Histology and histochemistry of the reproductive tract of the pulmonate snail,Bulinus truncatus,with observations on the effects of castration on its growth and histology

The reproductive tract of B. truncatus was investigated histologically in order to study possible effects of castration upon the accessory sex glands. In the female part of the reproductive tract—subdivided into albumen gland, oviduct, muciparous gland, oothecal gland, uterus, vagina and bursa copulatrix—13 histochemically different secretory cell types were distinguished. The majority produce different types of (acid) mucopolysaccharides. The roles of the various parts of the female tract in the production of an egg mass were elucidated by comparing the histochemistry of the egg mass to that of the female tract; the abundance and location of the cell types were also taken into account for this purpose.

The male part appeared to contain 12 histochemically different secretory cell types. These produce mainly (phospho lipoproteins together with some polysaccharides and neutral lipids.

Castration causes an acceleration of the growth of the snails. The volumes of female (albumen gland) and male (prostate gland) accessory sex glands were measured on histological sections. It appeared that growth of the albumen gland is not arrested by castration. This was not established beyond doubt for the prostate gland. The results suggest that the stimulating effects of the dorsal body hormone on the growth and synthetic capacity of the female accessory sex glands—such effects have been established for Lymnaea stagnalis—are not exerted via the ovotestis in B. truncatus.     

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)     

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;     

INBREEDING DEPRESSION,NEUTRAL POLYMORPHISM,AND COPULATORY BEHAVIOR IN FRESHWATER SNAILS: A SELF-FERTILIZATION SYNDROME

This paper examines the consequences of self-fertilization on life-history traits and neutral genetic polymorphism in natural populations of three species of hermaphrodite freshwater snails: Biomphalaria straminea, Bulinus globosus, and the aphallic species Bulinus truncatus. Life-history traits (fecundity, growth, hatching rate, and survival of offspring) are compared under laboratory conditions between isolated (obligatory selfing) and paired (outcrossing possible) snails in one population of B. straminea and B. globosus and two populations of B. truncatus. The genetic polymorphism of the same four populations is analyzed using electrophoretic markers in B. straminea and B. globosus and microsatellite markers in B. truncatus. In B. truncatus and B. straminea, isolated snails have a higher fecundity than paired snails, whereas the contrary is observed in B. globosus. For all populations, no difference in hatching rate and offspring survival is detected between the two treatments. Genetic analyses using microsatellite markers conducted in B. truncatus on progeny of paired snails reveal a high selfing rate in spite of high copulation rates, highlighting the difficulties of obtaining outcrossing in highly selfing snails. The high survival of selfed offspring in B. truncatus and B. straminea indicates that inbreeding depression is limited. The extent of inbreeding depression in B. globosus is less clear. Overall, fitness decrease in this species is limited to fecundity. The extent of allozyme polymorphism is very limited whereas a much higher variability is observed with microsatellites. Biomphalaria straminea and B. truncatus populations are also characterized by very low observed heterozygosities and large heterozygote deficiencies, whereas the B. globosus population does not exhibit such a deficiency. Overall these results allow the definition of a self-fertilization syndrome in hermaphrodite freshwater snails: selfing populations (such as those of B. straminea and B. truncatus studied here) are characterized by high selfing rates in spite of copulations, limited deleterious effects of selfing, limited neutral genetic polymorphism, and large heterozygote deficiencies.     

Physiological studies on Biomphalaria alexandrina and Bulinus truncatus,the snail vectors of Schistosommiasis

Summary The Warburg's manometric technique was used to measure the rate of oxygen consumption of the second generation of laboratory-reared snails, Biomphalaria alexandrina and Bulinus truncatus at two temperatures of 25° and 30°C. The individual weight of the experimental snails ranged between 40 and 78 mg for B. alexandrina, between 60 and 90 mg for B. truncatus.At 25°C, the uninfected snails B. alexandrina consumed oxygen at an average rate of 0.096 ± 0.020 ml/g wet wt/hr. The rate of oxygen consumption increased to an average of 0.147 ± 0.008 ml/g wet wt/hr for uninfected snails maintained at 30°C (about 53 per cent increase). The average RW value for uninfected snails maintained at 25°C was 0.80.The snail Bulinus truncatus showed higher oxygen requirements than the snail Biomphalaria alexandrina. At 25°C, it consumed oxygen at an average rate of 0.124 ± 0.016 ml/g wet wt/hr. At 30°C, the rate of oxygen consumption reached a value of 0.220 + 0.006 ml/g wet wt/hr. The average RQ for Bulinus truncatus maintained at 25°C was 0.87.The rate of oxygen consumption of the schistosome — infected Biomphalaria alexandrina snails, maintained at 25°C decreased to an average rate of 0.059 ± 0.010 ml/g wet wt/hr, (an average of 39 per cent decrease). The respiratory quotient (RQ) also decreased to an average value of 0.58. Further research is suggested to clarify the metabolism of both schistosome-infected and uninfected snails.Read at the Ist African Symposium on Bilharziasis, Cairo Egypt, U.A.R., February, 1969.From the Laboratory of Bilharziasis Research, National Research Centre, Dokki, Egypt, U.A.R.     

