THE EFFECT OF WATER QUALITY ON OVIPOSITION IN BIOMPHALARIA GLABRATA (SAY, 1818) (PLANORBIDAE), AND A DESCRIPTION OF THE STAGES OF THE EGG-LAYING PROCESS

With the overall goal of developing a method to reliably induce ovipositionin the freshwater pulmonate Biomphalaria glabrata, the effectsof water quality on female reproductive physiology were examined.Groups of snails were subjected to controlled experimental conditionsconsisting of a daily regimen of feeding and water change. Aftera period of acclimatiz-ation, egg mass (EM) output under theseconditions was relatively stable, and snails laid a majority(82.5%) of their EM during the initial 4 h following daily waterchange. When this regimen was perturbed by halting water changefor 24 h (dirty-water treatment), EM output was significantly inhibited.When water change was resumed, EM output returned to previouslevels within 4 h post-water change (PWC). This dirty-water treatmentfollowed by water change also resulted in a significant increasein mean EM size during the 4 h PWC when compared to controls.To better describe the events preceding egg-laying in B. glabrata,we then used these experimental manipulations to induce ovipositionin groups of snails, and dissected them during the 4 h followingwater change. Observations of the reproductive tracts of stimulatedsnails allowed us to divide the egg-laying process, from ovulationto oviposition, into discrete stages, after de Jong-Brink, Koop,Roos & Bergamin-Sassen (1982). Stage I was characterized bythe presence of ova in the hermaphroditic duct and carrefour,and fertilized, packaged eggs in the oviduct and muciparousgland. Stage II was characterized by the presence of packagedeggs in the othecal gland embedded in a mucous layer, constitutingthe egg mass to be laid on the substratum. No packaging eventswere occurring in the carrefour/albumen gland region duringthis stage. When snails were dissected immediately after oviposition(Stage III), unpackaged ova were observed in the hermaphroditicduct, carrefour, and oviduct. The mean time it took for snailsto reach Stage III was 120 6 49 min (SD), and this value wasstatistically different from the mean time to Stages I and II,showing that our induction protocol results in a temporal progressionthrough the egg- laying process. Gonadal oocyte density (oocytes/mm²of ovotestis) was quantified as a function of these stages ofthe reproductive cycle, and was found to be significantly lowerduring Stage II (fully formed egg mass in othecal gland) thanall other stages examined. Taken together, these results showthat female reproductive activity can be experimentally controlledthrough the manipulation of water quality, and that such a protocolis a valuable tool for addressing specific questions regardingthe reproductive physiology of B. glabrata. The implicationsof these results as they pertain to the regulation of femalereproductive activity in B. glabrata are discussed. (Received 15 January 1999; accepted 17 May 1999)     

SURFACING AND WATER LEAVING BEHAVIOUR OF THE FRESHWATER PULMONATE SNAILS LYMNAEA PEREGRA (MULLER), BIOMPHALARIA GLABRATA (SAY) AND BULINUS JOUSSEAUMEI (DAUTZENBERG)

Surfacing and water-leaving behaviour (quitting) of aquaticpulmonate snails was investigated in the laboratory. Regressioncoefficients of surfacing rate per hour for 16 snails in 200cm³ of water were 1.28 for L. peregra, 1.35 for B. glabrata(albino form), 0.47 for B. glabrata (pigmented form) and 0.17for B. jousseaumei. Disturbance, snail size and conditioningof the water were relatively unimportant factors; water volumeadjusted by depth was also unimportant up to 50 mm depth. Importantfactors controlling surfacing appeared to be population density,time of year, temperature, water volume adjusted by perimeterand dissolved oxygen concentration. The response to the latterwas not clear and both B. glabrata and L. peregra orientatedalmost as well to a nitrogen/water interface as to an air/waterinterface. Water-quitting regressed on volume, which had beenadjusted by perimeter variation, revealed a curvilinear relationshipfor B. glabrata, with maximum quitting at 1 snail per 7cm³ (1snail per 14cm of climbable perimeter). L. peregra showed anegative exponential curve, with maximum quitting at 1 snailper 3 cm³ of water (1 snail per 8 cm of climbable perimeter).These data could be relevant to design and management of irrigationchannels where bilharzia might occur. (Received 28 November 1990; accepted 22 October 1991)     

