Freshwater Snail Bulinus Research Articles

Molluscicidal Potency of Polygonum lanigerum Meisn on the Freshwater Snail, Bulinus globosus (Morelet)

ABSTRACT Casual observation reveals that the freshwater snail Bulinus globosus (Morelet), never preponderates in habitats that support the plant Polygonum lanigerum Meisn. An investigation on toxicity of aqueous extracts of the leaves and stem of this plant on Bulinus globosus in a 24 h static bioassay demonstrated toxicosis. The 24-h LC50 for the leaf and stem extracts were 29.9 and 35.8 mg/liter, respectively. The relative potency of the extracts from the two plant parts was not significantly different.

RESOURCE ALLOCATION AND STRESSFUL CONDITIONS IN THE APHALLIC SNAILBULINUS TRUNCATUS

An important parameter in the evolution of sexual polymorphisms in hermaphroditic organisms is the way resources are allocated to male and female functions by various morphs. Detecting differences in allocation between morphs may not always be possible under optimal conditions and may require stressful conditions. Here we investigate the allocation to various functions in the hermaphroditic, highly selfing, freshwater snail Bulinus truncatus, in relation to phally polymorphism. In natural populations, two morphs, euphallic individuals (regular hermaphrodites) and aphallic individuals (missing the male copulatory organ), co-occur at various ratios. To quantify whether the loss of the male organ in aphallics may be compensated for by other functions, we compared the fecundity, size, and survival of 123 aphallic and 111 euphallic snails originating from 53 families and three natural populations under optimal (25°C) and stressful (19°C and 30°C) temperatures. We also compared the hatching rate and survival of offspring of 10 aphallic and 10 euphallic snails per population at these three temperatures. Firstly, we confirmed a strong effect of temperature on the determination of the sexual morph. Secondly, we found that the two morphs did not differ in size, fecundity, hatching rate, or survival of offspring, suggesting no obvious cost of the male function in isolated snails, even under stressful conditions. However, a trade-off was observed: aphallic individuals laid more capsules, though with fewer eggs per capsule, than euphallic individuals. Thirdly, we found a linear variation of some parameters with the family aphally ratio, suggesting that fitness may be perceived in a frequency-dependent way. Our results are discussed with regard to the relative strength of selective and stochastic factors in the evolution of phally polymorphism.

The Influence of Self-Fertilization and Population Dynamics on the Genetic Structure of Subdivided Populations: A Case Study Using Microsatellite Markers in the Freshwater Snail Bulinus truncatus

The Influence of Self-Fertilization and Population Dynamics on the Genetic Structure of Subdivided Populations: A Case Study Using Microsatellite Markers in the Freshwater Snail Bulinus truncatus

Population dynamics inferred from temporal variation at microsatellite loci in the selfing snail Bulinus truncatus.

We analyzed short-term forces acting on the genetics of subdivided populations based on a temporal survey of the microsatellite variability in the hermaphrodite freshwater snail Bulinus truncatus. This species inhabits temporary habitats, has a short generation time and exhibits variable rates of selfing. We studied the variability over three sampling dates in 12 Sahelian populations (1161 individuals). Classical genetic parameters (estimators of Ho, He, f, selfing rate and Fst) showed limited change over time whereas important temporal changes of allelic frequencies were detected for 10 of the ponds studied. These variations are not easily explained by selection, sampling drift and genetic drift alone and may be due to periodic migration. Indeed the habitats occupied by the populations studied are subject to large temporal fluctuations owing to annual cycles of drought and flood. In such ponds our results support a demographic model of population expansions and contractions under which available habitats, after the rainy season, are colonized by individuals originating from a smaller number of refuges (areas that never dry out in the deepest parts of the ponds). In contrast, selfing appeared to be an important force affecting the genetic structure in permanent ponds.

Description of the Adult and Larval Stages of Tylodelphys xenopi (Trematoda: Diplostomidae) from Southern Africa

The strigeoid metacercaria Diplostomulum xenopi is commonly found in the pericardial cavity of Xenopus laevis laevis. This paper provides the first description of the adult obtained from the intestine of an experimental host, the darter, Anhinga melanogaster. Natural cercarial infections were found in specimens of the freshwater snail Bulinus tropicus collected from dams in the Free State. South Africa. The life cycle was experimentally completed and all stages were described by light and scanning electron microscopy.

