THE REPRODUCTIVE ANATOMY OF PAROPEAS ACHATINACEUM AND A NEW CONCEPT OF PAROPEAS (PULMONATA: ACHATINOIDEA: SUBULINIDAE)

The majority of subulinid land snails are known only as shellsand generic groupings need to be revised on the basis of theirinternal anatomy. Paropeas achatinaceum (new combination) isa synanthropic subulinid that is widely distributed around theIndo-Pacific region. Features of the genital anatomy and radulademonstrate that Paropeas should be rejected as a subgenus ofProsopeas and be recognised as a distinct genus. The radulaof Paropeas is more typical of a subulinid than is that of Prosopeaswhich proves to be highly modified for a carnivorous diet. Thespermatophore of Paropeas is inserted directly into the oviductwhere it releases sperm through its porous tail before beingdigested in the bursa copulatrix. (Received 23 September 1992; accepted 11 November 1993)     

High level of sperm competition may increase transfer of accessory gland products carried by the love dart of land snails

Postcopulatory adaptations that increase reproductive success compared to rivals, like the transfer of accessory gland products that promote paternity, are common when sperm competition occurs among males. In land snails, the dart shooting behavior and its adaptive significance, in promoting individual fitness through enhanced paternity of the successful dart shooter, have been considered such an adaptation. The fitness result gained is mediated by the transfer of mucus components on the love dart capable of altering the physiology of the receiver's reproductive tract. In this context, dart shooting and mucus transfer could be considered as processes targeted by sexual selection. While the effect of dart mucus is beneficial for the dart user, so far it has remained unknown whether its transport is greater when snails experience a higher level of sperm competition. Here, we report results of a study on inter‐ and intraspecific variations of dart and mucus gland morphometry, considered to be traits reflecting the ability of snails to adjust the production and transfer of mucus under varying sperm competition scenarios. We investigated four populations with different densities from four dart‐bearing species, Arianta arbustorum, Cepaea nemoralis, Cornu aspersum, and Helix lucorum. The results indicate that different adaptations of these traits occur among the studied species that all seem to achieve the same goal of transferring more mucus when sperm competition is higher. For example, the presence of longer and more branched mucous glands or an increase in dart surface most likely reflect increased mucus production and enhanced ability of mucus transport, respectively. Interestingly, the species for which the use of the dart is reported to be facultative, A. arbustorum, did not show any variation among the examined traits. To conclude, sexual selection in the form of sperm competition intensity seems to be an important selective force for these simultaneously hermaphroditic dart‐bearing snails, driving differences in sexual traits.     

COMPARATIVE LIFE-CYCLE, BIOMASS AND SECONDARY PRODUCTION OF THREE SYMPATRIC FRESHWATER GASTROPOD SPECIES

The life cycles, biomass and secondary production of three sympatricfreshwater basommatophoran snails, Lymnaea palustris (MÜller),Physa fontinalis Linnaeus and Anisus rotundatus (Poiret) werestudied during two years in a freshwater ditch. L. palustrisexhibited an iteroparous life-cycle whereas the two other speciespresented a semelparous life-cycle, adults died just after oviposition.L. palustris secondary production (dry weight) value was higher(P = 11 298.4 mg 0.1 m^–1 yr^–1) than those of P.fontinalis (P = 846.3 mg 0.1 m^–2 yr^–1) and A. rotundatus(P = 1192 mg 0.1 m^–2 yr^–1). (Received 16 March 1992; accepted 30 June 1992)     

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)     

FIELD OBSERVATIONS ON FEEDING OF THE LAND SNAIL HELIX ASPERSA MULLER

Feeding of the land snail Helix aspersa (Müller) was observedat monthly intervals. Three natural populations in Galicia (NW-Spain)were studied. At two sites only a few plants constituted thebulk of the diet and in spring the snails' diet had the highestdiversity (H'). In the third population feeding and distributionof Helix aspersa (Müller) were observed in a small plotwith permanent patches of Urtica dioica. Nearly one half offeeding snails fed upon Urtica dioica. Most of the other observations wereon Mentha suaveolens, Ranunculus repens and Gramineae. The diversity ofthe snails' diet showed seasonal variation with the maximumin the autumn months. Comparison between the availability ofthe different plant species and their contribution to the snails'diet showed that the snails did not eat at random; Urtica dioicawas eaten much more than expected from its occurrence and grasseswere strongly under-represented in the snails' diet. Temporalchanges of availability were significantly correlated with the amountseaten in the case of Urtica, but not for the other food plants.The distribution of the snails in the plot was significantlycorrelated with that of Urtica. Chemical analyses of the foodplants revealed Urtica as the species with the higher protein,ash and calcium contents. The strong preference of Helix aspersafor Urtica dioica could be explained by the value of Urticaas food or by its suitability as habitat for the snails. The largestproportions of green material in the snails' diet occurred inthe spring and juveniles ate more green material than adultsin the three populations. (Received 16 March 1998; accepted 30 November 1998)     

