Endemic species of Bulinus (Mollusca: Planorbidae) in Lake Malawi (= Lake Nyasa)

Bulinus nyassanus and B. succinoides are both endemic to Lake Malawi and for many years were known only from their shells. Recent collections of living material have made possible a study of the anatomy of both species and the application of biochemical and immunological techniques have indicated their affinities within Bulinus . Some interesting aspects of their ecology have also been revealed.     

Molecular identification of schistosome intermediate hosts: case studies of Bulinus forskalii group species (Gastropoda: Planorbidae) from Central and East Africa

African freshwater snails of the genus Bulinus act as intermediate hosts for schistosomes, trematode parasites responsible for medical and veterinary forms of schistosomiasis. The relationship between these snails and their parasites is an intricate one, with particular species of snail susceptible to infection only by certain species of schistosome. In common with other self-fertile hermaphrodite gastropods, Bulinus consists of a number of closely related species complexes with restricted gene flow between populations of each taxon. Consequently, despite their medical and veterinary importance as intermediate hosts, unambiguous identification and differentiation of planorbid snails such as these remains problematic, often confounding attempts to define the distribution and evolutionary relationships of conchologically similar taxa. Here we consider how morphological methods of discrimination can be used in conjunction with molecular based approaches to improve snail identification, thereby achieving a better understanding of the epidemiology of schistosomiasis. Data are presented from Central and East African taxa which illustrate how PCR-based methods have begun to be used in combination with traditional analyses in an integrated approach to characterize the genus Bulinus , specifically the B. forskalii species group. Particular emphasis is given to the analyses of Random Amplified Polymorphic DNA (RAPDs) and the mitochondrial gene cytochrome oxidase I (COI).     

A COMPARATIVE STUDY OF THE MATURE SPERMATOZOA OF BULINUS AFRICANUS (KRAUSS, 1848) AND B. GLOBOSUS (MORELET, 1866) (GASTROPODA: PLANORBIDAE)

The morphology of the mature spermatozoa of the closely-relatedfreshwater pulmonates, Bulinus africanus and Bulinus globosus,was examined using scanning and transmission electron microscopy.A comparison showed no useful differences that could be usedto distinguish the species though they did differ in one respectfrom Bulinus tropicus, the only other bulinid for which spermmorphology is known. (Received 12 August 1996; accepted 6 December 1996)     

A molecular phylogenetic analysis of Bulinus (Gastropoda: Planorbidae) with conserved nuclear genes

Jørgensen, A., Madsen, H., Nalugwa, A., Nyakaana, S., Rollinson, D., Stothard, J. R. & Kristensen, T. K. A molecular phylogenetic analysis of Bulinus (Gastropoda: Planorbidae) with conserved nuclear genes. —Zoologica Scripta, 40, 126–136. Mutational saturation of inspected DNA loci and topological incongruence in the phylogenetic inferences have previously confounded attempts to resolve the evolutionary relationships within the freshwater snail genus Bulinus. Traditionally, the 37 species of Bulinus are placed within the four species groups and the evolutionary divergence between groups is substantial. With an intention to shed new light on species group relationships, the present study was designed to investigate the basal divergences in the phylogeny of Bulinus using highly conserved nuclear genes. The resolved phylogeny inferred that the four species groups of Bulinus were monophyletic and Shimodaira‐Hasegawa topology tests found them to be significantly supported. The Bulinus truncatus/tropicus species complex and Bulinus wrighti (Bulinus reticulatus group) formed a well‐supported sister‐group relationship. The Bulinus africanus species group was the sister‐group to the clade (Bulinus truncatus/tropicus + B. wrighti) with the Bulinus forskalii species group as the sister‐group to these taxa. The sister‐group relationship between Indoplanorbis and Bulinus was non‐significant and the basal clade support of Bulinus improved upon exclusion of Indoplanorbis. The finding of basal long branches of Bulinus species originating from Madagascar strongly suggests the presence of additional cryptic species and an evolutionary scenario influenced by this island’s geological vicariance from the African mainland. Speciation by polyploidy was inferred to have evolved within a clade in the Bulinus truncatus/tropicus species complex. Although the monophyletic status of each species group was firmly supported, it was difficult to establish species group concepts equally across the variations and place this precisely in a specific temporal framework.     

