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Bulinus truncatus

About: Bulinus truncatus is a research topic. Over the lifetime, 414 publications have been published within this topic receiving 5640 citations.


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TL;DR: Evaluating ecological correlates of euphally in Nigerian populations of the freshwater gastropod, Bulinus truncatus, finds results consistent with hypotheses predicting an advantage of outcrossing due to temporal fluctuations in the biotic environment.
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.

58 citations

Journal ArticleDOI
01 Jul 1997-Genetics
TL;DR: The 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) and selfing appeared to be an important force affecting the genetic structure in permanent ponds.
Abstract: 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 H o , H e , 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.

55 citations

Journal ArticleDOI
TL;DR: The seasonal trends of the species were variable but basically bimodal with peaks in August (rainy season) and November/December (early dry season), suggesting that seasonal changes in snail density were probably influenced by these factors.
Abstract: The factors influencing patterns of snail distribution in Oyan Reservoir, a typically medium sized man-made reservoir in southwest Nigeria, were investigated once a month, for 28 months (August 1990-November 1992). During each monthly visit, seven stations were sampled for relative snail density, vegetation cover and physical and chemical properties of the lake water. Statistical analyses were performed to determine the influence of these factors on snail abundance and distribution. Seven aquatic snail species were found in the reservoir, namely Bulinus globosus, B. forskalii, B. truncatus, Lymnaea natalensis, Indoplanorbis exustus, Potadoma freethi and Potadoma moerchi. The relative proportion of these species was 17.6% (B. globosus), 16.1% (B. forskalii), 0.2% (B. truncatus), 12.9% (L. natalensis), 23.4% (I. exustus) and 29.8% (both Potadoma spp. combined) of 28 183 snails collected over the study period. The seasonal trends of the species were variable but basically bimodal with peaks in August (rainy season) and November/December (early dry season). These trends were similar to the water level and rainfall patterns, suggesting that seasonal changes in snail density were probably influenced by these factors. Spatial distribution of each snail species was similar along each shoreline but significantly different across the E-W transect. Similar trends occurred for conductivity, dissolved oxygen and biochemical oxygen demand suggesting that these factors may have affected snail distribution across shorelines. Ten species of aquatic vegetation were identified, six of which correlated positively and significantly with various snail species. The most important of the associating vegetation was Impatiens irvingii which correlated with all snail species and served as an indicator plant for Indoplanorbis exustus, an introduced snail species in Nigeria.

54 citations

Journal ArticleDOI
TL;DR: The stomach contents of the ampullarid species were characterized by large fragments of dead macrophyte tissue, while the composition of the finer particles showed a great resemblance to that of the pulmonate species.
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.

