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At least 1,153 records · Page 64Linked to original sources
PubMed2005

Partial selfing, ecological disturbance and reproductive assurance in an invasive freshwater snail.

Although reproductive assurance (RA) might play a central role in the evolution of the selfing rate, this hypothesis has never been seriously investigated in an hermaphroditic animal. We studied the mating system of the freshwater snail Physa acuta in which the availability of mating partners might be highly variable, because this species is an efficient colonizer occupying unstable habitats. A total of 11 populations differing in ecological disturbance regime (water level, openness) and snail densities were monitored over 2 years. The outcrossing rate was estimated in ca 10 families per population using microsatellite markers and the progeny-array approach. Components of fecundity and survival were recorded for each progeny. Predominant outcrossing (t(m)=0.94) was detected, with a few individuals (4%) purely selfing. The outcrossing rate did not explain among-family variation in fitness components. None of the predictions formulated under the RA hypothesis were verified: (i) selfing was related neither to disturbed habitats, nor to temporal density fluctuations, (ii) it was positively related to population density, (iii) it co-occurred with multiple paternity, and (iv) it did not induce delayed reproduction. Explanations for these negative results are discussed in light of other arguments supporting the RA hypothesis in P. acuta, as well as alternative theories explaining the occurrence of partial selfing, as either a genetically fixed or plastic trait.

Animals↗
PubMed1966

Protoplast formation and yeast cell-wall structure. The action of the enzymes of the snail, Helix pomatia.

1. The digestive juice of the snail Helix pomatia was used in the study of the degradation of isolated cell-wall preparations from a strain of Saccharomyces carlsbergensis. 2. The crude enzyme system was fractionated by gel filtration and the activities of the more specific fractions thus obtained were examined. 3. Results are discussed with respect to (a) the nature of various factors that are essential for protoplast formation and cell-wall dissolution and (b) structures envisaged in yeast cell walls that are responsible for the observed variations in susceptibility to attack by snail juice.

Cell Wall↗
PubMed1976

The beta-glucosidase in the gut contents of the snail Achatina achatina.

1. The enzyme beta-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.21) from the gut contents of active Achatina achatina exists in two molecular forms, beta-glucosidase C (mol.wt. about 82000) and D (mol.wt. about 41000). 2. Only the lower-molecular-weight species was found in the gut contents of aestivating snails or in extracts from their digestive glands and washed gut walls. 3. On re-activation of some aestivating snails, betion of ATP and Mg2+ to the isolated gut contents or to extracts from washed gut walls led to the formation of higher-molecular-weight forms of the enzyme, beta-glucosidase A (mol.wt. about 329000) and beta-glucosidase B (mol.wt. about 165000). 5. All these forms of the enzyme have similar pH optimum (pH 5.0-5.6). 6. The Michaelis constants (Km) and heat stability of the enzyme increased with increasing molecular complexity.

Adenosine Triphosphate↗
PubMed1979

Metabolism of cholecalciferol in land snails.

1. Radioactively labelled cholecalciferol was injected into the land snails Levantina hiersolyma and Theba pisana. Three metabolites (C, D and E), more polar than cholecalciferol, were found. 2. Metabolite C was found to be identical with 25-hydroxycholecalciferol. On injection of 25-hydroxy[26,27-3H]cholecalciferol, metabolite E was predominantly formed. Metabolite D was predominantly formed from cholecalciferol. Metabolites D and E differ from any known cholecalciferol metabolites. 3. The intestine was found to be the tissue capable of carrying out the transformation of 25-hydroxycholecalciferol into metabolite E. 4. 25-Hydroxycholecalciferol and metabolite E were localized in the digestive gland of the snail, the tissue responsible for the absorption of Ca2+ and its storage. Metabolite D was not localized in any specific tissue.

Animals↗
PubMed1988

Chemical-modification studies of a unique sialic acid-binding lectin from the snail Achatina fulica. Involvement of tryptophan and histidine residues in biological activity.

A unique sialic acid-binding lectin, achatininH (ATNH) was purified in single step from the haemolymph of the snail Achatina fulica by affinity chromatography on sheep submaxillary-gland mucin coupled to Sepharose 4B. The homogeneity was checked by alkaline gel electrophoresis, immunodiffusion and immunoelectrophoresis. Amino acid analysis showed that the lectin has a fairly high content of acidic amino acid residues (22% of the total). About 1.3% of the residues are half-cystine. The glycoprotein contains 21% carbohydrate. The unusually high content of xylose (6%) and fucose (2.7%) in this snail lectin is quite interesting. The protein was subjected to various chemical modifications in order to detect the amino acid residues and carbohydrate residues present in its binding sites. Modification of tyrosine and arginine residues did not affect the binding activity of ATNH; however, modification of tryptophan and histidine residues led to a complete loss of its biological activity. A marked decrease in the fluorescence emission was found as the tryptophan residues of ATNH were modified. The c.d. data showed the presence of an identical type of conformation in the native and modified agglutinin. The modification of lysine and carboxy residues partially diminished the biological activity. The activity was completely lost after a beta-elimination reaction, indicating that the sugars are O-glycosidically linked to the glycoprotein's protein moiety. This result confirms that the carbohydrate moiety also plays an important role in the agglutination property of this lectin.

