Modulation of swimming behavior in the medicinal leech

Expression of swimming in the medicinal leech (Hirudo medicinalis) is modulated by serotonin, a naturally occurring neurohormone. Exogenous application of serotonin engenders spontaneous swimming activity in nerve-cord preparations. We examined whether this activity is due to enhanced participation of swim motor neurons (MNs) in generating the swimming rhythm. We found that depolarizing current injections into MNs during fictive swimming are more effective in shifting cycle phase in nerve cords following serotonin exposure. In such preparations, the dynamics of membrane potential excursions following current injection into neuronal somata are substantially altered. We observed: 1) a delayed outward rectification (relaxation) during depolarizing current injection, most marked in inhibitory MNs; and 2) in excitor MNs, an enhancement of postinhibitory rebound (PIR) and afterhyperpolarizing potentials (AHPs) following hyperpolarizing and depolarizing current pulses, respectively. In contrast, we found little alteration in MN properties in leech nerve cords depleted of amines. We propose that enhanced expression of swimming activity in leeches exposed to elevated serotonin is due, partly, to enhancement of relaxation, PIR and AHP in MNs. We believe that as a consequence of alterations in cellular properties and synaptic interactions (subsequent paper) by serotonin, MNs are reconfigured to more effectively participate in generating and expressing the leech swimming rhythm.Abbreviations AHP Afterhyperpolarizing potential - DCC Discontinuous current clamp - DE Dorsal excitor motor neuron - DI Dorsal inhibitor motor neuron - IPSP Inhibitory postsynaptic potential - MN Motor neuron - PIR Postinhibitory rebound - VE Ventral excitor motor neuron - VI Ventral inhibitor motor neuron     

The role of touch,pressure and nociceptive mechanoreceptors of the leech in unrestrained behaviour

1. The maximum force exerted against an isometric force transducer by 6 leeches weighing 2.6–3.7 g, as they squeezed through apertures of different widths varied inversely with aperture width.
2. T cells in the leech skin code for velocity of indentation, not pressure or displacement. The frequency with which T cells fire is best described by two log functions, one for low, another for fast indentations. T cells responded to indentation velocities down to 10 μms^?1.
3. The average threshold pressure for 5 P cells was 150 kPa and for 5 N cells was 521 kPa.
4. We conclude from these data that when leeches explore their mechanical environment and initiate contact with external objects, the threshold pressure for N cells is rarely crossed. Of the three classes of mechanoreceptor, T cells are the main modality through which leeches obtain contact information, though P cells may occasionally be recruited for local pressure peaks.

     

Uptake of catecholamines and penetration of trypan blue after blood-brain barrier lesions

Summary Blood-brain barrier lesions were produced on rabbits which had been depleted of their endogenous monoamines with a large dose of reserpine. After the lesion, catecholamines and the blood-brain barrier indicator dye trypan blue were injected. After freeze-drying, the cellular distribution of the injected substances was observed in the fluorescence microscope.It was found that, in the injured areas, the monoamines and trypan blue had penetrated into the brain parenchyma, where the monoamines were taken up and concentrated in nerve terminals. Trypan blue was found diffusely in the neuropil, while the nerve cell bodies and axons exhibited no fluorescence of trypan blue. On the control side, this type of fluorescence of catecholamines or trypan blue could not be detected.The lesions applied seem to be quite specific for the blood-brain barrier, as an active and energy-dependent uptake of catecholamines could be demonstrated in central monoamine nerve terminals. Thus the results also show that these terminals have the same reserpine-resistant membrane pump in vivo as earlier demonstrated for peripheral adrenergic neurons, and for central neurons in vitro.This investigation has been supported by research grants (B 66-158 and B 66-257) from the Swedish Medical Research Council and by a Public Health Service Research Grant (NB 05236-02) from the National Institute of Neurological Diseases and Blindness. For generous supplies of drugs we thank the Swedish Ciba, Stockholm, Sweden for reserpine (Serpasil^®), the Swedish Pfizer, Stockholm, Sweden for nialamide (Niamid^®) and Hoechst Anilin AB, Göteborg, Sweden for -methylnoradrenaline (Corbasil^®).     