Profil parasitologique de deux formes de schistosomiase (formes urinaire et intestinale) dans dix sites du Burkina Faso (pays d’Afrique sub-saharienne)

In spite of great progress in schistosomiasis control during the last decade in Burkina Faso, this disease remains a public health concern in the country. Indeed, our study consisted of the analysis of parasitological data related to Schistosoma haematobium and Schistosoma mansoni and in malacological investigations. The prevalence rate of Schistosoma haematobium varies from 3.3% to 50.4% and from 3.3% to 39.1% for Schistosoma mansoni, but only in the western part of Burkina Faso. Schoolboys are more infested than girls, but the phenomenon is reversed in adults. Biomphalaria pfeifferi, Bulinus truncatus, Bulinus senegalensis and Bulinus globosus were collected during this study. Thus, the behavioral factors as well as the dynamics and the distribution of the intermediate mollusks play a major role in the persistence of the disease.     

A NOTE ON THE EFFECTS OF DRASTIC CHANGES IN TOTAL DISSOLVED SOLIDS ON THE AQUATIC PULMONATE SNAIL BULINUS (PHYSOPSIS) AFRICANUS KRAUSS

SUMMARY

THE transfer of a sample of Bulinus (Physopsis) africanus from water in their natural habitat containing 490 ppm TDS to a laboratory culture medium of 126 ppm TDS was found to be accompanied by a marked increase in the variability of the rate of oxygen consumption among individuals, and resulted in a 46% mortality. Transfer through the same gradient, but through two acclimatory stages of intermediate dissolved solid content, eliminated both these effects, suggesting an ability to acclimate and therefore to cope with the more gradual changes which may be expected to occur under field conditions.     

MALDI-TOF mass spectrometry for the identification of freshwater snails from Senegal,including intermediate hosts of schistosomes

Freshwater snails of the genera Biomphalaria, Bulinus, and Oncomelania are intermediate hosts of schistosomes that cause human schistosomiasis, one of the most significant infectious neglected diseases in the world. Identification of freshwater snails is usually based on morphology and potentially DNA-based methods, but these have many drawbacks that hamper their use. MALDI-TOF MS has revolutionised clinical microbiology and has emerged in the medical entomology field. This study aims to evaluate MALDI-TOF MS profiling for the identification of both frozen and ethanol-stored snail species using protein extracts from different body parts. A total of 530 field specimens belonging to nine species (Biomphalaria pfeifferi, Bulinus forskalii, Bulinus senegalensis, Bulinus truncatus, Bulinus globosus, Bellamya unicolor, Cleopatra bulimoides, Lymnaea natalensis, Melanoides tuberculata) and 89 laboratory-reared specimens, including three species (Bi. pfeifferi, Bu. forskalii, Bu. truncatus) were used for this study. For frozen snails, the feet of 127 field and 74 laboratory-reared specimens were used to validate the optimised MALDI-TOF MS protocol. The spectral analysis yielded intra-species reproducibility and inter-species specificity which resulted in the correct identification of all the specimens in blind queries, with log-score values greater than 1.7. In a second step, we demonstrated that MALDI-TOF MS could also be used to identify ethanol-stored snails using proteins extracted from the foot using a specific database including a large number of ethanol preserved specimens. This study shows for the first time that MALDI-TOF MS is a reliable tool for the rapid identification of frozen and ethanol-stored freshwater snails without any malacological expertise.     

The sugar chemoreception niches of Bulinus (physopsis) globosus (morelet) and Bulinus rohlfsi (clessin), the two most important snail hosts of Schistosoma haematobium (Bilharz) in West Africa

• 1.1.The behavioural responses of two species of freshwater pulmonate snails Bulinus (P.) globosus and Bulinus rohlfsi] to sugar gradients were investigated by means of diffusion olfactometers.
• 2.2.Both snail species proved to be very discriminating in their responses. Of the 17 sugars tested, 35.3%, namely d(−)glucuronic, maltotriose, maltose, cellobiose, d(−)arabinose, d(+)mannose proved to be statistically significant attractants or arrestants to B. rohlfsi. Only 23.5% of these sugars (maltotriose, maltose), d(+) mannose and d(+) xylose were significant attraetants or arrestants to B. (P.) globosus.
• 3.3.Glucuronic acid was a significant repellent to B. rohlfsi but none of the sugars was a repellent to B. (P.) globosus.
• 4.4.The results are compared with those obtained for other snail species and their relevance to the ecology and control of the snails are discussed.