Schistosoma mansoni: Long-term maintenance of clones by microsurgical transplantation of sporocysts

Schistosoma mansoni sporocysts originally derived from monomiracidially infected Biomphalaria glabrata snails were serially transplanted into the cephalopedal sinus of anesthetized snails by the microsurgical implantation of fragments of parasitized hepato-pancreas and ovotestis. Three to six passages each of five male and five female clones were maintained for as long as 2.0 years. Of the recipient snails which survived surgery, 87% released cercariae, usually beginning 5–7 weeks after surgery. The percentage of snails which released cercariae increased with successive passages. The mean survival time of surgically infected snails after cercarial emergence began was 9.2 ± 0.5 weeks, nearly the same as that of miracidially infected snails. Longevities of snails infected with male or female clones were similar. Recipient snail size and age did not influence cloning success. Beginning 5 weeks from the onset of cercarial emergence large numbers of cercariae (a mean of 3900/snail from male clones and 1300/snail from females) were obtained during each shedding period. These results clearly demonstrate that the microsurgical transplantation of sporocysts is a practical means of maintaining and expanding populations of genetically homogeneous schistosomes (clones).     

STARVATION, DESICCATION AND USE OF ALLOSPERM IN THE HERMAPHRODITE FRESHWATER SNAIL BIOMPHALARIA GLABRATA (GASTROPODA: PULMONATA)

Pairs of albino and pigmented snails were used to test the hypothesisthat the hermaphrodite freshwater gastropod Biomphalaria glabratawas able to conserve and use allosperm, despite periods of desiccationand starvation. In laboratory experiments, lots of twenty snailswere subject to 0, 5, 10, 15 AND 20 days starvation; similarlots of 20 snails were subjected to 0, 2, 4, 6, 8, 10 weeksof desiccation at R.H. 100%. After all periods of starvationand desiccation, albino parents were still producing significantnumbers of pigmented offspring, suggesting preferential cross-fertilizationusing stored allosperm. (Received 30 September 1993; accepted 23 December 1993)     

INFLUENCE OF NON-TARGET MOLLUSCS ON THE GROWTH OF BIOMPHALARIA GLABRATA INFECTED WITH SCHISTOSOMA MANSONI: CORRELATION BETWEEN GROWTH AND CERCARIAL PRODUCTION

The presence of non-target molluscs (nine species tested) resultedin a significant enhancement of the growth of Biomphalaria glabratainfected with Schistosoma mansoni. A positive significant correlationwas found between the mean final shell diameter of B. glabrataand the total cercarial production of S. mansoni. Two hypotheseson the mechanisms implied in these interactions are proposed. (Received 6 October 1989; accepted 5 December 1989)     

Effect of exposure to Echinostoma itliei miracidia on growth and survival of young Biomphalaria glabrata snails

Kuris A. M. 1980. Effect of exposure to Echinostoma liei miracidia on growth and survival of young Biomphalaria glabrata snails. International Journal for Parasitology10: 303–308. Exposure to miracidia of Echinostoma liei resulted in increased mortality and reduced growth of 1–2 mm albino Biomphalaria glabrata snails whether or not the snails became infected. Growth rates for infected and exposed but uninfected snails were significantly more variable than growth rates of unexposed snails. Retarded growth and increased mortality were detected as rapidly as seven to nine days after exposure. Neither growth nor survivorship of 4–6 mm snails was altered upon exposure to or infection by E. liei.     

Ribeiroia marini: pathogenesis and larval trematode antagonism in the snail, Biomphalaria glabrata

