Efficiency of the traditional practice of traps to stimulate black truffle production, and its ecological mechanisms

The black truffle Tuber melanosporum was disseminated all over the world, propelled by the development of a wide variety of empirical practices. A widespread practice, called ‘truffle trap’, consists of placing pieces of truffles into excavations dug under host trees, and of collecting truffle in these traps in the next years. This research aims at (1) evaluating the effect of this practice on fruitbody production based on the analysis of 9924 truffle traps installed in 11 orchards across T. melanosporum native area in France and (2) exploring the mechanisms involved in fruitbody emergence using traps where the genotypes of introduced truffles were compared with those of fruitbodies collected in the same traps. We confirmed that truffle traps provide a major and highly variable part of truffle ground production, representing up to 89% of the collected fruitbodies. We evidenced a genetic link between introduced spores and collected fruitbodies, and then demonstrated that truffle growers provide paternal partners for mating with local maternal mycelia. We also highlighted that soil disturbance stimulate the vegetative development of established maternal mycelia. This research supports that a widely used traditional practice enhances fruitbody production by shaping favorable conditions and providing sexual partners required for fruiting.

Glycation stimulates cutaneous monocyte differentiation in reconstructed skin in vitro

Glycation reaction is a recognized mechanism related to chronological aging. Previous investigations in cutaneous biology have considered the effect of glycation on the dermal matrix molecules, involved in tissue stiffening during skin aging. However, little is known about a possible direct effect of glycation upon cell differentiation. To address such issue, the effect of glycation has been re-investigated in a reconstructed skin model integrating monocytes that are cells capable of differentiating according to different pathways. The results showed that, in the absence of glycation, a small number of these CD45⁺ cells could differentiate either into dendritic-like cells (DC-SIGN⁺, BDC1a⁺, DC-LAMP⁺) or macrophage- like cells (CD14⁺, CD68⁺, CD163⁺) whereas, with glycation, the number of monocytes, dendritic cells, macrophage-like cells were found surprisingly increased. In-vivo our results showed also that dendritic and macrophage-like cells were increased and suggest a possible link with the age-dependent glycation level in the skin. In addition, we found that, unlike fibroblasts incorporated in the reconstructed skin, these cells expressed specific receptors for AGEs (RAGE and SRA). Taken altogether, our data show that cells of the monocyte lineage, in the presence of AGEs, can differentiate into dendritic or macrophage-like cells and could lead to a micro inflammatory environment.

Stability of a flow down an incline with respect to two-dimensional and three-dimensional disturbances for Newtonian and non-Newtonian fluids

Squire's theorem, which states that the two-dimensional instabilities are more dangerous than the three-dimensional instabilities, is revisited here for a flow down an incline, making use of numerical stability analysis and Squire relationships when available. For flows down inclined planes, one of these Squire relationships involves the slopes of the inclines. This means that the Reynolds number associated with a two-dimensional wave can be shown to be smaller than that for an oblique wave, but this oblique wave being obtained for a larger slope. Physically speaking, this prevents the possibility to directly compare the thresholds at a given slope. The goal of the paper is then to reach a conclusion about the predominance or not of two-dimensional instabilities at a given slope, which is of practical interest for industrial or environmental applications. For a Newtonian fluid, it is shown that, for a given slope, oblique wave instabilities are never the dominant instabilities. Both the Squire relationships and the particular variations of the two-dimensional wave critical curve with regard to the inclination angle are involved in the proof of this result. For a generalized Newtonian fluid, a similar result can only be obtained for a reduced stability problem where some term connected to the perturbation of viscosity is neglected. For the general stability problem, however, no Squire relationships can be derived and the numerical stability results show that the thresholds for oblique waves can be smaller than the thresholds for two-dimensional waves at a given slope, particularly for large obliquity angles and strong shear-thinning behaviors. The conclusion is then completely different in that case: the dominant instability for a generalized Newtonian fluid flowing down an inclined plane with a given slope can be three dimensional.

IL-1beta mediates MMP secretion and IL-1beta neosynthesis via upregulation of p22(phox) and NOX4 activity in human articular chondrocytes

OBJECTIVES

Osteoarthritis (OA) is characterized by a progressive alteration of the biochemical properties of the articular cartilage. Inflammation plays a major role in OA, particularly through the cytokine Interleukine-1β, promoting reactive oxygen species (ROS) generation and matrix metalloproteinases (MMP) synthesis by the chondrocytes, orchestrating matrix proteolysis. NADPH oxidases (NOX) are membrane enzymes dedicated to the production of ROS. Role of oxidative stress is well established in OA; however, contribution of NOX in this process is still poorly documented. In this study, we addressed the role of NOX in primary human articular chondrocytes (HAC) upon inflammatory conditions--namely IL-1β and OA.