Amino Acids↗
PubMed2002

3D in-vivo X-ray microtomography of living snails.

In this paper we report the first in-vivo scanning of living snails by desktop X-ray microtomograph with a resolution up to 10 m. Consecutive cross-sections were acquired without destroying the specimen. Subsequently, 3D images were reconstructed. The results clearly demonstrate the possibilities of in-vivo scanning. Processes of growth and regeneration of living snails were visualized over a period of time.

Animals↗
PubMed2001

Spatial analysis of allozyme and microsatellite DNA polymorphisms in the land snail Helix aspersa (Gastropoda: Helicidae).

The genetic structure of the land snail Helix aspersa was investigated for 21 populations collected along a road located in the polders of the Bay of Mont-Saint-Michel (Brittany, France), following a sampling scheme the area of which did not exceed 900 m in length. A total of 369 individuals were genotyped for five enzymatic markers and seven microsatellite loci. We used sequential hierarchical F-statistics at different spatial scales and spatial autocorrelation statistics to explore recent historical patterns involved in the observed genetic distribution. Whatever the statistics used, congruent levels of spatial genetic substructuring across loci were demonstrated, excepted for one allozyme locus. Overall spatial genetic arrangement matched in a substantial fashion theoretical predictions based on the limited dispersal power of land snails. Positive autocorrelation over short-distance classes may result from the development of genetically distinct patches of individuals organized in family-structured colonies. Therefore, spatial signatures of average I correlograms can be viewed as the expression of a stepping-stone model of population structure, sometimes involving external migrational events. Overall, the revealed pattern of population subdivision on a microgeographical scale was suggestive of a neighbourhood structure. Finally, microsatellite loci are especially suitable for the detection of small genetic clustering, and combining different classes of markers offers the potential to gain further insight into the description of spatial genetic variability over short temporal and geographical scales.

Animals↗
PubMed2003

Sperm length influences fertilization success during sperm competition in the snail Viviparus ater.

Sperm form and size is tremendously variable within and across species. However, a general explanation for this variation is lacking. It has been suggested that sperm size may influence sperm competition, and there is evidence for this in some taxa but not others. In addition to normal fertilizing sperm, a number of molluscs and insects produce nonfertile sperm that are also extremely morphologically variable, and distinct from fertilizing forms. There is evidence that nonfertile sperm play an indirect role in sperm competition by decreasing female remating propensity in Lepidopterans, but in most taxa the function of parasperm is unknown. We investigated the role of nonfertile (oligopyrene) sperm during sperm competition in the fresh water snail Viviparus ater. Previous studies found that the proportion of oligopyrene sperm increased with the risk of sperm competition, and hence it seems likely that these sperm influence fertilization success during competitive matings. In mating experiments in which females were sequentially housed with males, we examined a range of male characteristics which potentially influence fertilization success. We found that the size of oligopyrene sperm was the best predictor of fertilization success, with males having the longer sperm siring the highest proportion of offspring. Furthermore, we found a positive shell size and sperm concentration effect on paternity, and females with multiply sired families produced more offspring than females mating with only one male. This result suggests polyandry is beneficial for female snails.

Analysis of Variance↗
PubMed2003

A molecular phylogeography approach to biological invasions of the New World by parthenogenetic Thiarid snails.

The parthenogenetic snail Melanoides tuberculata, present in tropical fresh waters of most of the Old World before 1950, has now invaded the Neotropical area. The phylogeography of this snail was studied to evaluate the pathways and number of such invasions. Because of parthenogenetic reproduction, individuals are structured into genetical clones. Within populations from both the original and invaded areas, several morphologically distinct clones (referred to as morphs) often coexist but the amount of genetic divergence among morphs is unknown. Individuals from 27 morphs and 40 populations world-wide were sequenced at two mitochondrial genes (12S and 16S). Our phylogenetic reconstruction suggests that (i) most of the morphological variation observed in the New World predates invasion, (ii) at least six independent introductions have occurred, and (iii) invasive clones are found throughout most of the phylogenetic tree and do not come from a particular region of the area of origin. Two ideas are discussed in the light of these results. The first lies with the specificities of parthenogenesis in an invasion context. While in sexual species, independently introduced populations eventually merge into a single invasive population, in a parthenogenetic species independently introduced clones have distinct invasion dynamics and possibly exclude each other. Second, although repeated invasions in Melanoides may have an impact on indigenous molluscan faunas, their most likely effect is the world-wide homogenization of the invasive taxon itself.

