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At least 1,189 records · Page 66Linked to original sources
PubMed2006

Active and passive dispersal of an invading land snail in Mediterranean France.

1. Land snail dispersal abilities are considered poor; however, the current invasion of the French Mediterranean region by Xeropicta derbentina (Krynicki 1836), as well as the past invasions of this region by several other species, seems to contradict this view. 2. Using a multilevel approach, from individual experimentation to landscape analysis, the dispersal abilities and mechanisms allowing the passive dispersal of X. derbentina are studied. 3. The colonization of Provence occurred by stratified diffusion, where short-range active dispersal occurs side by side with long-range passive dispersal. 4. Active dispersal is not as limited as previously thought. In the field, the capture-mark-recapture method recorded a maximum distance covered of 42 m in 6 months within a radius of 38 m from the original release point. 5. Temperature and humidity, and therefore the time of year, influence the main type of dispersal. Dispersal is active during wet periods and essentially passive in dry and hot months. 6. Heat avoidance behaviour is one of the mechanisms allowing passive dispersal. 7. Passive dispersal via human activities is the main determinant of X. derbentina distribution within the landscape. In comparison to other species, X. derbentina is found more often in the vicinity of a communication route. 8. These results show that land snails can cover large distances in a lifetime. The potential for active and passive dispersal described in this paper enables X. derbentina to be a successful invasive species and explains the rapid spread and current distribution of this species.

Animals↗
PubMed2005

Age, phylogeography and population structure of the microendemic banded spring snail, Mexipyrgus churinceanus.

Recent theoretical and empirical studies of phylogeography and population structure indicate that many processes influence intraspecific evolutionary history. The present study represents the first examination of various forces influencing the spatial and temporal patterns of sequence variation in the freshwater Mexican banded spring snail, Mexipyrgus churinceanus. This snail occurs in one of the most critically endangered centres of freshwater endemism, the desert ecosystem of Cuatro Ciénegas. From cytochrome b mtDNA sequence variation, there is strong evidence of long-term isolation of three regions, suggesting that these regions represent evolutionarily distinct lineages. Molecular clock estimates of clade age indicate a time to most recent common ancestor of approximately 2.5 million years ago (Ma). The three regions differ considerably in the historical and demographic forces affecting population structure. The western populations have extremely low mtDNA diversity consistent with a severe bottleneck dating to 50,000 years before present (bp). The nearby Rio Mesquites drainage is characterized by fragmentation events, restricted gene flow with isolation by distance, and higher levels of mtDNA polymorphism. These patterns are consistent with the long-term stability of this drainage along with habitat heterogeneity and brooding contributing to population isolation and restricted gene flow. Southeastern populations show evidence of range expansion and a strong influence of genetic drift. Migration rates between drainages indicate very little gene flow between drainages except for asymmetric migration from the Rio Mesquites into both western and southeastern drainages.

Animals↗
PubMed2006

The recent history and population structure of five Mandarina snail species from subtropical Ogasawara (Bonin Islands, Japan).

The effect of Pleistocene climate change on the organisms of tropical and subtropical regions is rather poorly understood. We therefore studied the land snail genus Mandarina (Bradybaenidae) of oceanic Ogasawara (Bonin Islands, Japan), with the aim of using population genetic data to understand their recent history. Our analysis of a mitochondrial 16S ribosomal RNA region from more than 600 snails in five ground-living species suggests that populations on the small islands of Mukoujima, Anejima, Imotojima and Meijima, as well as on the low-lying southern and central parts of Hahajima, have probably undergone recent bottlenecks followed by subsequent expansions. Except between the main island of Hahajima and Mukouijima, there is almost no evidence for gene flow among islands even though the islands were connected repeatedly by land bridges through the Pleistocene. Within islands the population structure is severe, suggestive of a long-term, low level of gene flow (F(ST) is frequently greater than 0.5 among geographically close populations). Finally, there is a marked genetic patchiness, meaning that genetically close populations are sometimes separated by genetically distant populations. These patterns could be a consequence of expansion from bottlenecks, low active dispersal and founder effects caused by rare long-distance migrants. Unfortunately, the exact nature of the refugia and bottlenecks remains unknown because the palaeoclimate of this region is poorly understood. Dating the population size changes is also challenging because the molecular clock is uncertain. We suggest, however, that arid conditions or deforestation induced by decreased atmospheric CO(2) may have been the main factor in determining population size.

