Prosobranch Snail Research Articles

Spontaneous and hybrid origins of parthenogenesis in Campeloma decisum (freshwater prosobranch snail)

Spontaneous and hybrid origins of parthenogenesis in Campeloma decisum (freshwater prosobranch snail)

Predation of Biomphalaria and non-target molluscs by the crayfish Procambarus clarkii: implications for the biological control of schistosomiasis.

The North American crayfish Procambarus clarkii was examined under laboratory conditions for its ability to prey on Biomphalaria pfeifferi and B. glabrata, molluscan intermediate hosts of human schistosomiasis, and other, non-target gastropod species. Both male and female adult crayfish significantly reduced survival of neonate snails, even though alternative animal and plant foods were both available. In subsequent experiments, no differences in snail consumption were detected, for either adult or juvenile crayfish, in the presence or absence of a plant food alternative. Both adult and juvenile crayfish were able to consume small (2.5 mm) and large (17.5 mm) B. glabrata, suggesting that no size refuge from predation exists. Both adult and juvenile crayfish consumed Biomphalaria egg masses, although this consumption was significantly greater for juveniles. Procambarus clarkii adults were unable to consume substantial numbers of the relatively thick-shelled prosobranch snails Pila ovata and Lanistes carinatus. Crayfish did consume a third prosobranch, Melanoides tuberculata, and the pulmonate snail Physa acuta, but at a lower rate relative to consumption of Biomphalaria. Physa acuta, itself of North American origin, responded to the presence of crayfish by rapidly leaving the water and thereby avoided predation. Implications of these results for the biological control of schistosome-transmitting snails in East Africa are discussed.

Growth, food and respiration in the prosobranch snailPotamopyrgus jenkinsi(E. A. Smith) (Hydrobiidae, Mollusca)

Growth, food and respiration in the prosobranch snail<i>Potamopyrgus jenkinsi</i>(E. A. Smith) (Hydrobiidae, Mollusca)

Eradication of a sylvatic focus of Schistosoma mansoni using biological control by competitor snails

Abstract The Grand Etang Lake on the island of Guadeloupe (West Indies) is a sylvatic focus for Schistosoma mansoni Sambon,1907, characterized by surrounding populations of heavily infected Rattus rattus Linne, 1758, a low infection rate of an intermediate snail host, Biomphalaria glabrata (Say, 1818), and the absence of permanent human residents. In 1976, the prosobranch snail Ampullaria glauca (Linne, 1758) was accidentally introduced into the lake and caused a strong regression of the floating plant Pistia stratiotes L., which constituted the habitat of B. glabrata. Concomitantly, a rapid decline of murine schistosomiasis took place, and the parasite completely disappeared from around the lake by 1985. In 1987, a resurgence of the parasite was observed and a competitor/predator snail, Marisa cornuarietis (Linne, 1758), was introduced into the lake. Colonization by M. cornuarietis was rapid, and by 1989, the remaining associated P. stratiotes/B. glabrata colonies were eliminated, as was the S. mansoni infection in rats. Sampling carried out in 1990 and 1991 confirmed the eradication of both the snail host and its parasite.

Marine invasion processes: interactions between native and introduced marsh snails

We test two hypotheses to explain the success of a biological invader in marshes on the Pacific coast of North America. The first hypothesis focuses on the competitive superiority of an invading species over native species; the second hypothesis focuses on the absence of ecological equivalents in the aboriginal biota, such that no competitive interactions are necessary to facilitate successful invasion. As a model system we experimentally manipulated the introduced pulmonate snail Ovatella myosotis and the native prosobranch snails Assiminea californica and Littorina subrotundata. Manipulations included pair-wise enclosures to determine of Ovatella depressed the growth of the native;species; pair-wise associations to determine whether or not snails demonstrated negative or positive clustering; removal experiments to see if native snails invaded regions occupied by Ovatella, and reciprocal transplants on a vertical gradient to determine the physiological breath of the target species. In addition to monitoring population abundances of all three species seasonally, dietary overlap of these gastropods was also examined. No evidence of competitive superiority by Ovatella was found. Ovatella possesses the physiological capacities to exist in a semiterrestrial environment and is therefore able to take advantage of resources unavailable to native gastropods. We conclude that the successful establishment of this Atlantic snail in the Pacific Northwest did not arise at the expense of native species.

