COMPARATIVE FITNESS AND REPRODUCTIVE ISOLATION BETWEEN TWO BULINUS GLOBOSUS(GASTROPODA: PLANORBIDAE) POPULATIONS

Bulinus globosus, an intermediate host of schisto-somes, isa self-fertile hermaphrodite species whose regular mating systemis cross-fertilization. Fitness of selfing individuals originatingfrom two geographically remote populations (Elevi, Ivory Coast;Daikaina, Niger) was scored. Individuals were then paired eitherwith individuals from their own population, or with individualsfrom the other population. Electrophoretic analysis showed thatpairing ‘female’ Elevi and ‘male’ Daikainaindividuals results in only a low level of outcrossing, whereasthe reverse pairings produced almost only outcrossed offspring.This could reflect unilateral partial isolation between thetwo populations. However, analysis of fitness values withinand among groups of self-fertilizing and cross-fertilizing individuals,as well as electrophoretic data, suggest that selfing (or partialselfing) is the regular mating system in Elevi. Such experimentsare relevant to the biological control of schistosiomasis byintroducing resistant snails from allopatric populations, becausethey allow an assessment of the fate of introduced resistantgenes. (Received 30 December 1991; accepted 13 March 1992)     

COPULATORY ACTIVITY AND SPERM PRODUCTION IN BULINUS (PHYSOPSIS) GLOBOSUS (GASTROPODA: PLANORBIDAE)

Young Bulinus (Physopsis) globosus performed male copulatoryactivity and cross-fertilized other snails before their femalereproductive tracts were mature. The two most immature snailsshowed preputial eversion when secretion was present only inthe muciparous gland and at the carrefour region of the oviduct.Sixteen snails showed preputial eversion and four snails cross-fertilizedother snails when their oothecal glands and/or major portionof the oviducts contained either no secretion or only scantyamounts. When paired with a partner snail for 12 or 20 consecutive days,adult snails copulated as males on approximately 60% of thedays paired and up to 8 consecutive days. Virgin snails raisedin isolation copulated as male at the same rate as non-virgin,community-raised snails. Ability to copulate as male was notdependent upon previous experience as male or female. Aftera single copulation as male after 7 days isolation, the hermaphroditicducts of maleacting snails contained 87 000 sperm. Sperm productionoccurred at approximately 50 000 sperm.d-¹, until at 10 dayspost-copulation, snails contained 639 000 sperm. (Received 25 May 1982;     

OBSERVATIONS ON THE ECOLOGY OF BULINUS (PHYSOPSIS) GLOBOSUS (MORELET), B. (BULINUS) FORSKALII (EHRENBERG) AND LYMNAEA NATALENSIS (KRAUSS) IN RICE SWAMPS IN SIERRA LEONE.

Changes in population of Bulinus globosus, B. forskalii andLymnaea natalensis were studied in four different locationsnamed Sites A, B, C. and D in Bo town Sierra Leone. The snailpopulations and oxygen concentrations of water increased inthe rainy season. The biological oxygen demand did not havesignificant correlation with changes in snail populations inSites B and D. B. globosus was absent from Site A while B. forskaliiwas the predominant snail in Site C. Site D with the highestmean monthly conductivity of 176 µmhos contained 54% whileSite A with a similar reading of 90µmhos contained 1%of all snails found. (Received 22 May 1980;     

FACTORS AFFECTING THE GROWTH AND FECUNDITY OF BULINUS TROPICUS (KRAUSS) (GASTROPODA)

Growth, monitored as changes in wet weight or shell length,varies inversely with population density in closed cultures,irrespective of whether the volume of water is kept constant,or increased in proportion to the number of snails. Feedingand locomotor activity are also lower in high density populationsand the size differences recorded are reflected in the proteinand nucleic acid content of the snails. Similar attenuation of growth and inhibition occurs in snailscultured in continuously dialysed medium and the differencesare not attributable solely to changes in the inorganic ioncontent. Instead the results are consistent with the hypothesisthat some unidentified inhibitory compound accumulates in thewater. (Received 23 June 1986;     