DESIGN

HAC were collected from patients undergoing hip surgery. Chondrocytes were treated with IL-1β and NOX inhibitors Diphenylene Iodonium, GKT136901, Tiron and Heme oxygenase-1 before MMP expression and NOX activity assessment. Finally, NOX4 expression was compared between OA and non OA parts of hip cartilage (n = 14).

RESULTS

This study establishes for the first time in human that NOX4 is the main NOX isoform expressed in chondrocytes. We found a significant upregulation of NOX4 mRNA in OA chondrocytes. Expression of NOX4/p22(phox) as well as ROS production is enhanced by IL-1β. On the other hand, the use of NOX4 inhibitors decreased IL-1β-induced collagenase synthesis by chondrocytes. Moreover, our study support the existence of a redox dependant loop sustaining pro-catabolic pathways induced by IL-1β.

CONCLUSIONS

This study points out NOX4 as a new putative target in OA and suggests that NOX-targeted therapies could be of interest for the causal treatment of the pathology.

Stability of two-layer shear-thinning film flows

The stability of a two-layer film flow of non-Newtonian fluids is studied with a linear temporal approach. Shear-thinning fluids are considered, which follow the four-parameter inelastic Carreau model. A modified Orr-Sommerfeld equation system is obtained, which is solved by using a spectral Tau collocation method based on Chebyshev polynomials. The effects of density and viscosity stratification are considered, as well as the influence of the shear-thinning properties of the fluid. It is found that, when the viscosity is stronger in the upper layer, the base flow and the stability properties are almost not influenced by the change of the shear-thinning properties in this upper layer. In the other situations, the shear-thinning properties have an influence on the different instabilities, the long-wave surface instability and the short- and long-wave interface instabilities.

Statistical analyses of population genetic data: new tools, old concepts

Several methods or tests and various software are currently being developed for analyzing data in population genetics and ecology, which often rely on computer-intensive algorithms. The potential user is thus confronted with the painful experience of freedom and, in particular, has to makea priori choices between different methods. Using examples drawn from population genetics, we explain some of these recently developed tools.

Inferences on pathogenic fungus population structures from microsatellite data: new insights from spatial genetics approaches

Landscape genetics, which combines population genetics, landscape ecology and spatial statistics, has emerged recently as a new discipline that can be used to assess how landscape features or environmental variables can influence gene flow and spatial genetic variation. We applied this approach to the invasive plant pathogenic fungus Mycosphaerella fijiensis, which causes black leaf streak disease of banana. Around 880 isolates were sampled within a 50 × 50 km area located in a fragmented banana production zone in Cameroon that includes several potential physical barriers to gene flow. Two clustering algorithms and a new F(ST) -based procedure were applied to define the number of genetic entities and their spatial domain without a priori assumptions. Two populations were clearly delineated, and the genetic discontinuity appeared sharp but asymmetric. Interestingly, no landscape features matched this genetic discontinuity, and no isolation by distance (IBD) was found within populations. Our results suggest that the genetic structure observed in this production area reflects the recent history of M. fijiensis expansion in Cameroon rather than resulting from contemporary gene flow. Finally, we discuss the influence of the suspected high effective population size for such an organism on (i) the absence of an IBD signal, (ii) the characterization of contemporary gene-flow events through assignation methods of analysis and (iii) the evolution of the genetic discontinuity detected in this study.

Isolation by distance in a continuous population under stochastic demographic fluctuations

The local density of individuals is seldom uniform in space and time within natural populations. Yet, formal approaches to the process of isolation by distance in continuous populations have encountered analytical difficulties in describing genetic structuring with demographic heterogeneities, usually disregarding local correlations in the movement and reproduction of genes. We formulate exact recursions for probabilities of identity in continuous populations, from which we deduce definitions of effective dispersal () and effective density (D(e)) that generalize results relating spatial genetic structure, dispersal and density in lattice models. The latter claim is checked in simulations where estimates of effective parameters obtained from demographic information are compared with estimates derived from spatial genetic patterns in a plant population evolving in a heterogeneous and dynamic habitat. The simulations further suggest that increasing spatio-temporal correlations in local density reduce and generally decrease the product , with dispersal kurtosis influencing their sensitivity to density fluctuations. As in the lattice model, the expected relationship between the product and the genetic structure statistic a(r) holds under fluctuating density, irrespective of dispersal kurtosis. The product D sigma(2) between observed census density and the observed dispersal rate over one generation will generally be an upwardly biased (up to 400% in simulations) estimator of in populations distributed in spatially aggregated habitats.

