The role of Intelectin-2 in resistance to Ascaris suum lung larval burdens in susceptible and resistant mouse strains.

The underlying mechanism of predisposition to Ascaris infection is not yet understood but host genetics are thought to play a fundamental role. We investigated the association between the Intelectin-2 gene and resistance in F2 mice derived from mouse strains known to be susceptible and resistant to infection. Ascaris larvae were isolated from murine lungs and the number of copies of the Intelectin-2 gene was determined in F2 mice. Intelectin-2 gene copy number was not significantly linked to larval burden. In a pilot experiment, the response to infection in parental mice of both sexes was observed in order to address the suitability of female F2 mice. No overall significant sex effect was detected. However, a divergence in resistance/susceptibility status was observed between male and, female hybrid offspring. The responsiveness to Ascaris in mice is likely to be controlled by multiple genes and, despite a unique absence from the susceptible C57BL/6j strain, the Intelectin-2 gene does not play a significant role in resistance. The observed intra-strain variation in larval burden requires further investigation but we hypothesize that it stems from social/dominance hierarchies created by the presence of female mice and possibly subsequent hormonal perturbations that modify the intensity of the immune response.

The relationship between structurally different pyrrolizidine alkaloids and western flower thrips resistance in F(2) hybrids of Jacobaea vulgaris and Jacobaea aquatica.

Segregating plant hybrids often have more ecological and molecular variability compared to parental species, and are therefore useful for studying relationships between different traits, and the adaptive significance of trait variation. Hybrid systems have been used to study the relationship between the expression of plant defense compounds and herbivore susceptibility. We conducted a western flower thrips (WFT) bioassay using a hybrid family and investigated the relationship between WFT resistance and pyrrolizidine alkaloid (PA) variation. The hybrid family consisted of two parental (Jacobaea vulgaris and Jacobaea aquatica) genotypes, two F(1) genotypes, and 94 F(2) hybrid lines. The J. aquatica genotype was more susceptible to thrips attack than the J. vulgaris genotype, the two F(1) hybrids were as susceptible as J. aquatica, and susceptibility to WFT differed among F(2) hybrid lines: 69 F(2) lines were equally susceptible compared to J. aquatica, 10 F(2) lines were more susceptible than J. aquatica and 15 F(2) lines were as resistant as J. vulgaris or were intermediate to the two parental genotypes. Among 37 individual PAs that were derived from four structural groups (senecionine-, jacobine-, erucifoline- and otosenine-like PAs), the N-oxides of jacobine, jaconine, and jacoline were negatively correlated with feeding damage caused by WFT, and the tertiary amines of jacobine, jaconine, jacoline, and other PAs did not relate to feeding damage. Total PA concentration was negatively correlated with feeding damage. Among the four PA groups, only the total concentration of the jacobine-like PAs was negatively correlated with feeding damage. Multiple regression tests suggested that jacobine-like PAs play a greater role in WFT resistance than PAs from other structural groups. We found no evidence for synergistic effects of different PAs on WFT resistance. The relationship between PA variation and WFT feeding damage in the Jacobaea hybrids suggests a role for PAs in resistance to generalist insects.

Hybridism between Biomphalaria cousini and Biomphalaria amazonica and its susceptibility to Schistosoma mansoni.

Molecular techniques can aid in the classification of Biomphalaria species because morphological differentiation between these species is difficult. Previous studies using phylogeny, morphological and molecular taxonomy showed that some populations studied were Biomphalaria cousini instead of Biomphalaria amazonica. Three different molecular profiles were observed that enabled the separation of B. amazonica from B. cousini. The third profile showed an association between the two and suggested the possibility of hybrids between them. Therefore, the aim of this work was to investigate the hybridism between B. cousini and B. amazonica and to verify if the hybrids are susceptible to Schistosoma mansoni. Crosses using the albinism factor as a genetic marker were performed, with pigmented B. cousini and albino B. amazonica snails identified by polymerase chain reaction-restriction fragment length polymorphism. This procedure was conducted using B. cousini and B. amazonica of the type locality accordingly to Paraense, 1966. In addition, susceptibility studies were performed using snails obtained from the crosses (hybrids) and three S. mansoni strains (LE, SJ, AL). The crosses between B. amazonica and B. cousini confirmed the occurrence of hybrids. Moreover, hybrids can be considered potential hosts of S. mansoni because they are susceptible to LE, SJ and AL strains (4.4%, 5.6% and 2.2%, respectively). These results indicate that there is a risk of introducing schistosomiasis mansoni into new areas.

