of the hypotheses proposed to explain the maintenance of haplo-lethals. We found a disadvantage of biased strains in infection ability and high intra-tetrad mating rates. Biased strains had no higher competitive ability nor shorter latency and their higher spore production per flower appeared insufficient to compensate their disadvantages. These findings were only consistent with the hypothesis that haplo-lethals are maintained under a metapopulation structure because of high intra-tetrad selfing rates, founder effects and selection at the population level.

Basidiomycota↗
PubMed2005

High genetic diversity in French invasive populations of common ragweed, Ambrosia artemisiifolia, as a result of multiple sources of introduction.

Ambrosia artemisiifolia is an aggressive North American annual weed, found particularly in sunflower and corn fields. Besides its economic impact on crop yield, it represents a major health problem because of its strongly allergenic pollen. Ragweed was imported inadvertently to Europe in the 18th century and has become invasive in several countries, notably in the Rhône Valley of France. It has recently expanded in both the Provence-Alpes-Côte-d'Azur and Bourgogne regions. As first steps towards understanding the causes and mechanisms of ragweed invasion, genetic variability of French and North American populations was analysed using microsatellites. Overall genetic variability was similar in North America and in the Rhône-Alpes region, but within-population levels of genetic variability were surprisingly lower in native than in invasive French populations. French populations also exhibited lower among-population differentiation. A significant pattern of isolation by distance was detected among North American populations but not among French populations. Assignment tests and distribution of rare alleles did not point to a single origin for all French populations, nor for all individuals within populations and private alleles from different North American populations were found in the same French populations. Indeed, within all French populations, individual plants were roughly equally assigned to the different North American populations. Altogether, these results suggest that the French invasive populations include plants from a mixture of sources. Reduced diversity in populations distant from the original area of introduction indicated that ragweed range expansion probably occurred through sequential bottlenecks from the original populations, and not from subsequent new introductions.

Ambrosia↗
PubMed2005

The anther smut disease on Gypsophila repens: a case of parasite sub-optimal performance following a recent host shift?

The study of how parasites adapt to new hosts is of great importance for understanding the emergence of new diseases. Here, we report a study of the anther smut disease on Gypsophila repens (Caryophyllaceae). In contrast to what is usually found on other host species, infected natural populations of G. repens are extremely rare. Moreover, symptoms of diseased plants are incomplete and highly variable over the time. These results suggest that the fungus infecting G. repens is a case of a parasite not capable of exploiting its host optimally. Molecular analyses of Microbotryum violaceum strains infecting this and other Caryophyllaceae revealed that this sub-optimal behaviour probably resulted from a recent host shift from the morphologically similar plant Petrorhagia saxifraga. With its exceptionally low virulence and prevalence, but apparent self-sustainability, the disease on G. repens may thus represent an interesting case study for investigating the conditions leading to adaptation of parasites on new hosts.

Adaptation, Physiological↗
PubMed2004

Patterns of within population dispersal and mating of the fungus Microbotryum violaceum parasitising the plant Silene latifolia.

This study explores the patterns of dispersal and mating of the anther smut Microbotryum violaceum, a model species in genetics and evolutionary biology. A French metapopulation of the fungus collected from its caryophyllaceous host Silene latifolia was analysed using microsatellites. The genetic diversity was low, populations were strongly differentiated, and there was no pattern of isolation by distance among populations. There was a strong deficit in heterozygotes, confirming the high self-fertilisation rates suggested by previous studies. Within populations there was a strong pattern of isolation by distance, with identical genotypes being highly clustered. This indicates that fungal spores are dispersed mostly between adjacent plants, and such local dispersal is important for understanding the dynamics and evolution of this disease. Local clusters of identical heterozygous genotypes did not contain significantly fewer individuals than did clusters of homozygous genotypes. As selfing between products of independent meiotic events (intertetrad selfing) rapidly reduces heterozygosity, this suggests that intratetrad matings are frequent, which helps to explain the puzzling maintenance of a sex-ratio distortion in M. violaceum.