ALLOZYME VARIATION AMONG POPULATIONS OF BIOMPHALARIA PFEIFFERI (KRAUSS, 1848) (GASTROPODA: PLANORBIDAE) IN CAMEROON

Allozyme electrophoresis was used to study genetic diversityamong the freshwater, hermaphroditic snail Biomphalaria pfeifferiin Cameroon. Four of 19 loci studied were polymorphic. The allozymesfor two loci, aspartate aminotransferase-1 (AAT-1) and isocitratedehydrogenase (IDH), showed distribution patterns related toclimatic zones. AAT-1¹⁰⁰ and IDH¹⁰⁰ occurred predominantly inthe Tropical Climatic Zone, located in the northern half ofthe country. AAT-1¹⁴⁰ and IDH⁹⁰ were common in the EquatorialZone. Intrapopulation variations occurred in 5 of 19 populationsampled. Only one population, polymorphic for AAT-1 locus, waspanmictic. The other 4 populations were not in Hardy-Weinbergequilibrium. The deficiency of heterozygotes in those populationsis unusual for a member of the genus Biomphalaria and may bedue to a predominance of self-fertilization. Other explanationsinclude ecological factors or the presence of segregated sub-populationsthat do not outcross. This latter hypothesis is supported bythe total absence of heterozygotes for PGM alleles. (Received 24 August 1989; accepted 14 September 1989)     

COPULATION AS FEMALES AND USE OF ALLOSPERM IN THE FRESHWATER SNAIL GENUS BULINUS (GASTROPODA:PLANORBIDAE)

Each of 8 snails in 2 groups of Bulinus (Physopsis) globosus,1 group raised in isolation and 1 group raised in community,were paired for 14 consecutive days with a male-acting partnersnail. In each group, the experimental snails, which were notallowed to act as males, were able to copulate as females onapproximately 94% of the days paired. Two copulations as female,with the same male partner, occurred on 50% of the days thatthe snails were paired, in the 2 groups combined. Non-receptivefemale behaviour by the experimental snails occurred frequently,and copulation was prevented by such behaviour during 6 pairings,3 in each group. Young B. (P.) africanus first copulated as females when theywere 31–33 days old. The accessory sex glands of the femalereproductive tracts of these young female-acting snails containedmoderate to large amounts of secretion. B. (P.) africanus, which were raised in pairs, laidcross-fertilizedeggs in isolation for an average of 76 days, and 1559 eggs/snailwere deposited before cross-fertilization ceased. Cross-fertilizedeggs were produced for as long as 120 days. After 1 copulation as female, virgin B. (P.) africanus laidcross-fertilized eggs for an average of 78 days and deposited3654 eggs/snail before crossfertilization ceased. Cross-fertilizedeggs were produced for as long as 113 days. After 2 copulationsas female, 1 copulation on each of 2 consecutive days, virginB. (P.) africanus laid cross-fertilized eggs for an averageof 102 days and produced 4397 eggs/snail before cross-fertilizationceased. Cross-fertilized eggs were produced for as long as 123days. Snails which were homozygous for an allele governing mantlepigment pattern were raised with a partner which was homozygousfor a different pigment pattern. Young produced in a 4-day periodafter the snails were isolated were 100% heterozygous. The snailswere then rearranged into pairs with a partner of the same genotypefor 4 days, during which time 26% of the young produced werehomozygous. The snails were again isolated for 4 days, and 49%of the young produced during this 4-day period were homozygous.The results of this experiment strongly suggest that multipleoutcrossing occurred. In B. (P.) africanus, stored allosperm were used to fertilizeeggs after 1, 4 and 7 weeks of starvation; after 1 and 4 weeksof 15°C low temperature and 4 weeks of 15°C + 4 weeksof 10°C low temperature; and after 1 and 4 weeks of desiccation.After 8 weeks of desiccation, 2 of 3 surviving snails reproducedby self-fertilization and 1 snail did not reproduce. Too fewsnails survived 8 weeks of desiccation for a conclusion to bereached on the ability of allosperm to survive. (Received 1 June 1984;     