A mistaken report of the occurrence in India of the freshwater snail Bulinus and its relation to transmission of Schistosoma.

(1997). A mistaken report of the occurrence in India of the freshwater snail Bulinus and its relation to transmission of Schistosoma. Annals of Tropical Medicine & Parasitology: Vol. 91, No. 2, pp. 225-227.

Selfing, sexual polymorphism and microsatellites in the hermaphrodititic freshwater snailBulinus truncatus

Studies on the evolution of self-fertilization and sexual polymorphisms (the co-occurrence of several sexual morphs in a species) have focused on plants. Aphally, a sexual polymorphism occurring in gastropods, offers the opportunity to extend study of these issues to animals. We present progeny-array analyses of the selfing rate and correlated matings in the tropical freshwater snail Bulinus truncatus. This study is based on 447 offspring originating from 57 families and five natural populations. To overcome the lack of allozyme polymorphism, four polymorphic microsatellite markers were used. Selfing rates higher than 78 per cent were detected in all populations, and no correlation with the aphally ratio (the proportion of individuals lacking the male copulatory organ per population) was evident. Outcrossing was detected in 17 families only, and individual outcrossing rates were variable and did not depend on the sexual morph of the mother. These results illustrate the power of microsatellites for detailed genetic studies, indicate that high selfing rates may have a strong genetic basis, and unexpectedly suggest that phally polymorphism may be neutral with respect to selfing.

Stability and genetic basis of variability of phally polymorphism in natural populations of the self-fertile freshwater snailBulinus truncatus

SummaryWe investigated the genetic variability for phally polymorphism within and between natural populations of the hermaphrodite self-fertile freshwater snailBulinus truncatus. Phally polymorphism is characterized by the co-occurrence in natural populations of regular hermaphrodite individuals (euphallic) and individuals deprived of the male copulatory organ (aphallic). The two morphs can both self-fertilize and outcross. However, aphallic individuals cannot outcross as males. We examined the variation of the aphally ratio in 22 natural populations from Niger over two successive years. During the second years, populations were sampled three times at 3 week intervals. The aphally ratio was highly variable among populations at a given sampling data and remained relatively stable over time. For 10 of these populations, one population from Corsica and two from Sardinia, we also estimated the between- and within- population variability, analysing the aphally ratio of 346 families under laboratory conditions. The aphally ratio varied significantly among populations and was highly correlated with the aphally ratio of the natural populations. Some within-population variability, associated with a high value of the broad sense heritability, was observed in four populations out of 13. In these populations, aphallic individuals produced significantly more aphallic offspring than euphallic individuals. Our results indicate a strong genetic basis for aphally, with large genetic differences among populations and some genetic variability for aphally within populations. We discuss the adaptive and stochastic factors that may shape the distribution of the genetic variability for aphally.

The evolution of phally polymorphism in Bulinus truncatus (Gastropoda, Planorbidae): the cost of male function analysed through life-history traits and sex allocation

In the hermaphrodite freshwater snail Bulinus truncatus, two sexual morphs, euphallic (regular hermaphrodites) and aphallic individuals without a male copulatory organ, co-occur at various ratios in natural populations. Both aphallic and euphallic individuals can reproduce by selfing, but when outcrossing aphallic individuals can only play the female role. A comparison of life-history traits and sex allocation in these two forms provides the opportunity to investigate the evolution and maintenance of sexual polymorphisms. This study was performed to test whether a reallocation of resources from the lost male function to the female function occurs in aphallic snails at the level of both sex organs (sex allocation) and life-history traits. In a first experiment we compared life-history traits over a whole life-cycle under selfing between the two sexual morphs. In a second experiment, the sex organs were weighed to test for a difference in sex allocation between the two morphs. No difference in resource allocation to female function between the two morphs was observed in either experiment. This is in contrast to patterns frequently observed in sexually polymorphic plants, and in a previous study performed on aphally in the same snail species. We discuss the genetic and physiological hypotheses that could explain these results, and their consequences for the evolution and maintenance of phally polymorphism in B. truncatus.

Microsatellites and the genetics of highly selfing populations in the freshwater snail Bulinus truncatus.

