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PubMed2002

Characterisation of two snail genes in the gastropod mollusc Patella vulgata. Implications for understanding the ancestral function of the snail-related genes in Bilateria.

Snail genes have been found to play a role in mesoderm formation in two of the three clades of bilaterians, deuterostomes (comprising the chordates) and ecdysozoans (comprising the arthropods). No clear data are available on the role these genes play in development of the mesoderm in the third clade, that of lophotrochozoans (comprising annelids and molluscs). We identified two new members of the snail gene family in the gastropod mollusc Patella vulgata. Phylogenetic analysis showed that the two genes clearly belong to the snail sub-family. Their expression patterns do not indicate a role during early mesoderm formation. In fact, contrary to expectations, the snail genes of Patella were mostly expressed in the ectoderm. In view of the location of their expression sites, we suggest that these genes could be involved in regulating epithelial-mesenchymal transitions (EMT) and cell motility, as has recently been demonstrated for snail genes in vertebrates. This may well correspond to the ancestral function of these genes. The results are discussed in the light of the evolutionary origin of the mesoderm. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00427-002-0228-1.

Amino Acid Sequence↗
PubMedDate not supplied

Snails and snail farming: an introduction for the veterinary profession.

In the past veterinary interest in snails has been confined to their role in the transmission of disease; nowadays the trend to keep these animals in captivity--for food, for study, as 'companion animals'--means that the profession is increasingly likely to be consulted about their health, welfare or conservation. An understanding of the biology of snails is an important prerequisite to work with them. Land snails are hermaphrodite and have a complex reproductive system; other organs also show special adaptations. Management methods vary considerably and farmed snails can be maintained under extensive or intensive conditions. Methods for handling and transporting them are important considerations. There is little published information on the diseases and pathology of snails but suboptimum environment, poisons, nutritional deficiencies, predators and parasites are known to cause, or contribute, to their mortality.

Animal Husbandry↗
PubMed2003

Comparative studies on the internal defense system of schistosome-resistant and -susceptible amphibious snail Oncomelania nosophora 1. Comparative morphological and functional studies on hemocytes from both snails.

Two morphologically distinct blood cell types (hemocytes), Type I and Type II were found coexisting in hemolymph from two kinds of snails, Oncomelania nosophora strain, viz. from the Nirasaki strain (schistosome-resistant snail) and the Kisarazu strain (schistosome-susceptible snail). Ten min after inoculation of SRBC, the majority of Type I cells from Nirasaki strain flattened and spread over the surface of the glass plate by extending pseudopodia. In the Kisarazu strain, Type I cells adhered to the surface of substrate with spike-like filopodia, but did not form spreading lamellipodia. Type I cell from the Nirasaki strain phagocytosed SRBC but that from the Kisarazu strain did not. The starting time of recognition of foreign materials was slightly different in the Type I hemocytes from the two strains. Type II cells from both strains were round and lymphocyte-like. Ten or sixty min after incubation, Type II cells from neither strain adhered to the surface of substrate or SRBC, and did not phagocytose SRBC. Type II cells from the Nirasaki strain were quite similar to those from the Kisarazu strain. We concluded that Type I cells from the schistosome-resistant snail, Nirasaki strain, possessed higher phagocytic activity than those from the susceptible snail, Kisarazu strain, despite the morphological similarities of the hemocytes from both strains.

Animals↗
PubMed2004

Behavioural responses of the snail Lymnaea acuminata to carbohydrates in snail-attractant pellets.

Snail control is one of the most important tools in the campaign to reduce the incidence of fascioliasis. In order to attain this objective, the method of bait formulation in order to contain an attractant and a molluscicide is an expedient approach to lure the target snail population to the molluscicide. This study identifies certain carbohydrates, namely sucrose, maltose, glucose, fructose and starch, for preparing such baits. These were tested on Lymnaea acuminata, an intermediate host of the digenean trematodes Fasciola hepatica and Fasciola gigantica. The behavioural responses of snails to these carbohydrates were examined. Significant variations in behavioural responses were observed in the snail even when the five carbohydrates were used in low concentrations in snail-attractant pellets. Starch emerged as the strongest attractant for Lymnaea acuminata, followed by maltose.

Agar↗
PubMed2004

Effects of snail size on encystment of Echinostoma caproni in juvenile Biomphalaria glabrata (NMRI strain) and observations on the survival of infected snails.