Effective size of the hierarchically structured populations of the agent of malaria: a coalescent-based model

Using the coalescence theory, we derived a simple expression for the asymptotic inbreeding effective population size of Plasmodium falciparum, the most malignant agent of malaria, in relationship to F-statistics at different hierarchical levels. We consider the effective size of malaria parasites, both for the intrinsic interest of the result for the study of this medically important organism and as an example illustrating general arguments that should clarify effective size calculations in a wide range of organisms with complex life cycles and a hierarchical population structure. We consider in this study a model with four hierarchical levels (villages, oocyst infrapopulations, oocysts within infrapopulations and the oocyst). The derived expression is applicable to both island and isolation by distance models and is a function of three F-statistics: the genetic differentiation among villages (F(VT)), the genetic differentiation among oocyst infrapopulations (F(MV)) and, finally, the departure from panmixia (F(IM)) within oocyst infrapopulations. The logic of the derivation of effective size presented in this study is applicable to any organism showing the same levels of subdivision.

"Clonal" population structure of the malaria agent Plasmodium falciparum in high-infection regions

The population genetic structure of Plasmodium falciparum, the agent of malignant malaria, has been shown to be predominantly "clonal" (i.e., highly inbred) in regions of low infectivity; in high-infectivity regions, it is often thought to be panmictic, or nearly so, although there is little supporting evidence for this. The matter can be settled by investigating the parasite's genetic makeup in the midgut oocysts of the mosquito vector, where the products of meiosis can directly be observed. The developmental stages of P. falciparum are haploid, except in the oocysts of infected mosquito vectors, where two gametes fuse, diploidy occurs, and meiosis ensues. We have investigated genetic polymorphisms at seven microsatellite loci located on five chromosomes by assaying 613 oocysts in 145 mosquitoes sampled from 11 localities of Kenya, where malignant malaria is perennial and intense. There is considerable allelic variation, 16.3 +/- 2.1 alleles per locus, and considerable inbreeding, approximately 50% on the average. The inbreeding is caused by selfing (approximately 25%) and nonrandom genotype distribution of oocysts among mosquito guts (35%). The observed frequency of heterozygotes is 0.43 +/- 0.03; the expected frequency, assuming random mating, is 0.80 +/- 0.05. Linkage disequilibrium is statistically significant for all 21 pairwise comparisons between loci, even though 19 comparisons are between loci in different chromosomes, which is consistent with strong deviation from panmixia and the consequent reproduction of genomes as clones, without recombination between gene loci. This is of considerable evolutionary significance and of epidemiological consequence, concerning the spread of multilocus drug and vaccine resistance.

Genetic isolation between two sympatric host plant races of the European corn borer, Ostrinia nubilalis Hubner. II: assortative mating and host-plant preferences for oviposition

The European corn borer, Ostrinia nubilalis Hubner, colonized maize (Zea mays L.) after its introduction into Europe about 500 years ago and is now considered one of the main pests of this crop. In northern France, two sympatric host races have been described: one feeding on maize and the other on mugwort (Artemisia vulgaris L.) and hop (Humulus lupulus L.). In a previous study, we showed that mating between the two races may be impeded by differences in the timing of moth emergence and in the composition of the sex pheromone produced by the females. In this study, we further investigated the genetic isolation of these two races using strains from the maize (Z strain) and mugwort (E strain) races selected for diagnostic alleles at two allozyme loci. In a cage containing maize and mugwort plants and located in natural conditions, mating between individuals of the same strain occurred more often than mating between males and females of the E and Z strains. In particular, we obtained no evidence for crosses between Z females and E males. We also found that females of the Z strain laid their eggs almost exclusively on maize, whereas females of the E strain laid their eggs preferentially, but not exclusively, on mugwort. These results suggest that the genetic differentiation between the two host races may also be favored by host-plant preference, one of the first steps toward sympatric speciation.

Modelling the spatial configuration of refuges for a sustainable control of pests: a case study of Bt cotton

The 'high-dose-refuge' (HDR) strategy is widely recommended by the biotechnology industry and regulatory authorities to delay pest adaptation to transgenic crops that produce Bacillus thuringiensis (Bt) toxins. This involves cultivating nontoxic plants (refuges) in close proximity to crops producing a high dose of Bt toxin. The principal cost associated with this strategy is due to yield losses suffered by farmers growing unprotected, refuge plants. Using a population genetic model of selection in a spatially heterogeneous environment, we show the existence of an optimal spatial configuration of refuges that could prevent the evolution of resistance whilst reducing the use of costly refuges. In particular, the sustainable control of pests is achievable with the use of more aggregated distributions of nontransgenic plants and transgenic plants producing lower doses of toxin. The HDR strategy is thus suboptimal within the context of sustainable agricultural development.

Effective size in simple metapopulation models

A coalescent argument is used to derive the effective size in simple models with recurrent local extinctions. Several alternative methods of derivation of this result are given and compared to earlier analyses of this problem. The different methods described in this paper all give the same result, which differs from earlier ones. For two published sets of estimates of demographic parameters, metapopulation structure appears to result in a moderate reduction of effective size relative to total adult population size.