Direct chemically mediated synaptic transmission from mechanosensory afferents contributes to habituation of crayfish lateral giant escape reaction

The neural mechanism of habituation of the crayfish lateral giant-mediated escape reaction was analyzed electrophysiologically and pharmacologically. Upon repeated stimulation of tailfan afferents (at 0.2–1 Hz) lateral giant showed rapid habituation and failed to spike. Upon low-intensity sensory stimulation, the lateral giant responded with two subthreshold excitatory post-synaptic potentials, the and components. A third component, the ' component, was discriminated at the boundary of excitatory post-synaptic potentials between the late and early components with stimulation just subthreshold or suprathreshold to evoke lateral giant spikes. This ' component increased in amplitude with hyperpolarizing current injected into the lateral giants, although the amplitude of both the and components remained constant. Furthermore, bath application of the nicotinic antagonist, d-tubocurarine caused a rapid reduction in the amplitude of the ' component while the amplitude of the component was reduced gradually and that of the component remained unchanged. Single-hair stimulation indicated that some sensory afferents made direct connections with the lateral giants mediated by chemical synapses and form the potential of ' component of the lateral giants. Since lateral giant inactivation was associated with a reduction of excitatory post-synaptic potential amplitude of the ' component, connection from these afferents could contribute, at least in part, to lateral giant habituation.Abbreviations EPSP excitatory post-synaptic potential - LG lateral giant     

The properties and propagation of a cardiac-like impulse in the skin of young tadpoles

Summary The contact relationships of skin cells in late embryos and young larvae of Xenopus laevis are described. Superficial cells are joined by tight or gap junctions at their outer periphery but elsewhere simple appositions are found. All-or-none impulses are evoked in the skin by electrical or mechanical stimuli (Fig. 3). Evidence is presented in favour of the view that these impulses are generated by the majority of skin cells and not by some neuronal element in the skin. The impulse propagates throughout the skin from any stimulated point (at average speed of 7.7 cm/sec) even when the animal is in distilled water. However, removal of Na⁺ from solutions bathing the inner skin surface or treatment with Tetrodotoxin abolishes the impulse indicating that it is Na⁺ dependent. Current injected into skin cells spreads to others so it is suggested that the impulse propagates by direct current flow from cell to cell. The neuroid conduction system in the skin of Xenopus tadpoles is compared to similar systems in coelenterates and to the propagation of the vertebrate cardiac impulse.Partly supported by an S.R.C. Fellowship.     

Impairment of pancreatic acinar function by reserpine in vivo and in vitro

Summary Chronic reserpine treatment of animals, an experimental model for cystic fibrosis (CF), results in generalized exocrinopathy, impaired pancreatic secretion, and decreased pancreatic content of amylase. The mechanisms of altered acinar function and decreased amylase content in both CF and the reserpine-treated rat are unknown. To examine this alteration, the rate of [³H]phenylalanine (phe) incorporation into cellular protein was determined in pancreatic acinar cells after reserpine treatment of rats in vivo (7 d) and of cells in vitro (1 to 24 h). Acinar cells isolated from control, chronic reserpine-treated, and pair-fed rats were incubated in vitro with 0, 30, 50, or 100 μM reserpine. Reserpine treatment in vitro for 24 h of acinar cells from control rats significantly decreased amylase activity (20 to 70%), an effect similar to that of reserpine treatment in vivo. In vivo, reserpine treatment decreased [³H]phe incorporation (disintegrations per minute per milligram protein) 56% in freshly isolated cells, but did not alter intracellular specific activity (disintegrations per minute per nanomole phe, SA) of [³H]phe. Reserpine treatment (30 and 50 μM) in vitro for 1 h also decreased [³H]phe incorporation by freshly isolated cells from control (53 to 85%) and pair-fed (40 to 68%) rats. Reserpine treatment for 24 h in vitro significantly decreased [³H]phe incorporation by cells from control (82 and 98%), pair-fed (80 and 95%), and chronic reserpine-treated (90 and 97%) rats as compared with cells from respective in vivo treatments cultured with no reserpine. In vitro reserpine treatment also decreased the intracellular SA of [³H]phe in freshly isolated cells from control (14 and 36%) and pair-fed (35 and 39%) rats and in cultured cells from control (11 and 86%), pair-fed (60 and 88%), and chronic reserpine-treated (49 and 76%) rats. However, these alterations of SA by reserpine did not account for the decreased incorporation of [³H]phe into acinar protein, which remained significantly lower (70 to 88%) when expressed as total phe incorporation. These results suggest (a) that reserpine acts directly on acinar cells to alter function and (b) that the ability of the pancreas to synthesize digestive enzymes may be impaired in this model of cystic fibrosis. This study was supported in part by the Cystic Fibrosis Foundation, Bethesda, MD.     