Larval trematode antagonism between Ribeiroia marini and Schistosoma mansoni was studied in the snail Biomphalaria glabrata. A laboratory-raised Puerto Rican strain of B. glabrata was exposed to single and double infections with given numbers of: (1) embryonated eggs of R. marini from laboratory rats, and (2) miracidia of S. mansoni from mice. Snails were maintained in outside environmental tanks in San Juan, Puerto Rico and larval trematode interactions were examined in a series of five experiments. Snails of all sizes were highly susceptible to single infections with R. marini. Rediae and cercariae caused extensive damage to the digestive gland and ovotestis resulting in premature death of snails. Heavily infected snails were castrated and stopped laying eggs. Snails infected first with S. mansoni were only partly susceptible to superinfection with R. marini given on Day 23. In a reverse experiment, snails infected first with R. marini were only partly susceptible to a second infection with S. mansoni given on Day 23. In simultaneous exposures, snails developed double infections (22%) with R. marini dominant and S. mansoni sporocyst and cercaria production reduced. While R. marini is not a strong direct antagonist against established S. mansoni infections, it has several attributes as a possible biological control agent: hardy eggs easily produced in rats; high infectivity to snails of all ages; and ability to castrate and prematurely kill B. glabrata. The R. marini-rat system described here provides a convenient laboratory and field model for the study of intrasnail trematode antagonism and biological control.     

Shell mats associated with microsporida in Biomphalaria glabrata: genetic studies

Multilayered mats have been observed lining the shell of some Biomphalaria glabrata infected with Steinhausia brachynema. Occurrence of the mats is associated with extensive infection with the microsporidia in these snails, in contrast to most B. glabrata in which infection appears restricted to the intestinal wall. Observations suggest that this variation in pathology may be influenced by a genetic difference in the host snails.     

EFFECTS OF HEAVY METALS ON SURVIVAL AND GROWTH OF BIOMPHALARIA GLABRATA SAY (GASTROPODA: PULMONATA) AND INTERACTION WITH SCHISTOSOME INFECTION

The effects of dissolved Pb, Cd and Hg on growth and survivalof adult Biomphalaria glabrata Say. uninfected and infectedwith Schistosoma mansoni Sambon, were examined. Pb at concentrationsfrom 0.25–100 µM, Cd from 0.075–0.25 µMand Hg from 0.25–1 µM significantly reduced growthand survival of normal snails. With each metal the effects increasedwith increasing concentration. The LC 25 at 2 wks exposure was82 ± 19, 0.22 ± 0.04 and 0.94 ± 0.13 µM(x ± S.E.) for Pb, Cd and Hg, respectively. Snails exposedto heavy metals continued to be reproductively active, but theegg production was highly variable and no significant effectof heavy metal exposure was demonstrated. Infection also decreasedsurvival and growth of snail hosts and infected individualsexposed to heavy metals displayed the greatest mortality. TheLC 25 for infected snails at 2 wks exposure was 8 ± 3,0.9 ± 0.02 and 0.29 ± 0.08 for Pb, Cd and Hg respectively.A significant interaction between heavy metal exposure and infectionwas apparent. Infected snails were not reproductively active.Cercarial shedding by infected snails was significantly reducedin the presence of heavy metals and by 6 wks shedding had ceasedat the highest metal concentrations. (Received 20 May 1996; accepted 31 July 1996)     

PATTERNS OF SEXUAL ROLES ADOPTED BY THE SCHISTOSOME-VECTOR SNAIL BIOMPHALARIA GLABRATA (PLANORBIDAE)

Relatively little is known about the mating behaviour of hermaphroditefreshwater snails, many of which transmit the Schistosoma trematodesamong humans in developing countries. Knowledge of the breedingbiology of these snails could help in the design of schistosomecontrol programmes, as well as possibly contributing to ourunderstanding of the evolution of simultaneous hermaphroditismin animaL. Here we describe an experiment investigating thepatterns of sexual roles adopted by the Schistosoma mansoni-vectotsnail, Btmphalaria glabrata. During observations on groups offreely interacting snails, no individuals copulated significantlymore often in the male than in the female role, or vice versa.Only one individual showed a pattern of alternating sexual rolesover successive matings that differed significantly from a randomsequence of roles. There was no evidence for reciprocal copulationwith one particular partner, either between consecutive matings(unless they were temporarily isolated from other snails) orbetween non-consecutive matings (separated by copulations withother conspccifics). We discuss these results in the contextof sex allocation and ESS mating strategy theories. ^*Present address (or correspondence 1 G VERNON. Bioscan (UK).Standingford House, Cave Street, St. Clements, Oxford OX4 IBA. (Received 5 October 1995; accepted 6 November 1995)     

Growth rate and changes in tissue carbohydrates during schistosome infection of the snail biomphalaria alexandrina

Laboratory investigations were carried out to determine the growth rate, glycogen content of different body parts and glucose uptake in normal and schistosome-infected Biomphalaria alexandrina snails over a period of 45 days post infection. Infected snails grew at a faster rate. There were no significant differences in tissue water content and tissue dry weight of control and infected ones. A marked decrease in the glycogen content of female sex organs, mantle, digestive gland and muscles was observed in infected snails. Glucose utilization was also increased in infected snails.     