Animals↗
PubMed1996

Field tests of a village-based mollusciciding programme for the control of snail hosts of human schistosomes in Cameroon.

The feasibility of using unskilled workers at the district or village level to perform mollusciciding activities in arid regions of northern Cameroon was investigated. A simplified procedure for application to temporary ponds, the principal sites of schistosomiasis transmission in that region, was tested. This consisted of mixing the required quantity of niclosamide (Bayluscide, Bayer AG, Leverkusen) with pond water in a plastic watering can and applying the mixture around the circumference. To aid dispersion, the can was repeatedly swept from the perimeter toward the centre of the pond. Two ponds each were treated once near the end of the rainy season at 1 of 3 concentrations: 0.5, 1.0 and 1.5 p.p.m. Following treatment, 100% snail mortality was recorded at all concentrations. A simple, rapid method for determining the quantity of niclosamide needed to treat temporary ponds was also devised. Physical characteristics were determined for 16 potential schistosomiasis transmission sites in the region. An integration of those characteristics was used to develop a simplified scale indicating the quantity of niclosamide needed to treat ponds based on their circumference. The operational feasibility of a village based mollusciciding programme using those simplified procedures was then evaluated in 2 villages. Village health workers demonstrated a high accuracy (87%) in identifying potential schistosomiasis transmission foci and snail host populations were virtually eliminated from treated sites.

Animals↗
PubMed2003

Mitochondrial differentiation in a polymorphic land snail: evidence for Pleistocene survival within the boundaries of permafrost.

The genetic differentiation of populations having colonized formerly unsuitable habitats after the Pleistocene glaciations depends to a great extent on the speed of expansion. Slow dispersers maintain their refugial diversity whereas fast dispersal leads to a reduction of diversity in the newly colonized areas. During the Pleistocene, almost the entire current range of the land snail Arianta arbustorum has repeatedly been covered with ice or been subjected to permafrost. Owing to the low potential for dispersal of land snails, slow (re)colonization of the wide range from southern refugia can be excluded. Alternatively, fast, passive dispersal from southern refugia or survival in and expansion from multiple refugia within the area subjected to permafrost may account for the current distribution. To distinguish between these scenarios we reconstructed a phylogeography based on the sequences of a fragment of the cytochrome oxidase I from 133 individuals collected at 45 localities and analysed the molecular variance. Seventy-five haplotypes were found that diverged on average at 7.52% of positions. This high degree of diversity suggests that A. arbustorum is an old species in which the population structure, isolation and the hermaphroditic nature have reduced the probability of lineage extinction. The genetic structure was highly significant with the highest variance partition found among regions. Geographic distance and mitochondrial differentiation were not congruent. Lineages had overlapping ranges. The clear genetic differentiation and the patchy pattern of haplotype distribution suggest that colonization of formerly unsuitable habitats was mainly achieved from multiple populations from within the permafrost area.

Animals↗
PubMed2003

Environment-dependent inbreeding depression in a hermaphroditic freshwater snail.

Inbreeding depression was simultaneously studied under contrasted environments, laboratory and natural conditions, using individuals originating from 14 families of the freshwater snail Physa acuta. Both survival and growth of juveniles showed inbreeding depression under laboratory conditions. The same fitness components were monitored with mature snails either kept under laboratory conditions or released at a natural site and analysed using capture-mark-recapture models. Genetic composition of both samples was similar. Inbreeding depression on survival was highest in the laboratory while strong outbreeding depression was revealed in the field. Thus inbreeding depression may not be always higher under natural conditions, at the opposite of what is commonly assumed. We suggest that inbreeding depression is dependent on metabolic requirements imposed by the environment. Other evidences showing that inbreeding depression is environment-dependent are reviewed. We conclude that genetic models should include both genetic and environmental variance in inbreeding depression for studying mating system evolution.

Adaptation, Physiological↗
PubMed2004

Ecological and morphological patterns in communities of land snails of the genus Mandarina from the Bonin Islands.

The land snail genus Mandarina has undergone extensive radiation within the Bonin Islands in the west Pacific. The preferred above-ground vegetation heights of sympatric species were clearly different. They separated into arboreal, semi-arboreal, exposed ground and sheltered ground ecotypes. Shells of species with different ecotypes differ markedly, but shells of species with the same ecotype are very similar to each other. Shell morphologies of some phylogenetically distantly related species with the same ecotype were indistinguishable. Character evolution estimated parsimoniously using a phylogenetic tree suggests that the speciation among sympatric species is accompanied by ecological and morphological diversification. In addition, species coexistence of Mandarina is related to niche differentiation. The above findings suggest that ecological interactions among species contribute to the ecological and morphological diversification and radiation of these land snails in this depauperate environment.