Mechanoelectric transduction in nematocytes of a hydropolyp (Corynidae)

In sensitivity and ultrastructure of their cnidocil apparatus (CA), the nematocytes (stinging cells) of hydrozoans are analogous to hair cells of vertebrates and epidermal mechanoreceptors of insects. Intracellular recordings using current and voltage clamp in the capitate tentacles of the marine hydropolyp Stauridiosarsia producta (Corynidae) now revealed that depolarizing receptor potentials and receptor currents are generated in nematocytes (stenotele type) in response to mechanical stimulation of the CA. The responsive cells were identified by injection of Lucifer Yellow. For recording, the tentacles were isolated from the polyp and held by a suction capillary. Stimuli were applied by a glass probe moved electromagnetically or piezoelectrically.The mechanosensitivity of the nematocytes was found to be strictly limited to the CA. The characteristics of the mechanoelectric transduction were those typical of mechanoreceptor cells: phasic-tonic time course of an increase in membrane conductance; latency between stimulus and receptor response < 50 s; sigmoid relationship between receptor-response amplitude and stimulus amplitude; maximal increase in conductance of 15 nS; reversal potential between + 35 mV and — 10 mV; unspecific cation dependence and reversible blocking by streptomycin. The results suggest a direct mechanical control of unspecific cation channels such as has been found for mechanoreceptor cells.Suprathreshold receptor potentials elicit two forms of regenerative depolarization: non-inactivating, steplike potentials and action potentials. The latter can trigger discharge of the nematocyst.The discharge of nematocysts in the intact animal (without recording) in response to adequate stimuli was blocked by streptomycin and Na⁺ depletion in the same way as the receptor potential.Mechanoreceptor potentials are thus the beginning of a stimulus-induced electrical reaction cascade that ends in nematocyst discharge.     

Insulin-like Growth Factor-I cDNA Gene Transfer in vitro and in vivo

Our hypothesis is that gene transfer of an IGF-I CMV-cDNA with cholesterol containing cationic liposomes is an efficient tool for transient transfection of growth factors in vitro and in vivo. In vitro, we transiently cotransfected IGF-I cDNA with a CMV construct and a Lac Z CHKCHK-galactosidase cDNA/CMV construct using cholesterol containing cationic liposomes and measured CHKCHK-galactosidase and IGF-I mRNA and protein. In vivo, we subcutaneously injected 3-month-old male Sprague–Dawley rats with IGF-I cDNA and CHKCHK-galactosidase cDNA into rat skin. After IGF-I and CHKCHK-galactosidase were cotransfected into PC12 cells, Northern blot analysis showed that the peak time of IGF-I expression was 2 days for mRNA and 5 days for protein. In vivo, a cDNA/liposome ratio of 1:2 was most effective. IGF-I protein expression in IGF-I-transfected skin resulted in significant transfection from day 5 to day 7. In situ determination of CHKCHK-galactosidase activity confirmed that transfections resulted in a restricted expression area.     

Recruitment of beta-2-glycoprotein 1 to cell surfaces in extrinsic and intrinsic apoptosis

Apoptotic cells and phagocytes have developed a diverse array of distinct ligand-receptor systems that drive the recognition and uptake of dying cells. Phagocytes recognize apoptotic cells either directly, by binding to specific ligands at their cell surface, or indirectly, by binding to bridging proteins that bind these ligands. Previous observations showed that the plasma bridging protein 2GP1, binds PS containing vesicles, and enhances their binding and engulfment by phagocytes in vitro. In this study we show that apoptotic cells injected intravenously and intraperitonealy into syngeneic mice recruited the PS binding protein, 2GP1. Examination of peritoneal exudates and spleen thin sections showed that only the injected apoptotic cells picked up endogenous 2GP1. Recovery of cells from the peritoneum showed that apoptotic cells bearing 2GP1 were clustered around host peritoneal phagocytes. In addition, tissue sections from mice injected with Fas antibody showed colocalization of 2GP1 with TUNEL-positive apoptotic cells. These results provide evidence that endogenous 2GP1 binds apoptotic cells in vivo, suggesting that the protein plays an important physiologic role in the recognition of dying cells.     