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;     

Parasite influences on host life history: Echinostoma revolutum parasitism of Lymnaea elodes snails

Using field surveys and experimental infections, we investigated the influence of a trematode parasite on life history traits of adult Lymnaea elodes snails. We found that parasitism significantly affected the growth, fecundity, and survival of host snails. Within five of the six natural L. elodes populations we sampled, shell length of echinostome-infected hosts was significantly greater than for uninfected conspecifics. Furthermore, we show that gigantism occurs among experimentally infected snails due to an accelerated growth rate and size-selective mortality following an Echinostoma revolutum infection. The fecundity of infected snails sharply decreased beginning at 3 weeks post exposure (PE) and all egg production eventually ceased for most hosts by 5–6 weeks PE. Energy constraints, imposed by parasite development, alter the host energy budget. Early in the infection, parasite depletion of host energy reserves reduces host reproduction, but sufficient resources remain to allow accelerated host growth. Mortality was increased among host snails at two distinct stages: shortly after exposure and several weeks after cercariae were first released. We did not observe tissue degradation in snails during the first 4 weeks after exposure to the parasite, but destruction of host tissues was noted among snails dying later in the infection. Received: 5 September 1997 / Accepted: 19 November 1997     

POPULATION DENSITY EFFECTS ON GROWTH IN CULTURE OF THE EDIBLE SNAIL HELIX ASPERSA VAR. MAXIMA

The effects of population density on the growth of H. aspersaMÜller var. maxima under controlled environmental conditionswere examined. Inhibitory effects on snail growth and maturityresulting from increased population density, between 100–800snails m^–2 of floor area, were observed for a range ofcontainer cleaning frequencies. At all population densities,enhanced snail growth was observed when the frequency of containercleaning was increased to a two-day interval. No significantdifferences were recorded, following 19 weeks growth, betweenfinal mean weights of snails from containers cleaned less frequently.The lowest snail mortality was consistently recorded at thelowest population density in the most frequently cleaned containers.At all snail population densities three phases of growth wereobserved: (a) lag (0–5 weeks), (b) rapid (6–15 weeks)and (c) stable (16 weeks and over). During the first three weeksof growth, high population density had a positive effect ondiet consumption, food conversion efficiency and snail growth.Adverse population density effects increased progressively duringphase (b), typically following 9 weeks growth. Juvenile snailstransferred from high to low population densities during phase(b) continued to exhibit slower growth rates associated withhigh population densities. Food conversion efficiency of snailsin all treatments decreased throughout the experimental periodbut with no overall effect of container cleaning frequency apparent.Inherent growth variability of sibling snails was unaffectedby population density or container cleaning frequency. The importanceof the results for intensive snail culture is discussed. (Received 23 June 1994; accepted 1 December 1994)     

RANDOM AMPLIFIED POLYMORPHIC DNA (RAPD) MARKERS REVEAL CROSS-FERTILISATION IN BIOMPHALARIA GLABRATA (PULMONATA: BASOMMATOPHORA)

The freshwater, schistosome-transmitting snail, Biomphalariaglabrata is a simultaneous hermaphrodite which can reproduceby both cross-and selffertilisation, but despite the medicalimportance of this species, little is known about the matingstrategies adopted by wild-type individuals from natural populations.The identification of cross-fertilised progeny is a prerequisitefor both evolutionary studies of the relative fitness of differentreproductive strategies, and for the production of exclusivelyoutcrossed F₁ populations for genetic mapping of biologicallyimportant phenotypes, most notably, resistance to schistosomeinfection. In this study, parents, offspring and ‘syntheticoffspring’ (controls) from four families of B. glabratarecently derived from wild populations were analysed using theRandom Amplified Polymorphic DNA (RAPD) assay. RAPDs were usedbecause they reveal more genetic variation, require less tissue(juvenile snails were only 4–5 mm diameter) than proteinelectrophoresis, are less laborious than other molecular analyses,and do not require sequence data. Seven of the 19 arbitrarysequence, oligonucleotide primers used gave bands that werepolymorophic between pairs of parent snails. Scoring the offspringfor the presence/absence of these polymorphic bands showed thatall the offspring tested were the products of cross-fertilisation.This study provides the first demonstration of the applicabilityof the RAPD technique to an analysis of fertilisation in wild-typeB. glabrata. (Received 20 December 1994; accepted 27 March 1995)     