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)     

ALLOZYME COMPARISONS AMONG SPECIES OF THE BULINUS FORSKALII GROUP (GASTROPODA: PLANORBIDAE) IN CAMEROON

Allozyme comparisons were made for adult Bulinus forskalii,B. camerunensis, and B. senegalensis from populations in Cameroonusing starch gel electrophoresis. Fifteen loci were examinedbut no differences were found between B. forskalii and B. camerunensis,bringing into question the validity of B. camerunensis as aseparate species. Bulinus senegalensis differed from B. forskaliiand B. camerunensis in allozymes for acid phosphatase, alpha-glycero-phosphatedehydxogenase, hydroxybutyrate dehy-drogenase, and phosphoglucomutase.No differences were found, as reported elsewhere, between B.forskalii and B. senegalensis for aspartate amino-transferase,isocitrate debydrogenase, phosphogluco-isomerase, and xanthineoxidise. No polymorphism was seen in B. camerunensis or variousB. senegalensis populations examined. Three alleles for isocitratedehydrogenase were observed for B. forskalii. Mixed populationsof B. forskalii and B. senegalensis were found at four sitesbut no evidence of hybridization between these species was found. (Received 9 May 1988; accepted 30 August 1988)     

ALLOZYME COMPARISONS AND PLOIDY LEVELS AMONG SPECIES OF THE BULINUS TRUNCATUS/TROPICUS COMPLEX (GASTROPODA: PLANORBIDAE) IN CAMEROON

Allozyme electrophoresis, ploidy level, and, to a lesser extent,anatomy and shell morphology were used to characterize snailsof the Bulinus truncatus/tropicus complex in Cameroon. Starchgel electrophoresis revealed no intrapopulation variation within20 populations examined for 14 allozyme loci in 12 enzyme systems.Interpopulation differences in allozyme patterns were used todivide the populations studied into five groups. Each groupis distinguished by a unique combination of zymograms for hydroxybutyratedehydrogenase and isocitrate dehydrogenase. Four of these groupsare tetraploids and are identified as B. truncatus. Populationsof the most commonly found B. truncatus group are generallyaphallic, are frequently associated with transmission of S.haematobium, and generally occur at altitudes below 800 m abovesea-level. Populations of B. truncatus belonging to the otherthree groups are usually euphallic, not associated with S. haematobiumtransmision, and generally occur at altitudes above 1000 m.These four groups may represent distinct biotypes of B. truncatus.Populations belonging to the fifth group are diploid, euphallic,not associated with S. haematobium transmission, and occur inhabitats above 1000 m. This is the first confirmed report ofdiploid B. truncatus/tropicus-complex snails from this regionof Africa. They are tentatively identified as B. natalensis,a species previously thought to be limited to East and SouthernAfrica. (Received 31 October 1988; accepted 20 February 1989)     

ULTRASTRUCTURE OF THE MATURE SPERMATOZOA OF THE LAND SNAIL EPIPHRAGMOPHORA TUCUMANENSIS (DOERING, 1874) (GASTROPODA: HELICOIDEA)

The ultrastructure of the sperm of Epiphragmophora tucumanensis(Doering), a pulmonate land snail belonging to the family Xanthonychidae,was examined. The results showed that this spermatozoon presents a similarmorphology to the other advanced stylommatophoran sperm described.The most peculiar characteristic is the form of the nucleus,which is straight instead of helically coiled. An acrosome ispresent, composed of an apical vesicle and an acrosomal pedestal.The connecting piece or neck region is formed by a basal bodyplus a centriolar derivative. It is also the point of originof coarse fibres that accompany the axoneme. Thus, the axonemalcomplex exhibits a 9+9+2 pattern. The midpiece is an elongatedregion composed of paracrystalline and matrix materials (collectively,the mitochondrial derivative) enclosing a single glycogen helixand the axoneme. The mitochondrial derivative extends to theposterior tip of the spermatozoon. As observed in other stylommatophorans,both an annulus and a glycogen piece are absent. (Received 25 October 1993; accepted 4 February 1994)     