Fever in the leech,Nephelopsis obscura (Annelida)

Summary Leeches were placed in a 0.8 m linear temperature gradient from 0°C to 40°C. The temperature selected by the leeches was recorded over 30 min intervals; series of animals then received an injection of either pure sterile water,Escherichia coli endotoxin (LPS) at doses of 0.05, 0.25 and 10 g·g^–1, alcohol, or prostaglandin E₁ (PGE₁) at doses of 2 and 4 g·g^–1. After a latency of about 90 min, the leeches developed a dose-dependent fever in response to LPS. Maximal preferred temperature was near 29.6±1.4 whereas the control was 20.5±0.6°C. PGE₁ also evoked dose-dependent fevers of the same magnitude as LPS (30.0±1.0°C), but without latency. Another series of leeches received an injection of LPS of 10 g·g^–1 while in water containing 1.6 mg acetaminophen per 20 l water. Acetaminophen prevented the development of LPS fever. It is concluded that annelids respond to infection with a behavioral fever analogous to that of vertebrates.     

31P-NMR study on effects of electric shock on swimming leeches,Hirudo medicinalis

• 1.1. We evaluated the effect of electric shock on swimming leeches by measuring changes in high-energy phosphate metabolism using in vivo³¹P-NMR.
• 2.2. Leeches electrically stimulated during swimming showed anodal galvanotaxis, and stopped swimming with stimulation at strong current.
• 3.3. Comparison of the concentrations of high-energy phosphate metabolites before and after electric shock using ³¹P-NMR revealed a marked decrease in β-ATP and an increase in that of Pi.
• 4.4. Electric shock apparently induces excessive muscle fatigue in leeches, resulting in transient paralysis.

     

Spindle checkpoint and apoptotic response in α-particle transformed human bronchial epithelial cells

The mitotic spindle checkpoint and apoptosis in response to nocodazole, a microtubule-disrupting agent, were investigated in the -particle transformed human bronchial epithelial cell lines BERP35T1, BERP35T4 and the parental BEP2D cell line. When treated with 0.2 g/ml of nocodazole, BEP2D and BERP35T1 cells were efficiently arrested in the mitotic phase, whilst BERP35T4, a transformed cell line showing chromosomal instability, failed to be arrested as evidenced by a low G2/M fraction. BERP35T4 cells also showed a higher proportion of aneuploids when treated with nocodazole or not. Thus, the BERP35T4 cell line has a defect in spindle checkpoint function. The extent of apoptosis induced by nocodazole (0.3 g/ml) was significantly higher (2-fold to 2.5-fold) in BEP2D cells than in the two transformed cell lines. Furthermore, the induced apoptosis was found to occur predominantly before mitotic division in BEP2D cells. In BERP35T4 cells, however, 50% of induced apoptosis occurred before mitotic division and 50% occurred after division in binucleated cells when co-treated with cytochalasin B. The 5-CpG island of the Chfr gene, a mitotic checkpoint gene that functions in entry into metaphase, was found to be methylated in BERP35T4 cells but not in BEP2D cells. Consistent with methylation, the expression of the Chfr gene was markedly suppressed in BERP35T4 cells. Our results suggest that the impaired spindle checkpoint and abnormal apoptotic response may be related to the oncogenic progression of human bronchial epithelial cells initiated by exposure to -particles.     

