Showing papers on "Bulinus truncatus published in 1992"

Food selection by freshwater snails in the Gezira irrigation canals, Sudan

Abstract: Stomach content analysis was carried out on samples of the freshwater snail species Biomphalaria pfeifferi, Bulinus truncatus, Bulinus forskalii (Pulmonata, Planorbidae), Lymnaea natalensis (Pulmonata, Lymnaeidae), Melanoides tuberculata, Cleopatra bulimoides (Prosobranchia, Thiaridae) and Lanistes carinatus (Prosobranchia, Ampullariidae) from different irrigation canals in Sudan. In order to evaluate overlap in diet selection among these species, sites with two or more of the above-mentioned species present were selected. For some species food choice was examined in relation to size groupings. In addition, samples of Marisa cornuarietis (Prosobranchia, Ampullariidae) from small ponds in Sudan, samples of Biomphalaria pfeifferi and Helisoma duryi (Pulmonata, Planorbidae) from drainage canals in an irrigation scheme in northern Tanzania, and samples of H. duryi from fish ponds in the coastal area of Kenya were also analysed.

Aphally Versus Euphally in Self-Fertile Hermaphrodite Snails from the Species Bulinus truncatus (Pulmonata: Planorbidae)

Abstract: Different reproductive systems have evolved in hermaphrodite plants that allow species to reproduce simultaneously by both self-fertilization a d cross-fertilization (see Charlesworth and Charlesworth 1978; Lloyd 1979)-for example, cleistogamy (Schoen and Lloyd 1984) and gynodioecy (Gouyon and Couvet 1987). Aphally may be such a feature in hermaphrodite animals, particularly Pulmonate snails. Whereas the reproductive structure of snails usually consists of one hermaphrodite gonad and of male and female ducts with accessory glands, aphallic individuals lack the male copulatory organ (Geraerts and Joosse 1984; Tompa 1984). Aphally has been reported in land snails (Tompa 1984; Pokrysko 1987) and in freshwater snails of the genus Bulinus, the intermediate African host of the trematode Schistosoma that infects humans (Brown 1980). In Bulinus, aphallic individuals lack not only the copulatory organ but the prostate and vas deferens as well (Larambergue 1939). Bulinus species are self-fertile hermaphrodites whose usual mating system is cross-fertilization by unilateral copulation, in which one individual acts as male while the other acts as female (Larambergue 1939; Rudolph 1979; Rollinson et al. 1989). The foreign sperm is used for cross-fertilization almost immediately after copulation. If an individual is isolated after copulation, sperm storing allows outcrossing during the subsequent few months. However, the selfing rate increases in time as the sperm stored is exhausted or dies. Virgin isolated individuals also reproduce by selfing (Rudolph and Bailey 1985). A euphallic Bulinus is able to receive sperm, to self-fertilize, and to transfer its sperm to another individual by copulation, whereas an aphallic individual can only receive sperm and self-fertilize. Larambergue (1939) showed that, in Bulinus truncatus (contortus), pure euphallic, pure aphallic, and mixed populations can be found over the range of the species. He also showed that aphally has a genetic basis that appears polygenic. His results suggest that B. truncatus may be a partial selfer as a consequence of being aphallic (Larambergue 1939, p. 194). Our results support this hypothesis. A prediction of the theory of sex allocation (Charnov 1982), as applied to the case of B. truncatus, is that aphallic selfing snails can invest more in reproduction than euphallic ones because there is no cost related to the building and maintenance of male organs, if one assumes that both types of snails invest the same amount in growth and in survival. We addressed this question by studying the relative fitness of self-fertilizing aphallic and euphallic individuals. As expected, we show that aphallic snails lay more eggs than euphallics.

Temperature determination of male outcrossing ability in a simultaneous hermaphrodite.

Abstract: Phally, a genital dimorphism found in some species of self-compatible simultaneous hermaphrodites, presents an opportunity to examine factors maintaining outcrossing within an animal species in the presence of recombination. Both aphallics and euphallics can self-fertilize but only euphallics develop a functional penis and prostate allowing them to donate sperm. Previous studies of phally in the gastropod Bulinus truncatus (Mollusca: Pulmonata) suggest that phally may be under direct genetic control in some populations and strongly influenced by environmental factors in others. Experiments reported here identify temperature as a cue affecting phally determination in two populations of B. truncatus. In both populations, a higher proportion of euphallics was produced at low temperature (22 ± 1°C) than at high temperature (30 ± 1°C). Temperatures experienced by parents did not affect the proportion of euphallics they produced. Instead, phally was sensitive to temperature during the egg stage postoviposition and during the hatchling stage; the relative influence of temperature before and after hatching varied between populations. The total number of hatchlings reaching maturity at high and low temperature did not differ, but at low temperature, snails took longer to hatch and mature, and had lower survivorship. Just as studies of environmental sex determination have shed light on selective pressures influencing sex ratio evolution, we suggest that temperature-sensitive phally determination may shed light on the selective pressures maintaining outcrossing in B. truncatus.