Hermaphrodite tropical freshwater snails provide a good opportunity to study the effects of mating system and genetic drift on population genetic structure because they are self-fertile and they occupy transient patchily distributed habitats (ponds). Up to now the lack of detectable allozyme polymorphism prevented any intrapopulation studies. In this paper, we examine the consequences of selfing and bottlenecks on genetic polymorphism using microsatellite markers in 14 natural populations (under a hierarchical sampling design) of the hermaphrodite freshwater snail Bulinus truncatus. These population genetics data allowed us to discuss the currently available mutation models for microsatellite sequences. Microsatellite markers revealed an unexpectedly high levels of genetic variation with < or = 41 alleles for one locus and gene diversity of 0.20-0.75 among populations. The values of any estimator of Fis indicate high selfing rates in all populations. Linkage disequilibria observed at all loci for some populations may also indicate high levels of inbreeding. The large extent of genetic differentiation measured by Fst, Rst or by a test for homogeneity between genic distributions is explained by both selfing and bottlenecks. Despite a limited gene flow, migration events could be detected when comparing different populations within ponds.

The genetical and environmental determination of phally polymorphism in the freshwater snail Bulinus truncatus.

In some species of self-fertile pulmonate snails, two sexual morphs co-occur in natural populations: regular individuals and aphallic individuals that cannot transmit sperm to other snails. Purely aphallic populations therefore reproduce obligatorily by selfing. Understanding the evolution of aphally and selfing in these snails requires a precise knowledge of phally determination. In this paper, we investigate the genetic and environmental determination of aphally in Bulinus truncatus by a survey of the family (offspring) aphally ratio of 233 individuals originating from seven natural populations and a study of the reaction norm of the family aphally ratio to temperature using 60 individuals from 10 selfed lineages of one population. Our results indicate a high genetic variability for the determination of aphally between populations and within some populations, associated with a high level of genetic determination. Our second experiment indicates a significant temperature and lineage effect though no interaction between these two effects. We discuss our results in the framework of threshold models developed for dimorphic traits with polygenic inheritance. We propose that the sexual morph of an individual at a given temperature is determined by a temperature threshold value depending on both the individual genotype and probabilistic processes.

The freshwater snail Bulinus tropicus (Planorbidae) in Namibia, characterised according to chromosome number, enzymes and morphology

Freshwater snails collected in central Namibia, south-western Africa, from 15 populations belonging to the Bulinus truncatus/tropicus complex (Planorbidae) are characterised in respect of their chromosome number, morphology, egg proteins and enzymes. The population samples were all consistently diploid and euphallic. The findings are compared with observations on this group of snails in other areas of Africa. It is concluded that the Namibian populations belong to a single species, B. tropicus (Krauss, 1848), of which B. parietalis (Mousson, 1887) is probably a synonym. No evidence was found of any occurrence of the tetraploid species B. truncatus or of snails belonging to the B. africanus group; lack of a potential intermediate host therefore precludes transmission of Schistosoma haematobium in this area.

A description of the life stages ofEchinoparyphium elegans(Trematoda: Echinostomatidae)

The life cycle of Echinoparyphium elegans Looss 1899 is described from the Free State, South Africa.The freshwater snail Bulinus tropicus (Krauss 1848), the intermediate host of Calicophorort microbothrium (Paramphisto- mum microbothrium Fischoeder, 1901) in this area, serves as first intermediate host. The same snail species also harbours the metacercaria stage. Adults of this parasite were obtained by feeding infected snails to laboratory-reared rats. All stages of the life cycle were described by means of light and scanning electron microscopy. A natural infection was found in the cattle egret, Bubulcus ibis (Linnaeus 1758).

Metal-metal interactions in biological systems. Part IV. Freshwater snail Bulinus globosus