On the Evolutionary Stability of Dispersal to Sink Habitats

On the Evolutionary Stability of Dispersal to Sink Habitats

EFFECTS OF HERBIVORE SIZE AND HUNGER LEVEL ON PERIPHYTON COMMUNITIES1

ABSTRACTThe effects of herbivore size and hunger level were tested on lotic periphyton community structure and ash‐free dry mass (AFDM). My hypotheses were 1) that small herbivores would remove more periphyton per unit biomass than large herbivores of the same species because of energetic demands and 2) that within the same size class, starved herbivores would remove more periphyton than nonstarved herbivores. The herbivore used was the prosobranch snail Elimia clavaeformis Lea. Seven treatments were employed: 1) no snails (control); 2) small “starved” snails; 3) large “starved” snails; 4) small and large “starved” snails; 5) small fed snails; 6) large fed snails; and 7) small and large fed snails. Although snails removed significant amounts of periphyton AFDM relative to controls, neither snail size nor degree of starvation had a significant effect on loss of total AFDM. Small snails removed significantly more erect forms of Stigeoclonium tenue (C. A. Ag.) Kütz. than large snails, but snail size had no other significant effect. Starved snails removed significantly more Cocconeis placentula Ehr. than fed snails, suggesting that after the more susceptible growth forms (e.g. erect Stigeoclonium) were removed, Cocconeis cells became more vulnerable to grazing by hungry snails. When small and large snails were combined in chambers, large snails gained weight over time, whereas small snails lost weight. These results suggest that intraspecific competition may occur within populations of Elimia.

ON PALUDOMUS AND CLEOPATRA (THIARIDAE) IN AFRICA AND THE SEYCHELLES ISLANDS

The freshwater prosobranch snail Paludomus ajanensis Morelet, 1860 (Thiaridae), described from north east Africa (Ras Hafun) but re-found with certainty only in the Seychelles Islands, has been classified by 20th century authors in the genus Cleopatra, according to the shell and operculum. Examination of whole animals recently collected in the Seychelles showed that this species is indeed a Paludomus. ‘Cleopatra’ ajanensis of authors should not be regarded as an Afrotropical element in the fauna of the Seychelles; it is rather an Asian faunal link with Africa, if the African provenance attributed to P. ajanensis is correct.

Speciation of echinostomes: evidence for the existence of two sympatric sibling species in the complex Echinoparyphium recurvatum (von Linstow 1873) (Digenea: Echinostomatidae)

Evidence for the existence of 2 first intermediate host-specific sibling species of the 45 collar-spined echinostome Echinoparyphium recurvatum is presented. Experimental studies on their life-cycles were carried out under controlled laboratory conditions. The two entities were found to be morphologically indistinguishable in all major respects, yet they exhibited distinct biological characteristics. One of the sibling species utilizes the freshwater lymnaeid pulmonate snail Lymnaea peregra as first intermediate host, and the adults occur in the anterior small intestine of the wildfowl experimental definitive host Anas platyrhynchos. The other utilizes the freshwater mesogastropod prosobranch snail Valvata piscinalis as first intermediate host, and the adults occur in the posterior small intestine and rectum of A. platyrhynchos. The existence of the two sibling species in sympatry may be explained by the fact that the life-cycles of the two forms represent two distinct cycles of transmission serving to reduce excessive competition between them.