THE EFFECT OF SODIUM CHLORIDE CONCENTRATION ON GROWTH AND EGG LAYING OF HELISOMA DURYI, BIOMPHALARIA ALEXANDRINA AND BULINUS TRUNCATUS (GASTROPODA: PLANORBIDAE)

Helisoma duryi, Biomphalaria alexandrine and Bulinus truncatuswere maintained in media with seven different sodium chlorideconcentrations ranging from 0.6 to 32 mM. Growth of H. duryiwas significantly reduced only in the 32 mM NaCl treatment,while no significant effects were observed in the net reproductiverate or in egg-laying rates. Bulinus truncatus showed optimalgrowth within the range of 1 to 8 mM NaCl and the net reproductiveand egg-laying rates were reduced in the 32 mM NaCl treatment.Growth of B. alexandrina was reduced in the 16 and 32 mM NaCltreatments, while the net reproductive rate was reduced in the16 and 32 mM NaCl treatments, while the net reproductive ratewas reduced in media with more than 2.0 mM NaCl. Hatching ofB. truncatus eggs was not affected by the high NaCl concentrations,while the hatchability of H. duryi eggs was reduced in the 32mM treatment. Survival of newly-hatched H. duryi was best inthe 1 mM NaCl treatment while for B. truncatus survival wasreduced only in the 32 mM treatment. (Received 28 March 1988; accepted 7 April 1989)     

ALLOZYME VARIATION AMONG POPULATIONS OF BULINUS FORSKALII (EHRENBERG, 1831) (GASTROPODA: PLANORBIDAE) IN CAMEROON

Allozyme electrophoresis was used to study genetic diversityamong populations of the freshwater, hermaphroditic snail Bulinusforskalii in Cameroon. Three of 15 loci studied in 13 enzymesystems were polymorphic. Intrapopulation variation occurredin 8 of 32 populations sampled and heterozygotes were presentin 2 of these. Neither of these populations were in Hardy-Weinbergequilibrium. These findings are in agreement with reports thathave demonstrated a low genetic diversity in this very widelydistributed, eurytopic species and that have indicated thisspecies reproduces principally by self-fertilization. The restricteddistributions of rarer alleles in three loci may be due to anarrower habitat range for those phenotypes. For isocitratedehydrogenase and phosphoglucoisomerase, the faster alleleswere found throughout the range of B. forskalii extending fromthe Sahelian regions of the north to rain forest of the south.The slower, rarer alleles for these loci were restricted tothe equatorial rain forest regions. For hydroxybutyrate dehydrogenase,the opposite was true for the rarer allele, which was restrictedto a small region in the arid, tropical climate. (Received 27 April 1989; accepted 5 September 1989)     

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.     

AN EVALUATION OF RANDOM AMPLIFIED POLYMORPHIC DNA (RAPD) FOR THE IDENTIFICATION AND PHYLOGENY OF FRESHWATER SNAILS OF THE GENUS BULINUS (GASTROPODA: PLANORBIDAE)

The Random Amplified Polymorphic DNA (RAPD) assay was used tostudy genetic variation within and between 9 species of thegenus Bulinus and to determine whether RAPD profiles could beused as markers for identification purposes. RAPDs were generatedwith 8 primers of two different sizes (l0mers & 15mers)and were visualised using both polyacrylamide gel electrophoresis(PAGE) with silver staining and agarose gel electrophoresiswith ethidium bromide staining. The species groups of Bulinushad few similarities in their RAPD profiles and there was interspecificvariation within groups. Intrapopulation variation was observed,with all primers, for B globosus collected from a single sitein Zimbabwe PAGE/silver staining methods visualised a greaternumber of RAPDs in comparison with agarose/ethidium bromidemethods. Phenetic analysis indicated that distance estimatesbetween taxa were sometimes non-additive and the phylo-geneticanalysis of such non-metnc data is discussed. The resultantphenograms, constructed using a least squares method, were constrainedalmost into a polytomy with topologies often differing betweendata sets. It was concluded that this phenomenon was most likelyattributable to large nucleotide divergences between the speciesgroups which go beyond the phylogenetic scope of RAPD analysis.RAPD profiles, when used in conjunction with other taxonomicmethods, may contribute to the identification of species ofBulnus on a regional basis, but the observed variability ina natural population suggests that a diagnostic RAPD profilefor each species throughout its geographic range is unlikely. (Received 19 April 1995; accepted 1 September 1995)     