The toxicity against title snails of all Al, Cd, Co(II), Cr(III), Cu(II), Fe (III), Mg, Mn(II), Mo(VI), Ni(II), Pb(II), Se(VI), V(V) and Zn ions was checked in 96 h tests in the water of Kariba Lake. Based on the mortality — concentration relationship the toxicity order of the above ions against Bulinus globosus is Cu(II) > Ni(II) > Cd > Pb(II) > Zn > Al > V(V)> Cr(III)> Se(VI) > Fe(III) =Co(II)> Mn(II) > Mg > Mo(VI). Only Mg, Pb(II), Cu(II), Cd, Zn and Ni(II) ions are harmful to these snails as their mortality is observed at the naturally occuring concentrations. Other metal ions cause lethality at naturally unrealistic concentrations. The following pairs of metal ions were also checked for mutual interactions: Cd-Al, Cd-Co, Cd-Cr, Cd-Cu, Cd-Fe, Cd-Mg, Cd-Mn, Cd-Mo, Cd-Ni, Cd-Pb, Cd-Se, Cd-V, Cd-Zn, Cu-Al, Cu-Co, Cu-Cr, Cu-Fe, Cu-Mg, Cu-Mn, Cu-Mo, Cu-Ni, Cu-Pb, Cu-Se, Cu-V, Cu-Zn, Ni-Al, Ni-Co, Ni-Cr, Ni-Fe, Ni-Mg, Ni-Mn, Ni-Mo, Ni-Pb, Ni-Se, Ni-V, Ni-Zn, Pb-Al, Pb-Co, Pb-Cr, Pb-Fe, Pb-Mg, Pb-Mn, Pb-Mo, Pb-Se, Pb-V, Pb-Zn, Zn-Al, Zn-Co, Zn-Cr, Zn-Fe, Zn-Mg, Zn-Mn, Zn-Mo, Zn-Se, Zn-V. Synergism and antagonism were several times observed in various combinations of ions. The effect of metal-metal interactions on an accumulation of those metals in the flesh and shells of snails was also observed and measured.

Geographic compatibility of the freshwater snail Bulinus globosus and schistosomes from the Zimbabwe highveld

Populations of Bulinus globosus were sampled from two rivers, 60 kim apart, in nothern Zimbabwe, and offspring from each geographic strain reared in the laboratory. Schistosomes were harvested from each strain and also maintained in the laboratory. Cross-infection experiments were conducted, whereby snails of both geographic strains were exposed to parasites of both geographic strains. Compatibility was found to be related to: (i) the geographic origin of the snail, and (ii) an interaction between the geographic origin of snail and parasite, such that sympatric combinations of snails and parasites produced a greater proportion of compatible infections than allopatric combinations. Cercarial output of infected snails was found to be related to the geographic origin of the parasite, but not of that of the snail. It is suggested that, as the snails used were laboratory bred and naive to schistosome infection, differences in snail — schistosome compatibility were genetically determined, rather than an adaptive response. This study supports earlier work which suggests the existence of geographic compatibility amongst natural populations of snails and trematodes, indicative of either increased infectivity by the parasite, or decreased resistance by the snail.

A PROBLEM WITH THE ESTIMATE OF SELF-FERTILIZATION DEPRESSION IN THE HERMAPHRODITE FRESHWATER SNAIL BULINUS TRUNCATUS: THE EFFECT OF GROUPING.

The evolution of self-fertilization has been the subject of both numerous theoretical and empirical studies (reviewed by Jain 1976; Charlesworth and Charlesworth 1987; Uyenoyama et al. 1993; Jarne and Charlesworth 1993). These studies have shown that inbreeding depression, that is, the lowered fitness of inbred as compared with outbred individuals, is an important factor determining this evolution. Although most research has focused on plants, some studies have been performed on hermaphrodite animals (see Jarne and Charlesworth 1993) and particularly freshwater snails (see Jarne et al. 1993). Differences in survival rates between progeny of selfing and outcrossing individuals have been shown and interpreted as resulting from inbreeding depression. Selfing snails also have a lower fecundity than outcrossing snails. The whole effect (fecundity of parents and inbreeding depression of their progeny) has been referred to as self-fertilization depression (Jarne et al. 1991). However, specific problems may arise when estimating self-fertilization depression in animals. In experiments on hermaphroditic freshwater snails, selfed progenies have been produced usually by isolated virgin adults, and outcrossed progenies have been produced by grouped adults (review in Jarne et al. 1993). The effect of the mating system (outcrossing) and the effect of grouping are therefore associated when analyzing the results of outcrossing. It has been shown for various species of freshwater snails that both population density and size influence growth, survival, and fecundity (Chernin and Michelson 1956a,b; Thomas et al. 1974; Thomas and Benjamin 1974; Ahmed et al. 1986; Chaudhry and Morgan 1987). Increased density and population size is generally associated with a reduced fecundity and could lead to an underestimate of self-fertilization depression. In this paper, we investigate whether previous estimates of self-fertilization depression may have been biased by a grouping effect. By using aphallic individuals of the hermaphrodite freshwater snail Bulinus truncatus (see below), we can estimate the effect of grouping selffertilized for isolated and grouped snails. This is done by comparing the fitness of isolated snails with that of individuals at various group size and densities. Bulinus truncatus is a self-fertile hermaphrodite with two sexual morphs, euphallic and aphallic individuals, occurring in natural populations. Euphallic snails can self-fertilize as well as outcross as males or as females. Aphallic snails are characterized by the absence of the male copulatory organ (Larambergue 1939). They can selffertilize and receive sperm from an euphallic partner. However, they cannot transfer their own sperm to a partner (Larambergue 1939). No mutual exchange of sperm occurs during copulation in hermaphrodite freshwater snails: one individual acts as the female when its partner acts as the male. The determinism of aphally is still unclear; some results indicate a genetic determinism (Larambergue 1939), whereas others point strongly to the role of temperature (Schrag and Read 1992). A consequence of aphally is that purely aphallic populations can only self-fertilize. By using aphallic snails, the consequences of grouping can therefore be estimated without interference of the mating system. The aim of the present work is to test (1) whether a grouping effect occurs in the conditions previously used to analyze the self-fertilization depression (about 150 mL of water per snail with group size of 5 to 10 snails) (Jarne and Delay 1990; Jarne et al.

