Showing papers on "Bulinus truncatus published in 1994"

Ecological correlates of male outcrossing ability in a simultaneous hermaphrodite snail

Abstract: Abstr-act.-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 that can self-fertilize. Both aphallics and euphallics can self-fertilize, but aphallics cannot donate sperm because they do not develop a functional prostate and penis. In this field study of Nigerian populations of the freshwater gastropod, Bulinus truncatus (Mollusca: Pulmonata), we evaluate ecological correlates of euphally to test hypotheses predicting a selective advantage of outcrossing due to the production of genetically variable offspring. The prevalence of euphally across 49 populations ranged from 0% to 81%. We found no association between prevalence of euphally and any of the following: population density, snail density, mollusk species abundance, water pH, oxidation-reduction potential, dissolved oxygen content, habitat instability (as estimated by habitat type), human activity, vegetation density, desiccation rate, and water chemistry variation. There was a significant but weak correlation between conductivity and proportion of euphallics (r2 = 10%), with lower ion concentrations favoring higher levels of euphally. The prevalence of the most abundant trematode taxon (Xiphidiocercariae) correlated positively with proportion of euphallics, explaining 10% of the variation in proportion of euphallics after we controlled for mean snail age and time of year. Trematode richness (number of taxa per population) was not associated with proportion of euphallics across sites when we controlled for time of year. However, indexes of trematode diversity that incorporated both prevalence and richness did correlate significantly with proportion of euphallics. These results are consistent with hypotheses predicting an advantage of outcrossing due to temporal fluctuations in the biotic environment.

Variable microsatellites in the highly selfing snail Bulinus truncatus (Basommatophora: Planorbidae)

Abstract: Both restricted polymorphism and low heterozygosity are expected in selfing species (see Charlesworth ctal. 1993), a trend empirically confirmed in plants (Hamrick & Godt, 1990) and in freshwater snails (Stadler & Jame, in prep.). This particularly holds in the hermaphrodite freshwater snail Bulinus truncatus, one of the intermediate hosts of the trematode Schistosoma in Africa. Allozyme surveys detected no heterozygotes and almost no variability in this allotetraploid species (Njiokou et ul. 1993). This has been related to frequent population bottlenecks due to environmental variation and also to high aphally ratios which promote high selfing rates. The very low frequency of allozyme polymorphism clearly prevents the estimation of population genetic parameters such as gene flow and selfing rates. This prompted us to use microsatellite markers which have been shown to be highly variable and can be isolated in poorly known genomes (eg. Hughes & Queller, 1993). Here we report the characterization of microsatellite loci in B. truncatus. A genomic library was constructed following Ostrander et al. (1992) for DNA digestion and Rassman et al. (1991) for cloning. The library was screened for (CA), (GA) and (GATA) repeats. Fifty-eight (40) clones hybridized positively with the dinucleotide (tetranucleotide) probes. Thirty-three (7) clones were sequenced of which 22 (7) were more or less pure (CA) or (GA) repeats (GATA repeats) accounting for 24 (7) microsatellite loci. Two clones each contained two dinucleotide microsatellite loci separated by about 100 bp. Nineteen dinucleotide loci contained between 14 and 35 repeats and the remaining five loci had over 40 repeats with one locus containing 130 repeats. Three microsatellites were within 20 bp of the end of the cloned insert and we were therefore unable to design primers for PCR amplification. For the same reason only two out of the seven (GATA) loci could be used. The (GATA) loci contained between 30 and 50 repeats. Microsatellites appear to be as common in B. truncatus as

Temperature-Determined Outcrossing Ability in Wild Populations of a Simultaneous Hermaphrodite Snail

Abstract: Phally, a genital polymorphism found in some species of self-compatible simultaneous hermaphrodites, presents an opportunity to examine environmental and genetic influences on mating system traits. Both aphallics and euphallics can self-fertilize, but aphallics cannot donate sperm because they do not develop a functional penis and prostate. Previous studies of the freshwater gastropod Bulinus truncatus (Mollusca: Pul- monata) suggest that in at least some laboratory populations, phally is determined by temperature during egg and hatchling stages, with colder temperatures favoring the de- velopment of euphally. Here we provide evidence for temperature-influenced phally de- termination in natural populations of B. truncatus in northern Nigeria. The prevalence of euphally across 49 populations ranged from 0 to 81%. Levels of euphally increased sig- nificantly both within and across sites as temperatures decreased during the dry-cool season. Across sites, time of year (date) was the strongest single predictor of proportion of euphallics. When the effects of time of year were controlled for, there was a significant negative correlation between temperature during phally development and proportion of euphallics. In addition, maximum water temperature during the 1st wk of the study predicted pro- portions of euphallics in the next snail generation. A laboratory study of snails from three of these populations demonstrated that temperature sensitivities differed between popu- lations: one population that remained 100% aphallic over the course of field observations showed only low levels of temperature sensitivity in the laboratory, while a population that tripled in proportion of euphallics in the field showed strong levels of temperature sensitivity. Furthermore, individuals within populations varied in their temperature sen- sitivities. These results are discussed in light of the adaptive significance of labile phally determination.