Comparative Grazing Efficiency of Pulmonate and Prosobranch Snails

Radular structure and grazing effects of six snail species were examined to determine if differences in radular morphology might be related to resource partitioning through the selective removal of attached algae. Nutrient-releasing clay pots were incubated inside grazer exclosures in Douglas Lake, Michigan, for 25 days to generate a uniform growth of attached algae. The pots were collected, gently rinsed of loose material, and placed in laboratory aquaria. Five individuals of each snail (Physella gyrina, P. parkerii, Lymnaea emarginata, L. stagnalis, Helisoma anceps, and Elimia livescers) were each allowed to graze on a separate piece of clay pot. Algae on grazed and ungrazed substrata were examined using SEM and light microscopy. All snails visibly reduced algal density, leaving clearly defined grazing trails. The prosobranch Elimia livescens was significantly less effective (p < 0.05) than all pulmonates in removing attached algae. There were no significant differences among pulmonate species in grazin...

Sense receptors in Lobatostoma manteri (Trematoda, Aspidogastrea)

Sense receptors of the juvenile aspidogastrid Lobatostoma manteri infecting the digestive gland of the prosobranch snail Cerithium moniliferum were examined by transmission electron microscopy. At least eight types of presumptive sense receptors, some uniciliate and some non-ciliate, are described. Some of the receptors occur in thousands. This is the greatest variety of receptors ever described from a parasitic stage of a platyhelminth by electron microscopy.

Secondary Production of Two Subtropical Snails (Prosobranchia:Viviparidae)

Annual secondary production was determined for two subtropical populations of the prosobranch snails Viviparus subpurpureus (Say) and Campeloma decisum (Say). The two large, live-bearing detritivores were sampled from the littoral zone of a detritus rich, low gradient, alluvial plain stream in southern Louisiana. Production was estimated using the size-frequency method in two ways: (1) directly from sampling data and (2) using regression analyses to estimate the density of individuals in underrepresented size classes. Both methods included production of embryos. Annual standing stocks differed significantly between species (p < 0.025) and were relatively high at 16.0 g dry mass/m² for V. subpurpureus and 8.5 g dry mass/m² for C. decisum. Including under-represented size classes did not change mean annual biomass estimates for V. subpurpureus but did increase values for C. decisum from 8.5 to 10.2 g dry mass/m². The species also differed significantly in annual production (p < 0.05), with the magnitude of difference depending on the calculation method employed. Based on uncorrected sampling data, V. subpurpureus had a productivity of 35.7 g dry mass m^-2 yr^-1; with corrected data, productivity was 45.6 g dry mass m^-2 yr^-1. For C. decisum, productivity was 15.4 g dry mass m^-2 yr^-1 (uncorrected data) or 22.9 g dry mass m^-2 yr^-1 (corrected). Regardless of the calculation used, these results are still among the highest single-species production estimates reported for lotic macroinvertebrates.

Relative vulnerability of six freshwater gastropods to the leech Nephelopsis obscura (Verrill)

SUMMARY. 1. The vulnerability of six species of freshwater snails to the leech Nephelopsis obscura was determined in laboratory predation experiments.2. Nephelopsis was unable to prey on prosobranch snails with an operculum, but did consume certain pulmonate species though predation rates were low, ranging from one to two snails per leech per night at 20°C. Apparently, Nephelopsis does not actively select prey, but merely consumes those species most easily handled.3. Among pulmonates, leeches captured species in the following order: Physa gyrina (Say), Helisoma anceps (Menke). Lymnaea emarginata (Say) and Helisoma trivolvis (Say). Susceptibihty of size classes varied among snail species.4. Neither environmental structure, such as cobble or macrophytes, nor gastropod escape behaviors, such as clamping to substrates or vertical migration away from bottom‐feeding leeches, lowered capture rates by Nephelopsis.5. In 2 years sampling, only one of seven lakes, however, had appreciable abundances of Nephelopsis. It is therefore suggested that the rarity, low feeding rates, and lack of strong gastropod preference limit the effect of Nephelopsis on field gastropod distributions.

Decline of a sylvatic focus of Schistosoma mansoni in Guadeloupe (French West Indies) following the competitive displacement of the snail host Biomphalaria glabrata by Ampullaria glauca.