Host-parasite interactions in sympatric and allopatric populations of European bitterling.

Susceptibility to parasite infection was examined in a field experiment for four populations of 0+ juvenile European bitterling (Rhodeus amarus): one sympatric to local parasite fauna, one allopatric, and two hybrid populations. Significantly higher parasite abundance was recorded in the allopatric bitterling population, suggesting a maladaptation of parasites to their sympatric host. Type of parasite life cycle played an important role in host-parasite interactions. While the abundance of allogenic species between populations was comparable, a significant difference was found in abundance of autogenic parasite species between fish populations, with the allopatric population more infected. These results correspond with a prediction of higher dispersion probability and higher gene flow among geographically distant populations of allogenic species as compared to autogenic species. Increased susceptibility to parasites that do not occur within the natural host's geographical distribution was found in the allopatric host, but only for autogenic species. A difference in infection susceptibility was detected among populations of early-hatched bitterling exposed to infection during a period of high parasite abundance and richness in the environment. Differences in parasite abundance and species diversity among populations diminished, however, with increasing time of exposure. No difference was found within late-hatched populations, probably due to a lower probability of infection in late-hatched cohorts.

Critical role of dendritic cells in determining the Th1/Th2 balance upon Leishmania major infection.

The onset of T(h)1 immunity is in part regulated by genetic background. To elucidate the cell type carrying critical factors determining the T(h)1 response, we employed Rag-2(-/-) mice on Leishmania major-susceptible BALB/c and -resistant B10.D2 backgrounds. By using bone marrow (BM) chimeras generated by the transplantation of B10.D2 BM cells into BALB/c-Rag-2(-/-) mice, and vice versa, it was shown that hematopoietic cells carry factors determining the disease outcome and T(h)1 response against L. major infection. B10.D2-Rag-2(-/-) mice reconstituted with BALB/c CD4(+) T cells exhibited a T(h)1 response and controlled L. major infection. Wild-type BALB/c mice inoculated with L. major-parasitized B10.D2-Rag-2(-/-) splenocytes also exhibited a T(h)1 response and a mild disease outcome, whereas such a T(h)1 response was not induced when CD11c(+) dendritic cells (DCs) were depleted from parasitized B10.D2-Rag-2(-/-) splenocytes. T(h)1 response was reconstituted by the addition of L. major-parasitized B10.D2 DCs but not L. major-parasitized BALB/c DCs to DC-depleted parasitized B10.D2-Rag-2(-/-) splenocytes. These results indicate that DCs determine the outcome of the disease upon L. major infection.

High fusibility and chimera prevalence in an invasive colonial ascidian.

The formation of chimeric entities through colony fusion has been hypothesized to favour colonisation success and resilience in modular organisms. In particular, it can play an important role in promoting the invasiveness of introduced species. We studied prevalence of chimerism and performed fusion experiments in Mediterranean populations of the worldwide invasive colonial ascidian Didemnum vexillum. We analysed single zooids by whole genome amplification and genotyping-by-sequencing and obtained genotypic information for more than 2,000 loci per individual. In the prevalence study, we analysed nine colonies and identified that 44% of them were chimeric, composed of 2-3 different genotypes. In the fusion experiment 15 intra- and 30 intercolony pairs were assayed but one or both fragments regressed and died in ~45% of the pairs. Among those that survived for the length of the experiment (30 d), 100% isogeneic and 31% allogeneic pairs fused. Fusion was unlinked to global genetic relatedness since the genetic distance between fused or non-fused intercolony pairs did not differ significantly. We could not detect any locus directly involved in allorecognition, but we cannot preclude the existence of a histocompatibility mechanism. We conclude that chimerism occurs frequently in D. vexillum and may be an important factor to enhance genetic diversity and promote its successful expansion.