Animals↗
PubMed1996

Prevention of snail miracidia interactions using Phytolacca dodecandra (L'Herit) (endod) as a miracidiacide: an alternative approach to the focal control of schistosomiasis.

The effect of endod berry extract against schistosome miracidia has been tested to determine the sensitivity of these organisms to the molluscicide and to see whether miracidia subjected to sublethal doses of the toxicant will be able to infect their specific host snails. Short contact (30 min) LC50 of endod extract with miracidia of Schistosoma mansoni was 8.2 parts per million (p.p.m.) (95% CL 5-13). However, exposure of S. haematobium to sublethal doses of 3 p.p.m. for 30 min or overnight in open air ponds reduced their infectivity 3.5-5.6-fold when compared with controls. It is suggested that the toxicant could be used in low doses at transmission foci to reduce schistosome infection in snails. This could be done by using a controlled release system to apply the toxicant material at such foci where transmission is likely to occur.

Animals↗
PubMed2004

The close relationship between estimated divergent selection and observed differentiation supports the selective origin of a marine snail hybrid zone.

To study the role of divergent selection in the differentiation of the two morphs in a hybrid zone of the intertidal snail Littorina saxatilis, we compared the strength of the divergent selection acting on a series of shell characters (as estimated by the viability of snails in a reciprocal transplant experiment) with the contribution of these characters to the phenotypic differences between the morphs. We found a close correlation between selection and differentiation, which suggests a cause-effect relationship, i.e. that all present differentiation is the result of past divergent selection. In addition, divergent selection was a very important component of the total natural selection acting on shell measures. These novel results support previous evidence, based on allozyme analysis, of a parapatric origin for this hybrid zone. We discuss possible limitations of this interpretation and the circumstances under which allopatric differentiation would produce the same results. Phenotypic analysis of divergent selection may be a useful method of investigating the evolutionary mechanisms involved in differentiation processes.

Animals↗
PubMed2006

Phenotypic plasticity in two marine snails: constraints superseding life history.

In organisms encountering predictable environments, fixed development is expected, whereas in organisms that cannot predict their future environment, phenotypic plasticity would be optimal to increase local adaptation. To test this prediction we experimentally compared phenotypic plasticity in two rocky-shore snail species; Littorina saxatilis releasing miniature snails on the shore, and Littorina littorea releasing drifting larvae settling on various shores, expecting L. littorea to show more phenotypic plasticity than L. saxatilis. We compared magnitude and direction of vectors of phenotypic difference in juvenile shell traits after 3 months exposure to different stimuli simulating sheltered and crab-rich shores, or wave-exposed and crab-free shores. Both species showed similar direction and magnitude of vectors of phenotypic difference with minor differences only between ecotypes of the nondispersing species, indicating that plasticity is an evolving trait in L. saxatilis. The lack of a strong plastic response in L. littorea might be explained by limits rather than costs to plasticity.

Animals↗
PubMed1993

Positive and negative brain zones in the snail.

