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Thierry de Meeûs

Publications and source records attributed to Thierry de Meeûs.

15 recordsLinked to original sources
PubMed2007

Direct and indirect inferences on parasite mating and gene transmission patterns. Pangamy in the cattle tick Rhipicephalus (Boophilus) microplus.

Mating system plays a determinant role in the maintenance and distribution of genetic variation. Difficulties in applying standard methods of indirect inferences onto parasitic life-cycles partly explain the current lack of knowledge on parasite mating systems. The present study develops a combination of direct and indirect inference methods circumventing such difficulties, and illustrates in particular how such a combination modifies our understanding of the biology of the southern cattle tick, Rhipicephalus microplus. To directly assess how females and males pair in natural populations, we sampled 225 mating pairs, genotyped them at six microsatellite loci, and analysed the correlation between mating status and genetic relatedness. This analysis revealed pangamy, i.e. a random association of male and female genotypes. In addition, indirect methods inferred that sib-groups of ticks exploit distinct individual-cows, and hence that ticks probably move among cows during their parasitic lifetime. Altogether, these results negate the expectation of a high frequency of sib-mating, and show the coexistence of genetically diverging stocks within tick cohorts and populations. These results have several consequences for our understanding of R. microplus. For instance, while existing models of pesticide resistance management look perfectly applicable to this species, the epidemiological models of the micropathogens it vectors needs revision. More largely, the methods developed here would help clarify the evolutionary patterns of any dioceous parasite.

Animals↗
PubMed2006

Population genetics and molecular epidemiology or how to "débusquer la bête".

Parasites represent a great proportion of the world's living organisms and are of overwhelming significance because of their impact on hosts (evolutionarily, medically, agronomical and economically). The knowledge of the population biology of such organisms is thus of fundamental importance to population biologists. Most parasites cannot be studied by direct methods and their biology has to be assessed via indirect means, most notably using molecular markers. In this review, we present the molecular tools, the null models employed, the statistical tools available and the kinds of inferences one can make when using molecular markers to study the ecology/epidemiology of host-parasite systems (molecular ecology/molecular epidemiology). We conclude with relevant examples, most issued from our laboratory, to illustrate the pros and cons of such methods for the study of parasites, vectors, micropathogens and their hosts and briefly discuss future needs.

Animals↗
PubMed2006

Host sex and parasite genetic diversity.

Is the genetic diversity of parasites infecting male and female hosts equal or different? This is the question we address in this paper by studying the neutral genetic variability of the plathyhelminth trematode Schistosoma mansoni within males and females of its natural murine host Rattus rattus in the marshy forest focus of Guadeloupe (French West Indies). Using seven microsatellite markers, we demonstrate that parasites from male hosts are genetically more diversified than parasites from female hosts. Three hypotheses are discussed that could explain this pattern: 1) a host sex-specific duration of cercariae recruitment; 2) a difference in the behaviour of male and female hosts that would lead to the exposure of males to a greater diversity of parasites; and 3) a host sex-biased immunocompetence that would lead to the selection of more genetically diversified individuals in male than in female rats. This finding is the first empirical evidence that each host sex may play different roles in the maintenance of parasite genetic diversity and so in their evolutionary dynamics and epidemiology.

Animals↗
PubMed2006

Clonal population structure and genetic diversity of Candida albicans in AIDS patients from Abidjan (Côte d'Ivoire).

We have investigated the genotype at 14 enzyme-encoding loci in 275 isolates of the pathogenic yeast Candida albicans sampled from 42 HIV-positive patients (all but one with AIDS) from Abidjan (Côte d'Ivoire). We separately analyzed the following variables: patient, residence, age, gender, T cell count, hospitalization (yes or no), drug treatment, date of sampling, multilocus genotype, and serotype. The most important factors contributing to the genetic variability of C. albicans are individual patient and gender. Our data manifest that the population size of the parasite is relatively small within each patient, although larger in women than in men, and that, at least for the patients involved in the study, the transmission rate of C. albicans between human adults is very low. Most important is the inference that the prevailing mode of reproduction of C. albicans in natural populations is clonal, so that sexual reproduction is extremely rare, if it occurs at all.

AIDS-Related Opportunistic Infections↗
PubMed2006

Founder effects, inbreeding and effective sizes in the Southern cattle tick: the effect of transmission dynamics and implications for pest management.