Host-plant-associated genetic differentiation in Northern French populations of the European corn borer

The phytophagous insects that damage crops are often polyphagous, feeding on several types of crop and on weeds. The refuges constituted by noncrop host plants may be useful in managing the evolution in pest species of resistance to the Bacillus thuringiensis toxins produced by transgenic crops. However, the benefits of these refuges may be limited because host-plant diversity may drive genetic divergence and possibly even host-plant-mediated sympatric speciation. The European corn borer, Ostrinia nubilalis Hübner (Lepidoptera: Crambidae), is the main pest of maize in Europe and North America, where it was introduced early in the 20th century. It has a wide host range but feeds principally on mugwort (Artemisia vulgaris L.) and maize (Zea mays L.). O. nubilalis is found on mugwort only in the northern part of France, whereas it is found on maize throughout France. The extent of genetic variation at allozyme markers was investigated in populations collected from the two host plants over the entire geographical distribution of the European corn borer on mugwort in France. Allelic differentiation between pairs of populations and hierarchical analyses of pools of samples from each host plant indicate that the group of populations feeding on maize differed from the group of populations feeding on mugwort. Our results suggest (1) host-plant-related divergent selection at the genomic region surrounding the Mpi locus and (2) limited gene flow between the populations feeding on mugwort and those infesting maize fields. These data indicate that adults emerging from mugwort would not be useful for managing the evolution of resistance to the B. thuringiensis toxins in European corn borer populations.

Inbreeding and relatedness coefficients: what do they measure?

This paper reviews and discusses what is known about the relationship between identity in state, allele frequency, inbreeding coefficients, and identity by descent in various uses of these terms. Generic definitions of inbreeding coefficients are given, as ratios of differences of probabilities of identity in state. Then some of their properties are derived from an assumption in terms of differences between distributions of coalescence times of different genes. These inbreeding coefficients give an approximate measurement of how much higher the probability of recent coalescence is for some pair of genes relative to another pair. Such a measure is in general not equivalent to identity by descent; rather, it approximates a ratio of differences of probabilities of identity by descent. These results are contrasted with some other formulas relating identity, allele frequency, and inbreeding coefficients. Additional assumptions are necessary to obtain most of them, and some of these assumptions are not always correct, for example when there is localized dispersal. Therefore, definitions based on such formulas are not always well-formulated. By contrast, the generic definitions are both well-formulated and more broadly applicable.

Heterosis, marker mutational processes and population inbreeding history

Genotype-fitness correlations (GFC) have previously been studied using allozyme markers and have often focused on short-term processes such as recent inbreeding. Thus, models of GFC usually neglect marker mutation and only use heterozygosity as a genotypic index. Recently, GFC have also been reported (i) with DNA markers such as microsatellites, characterized by high mutation rates and specific mutational processes and (ii) using new individual genotypic indices assumed to be more precise than heterozygosity. The aim of this article is to evaluate the theoretical impact of marker mutation on GFC. We model GFC due to short-term processes generated by the current breeding system (partial selfing) and to long-term processes generated by past population history (hybridization). Various mutation rates and mutation models corresponding to different kinds of molecular markers are considered. Heterozygosity is compared to other genotypic indices designed for specific marker types. Highly mutable markers (such as microsatellites) are particularly suitable for the detection of GFC that evolve in relation to short-term processes, whereas GFC due to long-term processes are best observed with intermediate mutation rates. Irrespective of the marker type and population scenario, heterozygosity usually provides higher correlations than other genotypic indices under most biologically plausible conditions.

Are partial mantel tests adequate?

Partial Mantel tests were designed to test for correlation among three matrices of pairwise distances. We show through an example that these tests may be inadequate, because the associated P-value is not indicative of the type I error.

"Neighbourhood" size, dispersal and density estimates in the prickly forest skink (Gnypetoscincus queenslandiae) using individual genetic and demographic methods

Dispersal, or the amount of dispersion between an individual's birthplace and that of its offspring, is of great importance in population biology, behavioural ecology and conservation, however, obtaining direct estimates from field data on natural populations can be problematic. The prickly forest skink, Gnypetoscincus queenslandiae, is a rainforest endemic skink from the wet tropics of Australia. Because of its log-dwelling habits and lack of definite nesting sites, a demographic estimate of dispersal distance is difficult to obtain. Neighbourhood size, defined as 4piDsigma2 (where D is the population density and sigma2 the mean axial squared parent-offspring dispersal rate), dispersal and density were estimated directly and indirectly for this species using mark-recapture and microsatellite data, respectively, on lizards captured at a local geographical scale of 3 ha. Mark-recapture data gave a dispersal rate of 843 m2/generation (assuming a generation time of 6.5 years), a time-scaled density of 13 635 individuals * generation/km2 and, hence, a neighbourhood size of 144 individuals. A genetic method based on the multilocus (10 loci) microsatellite genotypes of individuals and their geographical location indicated that there is a significant isolation by distance pattern, and gave a neighbourhood size of 69 individuals, with a 95% confidence interval between 48 and 184. This translates into a dispersal rate of 404 m2/generation when using the mark-recapture density estimation, or an estimate of time-scaled population density of 6520 individuals * generation/km2 when using the mark-recapture dispersal rate estimate. The relationship between the two categories of neighbourhood size, dispersal and density estimates and reasons for any disparities are discussed.