Schistosomiasis in Dogon country, Mali: identification and prevalence of the species responsible for infection in the local community.

Abstract: The prevalence of schistosomiasis amongst the Dogon people in 4 villages and one school of the Bankass district of Mali was determined during 2 surveys in 1992; 1398 urine and 1199 stool samples were examined. The most common schistosome was Schistosoma haematobium, with an overall prevalence of 51.3%; S. mansoni had a prevalence of 12%. No S. intercalatum egg was seen in the stools. Biomphalaria pfeifferi and Bulinus truncatus were found in pools at the base of the Dogon cliffs; Bulinus forskalii was found in smaller numbers in brick pits. Two isolates from urine samples of children were identified as S. haematobium in the laboratory using an α-glycerophosphate marker, restriction enzyme analysis of ribosomal deoxyribonucleic acid (rDNA) and random amplification of polymorphic DNA. The isolates did not develop in Bulinus forskalii or B. crystallinus of the B. forskalii group. Some evidence for past hybridization of S. haematobium and S. intercalatum is provided by the enzyme and rDNA results as well as the positive Ziehl-Neelsen staining of polymorphic eggs in urine samples. The findings are discussed in relation to the published observations concerning schistosomiasis in travellers returning from this region of Mali.

Effects of Schistosoma haematobium infection on reproductive success and male outcrossing ability in the simultaneous hermaphrodite, Bulinus truncatus (Gastropoda: Planorbidae).

Abstract: The schistosome intermediate snail host, Bulinus truncatus (Mollusca: Planorbidae), has two reproductive (phally) morphs. Both aphallics and euphallics can self-fertilize, but aphallics cannot donate sperm because they do not develop a functional penis and prostate. This study investigated the interactions between phally and fitness consequences of Schistosoma haematobium infection in B. truncatus. Snails which developed patent infections produced 26% fewer eggs than controls and 35% fewer eggs than exposed snails which did not develop infections. This reduction was due to a lower lifetime production of egg masses and a smaller mean number of eggs/mass in infected snails relative to control or exposed snails. However, there was no evidence of increased mortality in infected snails. Contrary to reports of fecundity compensation in other intermediate host snails, egg production post-exposure during the pre-patent period did not increase relative to that of controls in either infected or exposed snails. Phally did not influence susceptibility to infection or length of the prepatent period. Furthermore, lifetime egg, egg mass and hatchling production, as well as mean eggs/mass and number of hatchlings reaching maturity, did not differ significantly between aphallics and euphallics within control of exposed experimental groups. However, within the infected group euphallics produced 38% fewer eggs, smaller egg masses, and fewer hatchlings reaching maturity than aphallics, supporting the prediction of a cost to the growth and maintenance of a full male tract. This cost was detectable only when snails were under the stress of infection. The proportion of euphallic offspring produced did not differ across experimental groups.(ABSTRACT TRUNCATED AT 250 WORDS)

A problem with the estimate of self-fertilization depression in the hermaphrodite freshwater snail bulinus truncatus: the effect of grouping.

Abstract: 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.

Distribution of intermediate mollusc hosts in human schistosomiasis in the Office of Niger (Mali).II. Role of different habitats in the transmission

Abstract: To determine the role of habitats in the schistosomiasis transmission all the year, a study on snail hosts distribution was carried out within various parts in the irrigated system of the "Office du Niger". Bulinus truncatus and Biomphalaria pfeifferi were the only snail hosts recorded. Densities were low and 85% (46/54) of breeding sites contained less than 50 snails collected per man/hour. Primary and secondary canals play the most important role in disease transmission because of the stability of these habitats, the pollution of human water contact by remnants of food and wastes which favourised the snail growth and infestation. Prevalences were 23.3% (46/197) in Bulinus truncatus and 2.5% (6/243) in Biomphalaria pfeifferi. The cercariae shedding was permanent, but the infection varied significantly according to the snail species, the period and to the area.

Population inhibitors in cultures of Bulinus truncatus rohlfsi

Abstract: Bulinus truncatus rohlfsi is a snail host of the human blood fluke Schistosoma haematobium. Observations on the dynamics of laboratory cultures of B. t. rohlfsi are presented from a series of exper...