Since its immigration in the Pacific island of New Caledonia in 1942 (i.e. about 240 tick-generations ago), the cattle tick Boophilus microplus has experienced a remarkable adaptive diversification there. In order to better understand the population factors involved, we have investigated the B. microplus population structure on that main host-species, Bos taurus. This study was based microsatellite loci and confirmed that the island colonization came along with a significant bottleneck. Knowledge on B. microplus biology led us to expect B. microplus populations to be composed of highly inbred lineages irregularly dispatched among the individual hosts belonging to the same herds. Instead, this study evidenced a weak inbreeding level and an absence of genetic differentiation within herds. Complementarily, a significant signal of isolation by distance exhibited that human-traffic of cattle does not promote high tick dispersal within the island. Finally, the tick density was found to be about a few hundreds of reproducing adults per squared kilometre, for a gene dispersal range of about a few hundred metres per tick generation. Results are discussed with regard to the evolution of new adaptive changes.

Animals↗
PubMed2005

Population genetics of complex life-cycle parasites: an illustration with trematodes.

Accurate inferences on population genetics data require a sound underlying theoretical null model. Organisms alternating sexual and asexual reproduction during their life-cycle have been largely neglected in theoretical population genetic models, thus limiting the biological interpretation of population genetics parameters measured in natural populations. In this article, we derive the expectations of those parameters for the life-cycle of monoecious trematodes, a group comprising several important human and livestock parasites that obligatorily alternate sexual and asexual reproduction during their life-cycle. We model how migration rates between hosts, sexual and asexual mutation rates, adult selfing rate and the variance in reproductive success of parasites during the clonal phase affect the amount of neutral genetic diversity of the parasite (effective population size) and its apportionment within and between definitive hosts (using F-statistics). We demonstrate, in particular, that variance in reproductive success of clones, a parameter that has been completely overlooked in previous population genetics models, is very important in shaping the distribution of the genetic variability both within and among definitive hosts. Within definitive hosts, the parameter F(IS) (a measure of the deviation from random mating) is decreased by high variance in clonal reproductive success of larvae but increased by high adult self-fertilisation rates. Both clonal multiplication and selfing have similar effects on between-host genetic differentiation (F(ST)). Migration occurring before and after asexual reproduction can have different effects on the patterns of F(IS), depending on values of the other parameters such as the mutation rate. While the model applies to any hermaphroditic organism alternating sexual and clonal reproduction (e.g. many plants), the results are specifically discussed in the light of the limited population genetic data on monoecious trematodes available to date and their previous interpretation. We hope that our model will encourage more empirical population genetics studies on monoecious trematodes and other organisms with similar life-cycles.

Animals↗
PubMed2005

Dispersal in a parasitic worm and its two hosts: consequence for local adaptation.

Characterizing host and parasite population genetic structure and estimating gene flow among populations is essential for understanding coevolutionary interactions between hosts and parasites. We examined the population genetic structure of the trematode Schistosoma mansoni and its two host species (the definitive host Rattus rattus and the intermediate host Biomphalaria glabrata) using microsatellite markers. Parasites were sampled from rats. The study was conducted in five sites of the Guadeloupe Island, Lesser Antilles. Mollusks display a pattern of isolation by distance whereas such a pattern is not found neither in schistosomes nor in rats. The comparison of the distribution of genetic variability in S. mansoni and its two host species strongly suggests that migration of parasites is principally determined by that of the vertebrate host in the marshy focus of Guadeloupe. However, the comparison between genetic differentiation values in schistosomes and rats suggests that the efficacy of the schistosome rat-mediated dispersal between transmission sites is lower than expected given the prevalence, parasitic load and migration rate of rats among sites. This could notably suggest that rat migration rate could be negatively correlated to the age or the infection status of individuals. Models made about the evolution of local adaptation in function of the dispersal rates of hosts and parasites suggest that rats and mollusks should be locally adapted to their parasites.

Animals↗
PubMed2004

Non-Mendelian transmission of alleles at microsatellite loci: an example in Ixodes ricinus, the vector of Lyme disease.

Microsatellite loci are usually considered to be neutral co-dominant and Mendelian markers. We undertook to study the inheritance of five microsatellite loci in the European Lyme disease vector, the tick Ixodes ricinus. Only two loci appeared fully Mendelian while the three others displayed non-Mendelian patterns that highly frequent null alleles could not fully explain. At one locus, IR27, some phenomenon seems to hinder the PCR amplification of one allele, depending on its origin (maternal imprinting) and/or its size (short allele dominance). DNA methylation, which appeared to be a possible explanation of this amplification bias, was rejected by a specific test comparing the amplification efficiency that did not differ between unmethylated and experimentally methylated DNA. The role of allele size in heterozygous individuals was then revealed from the data available on field collected ticks and consistent with the results of a theoretical approach. These observations highlight the need for prudence while inferring reproductive systems (selfing rates), parentage or even allelic frequencies from microsatellite markers, in particular for parasitic organisms for which molecular approaches often represent the only way for population biology inferences.

Alleles↗
PubMed2004

Clonal reproduction and linkage disequilibrium in diploids: a simulation study.