Bone marrow chimeric mice reveal a dual role for CD36 in Plasmodium berghei ANKA infection.

BACKGROUND: Adhesion of Plasmodium-infected red blood cells (iRBC) to different host cells, ranging from endothelial to red blood cells, is associated to malaria pathology. In vitro studies have shown the relevance of CD36 for adhesion phenotypes of Plasmodium falciparum iRBC such as sequestration, platelet mediated clumping and non-opsonic uptake of iRBC. Different adhesion phenotypes involve different host cells and are associated with different pathological outcomes of disease. Studies with different human populations with CD36 polymorphisms failed to attribute a clear role to CD36 expression in human malaria. Up to the present, no in vivo model has been available to study the relevance of different CD36 adhesion phenotypes to the pathological course of Plasmodium infection. METHODS: Using CD36-deficient mice and their control littermates, CD36 bone marrow chimeric mice, expressing CD36 exclusively in haematopoietic cells or in non-haematopoietic cells, were generated. Irradiated CD36-/- and wild type mice were also reconstituted with syngeneic cells to control for the effects of irradiation. The reconstituted mice were infected with Plasmodium berghei ANKA and analysed for the development of blood parasitaemia and neurological symptoms. RESULTS: All mice reconstituted with syngeneic bone marrow cells as well as chimeric mice expressing CD36 exclusively in non-haematopoietic cells died from experimental cerebral malaria between day 6 and 12 after infection. A significant proportion of chimeric mice expressing CD36 only in haematopoietic cells did not die from cerebral malaria. CONCLUSION: The analysis of bone marrow chimeric mice reveals a dual role of CD36 in P. berghei ANKA infection. Expression of CD36 in haematopoietic cells, most likely macrophages and dendritic cells, has a beneficial effect that is masked in normal mice by adverse effects of CD36 expression in non-haematopoietic cells, most likely endothelial cells.

Parasitological assessment in the hybrid surubim (Pseudoplatystoma reticulatum x P. corruscans), with uncommon occurrence of Monogenea parasites.

This study evaluated the parasite fauna of farmed hybrid surubim (Pseudoplatystoma reticulatum x P. corruscans) and the host-parasite-environment relationship in two fish farms located in Mato Grosso do Sul, Central Brazil, South America. A total of 120 hybrids from two different farms, 60 in each season (30 in the hot and 30 in cold season) were examined during a year. Water quality was weekly measured to evaluate the interaction among environmental conditions and parasitism. Histopathology was used to observe the effects of the parasites and environment on the fish gills. The ciliate protozoan Ichthyophthirius multifiliis and the monogeneans (Ameloblastella sp., Amphocleithrium paraguayensis, Vancleaveus ciccinus, V. fungulus and V. janacauensis) were the most prevalent parasites detected in both seasons in both farms, with prevalence above 80%. It was stated that parasites did not cause important damage in the health status of the hybrid surubim. These results might be related to general good management practices and environmental quality implemented by the fish farmers. The presence of uncommon monogenean parasites to this hybrid compared to their parents causing an environmental and ecological concern is here discussed.

Metazoan parasite communities: support for the biological invasion of Barbus barbus and its hybridization with the endemic Barbus meridionalis.