On the origin of the yolk protein ferritin in snails

Summary The iron storage protein, ferritin, is the major yolk protein in freshwater snails. In this report we show by in vitro labelling experiments that yolk ferritin of the snails Lymnaea stagnalis L. and Planorbarius corneus L. is an exogenous protein synthesized in the midgut gland and secreted into the hemolymph. Gonad and mantle tissue are inactive in the synthesis of yolk ferritin, but, together with the midgut gland, they synthesize another ferritin type (soma ferritin) which is not released into the hemolymph and which may be a housekeeping ferritin. Soma ferritin and yolk ferritin are not in a precursor/product relationship since subunits of both ferritins are synthesized as primary translation products in rabbit reticulocyte lysate programmed with poly (A)⁺ RNA from midgut gland and gonad. Results suggest that both ferritins are synthesized on different mRNAs (and possibly on different genes) so they may be regulated in a different way.     

Monoamines in the albumen gland,plasma, and central nervous system of the snail Biomphalaria glabrata during egg-laying

The potential role of selected biogenic monoamines and related compounds in the reproductive physiology of the freshwater snail Biomphalaria glabrata was investigated. Extracts of the albumen gland (AG), plasma, and central nervous system (CNS) were subjected to high pressure liquid chromatography with electrochemical detection (HPLC-ED), and under the extraction and separation conditions employed the following amines were detected: tyrosine, dihydroxyphenylalanine (DOPA), dopamine, and tryptophan in the AG; DOPA, tyrosine, and tryptophan in the plasma; DOPA, tyrosine, dopamine and 5-hydroxytryptamine in the CNS. These compounds were then quantified in individual samples taken from snails known to be in a particular stage of the egg-laying process. AG dopamine levels were highest in snails in the first stage of the reproductive process, when the AG is secreting perivitelline fluid around each fertilized ovum. Significant decreases in AG protein content during the later stages of the egg-laying process were also evident. Plasma tyrosine and DOPA levels were lowest in snails that contained a fully packaged egg mass, while no changes in monoamine content were observed in the CNS. These data provide insights into the role(s) that monoamines, especially catecholamine-related compounds, may play in B. glabrata reproductive physiology.     

Biochemical Composition of the Eggs of the Freshwater Snail Lymnaea stagnalis and Oviposition-induced Restoration of Albumen Gland Secretion

Summary

Galactogen and protein form the main constituents of the eggs of Lymnaea stagnalis. The amount of galactogen per egg is fairly constant, irrespective of the size of the egg mass or the age of the snail.

The restoration of the albumen gland, which produces the perivitelline fluid for the eggs, was studied in long-day (16 hr light-8 hr dark) snails after spontaneous oviposition. The wet wt of the gland and its galactogen and protein contents are markedly increased within 8 hr and reach a maximum at 32 hr after oviposition. These maxima correspond to the levels determined in snails that did not lay eggs for at least 1 to 2 days. The amounts of galactogen and of protein in the albumen gland are linearly related to the wet wt of this gland.

The restoration period of the albumen gland almost covers the mean egglaying interval. This implies synchronized cycles of albumen storage and egg formation.

The estimated amount of galactogen, released by the albumen gland during egg mass formation, is in accordance with that deposited in the eggs. In contrast, the wet wt of the eggs is 4.6 times higher than that of the released secretory material. Since after oviposition water uptake by the eggs in the egg mass is negligible, the perivitelline fluid, which is released by the albumen gland and surrounds the egg cell, must be diluted in the reproductive tract of the snail prior to oviposition.     