Founder Effect↗
PubMed2000

Population structure and mating biology of the polygynous ponerine ant Gnamptogenys striatula in Brazil.

Gnamptogenys striatula is a polygynous ponerine ant, whose colonies contain either several differentiated queens or several gamergates. Population structure, queen mating frequency and deviation from random mating were investigated in a north-eastern Brazilian population. Eight workers from each of 33 queenright colonies and 17 queens and their progeny (20-40 offspring) were genotyped using eight variable microsatellite markers. Population differentiation tests indicated limited gene flow at the scale of several kilometres, and tests of isolation by distance revealed population viscosity at the scale of a few metres. This population structure, together with the frequent colony migrations and fissions observed in the field, suggest that new nests are founded by budding in G. striatula. Genetic data showed that 13 of our 17 queens were single-mated and four were double-mated. The estimation of the range of maximal frequency of double-mated queens in the population was 0.232-0.259, demonstrating that mating frequency is low in G. striatula. The low estimated mean relatedness between the 17 queens and their mates (-0. 04 +/- 0.49) indicated no evidence of inbreeding in G. striatula.

Animals↗
PubMed1998

The minisatellite MSB1, in the fungus Botrytis cinerea, probably mutates by slippage.

A minisatellite was identified in the intron of the ATP synthase of the filamentous fungus Botrytis cinerea, and it was named MSB1. This is the second fungal minisatellite described to date. Its 37-bp repeat unit is AT-rich, and it is found at only one locus in the genome. The introns of 47 isolates of Botrytis species were sequenced. The number of tandem repeats varied only from 5 to 11, but there were many repeat variants. The structure of MSB1 is peculiar: the variants are in the same physical order in all individuals, and this order follows the most parsimonious tree. These original characteristics, together with a total lack of recombination between alleles of the flanking regions, suggest that MSB1 probably mutates by slippage. MSB1 was found in the intron of the ATP synthase of all of the Botrytis species analyzed, but the repeat unit was not found in any other genus examined, including Sclerotinia, which is the genus closest to Botrytis.

Adenosine Triphosphatases↗
PubMed1997

Telomeric DNA of Botrytis cinerea: a useful tool for strain identification.

Telomeric DNA was isolated from the phytopathogenic fungus Botrytis cinerea by PCR using only the oligonucleotide primer (CCCTAA)4. As with other filamentous fungi, B. cinerea has a short TTAGGG telomeric repeat. Telomere-linked restriction fragment length polymorphism (RFLP) was found in strains of B. cinerea isolated from different host plants collected from different regions at different periods. Almost every strain had a specific RFLP pattern, including those collected from the same plant one month apart. Thus, this marker appears to be an excellent tool to show the great polymorphism of B. cinerea strains by fingerprinting. The Southern blots of some strains of B. cinerea showed one band which was much more intense than the others, suggesting that the majority of telomere-associated sequences have the same sequence.

Base Sequence↗
PubMed1997

Effect of the direct nitric oxide donors linsidomine and molsidomine on angiographic restenosis after coronary balloon angioplasty. The ACCORD Study. Angioplastic Coronaire Corvasal Diltiazem.