Grand Etang lake in Guadeloupe is a focus of intestinal schistosomiasis characterized by the virtual absence of human contact and the presence of a heavily infested rat population. The lake, with a surface area of 0.03 km2, is situated in rain forest at an altitude of 450 m. Originally it contained an extensive belt of the floating plant Pistia stratiotes which provided a favourable habitat for Biomphalaria glabrata, the intermediate host snail of Schistosoma mansoni. In 1974 and 1975, a low prevalence (about 3%) of S. mansoni was observed in B. glabrata while a high prevalence (about 60%) was recorded in rats. The rat population was infected with another trematode, Ribeiroia guadeloupensis, which requires two intermediate hosts, B. glabrata and the fish Tilapia mossambica. In 1976, the prosobranch snail, Ampullaria glauca, was accidentally introduced into the lake. By 1980, this snail had spread over half of the lake and had caused marked regression of the P. stratiotes layer. Concomitantly, the population of B. glabrata declined to such a point that in 1985 only a small colony remained in the northern section of the lake. The consequences of these changes are reflected in a rapid decline of S. mansoni in the rat population from 61.3% in 1980 to 34.8% in 1981, 6.5% in 1982, 2.8% in 1983, 11.6% in 1984, and 0% in 1985 and 1986.

Two new digenetic trematodes from Australian freshwater fishes with notes on previously described species

Austrohalipegus anguillicola gen. et sp. nov. is described from the stomach of Anguilla reinhardtii Steindachner. Austrohalipegus is distinguished from other derogenid genera by the absence of filaments on its eggs, by the presence of blindly ending caeca, by having the ventral sucker in the middle of the body, by having the sinus-sac enclose only the hermaphroditic duct, and by the uterus which does not extend posterior to the vitellarium. Austrohalipegus anguillicola is distinctive in having a large temporary sinus-organ formed by a completely eversible hermaphroditic duct. Isoparorchis hypselobagri (Billet) is recorded as juveniles of 1–3 mm in length from the coelom and as larger juveniles and adults from the swim bladder of Tandanus tandanus Mitchell. The miracidium is typically hemiuroid and has a crown of apical spines and cilia in lateral bunches. Experimental infections in which the prosobranch snails Posticobia brazieri and Melanoides tuberculatus were fed embryonated eggs produced infections of mother sporocysts. It is postulated that the life-cycle includes an obligate period of development in the coelom of the definitive host for the Australian form of the species. Stegodexamene watsoni sp. nov. is described from the intestine of Maccullochella peeli (Mitchell). It is distinguished from the two other species of this genus by its considerably larger cirrus pouch and its more extensive vitellaria. Burnellus trichofurcatus (Johnston and Angel) is recorded from new hosts, Arius graeffei Kner and Steindachner and Neosilurus ater (Perugia). Aspects of its biology are discussed. Pretestis australianus Angel and Manter is recorded from a new host, Scortum hilli Castelnau, extending the known range of this species.

Reproductive effort and growth in the prosobranch snail, Viviparus ater.

We compared two populations of Viviparus ater from Lake Zürich and Lake Maggiore with respect to the reproductive investment of individual females throughout their lives. Based on field observations of the bumber and size of offspring and from measurements of the differences between growth rings on the shells we constructed a probabilistic model for the life history of the females. A simulation showed that the overall productivity of females was higher in Lake Zürich than in Lake Maggiore. The higher productivity of females in Lake Zürich was due to faster growth before maturity and higher fecundity after maturity. The reproductive effort, as measured by the percentage of assimulated energy used for reproduction, remained constant throughout the life of the females in Lake Zürich, whereas it declined with age in Lake Maggiore. We interpret this as the outcome of a reproductive strategy that avoids risks due to reckless reproduction, rather than as two different strategies which have been selected in response to different habitat types.