Distribution and variation of hemagglutinating activity in the hemolymph of Biomphalaria glabrata

A sensitive hemagglutination assay utilizing glutaraldehyde-fixed trypsinized calf erythrocytes (GTC) is described to test for agglutinin levels in hemolymph and albumen gland extracts from nine populations of Biomphalaria glabrata, and from B. straminea and B. obstructa. High levels of GTC-reactive hemagglutinin were found in all snail populations. There was no correlation between hemagglutinin titer and innate resistance of B. glabrata strains to Schistosoma mansoni. However, an increase in hemagglutinin titer occurs in B. glabrata M-RLc snails infected with Echinostoma lindoense and in snails sensitized and reexposed to this parasite.     

Effects of starvation on growth and reproductive apparatus of two immature freshwater snails Biomphalaria pfeifferi and Biomphalaria glabrata (Gastropoda: Planorbidae)

Starvation of immature snails of Biomphalaria pfeifferi and B. glabrata results in an arrest of growth and animals remain immature. Spermatogenesis is limited to spermatogonia (B.g.) or spermatocytes 1 (B.p.). The number and the size of oocytes remain inferior to that of controls. Animals show reduced genital tracts.Once feeding is restored, growth is resumed but wet weight and shell diameter do not reach the same level as in controls. Fecundity and gametogenesis do not differ from that in controls. Genital tracts weight is proportional to body weight.     

Testosterone,gonadotropins and androgen receptor during spermatogenesis of Biomphalaria alexandrina snails (Pulmonata: Basommatophora)

Endocrine regulation of reproductive processes of the snail Biomphalaria alexandrina is poorly recognized. Thus, the aims of the study were: (1) to acquire histological images of the ovotestis; (2) to determine the hemolymph concentrations of testosterone (T) and gonadotropic hormones (luteinizing hormone: LH and follicle stimulating hormone: FSH), (3) to demonstrate androgen receptor (AR) immunolocalization in the ovotestis, and (4) to show LH and FSH protein expression in cerebral ganglia of small (diameter shell: 4–6 mm), medium (7–11 mm) and large (12–16 mm) B. alexandrina snails. These three groups represented different reproductive stages of the snail. The AR immunoexpression was found in the periphery and inside the acini of small (immature) snails as well as in spermatocytes, spermatids, Sertoli cells, the interstitial cells and the acinus lining epithelium of medium (mature) snails. Low AR immunoexpression was demonstrated in the interstitial cells of large (aged) snails. The neurons at the periphery of the cerebral ganglia and connective sheath of the ganglia showed a positive FSH and LH immunostaining. T concentration in the hemolymph was higher in medium snails than in small and large snails. In contrast, LH concentration was higher in medium snails than in small and large snails. These data suggests that gonadotropins and T play a role in the gonadal development in B. alexandrina.     

Biomphalaria glabrata amoebocytes: Effect of Schistosoma mansoni infection on in vitro phagocytosis

The rate of phagocytosis by amoebocytes obtained from hemolymph of the pulmonate Biomphalaria glabrata infected with the trematode Schistosoma mansoni for 24 hr and 2, 4, and 6 weeks has been determined using the monolayer assay system. Amoebocyte preparations from snails infected for 4 and 6 weeks showed a gradual decrease in the phagocytic rates compared to those from uninfected controls. Snails harboring the parasite for 4 and 6 weeks also showed a significant increase in the number of amoebocytes in the hemolymph. No significant changes were detected in the rate of phagocytosis or number of amoebocytes in snails infected for 2 weeks or less. Alterations in the morphology and behavior of amoebocytes from infected snails were also noted.