A comparative study on the food-locating ability of Helisoma duryi, Biomphalaria camerunensis and Bulinus truncatus (Pulmonata : Planorbidae)

Abstract: 1. Helisoma duryi, a planorbid snail has been suggested as a biological control agent against the snail intermediate hosts of schistosomes, Biomphalaria and Bulinus species. It has been demonstrated that competition for food resources is involved. The aim of this paper is to compare the ability of these species to locate food sources. 2. The paper compares the accumulation of groups of Helisoma duryi, Biomphalaria camerunensis and Bulinus truncatus on varying amounts of two different artificial food preparations and the movement of individual snails of these three species when approaching a food source by analysing their tracks. 3. There were slight differences in the ability of H. duryi and B. camerunensis to locate food preparations, but both were superior to B. truncatus. The two types of food preparations differed markedly in their attraction of B. truncatus. H. duryi was less attracted to the food preparations with the two lowest amounts of food of both types than to preparations with larger amounts of food, while this was not observed for B. camerunensis and B. truncatus. Medium-sized H. duryi were superior to small and large snails in their ability to locate food, while no significant differences were found among three size groups of B. truncatus. 4. Analysis of snail tracks did not reveal an increased frequency of turning in any of the three species as the food source was approached. The reason for the higher accumulation of H. duryi and B. camerunensis on the food could in part be explained by their higher activity level. Other explanations are also discussed.

Seasonal patterns in the transmission of Schistosoma haematobium in Attaouia, Morocco

Abstract: In the Attaouia area, the density of Bulinus truncatus (Audouin, 1827), was monitored monthly for a period of one year in correlation with weather variations. Snails were active throughout the year and particularly abundant at the end of spring and summer. Two snail generations were found to overlap. The infection rate of B. truncatus reached a maximum of 3.5% in the summer when human water contact was frequent. A selective survey conducted in the village of Lamyayha showed that the prevalence of infection with S. haematobium among the local population was 21.2% who were passing from 10 to 80 eggs per 10 ml of urine.

Heritability of male outcrossing ability in the simultaneous hermaphrodite, Bulinus truncatus (Gastropoda: Planorbidae)

Abstract: The heritability of phally, a dichotomous trait defined by the functional state of the male reproductive tract, was measured in a laboratory population of the simultaneous hermaphrodite snail Bulinus truncatus by means of a breeding experiment and a selection experiment. Euphallic individuals develop a fully functional male and female tract and are capable of receiving and donating sperm. In aphallic individuals the male tract does not develop fully, preventing sperm donation. There was no evidence of a heritable component to phally in the breeding experiment, but the selection experiment demonstrated a slight heritable effect. In both experiments there was more variation in the observed proportion of euphallics than expected by chance alone and no evidence of line or family effects, implicating environmental determination of male outcrossing ability even under controlled laboratory conditions. Previous studies of populations of B. truncatus reported that the proportion of euphallics was under strong genetic control. We suggest that there may be population differences in the extent of environmental control over phally, analogous to that reported for sex determination.

Natural infection of Bulinus senegalensis by Schistosoma haematobium in a temporary pool focus in Niger: characterization by cercarial emergence patterns.

Abstract: The transmission in West Africa of Schisto&&a haematobium by Bulinus truncatus and B. globosus is well known (BROWN, 1980). On the contrary, B. senegalensis, widely distributed in the sub-desert and sahelian zone and associated principally with a temporary environment (BETTERTON et al., 1983), has been found naturally infected in Senegal and The Gambia only (VERCRUYSSE et al., 1985). In Niger, snail-schistosome infection experiments have proved that B. senegalensis is an excellent potential vector of S. haematobium originating from the sahelian zone (VERA et al., 1990). The purpose of this study was to establish and determine the natural role of B. senegalensis in the transmission of urinary schistosomiasis. The survey was carried out in 1988 in temporary rain-fed pools near the village of Bomberi, in the western part of Niger, 120 km north-east of Niamey in the south sahelian zone. A parasitological survey of schoolchildren in that village showed a prevalence of urinary schistosomiasis of 83% (77/92). A fortnightly hand collection of snails (lasting 20 min) was conducted from the time when the ponds filled until their drying up. The schistosomes were characterized by determining the emergence rhythms of cercariae under standardized laboratory conditions by means of a chronocercariometric apparatus (PAGÈS & THÉRON, 1990). The survey showed that B. senegalensis was the only snail species present in the ponds near the village which were used by human populations. That species was also the only one present in ponds located within a range of 10 km around the village. The populations of B. senegalensis developed after the filling of the ponds, in late June, and survived until their drying up between October and December. Only 3 of 600 snails (0.5%) collected in October 1988 released cercariae, characterized by peak emergence between 1200 h and 1400 h. Studies in our laboratory on several strains from different localities in Niger have shown that the mean shedding time (MST) was between 1200 h and 1400 h for S. haematobium and between 0800 h and 1000 h for S. bovis and S. curassoni (MOUCHET et al., 1990). Our results agree with those obtained by previous workers. For S. haematobium, the MST was between 1200 h and 1400 h, whether under natural outdoor conditions in South Africa (PITCHFORD & DU TOIT, 1976) or under experimental conditions identical to ours in Niger (PAGÈS & THÉRON, 1990). Different African strains of S. bovis were characterized by an MST between 0800 h and 1000 h under similar experimental conditions (MOUAHID et al., 1987; PAGÈS & THÉRON, 1990). These results indicate that the chronobiology of cercarial emergence can be used as a reliabie character for distinguishing between S. haematobium on one hand and S. bovis andS. curassoni on the other hand. Furthermore, in Niger, S. curassoni is present only in the eastern part of the country (MOUCHET et al., 1989). These results consequently allow us to affirm the natural infection of B. senegalensis by S. haematobium in the focus of

