Vertical movement and time allocation of a freshwater pulmonate snail

The paper presents an analysis of locomotion and location in a vertical water column of 10Biomphalaria glabrata, under constant conditions of light, temperature, and food availability. Individual snails varied in distance traveled, and in the percentage of time spent in different areas of the water column. Distance covered ranged from 53 cm to 100 cm h^–1 . Approximately 21% of locomotion was observed to be passive (floating up or sinking down). Snails spent approximately 58% of the time in the bottom section, 35% in the top section and only 7% in the middle region. The study provides baseline data that can be used to compare further studies ofBiomphalaria glabrata as various conditions are altered.     

Predation on leeches in a weedy pond

SUMMARY. 1. A range of sizes of Erpobdelta octoculata fL.), Glossiphonia complanata (L.) and Helobdella stagnalis (L.) were introduced to a small weeded pond harbouring invertebrate and amphibian predators. Control leeches were kept in protective cages. Subsequently, gut contents of potential predators were tested against three anti-leech sera, using the precipitin test. Five of fifteen species tested had fed on leeches; Agabus, Pyrrhosoma, Aeshna, Sympetrum and larval Trilurus.
2. The size distributions of introduced and surviving leeches were compared. Predation pressure had been greatest on smaller leeches and this may have accounted for the observed differential mortality between leech species.
3. It is concluded that predation may cause significant mortality in leech populations in weeded ponds, with severity determined by the types and abundance of predators present.     

Strategic aspects of time allocation in the ecology of a freshwater pulmonate snail

Summary The paper describes experiments designed to investigate the influence of starvation on responses to various constant stimuli by Biomphalaria glabrata (Say). The results are discussed in the context of the economic priorities involved in decisions to switch from one conflicting behaviour to another. Two pairs of conflicting behaviour patterns are discussed: to aggregate as opposed to feeding in isolation, and to move to the surface for pulmonary gaseous exchange as opposed to remaining submersed involved in feeding behaviour. This evolutionary, strategic perspective is pursued with a consideration of the tactics adopted by starved individuals in relation to obtaining food.formerly School of Biological Sciences, University of Sussex, Sussex     

Evidence for a novel FMRFamide-related heptapeptide in the pulmonate snail Siphonaria pectinata

Extracts of whole false limpets (Siphonaria pectinata) were analysed to determine their complement of FMRFamide-related peptides. As in other pulmonates, FMRFamide itself was found to account for only a portion of the immunoreactivity; the largest immunoreactive peptide peak eluted during HPLC under acidic conditions at the same position as a peak also found in other pulmonates. This major peak was resolved into two components by HPLC at neutral pH, and one component was identified as the heptapeptide amide, GDPFLRFamide, previously described from Lymnaea. The amino acid composition of the second component indicates that it is also a heptapeptide, but that it has two Asx (aspartic acid or asparaginyl) residues instead of the one found in the previously identified pulmonate heptapeptides.     

Locomotion in the pulmonate snail Melampus--I. The motor pattern

1. The patterned neural activity that drives muscular locomotor movements in Melampus is generated within the central nervous system. 2. In the transition from quiescent state to crawling, the pattern recorded in nerves and connectives changes from short-duration bursts in many units to the 60-100 sec cycle of events recorded during tethered crawling in the semi-intact snail. 3. Extracellularly recorded bursts and individually recognizable spikes in pedal nerves are correlated with movements that occur at each stage of the cyclically repeated crawl-steps. 4. Intracellularly recorded pedal neurons involved in locomotion receive excitatory drive, inhibitory drive, or alternating excitatory and inhibitory drive during the step cycle.     

On the defence strategy of Physa fontinalis (L.), a freshwater pulmonate snail

Summary Physa fontinalis (L.) gives a characteristic, chemically mediated escape response when stimulated by the majority of British leeches and flatworms. The snail responds rapidly and consistently to contact with all the molluskivorous leeches but also to three species which may be considered harmless. However, no response was given to Erpobdella octoculata, the most abundant and widespread of the harmless leeches. The flatworms generally evoked less strong reactions. The adaptive significance of the pattern of responsiveness is discussed. A weaker shell-shaking response is elicited in conspecifics and it is shown that this antisocial behaviour leads to a relatively spaced-out dispersion pattern. A possible adaptive advantage is the reduction of risk of detection by shell-crushing fish predators, to which the snails are otherwise extremely vulnerable.     