Estimating the rate of clonal reproduction in natural population of diploid organisms is recognised as being problematic and even the detection of strictly clonal populations is often controversial. One well-acknowledged signature of clonal reproduction is the generation of non-random associations between loci. Linkage disequilibrium (LD) is thus often used for estimating the amount of clonal reproduction. Here we explore with computer simulations the effect of the rate of clonal reproduction on LD estimates obtained from different estimators within a comprehensive parameter range. None of the LD estimators studied is able to accurately measure the proportion of clonal (or sexual) reproduction on its own, due to strong bias, incoherent behaviour, or huge variances. The joint use of several statistics is thus recommended for the estimation rates of clonal reproduction in natural populations. We hope that our work will provide useful tools for the study of clonal diploids, many of which can only be studied with molecular markers, as it is the case for medically important parasites.

Clone Cells↗
PubMed2003

The population genetics of clonal and partially clonal diploids.

The consequences of variable rates of clonal reproduction on the population genetics of neutral markers are explored in diploid organisms within a subdivided population (island model). We use both analytical and stochastic simulation approaches. High rates of clonal reproduction will positively affect heterozygosity. As a consequence, nearly twice as many alleles per locus can be maintained and population differentiation estimated as F(ST) value is strongly decreased in purely clonal populations as compared to purely sexual ones. With increasing clonal reproduction, effective population size first slowly increases and then points toward extreme values when the reproductive system tends toward strict clonality. This reflects the fact that polymorphism is protected within individuals due to fixed heterozygosity. Contrarily, genotypic diversity smoothly decreases with increasing rates of clonal reproduction. Asexual populations thus maintain higher genetic diversity at each single locus but a lower number of different genotypes. Mixed clonal/sexual reproduction is nearly indistinguishable from strict sexual reproduction as long as the proportion of clonal reproduction is not strongly predominant for all quantities investigated, except for genotypic diversities (both at individual loci and over multiple loci).

Alleles↗
PubMed2002

Genetic diversity and population structure of Plasmodium falciparum isolates from Dakar, Senegal, investigated from microsatellite and antigen determinant loci.

We investigated the genetic diversity and the population structure of 32 Plasmodium falciparum blood sample isolates (25 from Dakar city and suburbs and seven from other localities in Senegal) with two different types of molecular markers, 19 microsatellite and four antigenic determinant loci. Under the same technical procedure, microsatellite loci showed a mean number of alleles greater than that of antigenic loci. Both markers revealed that 15.6% of blood samples were multi-infected. Mean expected heterozygosity calculated from microsatellites and antigens was similar, 0.74 and 0.70, respectively. Significant linkage disequilibrium was observed from microsatellite loci and antigenic determinant loci. This suggests a non-panmictic structure for this sample that could be explained by two non-exclusive hypotheses: (i) a particular mating system (i.e. clonality), and/or (ii) a population structure in P. falciparum (i.e. Wahlund effect). Urban samples could have been drawn from a heterogeneous set of foci with different level of parasitic transmission. Moreover, no relationship was found between multilocus genotypes and different parameters (i.e. age, sex and blood group of parasitized patients; number of trophozoites per microliter of blood). The results are discussed taking into account recently published studies on malaria population biology.

Adolescent↗
PubMed2002

Parasites within the new phylogeny of eukaryotes.

In the past few years, molecular phylogenetic and cladistic analyses of the interrelationships of the living phyla have resulted in a radical reorganization of eukaryote groups. This reorganization has significance for parasitologists, in that it places as sister taxa some of the more speciose and highly parasitic phyla (nematodes and insects), reorganizes what is now recognized as paraphyletic sets of 'wormy taxa' as the Aschelmintha, and draws numerous bridges between different realms (plants, fungi and animals). This review attempts to explore the role of parasites within the phylogeny of eukaryotes. Extant described parasitic organisms are less common among the eukaryotes than is commonly admitted in the literature.

Animals↗
PubMed2002

Sex-biased genetic structure in the vector of Lyme disease, Ixodes ricinus.

We analyzed 725 Ixodes ricinus ticks (the principal vector of Lyme disease in Europe) collected in Switzerland in 1995 and 1996 (three and eight samples, respectively) and in Tunisia in 1996 (one sample) with five microsatellite markers. We found highly significant genetic differentiation between Swiss and Tunisian samples but detected almost no differentiation within Switzerland, even between those samples separated by the Alps. Interestingly, we found that I. ricinus females were more genetically related to one another than were males at a local scale, which would indicate a higher dispersal rate of immature males. Possible explanations for these findings in terms of sex-specific association of ticks with certain hosts (e.g., birds) and their epidemiological consequences are discussed.

Alleles↗