Fine wire electrodes were surgically implanted in two regions of the brain of the snail Helix aspersa. To receive electrical stimulation of the brain, a tethered snail was required to displace the end of a rod. Self-stimulation delivered to the parietal ganglion resulted in non-repetition of the operant response, whereas self-stimulation delivered to the mesocerebrum resulted in an increase in response frequency. The reinforcing effect of local extracellular stimulation of two brain zones was investigated in a semi-intact preparation of a closely related species with an identical cellular map (H. lucorum). It was found that mesocerebral stimulation increased the frequency of the reinforced spontaneous movement, but decreased the frequency of the same movement if its absence was reinforced. These results allow us to attribute positive reinforcing effects to this brain area, which is involved in the control of sexual behaviour. Different results were obtained by contingent stimulation of the rostral part of the parietal ganglia, where giant cells controlling avoidance behaviour are located. Stimulation of this zone resulted in a decrease in the frequency of the ongoing spontaneous movements. These findings make possible intracellular investigations of the mechanisms of positive and negative reinforcement.

Animals↗
PubMed1981

Cyclophosphamide as a potential chemosterilant for harmful snails.

Cyclophosphamide induced changes in the ovotestis of the snail Lymnaea acuminata, the vector of the giant liverflukes Fasciola hepatica and Fasciola gigantica were studied in order to explore potential of the drug as a chemosterilant for snails. The drug caused a dose dependent reduction in the levels of DNA, RNA and proteins and the activity of the enzyme alkaline phosphatase. It increased the activity of acid phosphatase and the levels of total free amino acids in the ovotestis. While the animals showed nearly total recovery in RNA and DNA levels 7 days after termination of drug treatment, changes produced in protein, amino acid levels and phosphatase activity did not show any recovery. It appears that cyclophosphamide, while affecting its primary targets i.e. DNA and RNA, irreversibly inhibits protein synthesis through other cellular enzymes as well.

Acid Phosphatase↗
PubMed1972

The antagonistic actions of calcium and magnesium on the superfused ventricle of the snail Helix pomatia.

1. The isolated, superfused half-ventricle of the snail (Helix pomatia) maintains a degree of tonic activity even when not beating, since the membrane is depolarized beyond the tension threshold. Beating may be initiated by lateral stretch of the ventricle and by 5-hydroxytryptamine.2. Ca and Mn each have a hyperpolarizing action, while K and to a lesser extent Na cause depolarization: the tonic activity of the ventricle is affected accordingly.3. An increase in the extracellular concentration of Mg also causes the tension to fall, but without change in membrane potential. It can also initiate beating.4. Contractures induced by 30 mM-K are steadily maintained, but start with a more-or-less distinct twitch-like contraction. A contracture induced by a concentration of K above about 50 mM is poorly sustained and is followed by a further brief contracture when the K concentration is reduced to normal.5. Relations between contracture tension and the concentrations of Ca and Mg accord with the hypothesis that the two ions compete for attachment to a binding site on the cell surface and that tension is proportional to the amount of bound Ca. On this hypothesis, the apparent dissociation constant of the Mg complex is 11.4 mM and that of the Ca complex 0.15 mM or less.6. This effect of Mg is like that of Na on frog ventricle and some of the differences in the behaviour of snail and frog ventricles are abolished by appropriate adjustment of the extracellular concentrations of these ions.

Animals↗
PubMed1976

The effects of lithium and sodium on the potassium conductance of snail neurones.

1. The iontophoretic injection of lithium into snail neurones reversibly increased the resting relative potassium permeability (PK). 2. Long exposures to snail Ringer containing 25 mM-Li and correspondingly reduced Na also caused an increase in PK. This did not occur with Ringer in which the same reduction of Na was made by replacing it with Tris. 3. Replacement of part of the Ringer Na by either Li or Tris led to proportional decreases in internal Na. 4. Injecting large quantities of Na into ouabain-treated cells caused effects similar to those of Li injection. Without ouabain, Na injection stimulated the electrogenic Na pump. 5. A number of tests failed to produce any clear evidence that intracellular Ca was involved in the response to Li.

Animals↗
PubMed1988

Changes in the surface pH of voltage-clamped snail neurones apparently caused by H+ fluxes through a channel.