Contact sensitizers specifically increase MHC class II expression on murine immature dendritic cells

Contact sensitivity is a T-cell-mediated immune disease that can occur when low-molecular-weight chemicals penetrate the skin. In vivo topical application of chemical sensitizers results in morphological modification of Langerhans cells (LC). Moreover, within 18 h, LC increase their major histocompatibility complex (MHC) class II antigens expression and migrate to lymph nodes where they present the sensitizer to T lymphocytes. We wanted to determine if such an effect could also be observed in vitro. However, because of the high genetic diversity encountered in humans, assays were performed with dendritic cells (DC) obtained from a Balb/c mouse strain. The capacity of a strong sensitizer, DNBS (2,4-dinitrobenzene sulfonic acid), to modulate the phenotype of bone marrow-derived DC in vitro, was investigated. A specific and marked increase of MHC class II molecules expression was observed within 18 h. To eliminate the use of animals in sensitization studies, the XS52 DC line was tested at an immature stage. A 30-min contact with the strong sensitizers DNBS and oxazolone, or the moderate mercaptobenzothiazole, resulted in upregulation of MHC class II molecules expression, analyzed after 18-h incubation. This effect was not observed with irritants (dimethyl sulfoxide and sodium lauryl sulfate) nor with a neutral molecule (sodium chloride). These data suggested the possibility of developing an in vitro model for the identification of the sensitizing potential of chemicals, using a constant and non animal-consuming material.

Upregulation of the Netrin Receptor (DCC) Gene during Activation of B Lymphocytes and Modulation by Interleukins

The DCC (deleted in colon cancer) gene has a brain restricted high expression pattern. It encodes a transmembrane protein of the immunoglobulin superfamily identified as the netrin-1 receptor. It might be a member of the so called "brain-lymphoid" molecules, which control key cell surface events. To test this hypothesis we have assessed the DCC mRNA level in human normal and malignant myeloid and lymphoid cells. A high mRNA content has been observed only in mature B cells at the secreting or presecreting stage. Expression of DCC was also assessed in the anti-CD40 model of immunopoiesis. Activation of purified tonsillar B cells by anti-CD 40 antibody strongly increased the DCC mRNA level and this effect was dramatically enhanced by the association of IL-2 + IL-10, which is a potent and selective in vitro inducer of the B cell memory phenotype. In contrast no effect has been detected after activation of T cells by anti-CD3. These data suggest that the DCC encoded netrin receptor is involved in B cell immunopoiesis.

Population genetics and dynamics of the black truffle in a man-made truffle field

The colonization dynamics of the black truffle in an artificial field were assessed through analyses of microsatellite and RAPD markers. The truffle field was composed of three tree species and mycelial inoculum of three different origins, and was monitored for the first three years of truffle production. We found very low levels of genetic diversity. Isolation by distance was detected only at the between-tree level. This could be interpreted as local colonization around each tree facilitated by the presence of the tree root system. At the larger spatial scale of the European range, the absence of isolation by distance corroborates the hypothesis of an impact of glaciation on genetic variation, followed by rapid postglaciation demographic expansion. In addition, genetic variation of harvested truffles was explained by neither inoculation origin, nor tree species. Our study questions the real impact of man-made inoculation of tree root systems with fungal mycelia.

A critical role for p38 mitogen-activated protein kinase in the maturation of human blood-derived dendritic cells induced by lipopolysaccharide, TNF-alpha, and contact sensitizers