53 citations

Journal ArticleDOI
TL;DR: To determine quantitatively whether Australorbis glabratus infested with C. limnaei were protected against invasion by miracidia of S. mansoni and by cercariae of an echinostome, the present study collected specimens from Physa heterostropha collected in Boston.
Abstract: Experiments demonstrated that infestation with the oligochaete worm, Chaetogaster limnaei, afforded a degree of protection to the snail Australorbis glabratus when the snail was exposed to Schistosoma mansoni miracidia. To a lesser extent, the oligochaetes protected snails exposed to echinostome cercariae. The presence of C. limnaei within the kidney of the snail Physa heterostropha is reported. An intimate association between the oligochaete worm Chaetogaster limnaei von Baer and various species of aquatic snails has long been recognized (von Baer, 1827), yet the nature of this relationship has not been adequately defined. Early naturalists considered C. limnaei to be a true parasite which was thought to feed upon the "slime" produced by the host. However, Wagin (1931) and subsequent investigators demonstrated that the oligochaete fed principally on microorganisms, and thus the worm has been considered a commensal. Wagin also observed that the oligochaete ingested cercariae and suggested that C. limnaei might be of value in controlling trematode transmission. While Krasnodebski (1936) confirmed Wagin's field observations and experimentally demonstrated that the oligochaete would ingest various types of cercariae, he did not believe that Chaetogaster could play a significant role in the control of trematodes. Backlund (1949) observed that cercariae of Fasciola hepatica were ingested by Chaetogaster, and Ruiz (1951) later reported a similar observation with respect to Schistosoma mansoni. Coelho (1957) noted that Chaetogaster frequently ingested S. mansoni miracidia, but commented that the worms did not protect snails from infection. HowReceived for publication 3 March 1964. * These studies were supported in part by Grants AI-00513 and 5 TI AI 46 from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Public Health Service, Bethesda, Maryland. 441 ever, Khalil (1961) presented circumstantial evidence suggesting that snails infested with C. limnaei were refractory to infection with Fasciola hepatica under laboratory conditions. The present study was initiated to determine quantitatively whether Australorbis glabratus infested with C. limnaei were protected against invasion by miracidia of S. mansoni and by cercariae of an echinostome. MATERIALS AND METHODS Specimens of C. limnaei were obtained from Physa heterostropha collected in Boston. The oligochaetes were freed by immersing the snails in 1% Urethan (ethyl carbamate) for 3 to 5 min. Anesthetized worms were collected by pipette, allowed to recover in charcoal-filtered tap water, and used immediately or colonized for later use (Brandwein, 1937). A Puerto Rican strain (PR-1) of Australorbis glabratus was used in all experiments. This snail strain has been maintained in our laboratory for several years and has been free from infestation with C. limnaei. Miracidia were hatched from eggs obtained from the livers of mice infected with a Puerto Rican strain of S. mansoni and were used within 30 min of emergence (Michelson, 1964). Cercariae of an unidentified echinostome were obtained from Physa heterostropha collected from local ponds. Five C. limnaei were added to individually isolated A. glabratus in 5-ml beakers containing 3 ml of charcoal-filtered tap water. The snail was confined with the oligochaetes for 1 hr or until all worms became attached. At this time and depending upon the experiment, one to five miracidia or ten cercariae were added to each beaker. After an exposure of approximately 16 hr, the snails from any one experiment were maintained together in a battery jar containing 2.5 liters of water. The battery jars were continually aerated, maintained at 25 ?+ 1 C, and the snails fed Romaine lettuce. ConThis content downloaded from 157.55.39.157 on Tue, 17 May 2016 04:47:34 UTC All use subject to http://about.jstor.org/terms 442 THE JOURNAL OF PARASITOLOGY, VOL. 50, NO. 3, JUNE 1964 TABLE I. Influence of Chaetogaster limnaei infestation on the rate of infection of snails exposed to S. mansoni miracidia and to echinostome cercariae. Snails with C. limnaeil Control snails Group no. No. positive/ No. positive/ no. exposed no. exposed 5 miracidia of S. mansoni per snail 12 2/7 4/8 22 7/18 14/20 32 1/5 5/6 4 5/10 8/10 5 2/10 10/10 Total 17/50 (34%) 41/54 (76%) 1 miracidium of S. mansoni per snail 6 1/10 5/10 7 2/15 7/15 Total 3/25 (12%) 12/25 (48%) 10 cercariae of echinostome sp. per snail 8 7/10 10/10 9 7/10 10/10 Total 14/20 (70%) 20/20 (100%) 1 All snails infested with 5 worms each. 2 Test groups 1, 2, and 3 had one, two, and one snails die before they could be examined for the presence of infection; these have not been included with the data. trol snails, free of C. limnaei, were exposed to miracidia