Operculum closing as a defence against predatory leeches in four British freshwater prosobranch snails

The defence reaction of operculum closing in response to the presence of the molluscivorous leech Glossiphonia complanata (L.) and the non-molluscivorous Erpobdella octoculata (L.) was studied in four species of freshwater prosobranch gastropod. Bithynia tentaculata (L.) and Valvata piscinalis (Muller) can distinguish between the leeches, reacting only to G. complanata. V. piscinalis is capable of a greater degree of distance chemoreception of the leech ‘scent’. Valvata cristata Muller and Potamopyrgus jenkinsi (Smith) did not react to either leech. V. cristata may not be a potential prey item for G. complanata, while P. jenkinsi is fed on by the leech, but is a relative newcomer to the freshwater fauna.

The life history of Pleurogenoides orientalis (Srivastava, 1934) (Trematoda: Lecithodendriidae).

The life history of Pleurogenoides orientalis (Srivastava 1934), a lecithodendriid trematode of frogs in India is reported and stages in the life history are described. Natural infections with cercariae, which are virgulate xiphidiocercous type, were found in the prosobranch snail Alocinma travancorica. Metacercarial cysts were found in dragon-fly naiads (Tholymis tillarga and Tramea limbata) and aquatic bugs (Laccotrephes griseus and Ranatra elongata) collected from a stream. Adults occurred in the intestine of the pong frog, Rana cyanophlyctis. Laboratory reared A. travancorica fed with eggs of P. orientalis started shedding cercariae from 30 days post feeding. Development of cercariae into infective metacercariae in dragon-fly naiads took 18 days. Mature flukes were recovered from the intestine of experimentally infected R. cyanophlyctis. The entire life cycle from egg to egg producing adult takes 2 1/2 to 3 months.

Age specific fecundity and size of offspring in the prosobranch snail, Viviparus ater.

Age specific fecundity and size of offspring were compared in two populations of Viviparus ater, one from Lake Zürich (Switzerland) and one from Lake Maggiore (Italy). Females were caged and their offspring sampled at weekly intervals. Average fecundity per female over one year was 19.6 and 14.7 offspring in Lake Zürich and Lake Maggiore, respectively. Average shell widths of offspring at birth in the two lakes were 8.5 mm and 7.4 mm. Fecundity did not change with age in Lake Zürich but decreased with increasing age of the snails in Lake Maggiore. Fecundity and offspring size were positively correlated with the size of the females in both lakes, but fecundity was higher and offspring were larger in Lake Zürich than in Lake Maggiore irrespective of the size of the females. An analysis of covariance, correcting for differences between the two lakes in the total fresh weight of the offspring produced annually, showed that females from the two lakes distributed their reproductive investment differently. Females in Lake Zürich produced relatively fewer but larger offspring than females in Lake Maggiore. This trade-off was hidden because females in Lake Zürich produced twice as much offspring biomass as females in Lake Maggiore. The possibility that different selection regimes might account for the observed differences is discussed.

DISTRIBUTION OF SEROTONIN-LIKE IMMUNOREACTIVITY IN THE CENTRAL NERVOUS SYSTEM OF THE PERIWINKLE,LITTORINA LITTOREA(GASTROPODA, PROSOBRANCHIA, MESOGASTROPODA)

The distribution of serotonin-like immunoreactivity was determined in whole-mounted ganglia of the central nervous system of the prosobranch snail, Littorina littorea, with the goal of establishing a basis for cellular comparisons between different gastropod nervous systems. While general similarities appear to exist with other species, the nervous system of Littorina appears to differ markedly from the nervous systems of the pulmonate and the opisthobranch gastropods with regard to its relatively large number of small, serotonergic cell bodies. Over 1500 cells in Littorina were tentatively identified as serotonergic. These cells and their processes were distributed through all the major ganglia, but the vast majority of immunoreactive cell bodies were found in the pedal ganglia. Most cells in the central nervous system were identified only as members of clusters, however, a few could be reliably identified as consistent individuals between preparations. Further histological and physiological studies are needed on prosobranch nervous systems before evolutionary relationships can be established at the cellular level with pulmonate or opisthobranch nervous systems.