An autoradiographic and cytophotometric study of oogenesis in a pulmonate snail,Planorbarius corneus

Summary The spatial and temporal patterns of macromolecular syntheses in oocytes and somatic auxiliary cells of the snail Planorbarius corneus have been investigated by autoradiography and cytophotometry. Oogenesis has been divided into three stages, comprising early meiosis up to diplotene (stage I), previtellogenetic growth phase (stage II), and vitellogenesis (stage III). No DNA synthesis was found in any oocyte stage. In stage-I oocytes, only nucleoli were found labelled with ³H-uridine. Oocyte nuclei of stage II and III actively synthesize RNA in nucleoli and chromosomes. The most intense incorporation of uridine in chromatin probably occurs during the previtellogenesis — vitellogenesis transition period during which cytological findings suggest well developed lampbrush chromosomes. RNA synthesis in amphinucleoli of stage-III oocytes is restricted to basophilic nucleolar parts, whereas acidophilic parts (protein bodies) neither synthesize nor store RNA. During vitellogenesis oocytes incorporate amino acids into yolk platelet proteins. Radioactive proteins are found in yolk platelet precursors 5 h after injection of the tracer and in yolk platelets 3 h thereafter. The labelling pattern suggests that oocytes synthesize certain hitherto unidentified yolk components. No evidence for the participation of follicle cells in synthesis and transport of vitellogenic proteins has been obtained from autoradiography. Cytological findings suggest an important role for these cells in oogenesis. They are highly active in RNA and protein synthesis. Cellular differentiation is accompanied by polyploidization of the nuclei which attain a highest DNA content of 256 c. Polyploidization probably occurs in incremental steps as indicated by complete endomitotic chromosomal cycles. Autoradiographs show that, during vitellogenesis, oocytes do not incorporate significant amounts of glucose, and only certain follicle cells were labelled with glucose, probably indicating the synthesis of glycogen.     

Urine composition and kidney function in the pulmonate freshwater snail Lymnaea stagnalis

• 1.1. Final urine is intermittently released from the pneumostome of the pulmonate freshwater snail Lymnaea slagnalis. A technique is described to sample this fluid.
• 2.2. The ionic composition of final urine greatly differs from that of haemolymph; Na⁺ and Cl⁻ are reabsorbed to a considerable degree. In lettuce fed snails K⁺ is excreted.
• 3.3. The urine Na⁺ and Cl⁻ concentrations are about 38 and 31 mM lower, respectively, than the haemolymph concentrations, also when the latter concentrations vary.

     

The shell matrix of the pulmonate land snail Helix aspersa maxima

In mollusks, the shell mineralization process is controlled by an array of proteins, glycoproteins and polysaccharides that collectively constitute the shell matrix. In spite of numerous researches, the shell protein content of a limited number of model species has been investigated. This paper presents biochemical data on the common edible land snail Helix aspersa maxima, a model organism for ecotoxicological purposes, which has however been poorly investigated from a biomineralization viewpoint. The shell matrix of this species was extracted and analyzed biochemically for functional in vitro inhibition assay, for amino acid and monosaccharides compositions. The matrix was further analyzed on 1 and 2D gels and short partial protein sequences were obtained from 2D gel spots. Serological comparisons were established with a set of heterologous antibodies, two of which were subsequently used for subsequent immunogold localization of matrix components. Our data suggest that the shell matrix of Helix aspersa maxima may differ widely from the shell secretory repertoire of the marine mollusks studied so far, such as the gastropod Haliotis or the pearl oyster Pinctada. In particular, most of the biochemical properties generally attributed to soluble shell matrices, such as calcium-binding capability, or the capacity to interfere in vitro with the precipitation of calcium carbonate or to inhibit the precipitation of calcium carbonate, were not recorded with this matrix. This drastic change in the biochemical properties of the landsnail shell matrix puts into question the existence of a unique molecular model for molluscan shell formation, and may be related to terrestrialisation.     