     

BULINUS AFRICANUS-GROUP SPECIES IN WEST AFRICA DIFFERENTIATED BY MORPHOMETRIC ANALYSIS (GASTROPODA, PLANORBIDAE)

In the present study 241 shells from snails belonging to theBulinus africanus-group in West Africa, were examined in a morphometricanalysis including ten characters. Principal component analysisand stepwise discriminant function analysis were used for analysisof the data. It was shown that Bulinus umbilicatus, B. jousseaumeiand B. globosus are clearly distinct on morphometric shell characters.Besides a general differentiation between the three species,the characters necessary for differentiation between them twoby two are found. The knowledge of the geographic distributionof B. umbilicatus and B. jousseaumei is significantly improved. (Received 18 March 1988; accepted 4 May 1988)     

Susceptibility of freshwater snails to the amphistome Calicophoron microbothrium and the influence of the species on susceptibility of Bulinus tropicus to Schistosoma haematobium and Schistosoma mattheei infections

The susceptibility of Bulinus tropicus, B. globosus, Biomphalana pfeifferi, Lymnaea natalensis, and Melanoides tuberculata to Calicophoron microbothrium was examined. Bulinus tropicus had the highest prevalence (65.0%), followed by B. pfeifferi (37.5%), B. globosus (6.8%), and M. tuberculata (5.9%). Lymnaea natalensis was refractory to infection. Bulinus tropicus snails infected with C. microbothrium alone or coinfected with either Schistosoma haematobium or S. mattheei 0, 7, 14, and 21 days after exposure to C. microbothrium produced C. microbothrium cercariae only.     

Contrasting temporal dynamics and spatial patterns of population genetic structure correlate with differences in demography and habitat between two closely-related African freshwater snails

The relationship between habitat stability, demography, and population genetic structure was explored by comparing temporal microsatellite variability spanning a decade in two closely-related hermaphroditic freshwater snails from Cameroon, Bulinus forskalii and Bulinus camerunensis . Although both species show similar levels of preferential selfing, microsatellite analysis revealed significantly greater allelic richness and gene diversity in populations of the highly endemic B. camerunensis compared to those of the geographically-widespread B. forskalii . Additionally, B. camerunensis populations showed significantly lower spatial genetic differentiation, higher dispersal rates, and greater temporal stability compared to B. forskalii populations over a similar spatial scale. This suggests that a more stable demography and greater gene flow account for the elevated genetic diversity observed in this geographically-restricted snail. This contrasts sharply with a metapopulation model (which includes extinction/contraction, recolonization/expansion, and passive dispersal) invoked to account for population structuring in B. forskalii . As intermediate hosts for medically important schistosome parasites, these findings have ramifications for determining the scale at which local adaptation may occur in the coevolution of these snails and their parasites.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 747–760.     

Microsatellites in the freshwater snail Bulinus globosus (Gastropoda: Planorbidae) from Zanzibar

Six microsatellite loci were isolated and characterized in Bulinus globosus, a freshwater snail with a wide distribution throughout sub‐Saharan Africa. Bulinus globosus is an intermediate host of Schistosoma haematobium, the causative agent of human urinary schistosomiasis. Microsatellites were tested using 32 snails from four populations collected from Pemba and Unguja islands of Zanzibar. The microsatellite loci displayed relatively low levels of variation, with between two and five alleles per locus. F_ST estimates indicate that gene flow is low, as has previously been suggested for other species of Bulinus.     

The suitability of several aquatic snails as intermediate hosts for Angiostrongylus cantonensis.