The mixed-species chorus as public information: tungara frogs eavesdrop on a heterospecific

Multispecies choruses represent a promising but uninvestigatedforum for public information. Although frogs exposed to a potentialpredator call more readily in the presence of conspecific callsthan in their absence, none are known to make comparable useof heterospecific calls. To test for heterospecific eavesdropping,we isolated calling male túngara frogs (Physalaemus pustulosus),presented them with a potential predator, and recorded theirresponses to playbacks of 1 of 4 stimuli: calls of a conspecific,a sympatric heterospecific (Leptodactylus labialis), an allopatriccongener (Physalaemus enesefae), or silence. We found that malescalled more in response to the L. labialis call than to eitherthe silent stimulus or the P. enesefae call. In contrast, theP. enesefae call did not result in significantly more callingthan the silent stimulus. The conspecific call was the mosteffective at promoting calling. The data indicate that túngarafrogs selectively attend to the call of a heterospecific. Wehypothesize that such heterospecific eavesdropping contributesto the emergent behavior of mixed-species choruses.     

BIOCHEMICAL COMPOSITION OF HELIX SNAILS: INFLUENCE OF GENETIC AND PHYSIOLOGICAL FACTORS

This paper describes the biochemical composition of differentspecies (Helix lucorum, Helix pomatia) and sub-species of snails(Helix aspersa aspersa, Helix aspersa maxima) reared in thesame conditions with a feed (‘Helixal’) speciallydesigned for edible snails. In addition, the composition ofwild H. pomatia and H. lucorum is presented to allow comparisonbetween snails of different origins. Analyses determined thepercentages of proteins, lipids and minerals. They reveal bothsimilarities and differences in composition according to thespecies and the part analysed (whole body, pedal mass, and visceralmass). H. pomatia contains the highest percentage of mineralmatter and the lowest percentage of lipids. Surprisingly, proteincontents are slightly different between artificially rearedH. aspersa maxima of 3 months old and wild H. pomatia. The resultsmake it possible to evaluate nutritional quality of snails withthe composition of the body of four edible snail species. (Received 16 September 1996; accepted 24 May 1997)     

INFLUENCE OF THE QUINOLIZIDINE ALKALOID CONTENT OF LUPINUS ALBUS (FABACEAE) ON THE FEEDING CHOICE OF HELIX ASPERSA (GASTROPODA: PULMONATA)

Adult Helix aspersa snails were maintained individually forone week in plastic cages with 9 living Lupinus albus plantsas their only food. Among these 9 plants, 3 chemotypes bitter,intermediate and sweet which differed in their alkaloid contentwere equally represented. Each day, the leaf surface grazed and the number of leaves attackedby the snails were recorded for each chemotype and each snail.A consumption/ attack (C/A) ratio was calculated by dividing thesurface grazed (C) by the number of attacks (A). The numberof attacks and the grazed area were positively correlated foreach chemotype during the whole experiment, and the snails atesimilar quantities of lupin each day. After 4 and 6 days ofexperiment, we noticed a rejection of the bitter chemotype infavor of the intermediate and sweet ones respectively. Afterthe 6th day, the surface grazed per attack was significantlyhigher on the sweet chemotype than on the bitter plants. Wehypothesize that rejection of the bitter chemotype might berelated to (i) an alkaloids reaction threshold associated withan increase in the amount of alkaloids in the wounded plantsand/or (ii) aversive ingestive conditioning. (Received ; accepted 16 April 1999)     

ULTRASTRUCTURAL LOCALIZATION OF COMPLEX CARBOHYDRATES AND PHOSPHATASES IN DIGESTIVE GLAND CELLS OF FEEDING AND HIBERNATING SNAILS, HELIX LUCORUM (GASTROPODA: HELICIDAE)