or cercariae in the same manner. Two weeks postexposure, control and Chaetogaster-infested snails were examined for the presence of S. mansoni sporocysts by the technique of Chernin and Dunavan (1962). Snails exposed to echinostome cercariae were examined 7 days postexposure for the presence of metacercariae. For this purpose the snail was removed from its shell, the mantle cut along its left margin and reflected to the right, and the pallial cavity examined under a 13 X dissecting microscope. Experimental results In five experiments a total of 54 snails, each infested with five Chaetogaster limnaei, were exposed individually to five S. mansoni miracidia and 17 (34%) of 50 snails which survived were found infected (Table I). By comparison, in the control groups of snails 41 of 54 snails (76%) were infected. Thus, a mean reduction in the rate of infection of 42% was associated with the presence of C. limnaei. In two additional experiments (Table I), snails harboring five C. limnaei were exposed individually to a single miracidium of S. mansoni. Of a total of 25 snails so exposed, three (12%) became infected. An infection rate of 48% (12/25 snails) occurred, however, in the two groups of control snails. A mean reduction of 36% in the infection rate was again observed to be associated with the presence of C. limnaei. Snails were exposed to echinostome cercariae in two experiments (Table I), and all the control snails were later found infected. However, only 70% (14/20) of the snails infested with C. limnaei had metacercarial cysts. In the first experiment 38 and 58 metacercarial cysts were recovered from the Chaetogaster-infested and control snails respectively, and in the second experiment 22 and 69 cysts respectively. Infected snails were found to have from three to eight cysts each. Miscellaneous observations The intensity of Chaetogaster infestation in snails under field conditions would appear to vary considerably. Backlund (1949) observed that no more than ten Chaetogaster were found on specimens of Lymnaea stagnalis and L. ovata; however, Krasnodebski (1936) noted as many as 300 worms on a single specimen of L. stagnalis, up to 60 worms on Physa fontinalis, and a mean of 1.3 worms on specimens of Ancylus lacustris. In our own experience, as many as 25 C. limnaei have been recovered from a single Physa heterostropha. In one collection of 105 P. heterostropha there was a mean of nine worms per snail. The heaviest infestations were found on older and larger snails, particularly those which had overwintered. Quantitative data concerning natural infestations of Chaetogaster on the snail Auistralorbis glabratus are not available, although infestations of field populations have been reported (Coelho, 1957). Natural infestations of South African populations of Bulinus tropicus, Bulinus africanus, and Biomphalaria pfeifferi have also been noted by Bayer (1955). Likewise, laboratory colonies of A. glabratus, as well as Bulinus truncatus and B. tropicus, have been observed to be infested with Chaetogaster (Khalil, 1961). Although it has generally been thought that C. limnaei acts as a commensal of snails, feeding principally on aquatic microorganisms, there is some evidence to suggest that this oligochaete may also be a parasite. The observation of Lankester (1870) of C. limnaei in the kidney of a single L. stagnalis has been overlooked. Our examination of both field and laboratory populations of P. heterostropha This content downloaded from 157.55.39.157 on Tue, 17 May 2016 04:47:34 UTC All use subject to http://about.jstor.org/terms MICHELSON-PROTECTIVE ACTION OF CHAETOGASTER ON SNAILS EXPOSED TO SCHISTOSOMA MANSONI TABLE II. Distribution of Chaetogaster limnaei in a collection of Physa heterostropha. Number C. limnaei present Snail no.1 On body surface and Inside in mantle cavity kidney 1 1 0 2 0 7 3 8 4 0 5 5 2 1 6 6 5 7 1 3 8 0 7 9 5 10 1 1 2 5 12 0 2 3 3 1 14 1 5 5 5 18 1 Five snails in this collection had no Chaetogaster and are not included in the table. revealed that under some circumstances large numbers of C. limnaei may be found within the kidney of the snail. In one group of P. heterostropha, examined 3 days after collection, 15 of 20 snails were infested. Fourteen of the 15 infested snails harbored 1 to 18 worms within the kidney; whereas only nine of these 15 snails had external infestations (Table II). Of further interest is the fact that snails could be free of external infestation while harboring numerous worms in their kidney. Histologic studies demonstrated that most of the oligochaetes were in the anterior portion of the kidney, but any part of the organ might harbor the worms (Fig. 1). No tissue reactions were observed in sections of snails so infected, although some oligochaetes appeared attached to the renal epithelium and renal concretions were observed in the intestinal tract of a few worms. Oligochaetes were not found in the kidney of experimentally infested A. glabratus.

50 citations


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