BACKGROUND: Nitric oxide (NO) donors, in addition to their vasodilator effect, decrease platelet aggregation and inhibit vascular smooth muscle cell proliferation. These actions could have beneficial effects on restenosis after coronary balloon angioplasty. METHODS AND RESULTS: In a prospective multicenter, randomized trial, 700 stable coronary patients scheduled for angioplasty received direct NO donors (infusion of linsidomine followed by oral molsidomine) or oral diltiazem. Treatment was started before angioplasty and continued until 12 to 24 hours before follow-up angiography at 6 months. The primary study end point was minimal lumen diameter, assessed by quantitative coronary angiography, 6 months after balloon angioplasty. Clinical variables were well matched in both groups. However, despite intracoronary administration of isosorbide dinitrate, the reference diameter in the NO donor group was significantly greater than in the diltiazem group on the preangioplasty, postangioplasty, and follow-up angiograms. Pretreatment with an NO donor was associated with a modest improvement in the immediate angiographic result compared with pretreatment with diltiazem (minimum luminal diameter, 1.94 versus 1.81 mm; P = .001); this improvement was maintained at the 6-month angiographic follow-up (minimal lumen diameter, 1.54 versus 1.38 mm; P = .007). The extent of late luminal narrowing did not differ significantly between groups (loss index in the NO donor and diltiazam groups, 0.35 +/- 0.78 and 0.46 +/- 0.74, respectively; P = .103). Restenosis, defined as a binary variable (> or = 50% stenosis), occurred less often in the NO donor group (38.0% versus 46.5%; P = .026). Combined major clinical events (death, nonfatal myocardial infarction, and coronary revascularization) were similar in the two groups (32.2% versus 32.4%). CONCLUSIONS: Treatment with linsidomine and molsidomine was associated with a modest improvement in the long-term angiographic result after angioplasty but had no effect on clinical outcome. The improved angiographic result related predominantly to a better immediate procedural result, because late luminal loss did not differ significantly between groups.

Aged↗
PubMed1997

Comparative efficacy of the intravenous administration of linsidomine, a direct nitric oxide donor, and isosorbide dinitrate in severe unstable angina. A French multicentre study. French Group of Investigators.

AIMS: Although linsidomine shares common properties with nitrovasodilators, it releases nitric oxide directly without catalytic involvement by thiols. We conducted a prospective, randomized, multicentre, parallel group, single-blind study to compare the efficacy of intravenous administration of linsidomine with that of isosorbide dinitrate in unstable angina. METHODS AND RESULTS: Between November 1990 and July 1992, 568 patients with suspected unstable angina (class IIIB of the Braunwald classification) received a continuous infusion of either linsidomine (1 mg.h-1 on average) or isosorbide dinitrate (2.5 mg.h-1 on average) for 72 h. All patients received concomitant aspirin and intravenous heparin, 81% beta-blockers and 38% calcium antagonists. Holter monitoring was performed in all patients and analysed blindly. Only 25% of the patients had at least one episode of chest pain during the study (24.6% vs 25.8% in the linsidomine and isosorbide dinitrate groups, P = 0.74), of which 12% were associated with ECG changes. Holter criteria yielded similar results in both groups: 33% of patients presented episodes of myocardial ischaemia (32.6% vs 33.9% in the linsidomine and isosorbide dinitrate groups, P = 0.74), while 45% showed episodes of ventricular arrhythmia (43.5% vs 46.5% in the linsidomine and isosorbide dinitrate groups, P = 0.48). The incidence of serious clinical events at 72 h (death, myocardial infarction or myocardial revascularization) was 6.5% (5% vs 8% in the linsidomine and isosorbide dinitrate groups, P = 0.17). CONCLUSION: Intravenous linsidomine is at least as efficacious as isosorbide dinitrate in the stabilization of patients with severe unstable angina.

Aged↗
PubMed1997

RFLP markers show genetic recombination in Botryotinia fuckeliana (Botrytis cinerea) and transposable elements reveal two sympatric species.

Molecular markers revealed that Botryotinia fuckeliana (the teleomorph of Botrytis cinerea), a haploid, filamentous, heterothallic ascomycete, contained a large amount of intrapopulation genetic variation. The markers were used to determine the mode of reproduction and the population structure of this fungus. We did not detect any differentiation between isolates from different organs, collection dates, varieties of grape, or locations in the Champagne region of France, but two unexpected sympatric populations were identified. One group of isolates (transposa) contained the transposable elements Boty and Flipper; the other (vacuma) did not. These groups differed from one another for all the other markers. RFLP markers showed that there was genetic recombination in both groups of isolates. We conclude that there are two sympatric populations of B. fuckeliana in Champagne. One species (transposa) seems to be local and well adapted, while the other one (vacuma) is presumably a heterogeneous migrant population.

Alleles↗
PubMed1996

Somatic activity of the mariner transposable element in natural populations of Drosophila simulans.