We investigated the involvement of mitogen-activated protein kinases (MAPKs) in the maturation of CD83(-) dendritic cells (DC) derived from human blood monocytes. Maturating agents such as LPS and TNF-alpha induced the phosphorylation of members of the three families of MAPK (extracellular signal-regulated kinase l/2, p46/54 c-Jun N-terminal kinase, and p38 MAPK). SB203580, an inhibitor of the p38 MAPK, but not the extracellular signal-regulated kinase l/2 pathway blocker PD98059, inhibited the up-regulation of CD1a, CD40, CD80, CD86, HLA-DR, and the DC maturation marker CD83 induced by LPS and TNF-alpha. In addition, SB203580 inhibited the enhancement of the allostimulatory capacity and partially prevented the down-regulation of FITC-dextran uptake induced by LPS and TNF-alpha. Likewise, SB203580 partially prevented the up-regulation of IL-1alpha, IL-1beta, IL-lRa, and TNF-alpha mRNA upon stimulation with LPS and TNF-alpha, as well as the release of bioactive TNF-alpha induced by LPS. DC maturation induced by the contact sensitizers 2,4-dinitrofluorobenzene and NiSO(4), as seen by the up-regulation of CD80, CD86, and CD83, was also coupled to the phosphorylation of p38 MAPK, and was inhibited by SB203580. The irritants SDS and benzalkonium chloride that do not induce DC maturation did not trigger p38 MAPK phosphorylation. Together, these data indicate that phosphorylation of p38 MAPK is critical for the maturation of immature DC. These results also suggest that p38 MAPK phosphorylation in DC may become useful for the identification of potential skin contact sensitizers.

In vitro human T cell sensitization to haptens by monocyte-derived dendritic cells

We previously reported that in vitro primary sensitization of hapten-specific T cells by cultured human epidermal Langerhans cells (LC) provides an alternative approach to discriminate strong contact sensitizers from irritants (Krasteva et al., 1996; Moulon et al., 1993). However, this LC-based immunoassay was limited by the availability of human skin samples. In the present study, we used monocyte-derived dendritic cells (DC) to analyse the autologous proliferative T cell response to several allergens. Monocytes were purified from the peripheral blood of healthy donors and cultured for 6-8 days in the presence of GM/CSF and IL-4 and then for 2 days in the presence of GM/CSF and TNFalpha. The resulting cells exhibited the phenotype of mature DC, as assessed by the strong expression of HLA-DR, CD80, CD83 and CD86 antigens. We showed that trinitrophenyl (TNP)-treated mature DC induced a significant T cell proliferative response in all experiments, while fluorescein isothiocyanate (FITC) gave positive results in about half of them. The prohaptens eugenol and isoeugenol induced significant proliferation in one out of eight and in four out of 12 experiments, respectively. Interestingly, in 16 assays T cells never proliferated in the presence of sodium lauryl sulfate (SLS)-treated DC. Thus, this in vitro model allows discrimination between strong contact sensitizers and irritants. It might be very useful, therefore, for restriction of animal experimentation.

Absence of evidence for isolation by distance in an expanding cane toad (Bufo marinus) population: an individual-based analysis of microsatellite genotypes

The cane toad (Bufo marinus) was introduced in 1935 in Australia, where it spread rapidly. We have tested for isolation by distance by analysing at a local geographical scale a continuous population using seven microsatellite markers and an individual-based method. The matrix of pairwise individual differentiation was not significantly correlated with that of geographical distance. Regression analyses gave a low positive slope of 0.00072 (all individuals) or a negative slope of 0.0017 (individuals with a distance higher than the previously estimated mean dispersal distance). The absence of evidence for isolation by distance favours the hypothesis that the substantial differentiation and autocorrelation previously observed at enzyme loci, mainly results from discontinuities in the colonization process with founder effects occurring at the time of the establishment of new populations.

Kin selection and natal dispersal in an age-structured population

We examine the effect of iteroparity on the evolution of dispersal for a species living in a stable but fragmented habitat. We use a kin selection model that incorporates the effects of demographic stochasticity on the local age structure and age-specific genetic identities. We consider two cases: when the juvenile dispersal rate is allowed to change with maternal age and when it is not. In the latter case, we find that the unconditional evolutionarily stable dispersal rate increases when the adult survival rate increases. Two antagonistic forces act upon the evolution of age-specific dispersal rates. First, when the local age structure varies between patches of habitat, the intensity of competition between adults and juveniles in the natal patch is, on average, lower for offspring born to older senescent mothers. This selects for decreasing dispersal with maternal age. Second, offspring born to older parents are on average more related to other juveniles in the same patch and they experience a higher intensity of kin competition, which selects for increasing dispersal with maternal age. We show that the evolutionary outcome results from a balance between these two opposing forces, which depends on the amount of variance in age structure among sub-populations.

Interleukin-10 in Epstein-Barr virus-associated post-transplant lymphomas

We used enzyme-linked immunosorbent assays (ELISA) to investigate the presence of interleukin-10 (IL-10) in the serum of patients developing post-transplant lymphomas. Serum IL-10 was detected in 14 out of 19 cases with a lymphoma or Hodgkin's disease, with higher values being observed in patients who had developed a lymphoma within the first few months post-transplantation, and who had an aggressive form of the disease. Eleven out of the 14 patients in whom IL-10 was detected had Epstein Barr virus-positive tumors. And 11 out of 14 patients died of lymphomas. In most of the patients who had detectable IL-10 at the time of diagnosis of the lymphoma, the IL-10 had not been present previously, but it was found in the serum of 7 out of 9 dialysis patients, and in 8 out of 17 stable transplant patients. We conclude that IL-10 plays a role in the development of the more severe forms of post-transplant lymphomas, and may be secreted by tumor cells. However. data from patients with chronic renal failure or patients undergoing immunosuppressive therapy must be treated with caution.