1. The surface and intracellular pH of snail neurones was recorded with microelectrodes while the membrane potential was reduced in 10 mV steps for a few seconds each or to positive values for periods of several minutes. 2. Depolarizations to positive membrane potentials caused rapid falls in surface pH (pHs) which varied from cell to cell and from one point to another on the surface of the same cell. 3. When pHi was normal or alkaline, the first few 10 mV steps of depolarization often caused a small pHs increase which changed to a decrease as the depolarization increased. The threshold potential at which the pHs increase changed to a decrease varied with pHi in a linear manner, so that at acid pHi values the threshold potential approached the normal resting potential. There was good agreement between the threshold and H+ equilibrium potentials calculated from pHi and pHs. 4. The size of the pHs decrease observed at a given pHi and depolarization depended on extracellular buffering power in a non-linear manner. Solutions buffered with 20 mM-NaHCO3 had similar surface buffering power to CO2-free solutions buffered with only 1-2 mM-HEPES, pH 7.5. 5. In 1 mM-HEPES pHs changes were larger, and pHi increases slower, than those seen in cells depolarized to the same potential in 20 mM-HEPES. The slowing of the rate of pHi increase suggests that the pHs changes occur all over the cell surface, and not only at the recording site. 6. With long-lasting depolarizations the size of the pHs decrease was proportional to the rate of pHi increase and thus, assuming a constant intracellular buffering power, to the rate of efflux of H+. 7. The results provide further evidence that snail neurones possess a channel permeable to H+ which is opened on depolarization. H+ efflux through this channel could cause rapid acidification of a confined extracellular space.

Animals↗
PubMed1989

The intrinsic intracellular H+ buffering power of snail neurones.

1. We measured intracellular pH (pHi) in snail neurones using pH-sensitive glass microelectrodes. We then calculated the intracellular buffering power (beta i) from the pHi changes associated with the influx or efflux of a variety of weak acids or bases. 2. The weak acid anions butyrate and propionate (20 mM) gave similar values for beta i but those measured using 20 mM-acetate were on average twice as great. 3. Although solutions were nominally CO2-free, blockage of pHi regulation with SITS (4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid) increased the sizes of the pHi changes upon weak acid addition and removal. The corresponding measured values of beta i were on average 26% lower with SITS than without. 4. With pHi regulation blocked, the use of 2.7% CO2 to measure beta i gave beta i values similar to those measured with butyrate or propionate. These values were about 50% less than those previously measured in snail neurones using CO2. 5. beta i values calculated from the pHi changes due to the removal of 5 mM of the weak bases trimethylamine, procaine and NH4Cl were all similar and comparable to those measured using butyrate or propionate. Removing the influence of pHi regulation on the undershoots after NH4Cl removal was found to decrease the apparent measured values of beta i by 10%. 6. Combining all the data (except the values obtained using CO2 and acetate), and adjusting for the errors due to pHi regulation reducing the sizes of the pHi changes, we found that the mean value for beta i was 10.4 +/- 0.6 mM (+/- S.E.M.) at a mean pHi of 7.36 +/- 0.05. 7. We also investigated the relationship between beta i and pHi using ionophoretic acid injection. By means of step-wise injections, with pHi regulation blocked, we found that at normal pHi levels beta i remained relatively constant. However, at a pHi of less than about 6.8 beta i increased with decreasing pHi.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1991

Muscarinic enhancement of the voltage-dependent calcium current in an identified snail neuron.