Animal Structures↗
PubMed2002

Modularity and reshuffling of Snail and Slug expression during vertebrate evolution.

Gene duplication has been a major mechanism for increasing genomic complexity and variation during evolution. The evolutionary history of duplicated genes has been poorly studied along the vertebrate lineage. Here, we attempt to study that history by analyzing the expression of two members of the Snail family, Snail and Slug, in representatives of the major vertebrate groups. We find a surprising degree of variability in a subset of the expression sites for both genes in different species. Although some of the changes can be explained by neofunctionalization or subfunctionalization, others imply reciprocal changes in the expression of the two genes and the reappearance of expression in sites lost earlier in evolution. Because these changes do not fit easily into current models, we need to invoke additional mechanisms acting on enhancer elements to distribute expression domains and functions of duplicated genes unequally during evolution.

Animals↗
PubMed1985

Biochemical and immunological evidence for a cardiodilatin-like substance in the snail neurocardiac axis.

Cardiac hormones, which have been isolated recently from mammalian atria, are potent regulatory peptides of blood pressure and blood volume. By using biochemical and immunological methods to determine cardiac hormones of the cardiodilatin family, this type of peptide hormone was detected in a neurosecretory system projecting from the subesophageal ganglion to the heart of the snail. The cardiodilatin-like molecule was characterized by its biological effects on mammalian vascular smooth muscle, by radioimmunoassay combined with high-performance liquid chromatography, and by immunocytochemistry. In mammals cardiodilatin-like peptides appear to serve purely endocrine functions. In contrast, in the snail they are present in a neuroendocrine system, the function of which remains to be established.

Animals↗
PubMed1995

Strong natural selection causes microscale allozyme variation in a marine snail.

Natural selection is one of the most fundamental processes in biology. However, there is still a controversy over the importance of selection in microevolution of molecular traits. Despite the general lack of data most authors hold the view that selection on molecular characters may be important, but at lower rates than selection on most phenotypic traits. Here we present evidence that natural selection may contribute substantially to molecular variation on a scale of meters only. In populations of the marine snail Littorina saxatilis living on exposed rocky shores, steep microclines in allele frequencies between splash and surf zone groups are present in the enzyme aspartate aminotransferase (allozyme locus Aat; EC. 2.6.1.1). We followed one population over 7 years, including a period of strong natural perturbation. The surf zone part of the population dominated by the allele Aat100 was suddenly eliminated by a bloom of a toxin-producing microflagellate. Downshore migration of splash zone snails with predominantly Aat120 alleles resulted in a drastic increase in surf zone frequency of Aat120, from 0.4 to 0.8 over 2 years. Over the next four to six generations, however, the frequency of Aat120 returned to the original value. We estimated the coefficient of selection of Aat120 in the surf zone to be about 0.4. Earlier studies show similar or even sharper Aat clines in other countries. Thus, we conclude that microclinal selection is an important evolutionary force in this system.

Animals↗
PubMed2002

Larval trematode infections in freshwater snails from the highveld and lowveld areas of Zimbabwe.

Between November 1998 and October 2000, freshwater snails were collected monthly from the highveld and lowveld areas of Zimbabwe to determine the occurrence of larval trematodes. A total of 13,789 snails, representing ten species, were collected from 21 sites and 916 (6.6%) harboured patent trematode infections. Eight morphologically distinguishable types of cercariae were identified. Bulinus tropicus had the highest overall prevalence of infection (13.1%). The echinostome was the most common type of cercaria recovered, contributing 38.2% of all infections. Schistosoma cercariae were recovered mainly from the highveld and comprised 8.0% of all infections. Amphistome cercariae contributed 37.6% of all infections and were recorded from both the highveld and lowveld areas with a peak prevalence occurring during the post-rainy period (March-May). The main intermediate host for amphistomes was B. tropicus. Infections in B. globosus, B. forskalii and Biomphalaria pfeifferi with amphistome cercariae are new records for Zimbabwe.

Animals↗
PubMed1978

Experimental studies on the suitability of aquatic snails as intermediate hosts for Paramphistomum cervi in Iraq.

Three of the most common species of aquatic snails in Iraq were examined for their susceptibility to infection with Paramphistomum cervi. Bulinus truncatus was the only susceptible species. No development occurred in Physa acuta or Lymnaea lagotis euphratica. These findings and a previous field observation that infection of B. truncatus with amphistome larvae is not uncommon indicate that B. truncatus is an intermediate host of P. cervi in Iraq. Young snails of B. truncatus were more susceptible to infection than older ones.

Animals↗