Enrichment of γ-linolenic acid from fungal oil by lipase-catalysed reactions

Summary Various lipases have been evaluated as biocatalysts for the enrichment of -linolenic acid from a commercial fungal oil derived from Mucor sp. by selective esterification of the fungal oil fatty acids with n-butanol or by selective hydrolysis of the oil. Lipase from M. miehei (Lipozyme), as compared to lipases from Candida cylindracea, Penicillium cyclopium, and Rhizopus arrhizus, was found to be most effective in the enrichment of -linolenic acid in unesterified fatty acids upon esterification of the fungal oil fatty acids with n-butanol. Thus, the -linolenic acid content could be raised from 10.4% in the starting material to 68.8% in the unesterified fatty acids. Selective hydrolysis of the fungal oil triacyglycerols using Lipozyme resulted in about 1.5-fold enrichment of -linolenic acid in the unhydrolysed acylglycerols. Other lipases tested, such as those from P. cyclopium, C. cylindracea, R. arrhizus, Penicillium sp. (Lipase G), porcine pancreas and Chromobacterium viscosum, were also rather ineffective in the enrichment of -linolenic acid by selective hydrolysis of the fungal oil triacylglycerols. Offprint requests to: K. D. Mukherjee     

Skin colonization byMalassezia furfur in healthy children up to 15 years old

The prevalence ofM. furfur, a lipodependent fungus, in the skin of 0 to 15-year-old healthy children was studied. Sterilized carpet was used to collect skin samples which were cultured in Oxgall medium (Difco) with 1% olive oil and incubated for 10 days at 37 °C.M. furfur was recovered in 17.8% of infants, with similar findings in both sexes. The highest prevalence ofM. furfur colonization was found among children of 0 to 18 months and 11 to 15-year-olds, with 23.3% and 26.7% respectively.Part of the Ms. thesis of Victor Silva Associação deMalassezia furfur com patologias com componente seborréico.     

Ultrastructure of the epidermis of Meara stichopi (Platyhelminthes,Nemertodermatida) and associated extra-epidermal bacteria

This preliminary mechanistic model of normal swimming and phototactic behaviour in individual Daphnia was constructed using data and assumptions based on experiments and observations. Swimming under constant light intensity is characterized by short periods of upward movements alternating with equal periods of downward movements. Two oscillators are proposed that generate these phases in swimming. Unexpected shifts in depth, as observed in D. magna and D. longispina, are also present in the swimming of the computer daphnid and thus seem to be inherent to the underlying mechanism. As in real daphnids, during relative decreases in light intensity of low velocity, positive phototactic upward swimming is stepwise. With increasing velocity in the change in light, these steps disappear. When the model is triggered by a natural increase in light at dawn, a small downward movement results. Migration distance can be increased to commonly found depths of migrating Daphnia by the introduction of a fish exudate factor into the model, which enhances the phototactic response. Since attenuation of light in the water affects the phototactic swimming response, it also influences migration distance. The results of model calculations agree quite well with an empirical relationship between Secchi disc depth and amplitude of diel vertical migration in a number of lakes.     

β-Glucuronidase activity in human T and B lymphocytes and the Tμ and Tγ subpopulations

Summary The -glucuronidase staining characteristics of isolated T cell populations and the T and T enriched fractions derived of them were studied. T lymphocytes were obtained from purified T lymphocytes by ox-IgG rosette sedimentation. The rosette-forming cells in the pellet were referred to as T lymphocytes, whereas the lymphocytes in the interface were referred to as T depleted or T lymphocytes. B cells were studied on rosetted mononuclear cells with either mouse erythrocytes or with Staphylococcus Aureus (Cowan I) bacteria, after a preceeding polyvalent anti-human Ig treatment of the cells. While B cells showed mostly no reactivity, T and T cells were respectively characterised by a dot-like and granular pattern of reactivity. These findings are in agreement with those observed by others after -naphthyl-acetate esterase or acid phosphatase staining. Within the T lymphocyte fraction, the T non-, non lymphocytes seemed to have a granular pattern of reactivity. The same staining pattern was found in non-B, non-T lymphocytes.     