A Problem with the Estimate of Self-Fertilization Depression in the Hermaphrodite Freshwater Snail Bulinus truncatus: The Effect of Grouping

A Problem with the Estimate of Self-Fertilization Depression in the Hermaphrodite Freshwater Snail Bulinus truncatus: The Effect of Grouping

Self-Fertilization Versus Cross-Fertilization in the Hermaphroditic Freshwater Snail Bulinus globosus

Self-Fertilization Versus Cross-Fertilization in the Hermaphroditic Freshwater Snail Bulinus globosus

Use of SEM and lectins to study Bulinus africanus leukocyte groups and their in vitro behavior over a time period

The external morphology and in vitro behavior of the leukocytes of the freshwater snail Bulinus africanus were studied by means of SEM while the possible existence of leukocyte subpopulations was investigated with the use of lectins. On the basis of morphological characteristics, two cell types namely the granulocytes (with a mean diameter of 6.5 μm) and hyalinocytes (with a mean diameter of 2.6 μm) were distinguished. Studies of the in vitro behavior of the granulocytes revealed a consecutive development of lamellipodium-like protruberances, microspikes (filopodia), and lamellipodia (pseudopodia). The spreading behavior of the granulocytes was apparently not dependent on serum factors since no differences were found in the spread of granulocytes in serum or in phosphate-buffered saline. With the lectin studies it was found that the lectins isolated from Canavalia ensiformis (concanavalin A) and Ricinus communis (castor bean agglutinin) were reactive with surface determinants of all the granulocytes whereas the lectin binding activity of Glycine max (soybean agglutinin) and Triticum vulgaris (wheat germ agglutinin) could not be inhibited by the appropriate inhibition sugars. No association could be found between granulocyte size and snail mass.

Population Biology of the Freshwater Snail Bulinus globosus in the Zimbabwe Highveld

(1) The population dynamics of Bulinus globosus (Morelet), an intermediate host for urinary schistosomiasis, were studied at five river sites in the Zimbabwe highveld for between 4 and 28 months. (2) Adult snail abundance, recruitment and loss rates were monitored at weekly intervals using a mark-recapture method. Growth rates were measured on caged snails. (3) Variations in abundance of the snails were related to water temperature and water flow. Peak densities at the sites ranged from 0 01 to 0-6 snails (of shell length > 5 5 mm) litre-1. Survival rate was negatively correlated with temperature. Losses due to rainy season floods ranged up to 99 9%. (4) The relationship between recruitment rate and temperature was described by a bell curve, with peak recruitment at 20 6 'C. Recruitment rate varied between sites. This may have been due to differences in food quality (vegetation), water chemistry and/or densitydependent effects. (5) Growth rates were positively correlated with temperature. (6) Bulinus globosus populations had a temperature-dependent seasonal cycle, with rapid increases in abundance during periods of favourable temperatures. Floods or drought caused variable and irregular reductions in abundance. The implications of these opportunistic' population dynamics for snail control are discussed.