The effects of snail size on encystment of Echinostoma caproni cercariae in neonatal and juvenile Biomphalaria glabrata (NMRI strain) snails were studied. Encystment in neonatal (0.7-1.1 mm shell diameter) and juvenile (2-3 mm shell diameter) snails was compared 24 h post-infection (PI) following individual exposure of snails of each size to 1, 5, 10, 25 and 50 cercariae. Significantly more cysts were recovered from juveniles exposed to 1, 5, 10 and 50 cercariae than from neonatals with comparable exposure. Size of B. glabrata was a major factor in determining cyst burden in this planorbid. Survival of infected versus uninfected neonatals and juveniles was also examined for 7 days. Neonatals exposed to 10 cercariae showed a significant decrease in survival at 3, 6 and 7 days PI when compared to the uninfected controls. There was no significant decrease in the survival of juveniles exposed to 10 cercariae compared to uninfected controls at any time point. Snail size was a factor in mortality associated with echinostome cercarial penetration and encystment.

Animals↗
PubMed1998

Experimental control of the schistosome-transmitting snail Biomphalaria pfeifferi by the ampullariid snail Pila ovata.

Adults of the African ampullariid snail Pila ovata were examined for their ability to control laboratory populations of the pulmonate snail Biomphalaria pfeifferi, a widespread, intermediate host of the human pathogen Schistosoma mansoni in sub-Saharan Africa. In a 6-week experiment conducted in large (100 x 60 x 60 cm) outdoor tanks containing floating macrophytes (Nymphaea caerula) and initially set up with one adult ampullariid for every three adult pulmonates, the numbers of B. pfeifferi egg masses were always about half those in similar tanks without P. ovata. Although, by week 6, the numbers of B. pfeifferi in the control tanks (without ampullariids) had increased 5-fold, from an initial mean of 30 snails/tank, there was no significant increase in the numbers of B. pfeifferi in the experimental tanks (containing ampullariids). Results of experiments conducted in indoor glass aquaria indicated that adult P. ovata rapidly attacked egg masses or neonates (< 2.5 mm shell diameter) of B. pfeifferi but had no effect on the adults. The adult ampullariids also significantly decreased cover by floating macrophytes over a 6-week period compared with that in similar but ampullariid-free aquaria. This decrease in plant cover is relevant to biological control of the schistosome vectors as macrophytes serve as food, shelter and oviposition sites for pulmonate snails. The present result indicate the ability of P. ovata to inhibit multiplication of B. pfeifferi populations, at least under laboratory conditions, both directly, through predation, and indirectly, by competition for resources. Pila ovata may therefore prove useful in the biological control of medically important, pulmonate snails.

Animals↗
PubMed2000

Variability of Fasciola hepatica infection in Lymnaea ovata in relation to snail population and snail age.

Bimiracidial infections of Lymnaea ovata with Fasciola hepatica were performed under laboratory conditions to determine the susceptibility of snails from six French populations to trematode infection. In five populations of L. ovata the prevalence of infection in the 1-mm groups ranged between 2.7% and 43.7% at day 35 postexposure; it decreased in the 2-mm snails and was zero in larger groups. In the snails from Thenay (periodically polluted brook) the prevalence of F. hepatica infection decreased from the 1-mm group to the 8-mm group (from 23.9% to 1.0%) and was zero in the 10-mm L. ovata. The total number of cercariae shed per snail was 18.3 in the 1-mm group, increasing to 117 in the 8-mm group. The latter findings could be interpreted as a consequence of periodic pollution in the brook of Thenay; pollution might disrupt the defense system of L. ovata and facilitate the subsequent larval development of F. hepatica.

Aging↗
PubMed2003

The effects of myrrh (Commiphora molmol) on the infected snails of Schistosoma sp. and their egg masses: effect on shedding of cercariae and on snail fecundity.

Myrrh has molluscicidal effect on infected Bulinus truncatus and Biomphalaria alexandrina snails at low concentrations (10 & 20 ppm respectively) after 24 hours exposure. The number of dead-snails increased with prolongation of exposure time. All Schistosoma free cercariae were killed by 2.5 ppm within 15 minutes. One day-old egg masses were more susceptible to the ovicidal effect of Myrrh than the five-day old ones. Both types of eggs were more resistant to the effect of Myrrh than the adult snails, embryogenesis began to stop at 20 ppm and eggs were all killed at 60 & 80 ppm. Shedding of cercariae of Schistosoma mansoni from infected B. alexandrina stopped at 1 ppm and was suppressed at 0.8 ppm. Snail fecundity decreased at 1 ppm.

Animals↗
PubMed1994

Acid-base status of a pulmonate land snail (Helix aspersa) and a prosobranch amphibious snail (Pomacea bridgesi) during dormancy.