BACKGROUND: Recently, human intervention enabled the introduction of Barbus barbus from the Rhône River basin into the Barbus meridionalis habitats of the Argens River. After an introduction event, parasite loss and lower infection can be expected in non-native hosts in contrast to native species. Still, native species might be endangered by hybridization with the incomer and the introduction of novel parasite species. In our study, we aimed to examine metazoan parasite communities in Barbus spp. populations in France, with a special emphasis on the potential threat posed by the introduction of novel parasite species by invasive B. barbus to local B. meridionalis. METHODS: Metazoan parasite communities were examined in B. barbus, B. meridionalis and their hybrids in three river basins in France. Microsatellites were used for the species identification of individual fish. Parasite abundance, prevalence, and species richness were compared. Effects of different factors on parasite infection levels and species richness were tested using GLM. RESULTS: Metazoan parasites followed the expansion range of B. barbus and confirmed its introduction into the Argens River. Here, the significantly lower parasite number and lower levels of infection found in B. barbus in contrast to B. barbus from the Rhône River supports the enemy release hypothesis. Barbus barbus × B. meridionalis hybridization in the Argens River basin was confirmed using both microsatellites and metazoan parasites, as hybrids were infected by parasites of both parental taxa. Trend towards higher parasite diversity in hybrids when compared to parental taxa, and similarity between parasite communities from the Barbus hybrid zone suggest that hybrids might represent "bridges" for parasite infection between B. barbus and B. meridionalis. Risk of parasite transmission from less parasitized B. barbus to more parasitized B. meridionalis indicated from our study in the Argens River might be enhanced in time as higher infection levels in B. barbus from the Rhône River were revealed. Hybrid susceptibility to metazoan parasites varied among the populations and is probably driven by host-parasite interactions and environmental forces. CONCLUSIONS: Scientific attention should be paid to the threatened status of the endemic B. meridionalis, which is endangered by hybridization with the invasive B. barbus, i.e. by genetic introgression and parasite transmission.

Molecular phylogeny and ultrastructure of Myxobolus cf. cuneus, a parasite of patinga hybrid and Henneguya pseudoplatystoma, a parasite of pintado hybrid.

Through morphological, histopathological and ultrastructural analysis of Myxobolus cuneus Adriano, Arana et Cordeiro, 2006 and Henneguya pseudoplatystoma Naldoni, Arana, Maia, Ceccarelli, Tavares, Borges, Pozo et Adriano, 2009 were identified infecting pacu respectively (Piaractus mesopotamicus) and hybrid pintado (Pseudoplatystoma corruscans x Pseudoplatystoma reticulatum) taken from Brazilian fish farms. The present study describes 18S rDNA sequencing of Myxobolus cf. cuneus infecting the spleen of farmed patinga, a hybrid fish resulting from the crossing of P. mesopotamicus x Piaractus brachypomus, and H. pseudoplatystoma found in farmed hybrid pintado from the state of Sao Paulo, Brazil. The study also provides new details of the host-parasite interface of M. cf. cuneus, which reveal that the plasmodial wall is composed of a single membrane connected to the plasmodium ectoplasm by numerous pinocytic canals. The plasmodia also displayed asynchronous development but had disporic pansporoblasts at different developmental stages; immature and mature spores were found at different depth levels of the plasmodium. Maximum likelihood phylogenetic analysis showed that M. cf. cuneus appeared as a sister species of Henneguya pellucida Adriano, Arana et Cordeiro, 2005 in a sub-clade composed mainly of myxosporean parasites of characiforms, and that H. pseudoplatystoma clustered in a sub-clade composed of Henneguya/Myxobolus spp. parasites of siluriform fish.

Development of stem borer resistant transgenic parental lines involved in the production of hybrid rice.

Stem borer resistant transgenic parental lines, involved in hybrid rice, were produced by Agrobacterium-mediated gene transfer method. Two pSB111 super-binary vectors containing modified cry1Ab/cry1Ac genes driven by maize ubiquitin promoter, and herbicide resistance gene bar driven by cauliflower mosaic virus 35S promoter were, used in this study. Embryogenic calli after co-cultivation with Agrobacterium were selected on the medium containing phosphinothricin. Southern blot analyses of primary transformants revealed the stable integration of bar, cry1Ab and cry1Ac coding sequences into the genomes of three parental lines with a predominant single copy integration and without any rearrangement of T-DNA. T1 progeny plants disclosed a monogenic pattern (3:1) of transgene segregation as confirmed by molecular analyses. Furthermore, the co-segregation of bar and cry genes in T1 progenies suggested that the transgenes are integrated at a single site in the rice genome. In different primary transformants with alien inbuilt resistance, the levels of cry proteins varied between 0.03 and 0.13% of total soluble proteins. These transgenic lines expressing insecticidal proteins afforded substantial resistance against stem borers. This is the first report of its kind dealing with the introduction of Bacillus thuringiensis (Bt) cry genes into the elite parental lines involved in the development of hybrid rice.