Sixteen species of aquatic snails of four families were tested by quantitative technique under standardized conditions for their suitability as intermediate hosts for Angiostrongylus cantonensis. These species were the planorbid snails Biomphalaria glabrata, Biomphalaria alexandrina, Planorbis planorbis, Planorbis intermixtus, Bulinus truncatus, Bulinus contortus, Bulinus africanus, Bulinus tropicus and Helisoma sp.; the lymnaeid snails Lymnaea natalensis, Lymnaea tomentosa, Lymnaea stagnalis, and Stagnicola elodes; the physid snail Physa acuta (an Egyptian and a German strain) and the ampullariid snails Marisa cornuarietis and Lanistes carinatus. All these snail species proved to be susceptible to infection with A. cantonensis, and first stage larvae reached the infective third stage in all of them. However, the rate and intensity of infection varied with different species. B. glabrata was the most susceptible snail species with a 100% infection rate and an average percentage recovery of third stage larvae of 26.1. This was followed by S. elodes and B. africanus, with a 100% infection rate and an average percentage recovery of third stage larvae of 15.6 and 14.6 respectively. The rest of snail species proved to be less susceptible. For comparative evaluation of the suitability of the various snail species as intermediate hosts of A. cantonensis a "Capacity Index" was determined. This index should provide a useful method for the evaluation of the suitability of various snails as intermediate hosts of nematode parasites under standardized conditions in the laboratory.     

Transmission of Schistosoma bovis in Mkulwe (Mbozi District, Mbeya region, southern highlands of Tanzania)

Various populations of laboratory bred bulinid snails were exposed to miracidia of Schistosoma bovis from Mbozi. The parasite is naturally transmitted by Bulinus globosus in the area. Laboratory infection revealed a good relationship with B. forskalii and B. globosus from Mbozi and a population of B. forskalii from Dar es Salaam (infection rates 100%, 63.6% and 41.7% respectively). Populations of B. globosus and B. nasutus from Dar es Salaam were refractory. It appears that both snail species (B. globosus and B. forskalii) present in Mbozi district transmit S. bovis.     

The effect of Schistosoma haematobium infection on the growth and fecundity of three sympatric species of bulinid snails

Three species of bulinid snails were monitored to determine the effect of infection with 2 sympatric strains of Schistosoma haematobium on longevity, growth, and reproductive output, from the onset of cercarial production until death. Bulinus senegalensis was least affected by infection, with total fecundity reduced by less than 34%. Infected Bulinus truncatus showed an acceleration in growth accompanied by a 63% reduction in fecundity, although the majority of snails continued to oviposit at a low level. The longest-lived snails in this study, Bulinus globosus, showed decreased growth and survival when infected. In addition a significant proportion of infected individuals of this species failed to oviposit, and those that retained some reproductive capacity produced fewer embryos than controls. Total fecundity of B. globosus was reduced almost 90% by infection with S. haematobium, yet long-term monitoring of individuals showed that reproductive activity recovered when parasite productivity was low. Results from this and similar studies indicate that the time of infection by a trematode in relation to reproductive maturity of the molluscan host is important in determining the subsequent effects on host growth and fecundity.     

Hemocytes of Bulinus truncatus rohlfsi (Mollusca: Gastropoda)

Two basic cell types occur in the hemolymph of Bulinus truncatus rohlfsi: granulocytes and hyalinocytes. Granulocytes are divided into three subtypes: (1) Granulocytes I, which account for 19% of the hemocytes, are small, young amoebocytes with 1–20 filopodia and small numbers of cytoplasmic granules, including some lysosomes; (2) granulocytes II, which account for 78% of the cells, are large, fully developed amoebocytes that possess 1–20 filopodia and many granules, both acidophilic and basophilic, including numerous lysosomes, phagosomes, and mitochondria; and (3) spent granulocytes, which are rare, have few filopodia, large accumulations of glycogen granules and prominent vacuoles in addition to lysosomes in the cytoplasm. These three subtypes of granulocytes probably represent ontogenetic stages within a single cell line. In addition, granulocytes with 40 or more filopodia and little ectoplasm, found in only 1 of 45 snails examined, probably reflect a pathologic condition. Hyalinocytes, which account for 3% of all hemocytes, are similar in size to mature granulocytes, but have few or no cytoplasmic granules and lack filopodia and glycogen granules. Total hemocyte concentration in hemolymph is 328,000 ± 188,000 cells/ml.     