The digestive gland of normally-fed snails Helix lucorum, aswell as that of snails which had hibernated for 4 months wereexamined by the use of cytochemical techniques for detectionof acid and alkaline phos-phatase, as well as of periodate-reactive(PA-TCH-SP technique), sulfated (HID-TCH-SP technique) and carboxylatedcarbohydrates (LID-TCH-SP technique). The cytochemical resultssupport the hypothesis of intracellular digestion via lysosomalactivity of material taken up by endocytotic processes by thecells of the digestive gland. Four months hibernation did notaffect the intracellular distribution of polysac-charides andphosphatases in the cells of the digestive gland of H. lucorumcompared to that in the control snails. In addition, hibernationaffected the percentage of the calcium cells which significantlyincreased compared to the non-hibernating snails, whiie thepercentages of the digestive and excretory cells remained almoststable. However, the periodate-reactive sulfated and carboxylatedpolysaccharides of the digestive gland cells decreased in thehibernated snails compared to the controls. The results suggestthat the cytochemistry of periodate-reactive, sulfated and carboxylatedpolysaccharides used in the present study could, also, be appliedto the study of lysosomal activities. (Received 1 October 1991; accepted 4 December 1991)     

NATURAL HISTORY AND POPULATION DYNAMICS OF THE LAND SNAIL HELIX TEXTA IN ISRAEL (PULMONATA: HELICIDAE)

Helix texta is endemic to the Mediterranean regions of Israel.It has a seasonal activity pattern which starts in the autumn,with the first rains, and dwindles towards the spring, whenthe snails dig into the ground for a six months long aestivation.A cold spell of 0°C will, however, terminate the activeseason of the adult snail, even in the middle of the rainy season.Survival of the young is very low and most of them (90%) donot survive their first year, because of the winter cold andthe summer drought. Massive predation of adult snails by wild boar was observedin December 1986: within a few days, about 50% of the adultsin the study in the area were eaten. A very rapid growth ofyoung and subadults was observed immediately after this predation.These observations suggest that the extent of recruitment ofnew adults to the population may be partly controlled by existingadults, through a growth-inhibiting pheromone in the mucus.After predation this inhibiting factor disappears, enablinga subsequent rapid growth of the young. In this manner, massive,irregular predation of the adults by a large predator, and changesin juvenile survival, result in sharp fluctuations in the agestructure of the population. The resulting pattern of unstablepopulation dynamics is different from that described for theEuropean species of Helix. (Received 16 January 1989; accepted 17 April 1989)     

DISTRIBUTION AND PRODUCTION OF THREE HYDROBIA SPECIES (GASTROPODA: HYDROBIIDAE) IN A SHALLOW COASTAL LAGOON IN THE BAY OF CADIZ, SPAIN

The abundance, life span, growth and production of the mud snailsHydrobia minoricensis, H. ulvae and H. ventrosa in a semi-naturallagoon system were studied by taking monthly samples at threesites during 1991 and 1992. The most abundant species, H. minoricensisoccurred at mean densities of 12834 to 26264 snails m^–2(10.7 to 25.8g dry weigh m^–2), depending on the site.The least abundant species, H. ulvae, occurred at mean densitiesof 185 to 353 snails m^–2 (3.2 to 2.2g dry weight m^–2).The numerical abundance and biomass of the three Hydrobia specieswere positively related to the biomass of benthic macroalgae(P<0.01). Although H. ulvae egg capsules were recorded throughoutthe year, newly hatched snailsof this species were not observed,in contrast to the other two species. The early spring and summercohorts of H. minoricensis and H. ventrosa seemed to be themost numerous. The average life spans of these two species wereestimated to be about 18 and 13 months respectively. Annualproduction estimates for the whole lagoon system were 29.0 (6.3),5.5 (0.8) and 5.2 (1.0)g dry weight (ash-free dry weight) m^–2yr^–1 for H. minoricensis, H. ulvae and H. ventrosa respectively.The annual P/B ratio was about 2 for H. minoricensis and H.ventrosa. (Received 5 July 1994; accepted 5 October 1994)     