Responses of bovine chimaeras combining trypanosomosis resistant and susceptible genotypes to experimental infection with Trypanosoma congolense.

West African N'Dama cattle have developed a genetic capacity to survive, reproduce and remain productive under trypanosomosis risk. The cellular and molecular bases of this so-called trypanotolerance are not known, but the trait is manifested by the N'Dama's greater capacity to control parasitaemia and anaemia development during an infection. In order to examine the role of the haematopoietic system in trypanotolerance, we have exploited the tendency for the placentas of bovine twin embryos to fuse. Placental fusion in cattle results in bone marrow chimaerism in twins. By comparison with the N'Dama, cattle of the East African Boran breed are relatively susceptible. We evaluated the role of the haemopoietic system in trypanotolerance by comparing the performance of five Chimaeric Boran/N'Dama twin calves with that of singletons of the two breeds. Chimaeric Boran/N'Dama pairs of twins were produced in recipient Boran cows by embryo transfer, and the majority of haemopoietic cells in all twinned individuals were of Boran origin. Thus, N'Dama chimaeras differed from N'Dama singletons in that the bulk of their haemopoietic system was derived from their susceptible Boran twins, while Boran chimaeras differed little from Boran control animals. All cattle became parasitaemic and developed anaemia. The N'Dama chimaeras did not manage their anaemia and white blood cell counts effectively. However, they were able to limit parasitaemia development. These results suggest that trypanotolerance is the result of two mechanisms, one that improves parasite control and is independent of the genetic origin of the haemopoietic tissue, and another that is influenced by haemopoietic tissue genotype and which improves control over anaemia. The capacity to maintain growth during infection was similarly dependent on the genetic origin of the haemopoietic tissue.

Parasitological assessment in the hybrid surubim (Pseudoplatystoma reticulatum x P. corruscans), with uncommon occurrence of Monogenea parasites / Avaliação parasitológica no híbrido surubim (Pseudoplatystoma reticulatum x P. corruscans), com ocorrência incomum de parasitos Monogenea

Abstract This study evaluated the parasite fauna of farmed hybrid surubim (Pseudoplatystoma reticulatum x P. corruscans) and the host-parasite-environment relationship in two fish farms located in Mato Grosso do Sul, Central Brazil, South America. A total of 120 hybrids from two different farms, 60 in each season (30 in the hot and 30 in cold season) were examined during a year. Water quality was weekly measured to evaluate the interaction among environmental conditions and parasitism. Histopathology was used to observe the effects of the parasites and environment on the fish gills. The ciliate protozoan Ichthyophthirius multifiliis and the monogeneans (Ameloblastella sp., Amphocleithrium paraguayensis, Vancleaveus ciccinus, V. fungulus and V. janacauensis) were the most prevalent parasites detected in both seasons in both farms, with prevalence above 80%. It was stated that parasites did not cause important damage in the health status of the hybrid surubim. These results might be related to general good management practices and environmental quality implemented by the fish farmers. The presence of uncommon monogenean parasites to this hybrid compared to their parents causing an environmental and ecological concern is here discussed.

Resumo Este estudo avaliou a fauna de parasitos do surubim híbrido cultivado (Pseudoplatystoma reticulatum x P. corruscans) e a relação hospedeiro-parasito-ambiente em duas pisciculturas localizadas no Estado do Mato Grosso do Sul, região Centro-Oeste, Brasil. Um total de 120 híbridos de duas fazendas, 60 em cada estação (30 na estação quente e 30 na fria), foram examinados durante um ano. A qualidade da água foi medida semanalmente para avaliar a interação entre as condições ambientais e o parasitismo. Histopatologia foi usada para observar os efeitos dos parasitos e do ambiente nas brânquias dos peixes. O protozoário ciliado Ichthyophthirius multifiliis e Monogenea (Ameloblastella sp., Amphocleithrium paraguayensis, Vancleaveus ciccinus, V. fungulus e V. janacauensis) foram os parasitos mais prevalentes detectados em ambas estações nas duas fazendas, com prevalências acima de 80%. Observou-se que os parasitos não causaram danos ao estado de saúde do surubim híbrido. Esses resultados estão relacionados às boas práticas de manejo e qualidade ambiental implementada pelos produtores. É discutida a presença incomum de Monogenea para esse híbrido, comparado com seus progenitores, podendo causar preocupação ambiental e ecológica.