1. In the F1 neuron of the snail Helix aspersa bathed in a Ba2+ and 4-aminopyridine-containing saline, carbamylcholine (CCh) enhanced the inward current carried by Ba2+ through the voltage-dependent Ca2+ channels. 2. This effect of CCh on the F1 neuron was not affected by the nicotinic antagonists (+)-tubocurarine and hexamethonium, but it was mimicked by oxotremorine and blocked by both atropine and pirenzepine. 3. The intracellular injection of GTP gamma S (guanosine 5'-O-(3- thiotriphosphate] into the F1 neuron caused both a decrease in Ca2+ current and a blockade of the CCh-induced enhancement of the Ca2+ current. 4. Neither cyclic AMP, cyclic GMP nor arachidonic acid mimicked the effect of CCh on the Ca2+ current in the F1 neuron. In contrast, the intracellular injection of EGTA blocked the CCh-induced enhancement of the Ca2+ current thus suggesting that cytosolic Ca2+ is involved in the CCh-induced response. 5. We then investigated the possible role of inositol 1,4,5-trisphosphate (InsP3) and Ca(2+)-dependent protein kinases in the CCh-induced enhancement of the Ca2+ current. The intracellular injection of InsP3 in the F1 neuron elicited no consistent change in the Ca2+ current. Diacylglycerol analogues (OAG and DOG) decreased the Ca2+ current amplitude, i.e. an effect opposite to that produced by CCh. This effect of the diacylglycerol analogues resulted from the activation of protein kinase C (PKC) since it was blocked by staurosporine. In addition, staurosporine did not affect the CCh-induced increase in Ca2+ current. 6. The intracellular injection of either Ca(2+)-calmodulin-dependent protein kinase II (Ca(2+)-CaM-PK) or a peptide inhibitor of this enzyme into the F1 neuron affected neither the Ca2+ current nor its enhancement by CCh. 7. We conclude that the CCh-induced enhancement of the Ca2+ current in the snail F1 neuron involves the activation via muscarinic receptors of an intracellular transduction mechanism in which cytosolic Ca2+ plays a key role. However, InsP3, protein kinase C and Ca(2+)-CaM-PK do not appear to be directly involved in this CCh-induced response.

Action Potentials↗
PubMed1996

Relationship between intracellular calcium and its muffling measured by calcium iontophoresis in snail neurones.

1. We have measured intracellular free calcium ion concentration ([Ca2+]i) with fura-2, and intracellular chloride with chloride-sensitive microelectrodes, in voltage-clamped snail neurones. By making iontophoretic injections of CaCl2 we have investigated calcium muffling, the sum of the processes which minimize the calcium transient, at different values of [Ca2+]i. 2. By injection of calcium into cell-sized droplets of buffer we measured the calcium transport index. It was stable over the range pCa 6-7.4 (0.48 +/- 0.06 measured at pCa 6.70 +/- 0.12, n = 5). 3. Measurement of intracellular chloride activity during a series of fura-2-KCl pressure injections revealed a nearly linear relationship between fura-2 Ca(2+)-insensitive fluorescence and the sum of the increments in intracellular chloride. This allowed us to calculate the intracellular fura-2 concentration ([fura-2]i). 4. The rate of recovery of [Ca2+]i following a depolarization-induced load was increased by low [fura-2]i (10-20 microM) but decreased by higher [fura-2]i (40-80 microM). These effects are consistent with the addition of a mobile buffer to the cytoplasm. 5. Iontophoresis of Ca2+ at various membrane potentials allowed us to calculate the intracellular calcium muffling power (the amount of calcium required to cause a transient tenfold increase in [Ca2+]i per unit volume) and calcium muffling ratio (number of Ca2+ ions injected divided by the maximum increase in [Ca2+]i per unit volume) at different values of [Ca2+]i. 6. Calcium muffling power at resting [Ca2+]i was approximately 40 microM Ca2+ (pCa unit)-1, (about 250 times less than for hydrogen ions). It increased linearly about fivefold with [Ca2+]i over the range 20-120 nM (10 cells, 153 measurements) and therefore exponentially with decreasing pCa. 7. The calcium muffling ratio appeared to be constant (361 +/- 14, n = 10 cells, 130 measurements) over the range 20-120 nM Ca2+. 8. In three experiments we modelled the additional calcium buffering power produced by multiple pressure injections of fura-2 into voltage-clamped snail neurones. Back-extrapolation of the increases in calcium buffering power allowed us to calculate the calcium muffling power of the neurones. 9. Small increases in [fura-2]i (approximately 10 microM) significantly increased intracellular calcium muffling power in individual experiments. However, the variability among neurones in intracellular calcium muffling power was large enough to obscure the additional buffering produced by fura-2 in pooled experiments.