LIFE HISTORY AND POPULATION DYNAMICS OF COCHLICELLA ACUTA (MuLLER) (GASTROPODA: HELICIDAE) IN A PASTURECEREAL ROTATION

The conical snail Cochlicella acuta was sampled over a 3-yearperiod in a pasture-cereal rotation and a nearby roadside wastelandat Hardwicke Bay, South Australia. The life cycle of C. acuta was primarily biennial in the agriculturalfields, with offspring being produced in large numbers in thepasture phase but not the cereal phase of the rotation. Thebreeding season lasted from autumn to spring. Snails were mostabundant in spring and summer, especially near the edges offields. During summer, snails aggregated on robust weeds suchas Reseda lutea. Many snails were killed by burning pasturesin autumn, prior to sowing crops. Snails were more abundantand smaller in size in the roadside wasteland than in the agriculturalfields. Strategies for the control of C. acuta in pasture-cereal rotationsare discussed. (Received 9 April 1990; accepted 10 August 1990)     

RELATIVE IMPORTANCE OF AIRBORNE ODOURS AND TRAILS IN THE GROUP HOMING OF LIMACUS FLAVUS (LINNAEUS) (GASTROPODA, PULMONATA)

The relative importance of airborne odours and con-specifictrails in the group homing of Limacus flavus has been studiedin the laboratory using an Y-olfac-tometer and trail followingtests. The slugs showed positive anemotaxis along air flowspassing through shelters inhabited or recently inhabited byconspecifics. In the choice between single and group shelters,the animals headed preferentially towards the latter ones. L.flavus is able to discriminate between conspecific and heterospecific(Limax maximus) shelters. Trail following tests failed to showsignificant trail superimposition, but did show a significantdeflection of the test slug path towards the marker after crossing.In direct comparison, distant chemoreception prevailed overtrail following in the orientation towards conspecifics (Received 10 August 1987;     

THE PHYSIOLOGICAL EFFECTS OF AQUEOUS SUSPENSIONS OF PLANT MOLLUSCICIDES ON HELISOMA DURYI (GASTROPODA: PLANORBIDAE)

The behavioural and physiological responses of Heltsoma duryito solutions of three South African medicinal, mollusricidalplants (Warburgia salutans, Gardenia thunbergia and Apodytesdimidiata subsp dimidiata) were investigated. Clinical signsof toxic-lty, oxygen consumption, heart rate and water uptakewere used to assess response to these mollus-cicides. All plantsproduced symptoms characteristic of the distress syndrome describedby Harry & Aldrich (1963). Haemolysis, however, occurredonly in response to extracts of G. thunbergia. Respiratory failurein snails exposed to the W. salutans and G. thunbergia did notappear to be the primary cause of mortality. All plants produceda significant lowering of heart rate at lethal concentrations.Water unbalance, which is a commonly suggested effect, did notoccur. The difficulty of inferring mode of action from observedeffects is emphasized. Although some responses are common tothe three plant mollusci-cides under investigation, the differencesclearly indicate the potential for alternative modes of action. (Received 14 November 1995; accepted 17 April 1996)     

GROWTH, MORTALITY, AND FEEDING RATES OF THE SNAIL HELIX ASPERSA AT DIFFERENT POPULATION DENSITIES IN THE LABORATORY, AND THE DEPRESSION OF ACTIVITY OF HELICID SNAILS BY OTHER INDIVIDUALS, OR THEIR MUCUS

When reared at high densities, young Helix aspersa show lessshell growth, even if waste products are removed. They alsofeed less, and show increased mortality. It is suggested thatthese effects are linked to reduced activity. Juveniles showreduced activity in the presence of adults or their mucus. Mucusof adult Cepaca nemoralis also depresses the activity of bothadult and young Helix and Cepaea. ^* Present Address: Unit Zoologi, Universiti Kebangsaan Malaysia,Jalan Pantai Baru, Kuala Lumpur, West Malaysia. (Received 12 May 1981;     

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)     

Avoiding a compromise between sexual selection and species recognition: female swordtail fish assess multiple species-specific cues

Females increase their risk of mating with heterospecifics whenthey prefer the traits of conspecifics that overlap with traitsfound in heterospecifics. Xiphophorus pygmaeus females havea strong preference for larger males, which could lead to femalespreferring to mate with heterospecific males; almost all sympatricX. cortezi males are larger than X. pygmaeus males. In thisstudy, we show that X. pygmaeus females preferred the chemicalcues from conspecifics over those of X. cortezi males. However,preference for the chemical cues of conspecifics could not reversethe preference for larger heterospecific males. Only when femaleswere presented with two species-specific cues (vertical barsand chemical cues) did more females spend more time on averagewith the smaller conspecific males. These results support the"backup signal" hypothesis for the evolution of multiple preferences;together, the two species-specific cues increased the accuracywith which females were able to avoid heterospecific males.In addition, the results suggest that in those situations inwhich the traits of conspecifics overlap with traits found inheterospecifics, females can use the assessment of multiplecues to avoid mating with heterospecifics without compromisingtheir preference for the highest-quality conspecific.     