The freshwater snail Bulinus tropicus (Planorbidae) in Namibia, characterised according to chromosome number, enzymes and morphology

Freshwater snails collected in central Namibia, south-western Africa, from 15 populations belonging to the Bulinus truncatus/tropicus complex (Planorbidae) are characterised in respect of their chromosome number, morphology, egg proteins and enzymes. The population samples were all consistently diploid and euphallic. The findings are compared with observations on this group of snails in other areas of Africa. It is concluded that the Namibian populations belong to a single species, B. tropicus (Krauss, 1848), of which B. parietalis (Mousson, 1887) is probably a synonym. No evidence was found of any occurrence of the tetraploid species B. truncatus or of snails belonging to the B. africanus group; lack of a potential intermediate host therefore precludes transmission of Schistosoma haematobium in this area.External Scientific Staff of the Medical Research Council of the UK     

Release of proteins and polysaccharides from the albumen gland of the freshwater snail Helisoma duryi : effect of cAMP and brain extracts

The albumen gland is a compound tubular exocrine gland found in the female reproductive tract of freshwater pulmonate snails such as Helisoma duryi. It secretes a perivitelline fluid, composed of protein and polysaccharide complexes, and coats each fertilized egg. A 288-kDa native glycoprotein, composed of several 66-kDa subunits, was identified in soluble extracts of albumen gland. Forskolin stimulates the release of secretory granules, containing both proteins and polysaccharides, from the cytoplasm of the glandular cells. An acid extract of the central nervous system or the adenosine-3′,5′-cyclic monophosphate (cAMP) analogue 8-bromo cAMP, stimulates protein secretion from the gland. Pretreatment of the albumen gland with cAMP antagonist (R_p isomer of cAMP) inhibits the stimulatory effect of a brain extract. Digestion of brain extract with proteolytic enzymes abolishes its activity, suggesting the factor from the brain is peptidergic. The neuroactive agents serotonin, Phe-Met-Arg-Phe-amide, Tyr-Gly-Gly-Phe-Met-Arg-Phe-amide, small cardioactive peptide B, and caudodorsal cell hormone were also tested for potential secretion-promoting ability. Brain extracts were partially purified with a Sep-Pak C₁₈ reverse-phase cartridge and indicate the peptide is relatively hydrophobic. These results suggest that a brain peptide promotes the secretion of perivitelline fluid, and this is mediated by the adenylate cyclase/cAMP signal transduction pathway. Accepted: 19 December 1997     

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.     

The effect of temperature,darkness, starvation and various food types on growth,survival and reproduction of Helisoma duryi,Biomphalaria alexandrina and Bulinus truncatus (Gastropoda: Planorbidae)

Helisoma duryi has been proposed as a biological control agent in schistosomiasis due to its superiority in laboratory competition experiments with various species of the intermediate host snails. Therefore it was considered important to evaluate the response of this snail species and the intermediate host species, Biomphalaria alexandrina and Bulinus truncatus, to various physical, chemical and biological factors under laboratory conditions in order to obtain information on the similarities in the ecological niches of these species. The factors considered in the present paper are: temperature, darkness, starvation and food. All three species had optimal growth and egg laying at 26–28 °C. Only H. duryi survived for a longer period at 33°C and it was capable of starting egg laying at this temperature although the onset was delayed. However, low temperature (18°C) caused a relatively larger decrease in egg laying of H. duryi than in the other two species. Growth and egg laying was reduced for H. duryi and B. truncatus kept under darkness and B. alexandrina could not tolerate maintenance under darkness. A few days of starvation of juvenile snails had no effect on later growth and egg laying capacity of the survivors, although mortality in B. truncatus was increased. B. alexandrina had a lower tolerance to starvation than the other two species. Egg laying of snails fed only one of the three laboratory food types decreased for all three species in the order: Vov-vov (dog food in dry pellets), Tetramin (fish food) and lettuce. Combinations of lettuce and one or more proteinaceous food types gave optimal growth and egg laying for all three species.     

Histochemistry and ultrastructure of the albumen gland duct of the prosobranch gastropod Pomacea paludosa

Summary

The albumen gland duct passes through the base of the albumen gland. It consists of a single layer of cells composed of ciliated and secretory cells. Sulfated and non-sulfated acid mucopolysaccharides are secreted by the cells of the albumen gland duct. Cell resembling neurosecretory cells are also found between the ciliated and secretory cells. The secretion products probably contribute to the formation of the albumen layer which surrounds the fertilized egg.     

Dopaminergic neurons in the brain and dopaminergic innervation of the albumen gland in mated and virgin helisoma duryi (mollusca: pulmonata)

Background

Dopamine was shown to stimulate the perivitelline fluid secretion by the albumen gland. Even though the albumen gland has been shown to contain catecholaminergic fibers and its innervation has been studied, the type of catecholamines, distribution of fibers and the precise source of this neural innervation has not yet been deduced. This study was designed to address these issues and examine the correlation between dopamine concentration and the sexual status of snails.