Genetic differentiation in populations with different classes of individuals

I formulate and analyse a model of population structure with different classes of individuals. These different classes may be age classes, other demographic classes, or different types of habitats homogeneously distributed over a geographical area. The value of population differentiation under an island model of dispersal and the increase of differentiation with geographical distance in one- and two-dimensional "isolation by distance" models are then obtained for a generalization of the FST measure of population structure, as a function of "effective" mutation, migration, and population size parameters. The relevant effective subpopulation size is related to the "mutation effective population size" of a single isolated subpopulation and, in models of age-structured populations, to the inbreeding effective population size.

A stable triple Wolbachia infection in Drosophila with nearly additive incompatibility effects

Drosophila simulans strains infected with three different Wolbachia strains were generated by experimental injection of a third symbiont into a naturally double-infected strain. This transfer led to a substantial increase in total Wolbachia density in the host strain. Each of the three symbionts was stably transmitted in the presence of the other two. Triple-infected males were incompatible with double-infected females. No evidence was obtained for interference between modification effects of the different Wolbachia strains in males. Some incompatibility was observed between triple-infected males and females. However, this incompatibility reaction is not a specific property of triple-infected flies, because it was also observed in double-infected strains.

Contact sensitizers decrease 33D1 expression on mature Langerhans cells

Langerhans cells play a critical role in allergic contact hypersensitivity. In vivo, these cells capture xenobiotics that penetrate the skin and transport them through the lymphatic vessels into regional lymph nodes for presentation to T cells. During this migration step, Langerhans cells become mature dendritic cells according to their phenotype and their high immunostimulatory capacity. In vitro, when isolated from the skin and cultured for 3 days, Langerhans cells undergo similar phenotypic and functional maturation. In this study, the capacity of sensitizers, irritants and neutral chemicals to modulate the surface marker expression and morphology of pure mature murine Langerhans cells in vitro was examined. Contact with 4 sensitizers (2,4-dinitrobenzenesulfate, 4-ethoxymethylene-2-phenyl-2-oxazolin-5-one, p-phenylenediamine, mercaptobenzo-thiazole) resulted in a rapid, specific, marked fall in 33D1 expression, a murine specific dendritic cell marker. No effect was observed with 2 neutral chemicals (sodium chloride, methyl nicotinate) or 2 irritants (dimethyl sulfoxide, benzalkonium chloride). Nevertheless, sodium lauryl sulfate, a very irritant detergent, altered morphology and down-regulated all membrane markers. These preliminary data suggest that in vitro modulation of 33D1 expression by strong sensitizers may be an approach to the development of an in vitro model for the identification of chemicals that have the potential to cause skin sensitization and to distinguish them as far as possible from irritants.

Wolbachia infections are distributed throughout insect somatic and germ line tissues

Wolbachia are intracellular microorganisms that form maternally-inherited infections within numerous arthropod species. These bacteria have drawn much attention, due in part to the reproductive alterations that they induce in their hosts including cytoplasmic incompatibility (CI), feminization and parthenogenesis. Although Wolbachia's presence within insect reproductive tissues has been well described, relatively few studies have examined the extent to which Wolbachia infects other tissues. We have examined Wolbachia tissue tropism in a number of representative insect hosts by western blot, dot blot hybridization and diagnostic PCR. Results from these studies indicate that Wolbachia are much more widely distributed in host tissues than previously appreciated. Furthermore, the distribution of Wolbachia in somatic tissues varied between different Wolbachia/host associations. Some associations showed Wolbachia disseminated throughout most tissues while others appeared to be much more restricted, being predominantly limited to the reproductive tissues. We discuss the relevance of these infection patterns to the evolution of Wolbachia/host symbioses and to potential applied uses of Wolbachia.

Genetic differentiation within and between two habitats

We investigate the usefulness of analyses of population differentiation between different ecological types, such as host races of parasites or sources and sink habitats. To that aim, we formulate a model of population structure involving two classes of subpopulations found in sympatry. Extensions of previous results for Wright's F-statistics in island and isolation-by-distance models of dispersal are given. It is then shown that source and sinks cannot in general be distinguished by F-statistics nor by their gene diversities. The excess differentiation between two partially isolated classes with respect to differentiation within classes is shown to decrease with distance, and for a wide range of parameter values it should be difficult to detect. In the same circumstances little differentiation will be observed in "hierarchical" analyses between pools of samples from each habitat, and differences between levels of differentiation within each habitat will only reflect differences between levels of gene diversity within each habitat. Exceptions will indicate strong isolation between the different classes or habitat-related divergent selection.