Oral water ingestion in the pulmonate freshwater snail,Lymnaea stagnalis

InLymnaea stagnalis, oral uptake of ambient medium was studied using⁵¹Cr-ethylenediaminetetra-acetic acid. In normal snails Cr-ethylenediaminetetra-acetic acid uptake showed two components: a high uptake rate within the first hour followed by moderate uptake proportional with time. The tracer accumulated mainly in the digestive system. All animals showed initial, transient uptake. Moderate uptake proportional with time did not occur in snails in which the buccal ganglia had been extirpated, in which both the buccal ganglia had been extirpated and the oesophagus was sectioned, or in snails provided with an oesophageal fistula. These snails did not accumulate tracer in the intestinal system. This type of tracer accumulation clearly represented oral ingestion of surrounding water. The oral water ingestion rate ranged from 8 to 12 μl·h⁻¹·g⁻¹. Assuming complete absorption, this accounts for 20–30% of the urine production rate. At low external concentrations the contribution of oral water ingestion to Na⁺ balance is negligible. However, its importance will grow with increasing external concentrations and becomes a major factor at higher concentrations. The ingestion rate increased almost sixfold when starving snails were allowed to feed. It is suggested that oral water ingestion is a consequence of making bite cycles and swallowing.     

Neuronal and non-neuronal responses to nerve crush in a pulmonate snail,Melampus bidentatus

Immunohistochemical and ultrastructural techniques were used to study sequelae of nerve injury in the pulmonate snail Melampus bidentatus. Either pedal or tentacle nerves were crushed, severing all axons, and recovery was monitored over 15 days. The axons regenerated from the segment attached to the soma, with no evidence of fusion of proximal and distal segments. The medium to large axons of central neurons, including those monitored with serotonin immunohistochemistry, grow distally across the path of smaller axons extending centrally from peripheral somata. The regions into which the growing axons projected were a focus of phagocytic activity. Cells previously labeled by PKH-26PCL, a fluorescent marker for phagocytic activity, were attracted to the crushed nerve within 6 h and were a consistent feature in the vicinity of the injury for at least 9 days, gradually extending their range as repair progressed in both directions from the crush. Repair proceeded within an intact sheath, and many sheath cells survived the crush, although the nuclear dye Hoechst 33258 revealed an initial distortion of their nuclei. The concentration of cells in the sheath in the crushed region increases after the crush, with the packing of nuclei peaking at 3 days and gradually returning to control conditions; this probably reflects migration of resident sheath cells. Cell division is rare in the sheath of intact nerves, but labeling with bromodeoxyuridine increases at the crush site between 4 and 9 days, indicating that cell replacement also occurs at the site. Electronic Publication     

Redial generations of Fasciola gigantica in the pulmonate snail Lymnaea truncatula.

Lymnaea truncatula, 4 mm in height, were subjected to infection by a single miracidium of Fasciola gigantica, then raised at 23 degrees C until day 60 of the experiment. Histological study of these snails demonstrated a mean redial burden of 34 parasites at day 60, of which one third were degenerating forms. The mean number of living independent rediae did not exceed 5 for the first and second generations. Conversely, in subsequent generations there were as many as 18 rediae per snail at day 60. The first living redia of the first generation in particular gave rise to daughter rediae. Mature rediae appeared at day 35 and especially concerned the first and second generations at day 60. The authors conclude that development of the first and second redial generations occurs during the same period, and that the forms of the first cohort of the second generation are produced from the first redia of the first generation which originated from the sporocyst.     

Molecular identification of symbionts from the pulmonate snail Biomphalaria glabrata in Brazil

The icthyosporean, Capsaspora owczarzaki, a known predator of Schistosoma mansoni sporocysts in vitro, is more prevalent in laboratory-reared strains of the intermediate snail host, Biomphalaria glabrata resistant to S. mansoni, than from the susceptible M line strain. We examined whether B. glabrata resistant to the NIH-PR-1 strain of S. mansoni from 2 regions in Brazil were also host to C. owczarzaki. Symbiont presence was examined using hemolymph culturing and nested polymerase chain reaction of snail genomic DNA with primers designed to specifically amplify sequences from relatives of the Icthyosporea. All B. glabrata of the resistant Salvador strain from the laboratory of Dr. Lobato Paraense in Rio de Janeiro, Brazil (n = 46) tested negative for symbionts. Three of 18 semiresistant 10-R2 B. glabrata from the laboratory of Dr. Barbosa in Recife, Brazil tested positive for C. owczarzaki. Another icthyosporean, Anurofeca sp., was identified from 1, 10-R2 snail and from 2 of 12 field-collected B. glabrata from Praia do Forte Orange, Ilha de Itamaracá. Snails from 2 other sites, Hotel Colibri, Pontezinha and Praia do Sossego, Ilha de Itamaracá, were negative for Anurofeca. Two genera of ciliates were also identified. Paruroleptus sp. was found in 4, 10-R2 snails and Trichodina sp. was identified in 2 field-collected snails from Praia do Forte Orange and Praia do Sossego.     