Food partitioning by lake-dwelling triclads and glossiphoniid leeches: field and laboratory experiments

The triclads Polycelis tenuis and Dugesia polychroa and the glossiphoniid leeches Glossiphonia complanata and Helobdella stagnalis are abundant on the stony shores of productive British lakes. All species are food limited and there is considerable overlap in the diets of these triclads and leeches. This paper investigates interactions between the two groups using field and laboratory experiments to try to identify the mechanism of their co-existence. Triclad and leech numbers were manipulated inside experimental enclosures, mathced by controls, erected on the stony shore of an eutrophic English lake. Increasing the numbers of P. tenuis and D. polychroa prior to the reproductive season in spring resulted in a significant decrease in the numbers and body size of G. complanata and H. stagnalis compared with control populations in the summer months, and vice versa. However, increases and decreases were temporary with a readjustment of numbers and body size to control levels in the autumn after reproduction had ceased. It is suggested that increasing the numbers of either group elevated the severity of both intra- and interspecific competition for food. The condition of prey may, in part, determine the strength of competition, and this was examined in laboratory experiments in which different densities and ratios of P. tenuis and H. stagnalis were offered either live of recently crushed Asellus aquaticus. In monospecific controls, growth rates of P. tenuis were greater when fed on crushed than live Asellus, but there was no significant difference in the growth of H. stagnalis fed either live or crushed prey. In mixed cultures of predators, P. tenuis and H. stagnalis were the superior competitors when fed on crushed and live Asellus, respectively. However, when competitive pressure was low, at low densities of predators, the presence of H. stagnalis in mixed cultures fed on live prey was beneficial to the growth of P. tenuis. These results are explained in terms of the greater ability of triclads to detect damaged prey, leaking body fluids, due to their sophisticated chemosensory system, and the ability of leeches to capture live prey due to the presence of suckers. It is concluded that co-existence of the two groups in British lakes is assisted by the partitioning of food on a live or damaged basis.     

Direct current electric field in some teleost species: Effect of medium salinity

Summary A direct current electric field up to 3 mV/ cm was recorded in 33 sea water around the fishMyoxocephalus brandti, Hexogrammos octogrammos, Enophrys diceraus, Pleuronectes stellatus, Bathimaste r derjugini, Sebastes scorpaeniformis. The body surface potentials were positive in relation to the external and internal media; they attained 10 mV and slowly varied near the mean value at every point. The potentials at the surface points of individual skin sections adjoining the oral and branchial cavities, the anal orifice and peripheral fin sections were normally characterized by polarities opposite to those of body surface potentials (in sea water they were negative in relation to the external medium).When placed in sea water during their fresh water cycle, the salmonOncorhynchus keta and the fresh water fishSalvelinus alpinus andMisgurnus fossilis had no d.c. field.In fresh water containing less than 0.03 salt, a d.c. field up to 25 mV/cm was recorded around all the above mentioned species. The potentials had an opposite polarity to that recorded in sea water.The distribution of potentials over the fish surface depends on the species. The potentials at some points of the body surfaces were found to vary when other fish or metal objects were placed in the aquarium.The parameters of the direct current electric field generated by a whole fish and by isolated skin pieces were identical and varied by the same law with changed medium salinity. Thus it may be assumed that the d.c. electric field around the fish is produced by active electrogenic ion transport mechanisms localized in the skin.     

Differentiation betweenPhaeocystis pouchetii (Har.) Lagerheim andPhaeocystis globosa Scherffel

An Arctic clone ofPhaeocystis pouchetii LAGERHEIM was compared toPhaeocystis globosa SCHERFFEL isolated from the southern North Sea with regard to temperature tolerance and colony shapes. Already youngP.pouchetii colonies (<100 m) show the typical distribution of the cells in groups, separated from each other by wide zones of cell-free mucilage; the maximum colony size is ca 2 mm in diameter.P.pouchetii colonies form clouds with bubble-like vesicles, spherical colony-shapes are seldom found.P.globosa colonies are spherical up to a size of 2 mm; the cells are distributed homogeneously over the periphery of the colonies. A pouchetii-like distribution of cells never occurs either in the spherical young colonies or in the pear-shaped old colonies (size up to 8 mm). A development from the colony shape of the globosa-type to the pouchetii-type or vice versa was never found. Therefore the colony shape has to be considered a constant distinctive character. Single cells ofP.pouchetii andP.globosa cannot be separated from each other by using the light microscope; this also holds for the flagellates and the non-motile cells.P.pouchetii grows well between 0°C and 14°C,P.globosa between 4°C and 22°C, respectively. Because of the distinctive differences in the morphology of the colonies and the differences in temperature tolerances we propose thatPhaeocystis globosa should no longer be considered conspecific withPhaeocystis pouchetii.     

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.