Experimental taxonomy of Bulinus (Gastropoda: Planorbidae): the West and North African species reconsidered, based upon an electrophoretic study of several enzymes per individual

Horizontal starch gel electrophoresis was used to score mobilities of seven different enzymes in species of Bulinus from North and West Africa. An account of the intra- and inter-population variation observed was given. Based on the data obtained it was suggested that enzymic data should be used as taxonomic characters in parallel with morphological and anatomical characters. It is suggested that enzymic characters could be used to place taxa into synonymy if the data are collected in such a way that one can write up an enzyme profile for the single individual. The nine taxa of Bulinus known to occur in North and West Africa were revised, the taxon B. jousseaumei was synonymized with B. globosus , and the two taxa B. guernei and B. rohlfsi were synonymized with B. truncatus. As a result of the revision only six species could be recognized as valid from the area, these being B. forskalii, B. globosus, B. senegalensis, B. truncatus, B. ugandae and B. umbilicatus. Finally, some enzymic characters are suggested that may be used for a reliable identification of these morphologically very difficult taxa.     

OBSERVATIONS ON SHELL MORPHOLOGY, ENZYMES AND RANDOM AMPLIFIED POLYMORPHIC DNA (RAPD) IN BULINUS AFRICANUS GROUP SNAILS (GASTROPODA: PLANORBIDAE) IN ZANZIBAR

The taxonomic status of Bulinus globosus and B. nasutus as separatespecies remains unclear, espécially in areas of EastAfrica where their distribution overlaps. In order to throwfurther light on this question, a study was carried out on snailscollected from the islands Unguja and Pemba, collectively knownas Zanzibar, which lie in the Indian Ocean close to mainlandAfrica. In total, 169 snails from 22 sample sites were characterisedby three methods: morphometric analysis of 15 shell measurements,enzyme analysis involving three enzyme systems and analysiswith random amplified polymorphic DNA (RAPD). Enzyme analysesindicated that both B. nasutus and B. globosus were presenton each island and their distribution was allopatric. Shellvariation was considerable but did not clearly differentiatethese taxa. Similarly, RAPD analysis indicated substantial geneticvariation with in and between samples; more often than not,no two RAPD profiles were identical within the sample. On Pemba,B. globosus is more widely dispersed than B. nasutus which isconfined to the eastern coast of the central region. On Unguja,B. globosus is found in more northern areas than B. nasutus. (Received 15 August 1996; accepted 31 January 1997)     

Molecular data suggest that microsporidian parasites in freshwater snails are diverse

Microsporidian parasites infect almost all invertebrate and vertebrate hosts and have significant effects on individual and population fitness. Phylogenetic analysis demonstrates that the phylum is highly divergent and that some lineages show strong associations with host taxa. We here examine the diversity and distribution of parasites in gastropod molluscs to test for host-parasite co-association. 16 populations representing 10 species of freshwater snails were screened using microsporidian specific small subunit rDNA primers. Four novel microsporidian parasite sequences were detected within populations of three host species from the genera Bulinus, Biomphalaria and Planorbis. Prevalence ranged from 5 to 84%. Phylogenetic analysis of these novel sequences reveals that they group together as a paraphyletic assemblage in the microsporidian tree basal to the two lineages containing the genera Encephalitozoon and Nosema. Preliminary observation of one microsporidian infection, show parasites distributed in all tissue systems of Bulinus globosus. However, infection is most prevalent in the digestive gland while also in the egg sacs, suggesting that the microsporidium is using a mixed strategy of horizontal and vertical transmission in this population.     

Predation on snails by an indigenous fish,Sargochromis codringtonii,in ponds in Zimbabwe

The extent to which Sargochromis codringtonii (a known predator of snails) can control snail numbers was investigated in cementlined ponds in order further to evaluate the fish's potential as an agent for the biological control of fresh water snails, especially Bulinus globosus which is the intermediate host for Schistosoma haematobium in Zimbabwe. Bulinus tropicus of all sizes were vulnerable to predation by fish, but both Melanoides tuberculata and Bulinus globosus with shell heights greater than 10mm seemed to be less so. Surprisingly, the density of B. globosus was lower in ponds without fish than in ponds with fish, while the density of B. tropicus was very high in ponds without fish. It was not possible to conclude whether B. globosus benefited by the presence of fish, or was less palatable to the fish than B. tropicus, or whether the high density of B. tropicus in ponds without fish exerted competitive effects on B. globosus. Consequently, further experiments are required to determine whether S. codringtonii can reduce populations of B. globosus in the absence of B. tropicus.