Changes in metabolism and acid-base status were compared during dormancy in the pulmonate land snail Helix aspersa and a prosobranch amphibious snail Pomacea bridgesi. The typical condition of higher blood PCO2 and bicarbonate levels for air-breathing versus water-breathing vertebrates was shown for the two snail species. When exposed to dry air for 24 hr, both species depressed oxygen uptake by about 65%. In Pomacea, hypercapnia (increase in hemolymph PCO2 from 5.5 to 18 torr) resulting from dormancy produced no significant change in pH due to large increases in bicarbonate (over 17 mmol/l). In Helix, on the other hand, hypercapnia (increase in hemolymph PCO2 from 13 to 18 torr) resulting from dormancy produced a significant decrease in pH and a less than 7 mmol/l increase in bicarbonate. Pre-existing high levels of bicarbonate in Helix may prevent compensation of hypercapnia resulting from dormancy, similar to the case described for air-breathing vertebrates. Complete compensation of respiratory acidosis during the first 24 hr of dormancy in Pomacea suggests that metabolic rate suppression is independent of pH.

Acid-Base Equilibrium↗
PubMed1990

Interaction in the laboratory between Helisoma duryi, a possible competitor snail, and Biomphalaria pfeifferi, snail intermediate host of Schistosoma mansoni.

The planorbid snail, Helisoma duryi, has been proposed as a possible biocontrol agent against the intermediate host snails of schistosomiasis. In an attempt to evaluate the possible effect of interference between H. duryi and Biomphalaria pfeifferi, life-tables were compiled for these two snail species maintained both in the presence of each other and separately. The calculated population parameters indicated that H. duryi had a higher innate capacity of increase, net reproduction rate and finite rate of increase as well as a longer lifespan than the target species. However, the biological potential of B. pfeifferi was not influenced by the presence of H. duryi, and the latter appears to be unable to act as competitor against B. pfeifferi under similar prevailing conditions. It is possible that the situation might change under conditions of crowding and starvation.

Animals↗
PubMed1992

The neuropeptide schistosomin and haemolymph from parasitized snails induce similar changes in excitability in neuroendocrine cells controlling reproduction and growth in a freshwater snail.

Infection of the snail Lymnaea stagnalis with the schistosome parasite Trichobilharzia ocellata results in inhibition of reproduction and in giant growth. Parasite-related effects on the neuroendocrine centres that control these processes were studied electrophysiologically. Haemolymph from infected snails reduced the excitability of the caudodorsal cells, which control egg laying. In contrast, the excitability of the growth-controlling Light Green Cells was increased under these conditions. The endogenous anti-gonadotropic neuropeptide schistosomin, the presence of which is strongly enhanced in parasitized snails, induced similar effects. Schistosomin apparently plays an important role in the balance between reproduction and growth in Lymnaea. This balance is severely disturbed during parasitic infection, probably as a result of the release of the peptide.

Animals↗
PubMed1982

Transmission of Schistosoma mansoni from man to snail: laboratory studies on the influence of snail and miracidial densities on transmission success.

The relationship between infection success, the density of Schistosoma mansoni miracidia and the density of the snail host Biomphalaria glabrata was examined experimentally. Within laboratory infection arenas, the distribution of miracidial infections/snail was approximately uniform and the net rate of snail infection was directly positive binomial to miracidial density. In contrast, however, the rate of infection declined exponentially as snail density increased. Mathematical models are developed to aid in the estimation of infection rates and experimental results are discussed in the context of the transmission dynamics of schistosomiasis.

Animals↗
PubMed1975

Control of snail hosts of bilharziasis in Egypt. 2. Effect of triphenyltin hydroxide (Du-Ter) on carbohydrate metabolism of the snails Biomphalaria alexandria and Bulinus tuncatus.

Previous work has shown that the aerobic oxidation of certain intermediates of Krebs cycle by the snail B. alexandrina and B. truncatusis inhibited by TPT. This paper reports data on the effect of TPT on glucose utilization, glycolysis, glycogen content, and glucone ogenesis in snail tissue preparations. The compounds at its LC50 inhibited gluconeogenesis, stimulated glycolysis and markedly reduced the glycogen content and glucose utilization in both snails. However, the effects were more pronounced in B. truncatus than in B. alexandrina. Possible interpretations of these findings are discussed with reference to published arrangements for regulation of gluconeogenesis and glycolysis, coupling of electorn transport to ATP synthesis and also to our present knowledge of the chemical and biological specificity of TPT.

Animals↗
PubMed1976

Studies on resistance in snails. 6. Escape of Echinostoma lindoense sporocysts from encapsulation in the snail heart and subsequent loss of the host's ability to resist infection by the same parasite.