Associations of planting date, drought stress, and insects with Fusarium ear rot and fumonisin B1 contamination in California maize.

Fusarium ear rot, caused by Fusarium verticillioides, is one of the most common diseases of maize, causing yield and quality reductions and contamination of grain by fumonisins and other mycotoxins. Drought stress and various insects have been implicated as factors affecting disease severity. Field studies were conducted to evaluate the interactions and relative influences of drought stress, insect infestation, and planting date upon Fusarium ear rot severity and fumonisin B1 contamination. Three hybrids varying in partial resistance to Fusarium ear rot were sown on three planting dates and subjected to four irrigation regimes to induce differing levels of drought stress. A foliar-spray insecticide treatment was imposed to induce differing levels of insect injury. Populations of thrips (Frankliniella spp.), damage by corn earworm (Helicoverpa zeae), Fusarium ear rot symptoms, and fumonisin B1 levels were assessed. There were significant effects of hybrid, planting date, insecticide treatment, and drought stress on Fusarium ear rot symptoms and fumonisin B1 contamination, and these factors also had significant interacting effects. The most influential factors were hybrid and insecticide treatment, but their effects were influenced by planting date and drought stress. The more resistant hybrids and the insecticide-treated plots consistently had lower Fusarium ear rot severity and fumonisin B1 contamination. Later planting dates typically had higher thrips populations, more Fusarium ear rot, and higher levels of fumonisin B1. Insect activity was significantly correlated with disease severity and fumonisin contamination, and the correlations were strongest for thrips. The results of this study confirm the influence of thrips on Fusarium ear rot severity in California, USA, and also establish a strong association between thrips and fumonisin B1 levels.

Heterozygosity and parasite intensity: lung parasites in the water frog hybridization complex.

In hybridogenetic systems, hybrid individuals are fully heterozygous because one of the parental genomes is discarded from the germinal line before meiosis. Such systems offer the opportunity to investigate the influence of heterozygosity on susceptibility to parasites. We studied the intensity of lung parasites (the roundworm Rhabdias bufomis and the fluke Haplometra cylindracea) in 3 populations of water frogs of the Rana lessonae-esculenta complex in eastern France. In these mixed populations, hybrid frogs (R. esculenta) outnumbered parental ones (R. lessonae). Despite variation in parasite intensity and demographic variability among populations, the relationship between host age and intensity of parasitism suggests a higher susceptibility in parentals than in hybrids. Mortality is probably enhanced by lung parasites in parental frogs. On the other hand, while parental frogs harboured higher numbers of H. cylindracea than hybrid frogs, the latter had higher numbers of R. bufonis. Despite such discrepancies, these results support the hybrid resistance hypothesis, although other factors, such as differences in body size, age-related immunity, differential exposure risks and hemiclonal selection, could also contribute to the observed patterns of infection.

Historical mammal extinction on Christmas Island (Indian Ocean) correlates with introduced infectious disease.

It is now widely accepted that novel infectious disease can be a leading cause of serious population decline and even outright extinction in some invertebrate and vertebrate groups (e.g., amphibians). In the case of mammals, however, there are still no well-corroborated instances of such diseases having caused or significantly contributed to the complete collapse of species. A case in point is the extinction of the endemic Christmas Island rat (Rattus macleari): although it has been argued that its disappearance ca. AD 1900 may have been partly or wholly caused by a pathogenic trypanosome carried by fleas hosted on recently-introduced black rats (Rattus rattus), no decisive evidence for this scenario has ever been adduced. Using ancient DNA methods on samples from museum specimens of these rodents collected during the extinction window (AD 1888-1908), we were able to resolve unambiguously sequence evidence of murid trypanosomes in both endemic and invasive rats. Importantly, endemic rats collected prior to the introduction of black rats were devoid of trypanosome signal. Hybridization between endemic and black rats was also previously hypothesized, but we found no evidence of this in examined specimens, and conclude that hybridization cannot account for the disappearance of the endemic species. This is the first molecular evidence for a pathogen emerging in a naïve mammal species immediately prior to its final collapse.