The characteristics of the mariner transposable element in natural populations of Drosophila simulans from different parts of the world were analysed. The somatic excision rate (estimated from a test-cross with a reference strain), the average number of copies (determined by Southern blots), and the presence of deleted copies (detected by polymerase chain reaction amplification) were estimated for each population. There was a great variability in the somatic excision rate, measured as the percentage of mosaic males, both within and between populations. The population effect was highly significant. The average copy number also varied widely and was correlated with the excision rate. Rare deleted elements were detected by polymerase chain reaction and Southern blots. Percentage of mosaic males increased in strains kept for a long time at low temperature, and the somatic excision rate increased with the latitude of origin of populations. Therefore, these results strongly suggest that temperature could be involved in the regulation of mariner somatic excision in D. simulans.

Animals↗
PubMed1996

[Linsidomine, direct donor of EDRF/NO: a new treatment for unstable angina].

Linsidomine 10 mg, administered intravenously, has become available for the treatment of unstable angina since the beginning of 1996. It reinforces a range which consists of oral molsidomine, 2 and 4 mg, and the 1 mg intracoronary linsidomine dosage, thereby providing a more complete management of symptomatic coronary patients. Linsidomine is a direct donor of EDRF/NO which has an action on blood vessels (reduction of preload and dilatation of the large epicardial coronary vessels) and on platelets (inhibition of aggregation) without risk of tolerance. Linsidomine was compared with parenteral isosorbide dinitrate in a large scale French trial in patients with severe unstable angina (Braunwald's Class IIIb). The results showed linsidomine to be an effective treatment of unstable angina, controlling 75% of patients with a low incidence of severe clinical events (death, myocardial infarction, emergency myocardial revascularisation). In addition, intravenous linsidomine was well tolerated clinically, especially in terms of symptomatic hypotension.

Adult↗
PubMed1993

Iatrogenic complications in adult intensive care units: a prospective two-center study.

OBJECTIVES: a) To evaluate the frequency, types, severity, and morbidity of iatrogenic complications; b) determine associated factors that favor iatrogenic complications; and c) suggest new or more efficient protective measures that may be taken to improve patient safety. DESIGN: Prospective, observational study. SETTING: Two ICUs in France. PATIENTS AND METHODS: The study included 382 patients (age > or = 15 yrs; 400 consecutive admissions). Patients were monitored by two physicians in each ICU to assess all iatrogenic complications occurring during their ICU stay, with the exception of adverse effects of drugs. An iatrogenic complication was defined as an adverse event that was independent of the patient's underlying disease. RESULTS: We observed 316 iatrogenic complications in 124 (31%) of the 400 admissions. Of these iatrogenic complications, 107 (in 53 [13%] of the 400 admissions) complications were major, three leading to death. Severe hypotension, respiratory distress, pneumothorax, and cardiac arrest represented 78% of the major iatrogenic complications. Fifty-nine percent of the major iatrogenic complications had clearly identified associated factors. Human errors accounted for 67% of these factors. Patients > 65 yrs (adjusted odds ratio = 2.6, 95% confidence interval: 1.4 to 4.9) and those patients admitted with two or more organ failures (adjusted odds ratio = 4.8, 95% confidence interval: 2.5 to 9.2) were more likely to develop major iatrogenic complications. High or excessive nursing workload also led to an increased risk of major iatrogenic complications. Persistent morbidity, secondary to iatrogenic complications at the time of discharge, was present in five survivors. The risk of ICU death was about two-fold higher for the patients with major iatrogenic complications than in the remaining patients after adjusting for the Organ System Failure Score and the prognosis of the disease (relative risk = 1.92, 95% confidence interval: 1.28 to 2.56). CONCLUSIONS: Major iatrogenic complications were frequent, associated with increased morbidity and mortality rates, related to high or excessive nursing workload, and were often secondary to human errors. To improve patient safety in our ICUs, preventive measures should be targeted primarily on the elderly and the most severely ill patients. Special attention should be given to improving the organization of workload and training, and promoting wider use of noninvasive monitoring.

Adult↗