Results

Dopaminergic neurons were found in all ganglia except the pleural and right parietal, and their axons in all ganglia and major nerves of the brain. In the albumen gland dopaminergic axons formed a nerve tract in the central region, and a uniform net in other areas. Neuronal cell bodies were present in the vicinity of the axons. Dopamine was a major catecholamine in the brain and the albumen gland. No significant difference in dopamine quantity was found when the brain and the albumen gland of randomly mating, virgin and first time mated snails were compared.

Conclusions

Our results represent the first detailed studies regarding the catecholamine innervation and quantitation of neurotransmitters in the albumen gland. In this study we localized catecholaminergic neurons and axons in the albumen gland and the brain, identified these neurons and axons as dopaminergic, reported monoamines present in the albumen gland and the brain, and compared the dopamine content in the brain and the albumen gland of randomly mating, virgin and first time mated snails.     

THE HISTOCHEMICAL LOCALIZATION OF PHOSPHATASES AND ESTERASES IN AUST RALORBIS GLABRATUS

The presence and distribution of two groups of enzymes has been determined histochemically on sections of the schistosome-bearing snail Australorbis glabratus. By the use of specific inhibitors, attempts have been made to characterize further the enzymes occurring in the various organs and tissues.
As a result of this study it has been found that alkaline and acid phosphatase are widely distributed but have identical localizations only in the kidney and albumen gland. Both enzymes react typically to the action of the usual inhibitors.
Among the non-specific esterases. an enzyme corresponding to the mammalian A-type esterase (aromesterase) is present in the brain; while a B-type esterase (aliesterase) is located in the digestive gland, intestine, and on the glandular region of the foot surface.
A "true" lipase (an esterase acting on an undissolved substrate) is found principally in the albumen gland, with an indication of its presence in the digestive gland and in portions of the digestive tract.
An enzyme with the properties of an acetylcholinesterase occurs in the radula sac, oesophagus, preputium, junction of carrefour and oviduct, and amoebocytes. A positive reaction for cholinesterase is also obtained with frozen sections of brain but, although this enzyme has been shown biochemically to hydrolyse acetylcholine and is inhibited by low concentrations of eserine. it is remarkably resistant to the action of organophosphorous compounds, and its true nature cannot he stated with certainty.     

Distribution of freshwater snails in the river Niger basin in Mali with special reference to the intermediate hosts of schistosomes

Snail surveys were carried out in various parts of Mali. All areas surveyed are part of the Niger basin being either affluents or irrigation schemes fed by this river. The snail species present varied greatly between areas. The following potential hosts of schistosomes were recorded: Biomphalaria pfeifferi, Bulinus truncatus, B. globosus, B. umbilicatus, B. forskalii and B. senegalensis. In the large irrigation schemes, i.e. ‘Office du Niger’ and Baguinéda, only B. pfeifferi and B. truncatus appear to be intermediate hosts. Snail distribution appeared to some extent to be focal and high snail densities appeared to be associated with human water contact activities, which apparently create favourable biotopes for the snails. This is probably due to an alteration of the vegetation and an increase of the trophic status of the site by contamination with food remnants and other debris. The larger irrigation canals or lakes in these schemes play an important role in the transmission of human schistosomes and transmission appears to be very focal in these habitats. Infected snails are almost exclusively found in well-defined human water contact sites (WCS). Local infection rates with schistosomes were often high (i.e. up to 27% in B. pfeifferi). In urban areas (i.e. Bamako), transmission patterns are more variable. In Bamako schistosome-infected B. truncatus were found in the Niger river. A number of smaller semi-permanent or permanent streams are very important transmission sites, and schistosome infections were recorded from B. pfeifferi, B. truncatus and B. globosus. Schistosome infection rates in B. pfeifferi were often high (up to 30%). In a new lake at Sélingué, B. truncatus was found to be widely distributed only about a year and a half after the dam was constructed, and in some sites schistosome infections were recorded.     

The connective tissue index of <Emphasis Type="Italic">Helix aspersa</Emphasis> as a metal biomarker

The digestive gland of adult land snails, Helix aspersa, sampled from four different sites in São Miguel island (Azores) was submitted to chemical analyses, autometallography and haemalum/eosin staining, in order to quantify the relative abundance of heavy metals, calcium cells and connective tissue cells. Metals were visualized, through light microscopy, as black silver deposits mostly in the connective tissue cells. Metal levels, essentially of Cu and Fe, were related to the relative volumetric density of connective tissue cells but not to the relative volumetric density of calcium cells from the digestive gland epithelium. Thus, the connective tissue index presented herein is suggested as a biomarker of Cu exposure in terrestrial mollusks.     