Animals↗
PubMed2005

Web-spinning caterpillar stalks snails.

Moths and butterflies compose one of the most diverse insect orders, but they are overwhelmingly herbivorous. Less than 0.2% are specialized predators, indicating that lepidopteran feeding habits are highly constrained. We report a Hawaiian caterpillar that specializes on snails, a unique food source requiring an unusual feeding strategy. The caterpillar uses silk to restrain live prey. All caterpillars have silk glands, but none are known to use silk in this spiderlike fashion. Considering the canalization of caterpillar diets, evolution to attack and feed on snails is an anomaly. Hawaii s isolation and consequently disharmonic biota likely promote evolutionary experiments that occur nowhere else.

Animals↗
PubMed2004

Aquatic snails, passive hosts of Mycobacterium ulcerans.

Accumulative indirect evidence of the epidemiology of Mycobacterium ulcerans infections causing chronic skin ulcers (i.e., Buruli ulcer disease) suggests that the development of this pathogen and its transmission to humans are related predominantly to aquatic environments. We report that snails could transitorily harbor M. ulcerans without offering favorable conditions for its growth and replication. A novel intermediate link in the transmission chain of M. ulcerans becomes likely with predator aquatic insects in addition to phytophage insects. Water bugs, such as Naucoris cimicoides, a potential vector of M. ulcerans, were shown to be infected specifically by this bacterium after feeding on snails experimentally exposed to M. ulcerans.

Animals↗
PubMed1987

Extracellular acidification at the surface of depolarized voltage-clamped snail neurones detected with eccentric combination pH microelectrodes.

A new design of double micropipette was used to measure intracellular pH, membrane potential, and surface pH of superfused snail neurones. A third double micropipette was used to control the membrane potential via a CsCl-filled barrel and inject HCl iontophoretically. In one series of experiments the surface pH fell by up to one-third of a pH unit when the membrane potential was clamped to 20 mV, pHi was initially 6.7, and extracellular pH was about 7.4 in a medium buffered either with 2 mM HEPES or 2.7% CO2 and 20 mM bicarbonate. In a second series in which surface pH was observed during brief depolarizations to different potentials with different pHi, the potential at which the surface began to acidify varied with pHi with a slope of 32 mV per pH unit. The results confirm that H+ ions leave depolarized snail neurones if the electrochemical gradient is favourable and show that CO2-bicarbonate buffered solutions have a low effective extracellular buffering power for rapid additions of acid.

Animals↗
PubMed2002

Primary causes of decreased mitochondrial oxygen consumption during metabolic depression in snail cells.

Cells isolated from the hepatopancreas of estivating snails (Helix aspersa) have strongly depressed mitochondrial respiration compared with controls. Mitochondrial respiration was divided into substrate oxidation (which produces the mitochondrial membrane potential) and ATP turnover and proton leak (which consume it). The activity of substrate oxidation (and probably ATP turnover) decreased, whereas the activity of proton leak remained constant in estivation. These primary changes resulted in a lower mitochondrial membrane potential in hepatopancreas cells from estivating compared with active snails, leading to secondary decreases in respiration to drive ATP turnover and proton leak. The respiration to drive ATP turnover and proton leak decreased in proportion to the overall decrease in mitochondrial respiration, so that the amount of ATP turned over per O2 consumed remained relatively constant and aerobic efficiency was maintained in this hypometabolic state. At least 75% of the total response of mitochondrial respiration to estivation was caused by primary changes in the kinetics of substrate oxidation, with only 25% or less of the response occurring through primary effects on ATP turnover.

Adenosine Triphosphate↗