Influence of rearing and experimental temperatures on predator avoidance behaviour in a freshwater pulmonate snail

1. Predicted increases in the temperature of freshwaters is likely to affect how prey species respond to predators. We investigated how the predator avoidance behaviour of the freshwater pulmonate snail Lymnaea stagnalis is influenced by the temperature at which it was reared and that at which behavioural trials were carried out. 2. Crawl‐out behaviour of juvenile snails from two populations (high predation risk versus low predation risk) reared at either 15 or 20 °C was assessed in response to predation cues (predatory fish kairomones and conspecific alarm cues) in behavioural trials at both 15 and 20 °C. 3. Trial temperature had a significant effect on the time that snails spent in avoidance, regardless of their population of origin. Crawl‐out behaviour was greater during behavioural trials at 15 °C, but there was no effect of trial temperature on the speed with which animals showed avoidance behaviour. 4. There was no interactive effect of rearing temperature (RT) and trial temperature, but the effect of RT on avoidance behaviour did differ between populations. For an RT of 15 °C, snails from the South Drain (high risk) population showed a more rapid and longer avoidance response than those from the Chilton Moor (low risk) population. In contrast, for snails reared at 20 °C, there was no difference between populations for the duration of the avoidance response and snails from Chilton Moor crawled out faster than those from South Drain. 5. Hence, whilst (predictable) differences relative to natural predation threat in crawl‐out behaviour were apparent at 15 °C, raising the developmental temperature to 20 °C eliminated or, in the case of latency, reversed these differences. This suggests that L. stagnalis populations that cohabit with predatory fish and experience high developmental temperatures may have a reduced ability to respond to fish predation risk.     

Locomotion in the pulmonate snail Melampus--II. Recovery after pedal ganglion excision

1. When one pedal ganglion is removed, snails first crawl using the unoperated side of the foot, but in 4-8 weeks the operated side exhibits an anterior-to-posterior gradient of recovery. 2. A ganglion bud bridges the site of the missing ganglion and axons project from intact central ganglia into the foot. 3. Rhythmic activity in right and left pedal nerve pairs is correlated during locomotion in the regenerated snails. 4. The oscillator in the remaining pedal ganglion drives bilaterally coordinated activity. Regenerated projections from the cerebral ganglia through the bud to the remaining pedal ganglion suffice to initiate locomotion.     

Osmotically-induced volume changes in isolated cells of a pond snail

• 1.1. To assess whether the stretch-activated (SA) channels in snail cells could contribute to osmoregulation, information is needed about the behaviour of the cells under anisosmotic conditions.
• 2.2. Cells of Lymnaea stagnalis were therefore examined during acute hyposmotic stress (HOS).
• 3.3. Kidney, heart and neuronal cells (monitored photographically) swelled less than expected for strictly semipermeable cells, but exhibited no regulatory volume decrease.
• 4.4. Long-term viability of the cells was not compromised following acute hyposmotic stress.
• 5.5. Quinidine, which blocks SA channels in Lymnaea, intensified stress-induced swelling most markedly in kidney cells.
• 6.6. The data can, however, be explained without invoking recruitment of SA channels.

     

Respiratory behavior in the pond snail Lymnaea stagnalis

Summary This study describes the neural basis of respiratory behavior in a pulmonate mollusc, Lymnaea stagnalis. We describe and identify muscles of the respiratory orifice (pneumostome) and mantle cavity as well as relevant motor neurons innervating these muscles. All of these identified motor neurons are active during spontaneously occurring respiratory behavior and a sporadically occurring synaptic input, termed Input 3, controls the activities of these motor neurons. This spontaneous input can also be recorded from isolated brain preparations, suggesting that the respiratory motor program is generated centrally. However, evidence is also presented that in semi-intact preparations the role of peripheral feedback is important for the initiation and termination of respiratory behavior in Lymnaea.