Hybridism between Biomphalaria cousini and Biomphalaria amazonica and its susceptibility to Schistosoma mansoni

Molecular techniques can aid in the classification of Biomphalaria species because morphological differentiation between these species is difficult. Previous studies using phylogeny, morphological and molecular taxonomy showed that some populations studied were Biomphalaria cousini instead of Biomphalaria amazonica. Three different molecular profiles were observed that enabled the separation of B. amazonica from B. cousini. The third profile showed an association between the two and suggested the possibility of hybrids between them. Therefore, the aim of this work was to investigate the hybridism between B. cousini and B. amazonica and to verify if the hybrids are susceptible to Schistosoma mansoni. Crosses using the albinism factor as a genetic marker were performed, with pigmented B. cousini and albino B. amazonica snails identified by polymerase chain reaction-restriction fragment length polymorphism. This procedure was conducted using B. cousini and B. amazonica of the type locality accordingly to Paraense, 1966. In addition, susceptibility studies were performed using snails obtained from the crosses (hybrids) and three S. mansoni strains (LE, SJ, AL). The crosses between B. amazonica and B. cousini confirmed the occurrence of hybrids. Moreover, hybrids can be considered potential hosts of S. mansoni because they are susceptible to LE, SJ and AL strains (4.4 percent, 5.6 percent and 2.2 percent, respectively). These results indicate that there is a risk of introducing schistosomiasis mansoni into new areas.

Temporal cline in a hybrid zone population between Fraxinus excelsior L. and Fraxinus angustifolia Vahl.

The two closely related ash species Fraxinus excelsior L. (common ash) and Fraxinus angustifolia Vahl (narrow-leaved ash) have a broad contact zone in France where they hybridize. However, little is known about the local structure of hybrid zone populations and the isolation mechanisms. We assessed the potential effect of floral phenology on the structure of a riparian ash hybrid zone population in central France. The distribution of flowering times was unimodal and lay between the flowering periods of the two species. Using microsatellite markers, we detected isolation by time, which has possibly originated from assortative mating. Multivariate analyses indicated that morphological variation is not distributed at random with respect to flowering times. Spatial autocorrelation analyses showed that temporal and spatial patterns were tightly linked. Interestingly, despite the fact that the population shows isolation by time, neighbourhood size and historical dispersal variance (sigma = 63 m) are similar to those detected in pure stands of F. excelsior where individuals flower rather synchronously and hermaphrodites are not the most frequent sexual type. Trees flowering at intermediate dates, which comprised the majority of the population, produced on average more flowers and fruits. We detected no significant differences in floral parasite infections relative to reproductive timing, although there was a tendency for late flowering trees to suffer from more gall attack. We discuss the impact of temporal variation in fitness traits and their possible role in the maintenance of the hybrid zone.

Specific identification of Egyptian Biomphalaria species and possible hybrids using the polymerase chain reaction based on nuclear and mitochondrial loci.

The snail historically implicated in the transmission of Schistosoma mansoni in Egypt is Biomphalaria alexandrina. The problem of schistosomiasis in Egypt has been complicated in recent years by the introduction of Biomphalaria glabrata, which has been reported to hybridize with B. alexandrina. Both introduced and hybrid snails also pose a threat with respect to S. mansoni transmission. As morphological differentiation of these snails is difficult, using three DNA loci, nuclear ITS1 and ITS2, and mitochondrial ND1, PCR-based assays were developed to identify these species and possible hybrids. The assays are rapid, reproducible, sensitive and specific. This technique may be used in field surveys to study the distribution of the two species of intermediate host and their putative hybrids in Egypt.