Formation of amebocyte aggregates in the ventricular cavity of Biomphalaria glabrata, induced by developing sporocysts of Echinostoma lindoense, does not always result in destruction of the parasites, as the sporocysts occasionally escape encapsulation in the heart. When this occurs, a remarkable loss of protective capacity follows and the host snails become highly susceptible to reinfection with the same species--even more so than in control susceptible snails exposed for the first time. Although the amebocyte-producing organ is considerably enlarged after a first infection and shows numerous mitoses, the amebocytes produced by snails harboring an "escaped" infection in the heart appear unable to attack the parasites of the first or of the second exposure. Instead, the amebocytes produced accumulate in the loose connective tissues between the liver lobuli, where early developmental stages of the parasites do not occur. These amebocytes apparently have lost their ability to recognize the parasites as foreign.

Animals↗
PubMed1990

Land snails as experimental animals: a study of the variability and distribution of individual weights in Helix aspersa snails born from the same clutch.

A study was carried out to examine the distribution of individual weights in Helix aspersa snails, the aims being to establish the best estimate of the ponderal growth and also to obtain a model growth curve. Four groups of 20 snails from the same clutch were analysed and kept under experimental conditions from birth up to 6 months. The variability of their individual weights within groups was studied by calculating the coefficients of variation every 15 days. At the same time, the assumed normal distribution of those weights was being tested. The coefficients of variation increased with age and the assumed normal distribution of individual weights had to be rejected. By means of a log transformation of the original data, a model growth curve was constructed, and was used to assess the possibility of estimating age from weight. We finally reached the conclusion that median weight, rather than the mean, would be a better measure of central tendency to use until it is possible to obtain selected populations. The difficulty of estimating age from weight is emphasized.

Age Factors↗
PubMed1976

Biology of the snail-killing fly, Sepedon spangleri Beaver (Diptera: Sciomyzidae). II. Ability of the larvae to kill snails of medical importance in Thailand.

S. spangleri larvae preferred five species of non-operculate snails; Gyraulus convexiusculus Hutton, Segmentina hemisphaerula Benson, Hippeutis umbilicalis Benson, Indoplanorbis exustus Larambergue, and Trochobis trochoideus Benson. They occasionally consumed the operculate snails: Melanoides tuberculata Muller, Lithoglyphopsis aperta, Hubendickia siamensis Brandt, Lacunopis munensis Brandt, Tarebia granifera, Lamarch and Viviparus sp. but were innocuous to Bithynia laevis Lea.

Animals↗
PubMed1981

Population studies on Oncomelania quadrasi, the snail intermediate host of Schistosoma japonicum, in the Philippines. 2. Necessary sample size for snail density survey.

In order to save time and manpower for the density surveys of Oncomelania quadrasi, the snail host of Schistosoma japonicum in the Philippines, the minimal necessary sample size (q) was determined using a formula, q greater than t2/E2(1d - 1 + 1/-x). This formula is based on the Id dispersion index [2, 3] which varies with the degree of clumping of unevenly distributed animals. A nomograph was prepared for the ready determination of the necessary sample size for various degrees of clumping (Id) and mean density (-x) to be encountered in the field. The reliability of the sampling procedure with an interval of 5 m distance, which has been adopted to the routine snail survey in the Philippines, was examined using the relative error (E). The relative errors calculated ranged below or around 20% (E = 0.2). Therefore, the existing sampling method was proven to be highly reliable as the field survey. Comparison was made between the sample size actually taken and the minimum needed theoretically determined by this method, by adopting the Student's t = 1 and relative error E = 0.3 as a permissible reliability level in the field. The actual sample size was more than twice the minimum needed for 21 out of 30 populations surveyed and less than the needed in 5 of the 30 surveys.

Animals↗
PubMed2005

Respiratory burst of Biomphalaria glabrata hemocytes: Schistosoma mansoni-resistant snails produce more extracellular H2O2 than susceptible snails.

The production of reactive oxygen species by hemocytes from the gastropod Biomphalaria glabrata has been linked to their ability to kill the trematode parasite Schistosoma mansoni. For 2 laboratory strains of the snail, 1 resistant (13-16-R1) and 1 susceptible (MO) to the PR1 strain of S. mansoni, we compared hemocyte production of extracellular hydrogen peroxide when stimulated with the protein kinase C agonist phorbol myristate acetate (PMA). The time course of the PMA-induced response is similar in both strains with respect to onset, peak production, and termination of the respiratory burst. However, the magnitude of the response differs between strains, in that hemocytes from resistant snails generate significantly more hydrogen peroxide. These findings suggest that the capacity to produce hydrogen peroxide could be critical in determining susceptibility or resistance to S. mansoni.

Animals↗