Vertical spatial behaviour patterns of Lymnaea truncatula in relation with origin of snails, infection with Fasciola hepatica, and experimental environment

Abstract: Ethological studies were carried out on three Moroccan populations of Lymnaea truncatula of which two of them were living in a flooding irrigation system (Tassila, Oued Massa valley) and the third in a nonirrigated habitat. Most of the Tassila snails were found in the deep water zone. Two factors significantly influenced the presence of snails in this zone : the water current velocity, and parasitic infection of the molluscs. In the presence of other factors (lack of food, the presence of the snail Physa acuta ), the L. truncatula were recovered more frequently in zones outside of the water and just beneath the water’s surface. Despite the modifications noted in snail distribution, Bulinus truncatus did not appear to be a competitor. Lastly, habitat drying resulted in partial or complete burrowing of 50 % of snails.

Investigation of the Molluscicidal Activity of Tamarindus indica

Abstract: Extracts from Tamarindus indica L. (Leguminosae) fruit pulp were found to have molluscicidal activity against Bulinus truncatus snails. Activity was thought to be due to the presence of saponins.

[Population dynamics and infestation of Bulinus truncatus and Bulinus forskalii by schistosomal larvae in the Sudan-Sahelian zone of Cameroon].

Abstract: The evolution of the population densities of Bulinus truncatus and Bulinus forskalii has been studied during 18 months in a number of sites of the Sudan-Sahelian zone of Cameroon, in relation to certain environmental factors. Only the altitude of the water in the sites has an influence on the density of the snails. The populations of B. truncatus present a greater proportion of young molluscs during the entire year, with the exception of the last months of the dry season. The population dynamics of B. forskalii varies depending on whether the environment is temporarily stagnant, temporarily running or stable. The proportions of B. truncatus and B. forskalii that emit cercariae of schistosomes are 1.2% and 0.8% respectively. Study of the adult worms obtained after infestation of the laboratory mammals show that B. truncatus emits cercariae of Schistosoma haematobium at the end of the dry season and at the beginning of the rainy season. We have not been able to identify precisely the cercariae emitted by B. forskalii, which raises the necessity of further systematic studies being carried out on the schistosomes of Cameroon.

In a simultaneous hermaphrodite

Abstract: Phally, a genital dimorphism found in some species of self-compatible simultaneous hermaphrodites, presents an opportunity to examine factors maintaining outcrossing within an animal species in the presence of recombination. Both aphallics and euphallics can self-fertilize but only euphallics develop a functional penis and prostate allowing them to donate sperm. Previous studies of phally in the gastropod Bulinus truncatus (Mollusca: Pulmonata) suggest that phally may be under direct genetic control in some populations and strongly influenced by environmental factors in others. Experiments reported here identify temperature as a cue affecting phally deter- mination in two populations of B. truncatus. In both populations, a higher proportion of euphallics was produced at low temperature (22 ? 1?C) than at high temperature (30 ? 1?C). Temperatures experienced by parents did not affect the proportion of euphallics they produced. Instead, phally was sensitive to temperature during the egg stage postoviposition and during the hatchling stage; the relative influence of temperature before and after hatching varied between populations. The total number of hatchlings reaching maturity at high and low temperature did not differ, but at low temperature, snails took longer to hatch and mature, and had lower survivorship. Just as studies of environmental sex determination have shed light on selective pressures influencing sex ratio evolution, we suggest that temperature-sensitive phally determination may shed light on the selective pressures maintaining outcrossing in B. truncatus.