The UDP-galactose 4-epimerase of the albumen gland of Lymnaea stagnalis and the effects of photoperiod,starvation and trematode infection of its activity

• 1.1. Kinetic aspects of the enzyme UDP-galactose 4-epimerase in crude homogenates of the albumen gland of the snail Lymnae stagnalis were estimated. The mean values of the Km for UDP-galactose and for NAD are 0.343 and 0.097 mM, respectively. The enzyme is inhibited by NADH. It is inactivated by freezing and raised temperature (25°C), but it can be reactivated by NAD.
• 2.2. In the albumen gland the epimerase activity is 10–100 times higher than in other tissues, reflecting the high turnover of glucose to galactose, essential for the synthesis of galactogen in this organ.
• 3.3. In fed snails long day conditions stimulates albumen gland epimerase activity, coinciding with high egg production.
• 4.4. In starved snails a fairly high residual activity of the enzyme is maintained, irrespective of photoperiod or egg production.
• 5.5. Trematode infection leads to a considerable reduction of the epimerase activity.
• 6.6. The results indicate that the epimerase activity in fed snails, when the gland shows a regular release, reflects long-term adaptations (photoperiod). In starved and parasitized snails, when no regular release or product occurs, a basic epimerase activity is maintained. This might be important for a rapid restoration of egg production after the termination of adverse conditions.

     

Morphological and histological study of the genital ducts ofCryptazeca monodonta (Pulmonata,Orthurethra), with special emphasis on the auxiliary copulatory organ

Summary The genital system ofCryptazeca monodonta is very similar to those reported for semidiaulic stylommatophores, but with some specific features. The fertilization pouch is simple and surrounded by subepithelial goblet gland cells. The spermoviduct has two different grooves: the oviductal channel and the spermatic groove, which run together with a blind-ending allospermiduct that opens into the lumen of the free oviduct. The vagina has a thick muscular wall with numerous pigmentary cells embedded in it. The vas deferens diverges from the spermiduct and becomes mainly glandular just before it joins the penis. This genital system is equipped with an auxiliary copulatory structure that consists of two independent and complementary organs. One of them is located just before the fusion of the free oviduct and the spermatheca stalk lumina and consists mainly of a thick mass of connective tissue. The other is a muscular sarcobellum located inside the penis. Both these organs are covered by small papillae whose connective cells are stacked. Each papilla has a solid spine on its top, which seems to be of mesenchymatous origin. As in other stylommatophores, the auxiliary copulatory organ is equipped with an adjoining gland, which inCryptazeca is next to the sarcobellum.Abbreviations ACO auxiliary copulatory organ - ag albumen gland - al allospermiduct - c connective aggregate of ACO - cc connective cells of ACO papillae - cf connective fibres - ep epiphalus - fo free oviduct - fp fertilization pouch - gl.c gland cells of sarcobellum - hd hermaphroditic duct (distal portion) - m muscle fibres - ov oviduct - p penis - pc penial caecum - pp papillae of ACO - pr prostatic gland - prm penial retractor muscle - p.sh penial sheath - s spermatheca - sc sarcobellum - SEM scanning electron micrograph - sov spermoviduct - sp spine - spd spermiduct - ss spermatheca stalk - v vagina - vd vas deferens     

DEVELOPMENT OF ACCESSORY SEXUAL ORGANS IN BIOMPHALARIA GLABRATA (PLANORBIDAE) IN RELATION TO TIMING OF INFECTION BY SCHISTOSOMA MANSONI: CONSEQUENCES FOR ENERGY UTILIZATION PATTERNS BY THE PARASITE

The growth rates of ovotestis and individual accessory sexualorgans (ASO) of Biomphalaria glabrata snails were studied forcontrols and for immature and mature snails infected with Schistosomamansoni. The infection of immature B. glabrata strongly delaysgrowth of the ovotestis and inhibits the development of theaccessory sexual organs. There is no significant differenceup to 2 weeks post infection in the volume of the ovotestisand the ASO between mature infected B. glabrata and controlsnails. From 3 to 4 weeks post infection there was a reductionin the volume of the ovotestis and the ASO of infected matureB. glabrata; then growth of the ovotestis, albumen gland andfemale organs was stopped, but the effect of infection was lessconsistent for the male organs. For a parasite, immature andmature snails have to be considered as two different resourceenvironments, each having at infection time a particular patternof resource allocation, towards growth for juvenile and towardsreproduction for adult snails, changing the possible energyutilization patterns which can be used by the trematode. (Received 29 January 1993; accepted 22 April 1993)