GENETIC AND MORPHOLOGICAL VARIATION OF POPULATIONS BELONGING TO THE BULINUS TRUNCATUS/TROPICUS COMPLEX (GASTROPODA; PLANORBIDAE) IN SOUTH WESTERN ZIMBABWE

Aquatic snails from south western Zimbabwe belonging to theBulinus trunscatus/tropicus complex vary widely in shell formsuggesting that more than one taxon could be present. This possibilitywas investigated by making observations on snail samples from13 populations from the Plumtree area, in respect of allozymevariation (5 polymorphic loci), shell morphology (9 variables),copulatory organ and chromosome number. Comparative data wereobtained from snails from north western Zimbabwe identifieddefinitely as B. tropicus. Analysis of the genetic structurerevealed a high degree of polymorphism (P) ranging from 0.29–0.80among populations from Plumtree and expected heterozygosity(H_e) from 0.02–0.22. No enzymatic diagnostic loci werefound which could differentiate the different morphs or populationsand discriminant function analysis on the morphological datashowed an overlap of morphs among populations. Snails analyzedfor chromosome number were all diploid (2n = 36). Snails exposedto Schistosoma haematobium mira-cidia were all refractory. Thisinformation supports the view of a single species, B. tropicus,which is differentiated due to migration barriers and whereenvironmental variables might be implicated in the morphometricdivergence. (Received 31 July 1995; accepted 15 January 1998)     

THE INFLUENCE OF FOOD DEPRIVATION ON THE LOCOMOTOR ACTIVITY OF SLUGS

Experimental animals used in studies of feeding behaviour areusually starved prior to observation, although little is knownof the behavioural effects of such pre-experimental treatment.This study investigated the effect of food deprivation on thelocomotor activity of two species of slugs, Deroceras reticulatumand Milax budapestensis. Locomotor activity was measured bythe quantitative assessment of mucus trails. The more surfaceactiveD. reticulatum showed a marked increase in its locomotoractivity when deprived of food, whereas the locomotor activityof M. budapestensis decreased. The implications of the resultsare discussed in relation to the ‘life-styles’ ofthe two species and the possible implications for the controlof slugs in the potato crop. ^*Present address: 59 Valley Park Drive, Clanfield, Hants. PO80PL. (Received 24 May 1986;     

Shell-Boring Mechanism of the Gastropod, Purpura (Thais) lapillus: a Physiological Demonstration of the Role of Carbonic Anhydrase in the Dissolution of CaCO3

Measurement of carbonic anhydrase (CA) activity in homogenatesof accessory boring organs of the muricid gastropod,Purpuralapillus, by Meldrum and Roughton's manometric method showedthat CA is always present in boring as well as in inactive ABOs,but in variable amounts. Tests by the same method on whole ABOsin an isotonic solution were negative, proving that CA remainsintracellularly. Experiments in vivo on inhibition and activation demonstratedclearly that CA is responsible for demineralization of the valvesof lamellibranchs by Purpura:(a) at low concentrations of Diamox,partial inhibition of the enzymeoccurred, that is, the numberof complete holes decreased or disappeared and etchings increased;and at higher concentrations full inhibition took place. Inhibitionis reversed when snails are replaced in normal sea water; (b)action of pure CO₂ or mixtures of CO₂ and O₂ accelerated boring:in the optimal mixture, three times more boreholes were producedby snails than in the controls, and in about half the time.Under these conditions the reaction catalyzed by CA goes tothe right with hydration of CO₂ and is accompanied by releaseof H⁺ ions; in the presence of an increased concentration ofCO₂, the reaction is intensified and results in an additionalrelease of H⁺ ions. Consequently, destruction of CaCO₃ by theABO of Purpura in sea water enriched with CO₂ is accelerated. To identify the nature of the exchanged ion, we tested the effectof NaCl and KC1 on the boring mechanism in vivo by increasingthe amount of these salts in the seawater of snails with prey.In this case augmentation of the boring activity was noticed.These results suggest that the boring activity is accompaniedby complex ionic exchanges.