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)     

THE EFFECT OF VARYING RELATIVE DENSITY AND VARYING FOOD SUPPLY ON INTERSPECIFIC COMPETITION BETWEEN HELISOMA DURYI AND BULINUS TRUNCATUS (GASTROPODA, PLANORBIDAE)

Interspecific competition between Helisoma duryi and the intermediatehost of schistosomes, Bulinus truncatus results in reduced growthand reproduction of B. truncatus and the effects are more pronouncedas the density of H. duryi is increased. The drastic reductionin reproduction of B. trunauus is the result of a predationby H. duryi on egg masses. It appears that increasing the foodsupply cannot completely eliminate the effects of competition.Although the growth and reproduction of B. truncatus in competitionwith H. duryi increases significantly with the increased foodsupply, both growth and reproduction are still reduced comparedto control snails given the same amount of food. The effectsof food supply and competition on the allometric size-weightrelationships of the two species are slight. (Received 23 February 1987; accepted 4 May 1988)     

THE BIOMPHALARIA HAVANENSIS COMPLEX (GASTROPODA: PLANORBIDAE) IN CUBA: A MORPHOLOGICAL AND GENETIC STUDY

Conchological, anatomical and genetic characteristics werecompared among several populations of the Biomphalaria havanensis complexfrom Cuba and other localities in the Caribbean region. Two morphometricmeasures (height and diameter) distinguished two closely similarmorphs of the shell. The reproductive system also separated thesemorphs, particularly upon comparison of sizes of the penis sheathand the preputium. The two morphological groups differed in9 to 12 fixed alleles according to population. Further allozymicdata analyzed in the present work confirmed this difference.The results strongly support the assumption that the B. havanensis complexincludes two distinct species: B. havanensis, for which thetype locality is the swampy area near the vicinity of Havana,Cuba and Biomphalaria sp. a species which commonly occurs inCuba and in Dominican Republic. The taxonomic identity of Biomphalariasp. is discussed. (Received 28 January 2000; accepted 15 August 2000)     

MATING SYSTEM ANALYSIS USING PROTEIN ELECTROPHORESIS IN THE SELF-FERTILE HERMAPHRODITE SPECIES BULINUS TRUNCATUS (GASTROPODA: PLANORBIDAE)

Uniparental reproduction in the tetraploid hermaphrodite speciesBulinus truncatus has been suggested to occur via self-fertilization,on the basis of cytological and genetic studies. However, recentanalyses of population genetic structure by protein electrophoresisindicated the occurrence of multi-banded phenotypes referredto as ‘fixed hetero-zygosity’. Although intrapopulationand geographical variation of multibanded phenotypes occur,many populations bear only one type of such patterns. This ledto the suggestion that parthenogenesis may well be the matingsyste in B. truncatus. However, such fixed heterozygosity patternsare expected in some tetraploid species in which double disomicinheritance of alleles occurs. It is therefore not possibleto determine from population genetic structure analysis alonewhether segregation occurs or not. Here, we investigate thestability of such patterns over one generation of uniparentalreproduction among four populations. We also present resultsof crossing experiments between individuals from two populations,using two diagnostic loci to analyse their offspring. Our resultsclearly indicate Mendelian segregation of alleles, and confirmsexual reproduction by self-fertilization and cross-fertilization.We interpret the multibanded patterns observed in populationsas the product of both diploid loci of the tetraploid genomewhen they are monomorphic for different alleles. Our study alsoallows us to suggest that partial selfing may be the regularmating system in B. truncatus. (Received 12 February 1992; accepted 7 September 1992)