Analysis of population structure in autotetraploid species

Population structure parameters commonly used for diploid species are reexamined for the particular case of tetrasomic inheritance (autotetraploid species). Recurrence equations that describe the evolution of identity probabilities for neutral genes in an "island model" of population structure are derived assuming tetrasomic inheritance. The expected equilibrium value of FST is computed. In contrast to diploids, the correlation of genes between individuals within populations with respect to genes between populations (FST) may vary among loci due to the particular segregation patterns expected under tetrasomic inheritance and is consequently inappropriate for estimating demographic parameters in such populations. We thus define a new parameter (rho) and derive its relationship with Nm. This relationship is shown to be independent from both the selfing rate and the proportion of double reduction. Finally, the statistical procedure required to evaluate these parameters using data on gene frequencies distribution among autotetraploid populations is developed.

Phylogeny and PCR-based classification of Wolbachia strains using wsp gene sequences

Wolbachia are a group of intracellular inherited bacteria that infect a wide range of arthropods. They are associated with a number of different reproductive phenotypes in their hosts, such as cytoplasmic incompatibility, parthenogenesis and feminization. While it is known that the bacterial strains responsible for these different host phenotypes form a single clade within the alpha-Proteobacteria, until now it has not been possible to resolve the evolutionary relationships between different Wolbachia strains. To address this issue we have cloned and sequenced a gene encoding a surface protein of Wolbachia (wsp) from a representative sample of 28 Wolbachia strains. The sequences from this gene were highly variable and could be used to resolve the phylogenetic relationships of different Wolbachia strains. Based on the sequence of the wsp gene from different Wolbachia isolates we propose that the Wolbachia pipientis clade be initially divided into 12 groups. As more sequence information becomes available we expect the number of such groups to increase. In addition, we present a method of Wolbachia classification based on the use of group-specific wsp polymerase chain reaction (PGR) primers which will allow Wolbachia isolates to be typed without the need to clone and sequence individual Wolbachia genes. This system should facilitate future studies investigating the distribution and biology of Wolbachia strains from large samples of different host species.

Comparative analysis of microsatellite and allozyme markers: a case study investigating microgeographic differentiation in brown trout (Salmo trutta)

A comparative study between microsatellite and allozyme markers was conducted on natural populations of resident brown trout (Salmo trutta) sampled over a reduced geographical scale and on hatchery strains. The higher level of polymorphism observed at microsatellite loci resulted in higher power of statistical tests for differentiation among population samples and for genotypic linkage disequilibrium. Genetic distances of Cavalli-Sforza and Edwards were on average two times larger for microsatellites than for allozymes but multilocus FST estimates computed over the entire set of populations were not significantly different for both categories of markers. Assignment tests of individual fish to the set of sampled populations demonstrated a much higher efficiency of microsatellites compared to allozymes. Pairwise multilocus FST estimates were significantly correlated to waterway distances and there was a significant tendency for the incorrectly classified individuals to be assigned to one of the nearest populations, indicating that isolation-by-distance acted significantly on brown trout populations. This increase of differentiation with distance was higher for allozymes than for microsatellites. Traditional measures of genetic differentiation (Cavalli-Sforza and Edwards' chord distance and FST) were compared for microsatellites to recently proposed statistics taking into account allele size differences (Goldstein's distance and PST). Using Goldstein's distance for neighbour-joining analysis did not improve the tree structure resolution. Multilocus estimates of PST and FST were not significantly different when computed over the entire set of populations but no significant correlation was detected between matrices of pairwise multilocus PST estimates and waterway distances.

Pleiotropy of adaptive changes in populations: comparisons among insecticide resistance genes in Culex pipiens

Resistance to toxicants is a convenient model for investigating whether adaptive changes are associated with pleiotropic fitness costs. Despite the voluminous literature devoted to this subject, intraspecific comparisons among toxicant resistance genes are rare. We report here results on the pleiotropic effect on adult survival of Culex pipiens mutants involved in the same adaptation: the resistance to organophosphorus insecticides. This field study was performed in southern France where four resistance genes sequentially appeared and increased in frequency in response to intense insecticide control. By repeated sampling of overwintering females through winter, we analysed the impact of each of three resistance genes on adult survival. We showed that (i) the most recent gene seems to be of no disadvantage during winter, (ii) the oldest affects survival in some environmental conditions, and (iii) the third induces a constant, severe and dominant survival cost. Such variability is discussed in relation to the physiological changes involved in resistance.