Role of the Age Factor in Eye Regeneration in the Gastropod Achatina fulica

The dependence of the ability to regenerate the eye on the age of experimental animals was studied in the snail Achatina fulica. The degree of regeneration was estimated by light-microscopic and electrophysiological methods and by analyzing the motor response to visual stimuli. In older age groups, the number of regenerated eye-bearing tentacles decreased, whereas the period of regeneration increased. The regenerated eyes of the snails operated at the age of more than two months remained smaller than normal eyes even after six months. Regeneration of the distal part of the optic nerve was observed, and the regenerated eyes recovered the ability to respond to stimulation by light. In the electroretinogram, the responses of the regenerated eye, compared to the control, were characterized by lower amplitude and longer repolarization and refractory periods. Manifestations of the motor response to visual stimuli in the young snails with regenerating eyes could be regarded as evidence for the recovery of connection between the organ of sight and the central ganglia.     

Consequences of food-attraction conditioning in Helix: a behavioral and electrophysiological study

Food-attraction conditioning is a learning phenomenon by which adult Helix pomatia acquire the ability to locate food through exposure to that particular food. Food-conditioned snails can be distinguished from naive snails during their approach to food. Naive snails keep their tentacles upright — whereas food-conditioned animals bend the tentacles down-ward, in a horizontal orientation, pointed in the direction of the food.Tentacle musculature is innervated by two peritentacular nerves (PTn), each projecting to approximately one hemi-section of the tentacle wall. Stimulating the peritentacular nerves caused the tentacles to bend downward in a manner reflecting the full complement of tentacle movements performed by conditioned snails.The neural correlate of tentacle movements was investigated in isolated ganglion preparations with the posterior tentacles attached. PT nerve activity was recorded while the olfactory epithelia were stimulated with natural food odors. Preparations obtained from conditioned animals responded with a substantial increase in unit activity (mean increase 280%) to stimulation with odor of the conditioned food but not to other odors. Preparations from naive animals did not respond to food odor stimulation. The electrophysiological results demonstrated that plasticity due to conditioning the snails in vivo survived dissection and could be monitored in vitro.Abbreviations ext PTn external peritentacular nerve - int PTn internal peritentacular nerve     

Magnetic orientation in the semi-terrestrial amphipod, Orchestia cavimana, and its interrelationship with photo-orientation and water loss

ABSTRACT. Orchestia cavimana Heller (Amphipoda, Talitridae) were shown to orient to the geomagnetic field as well as to an anisotropic light field. When tested in an isotropic light field the orientation in the geomagnetic field was either in or opposite to the compass direction of the light vector of the anisotropic light field in which the animals had lived before the test, and this orientation was upset predictably by changing the magnetic field with Helmholtz coils. The polarity of the reaction in both magnetic orientation and photo-orientation was correlated with pre-experimental water loss. The magnetic orientation of O. cavimana is compared with that of Tenebrio molitor , and its biological significance discussed.     

The menotactic orientation of the prosobranch mollusc Littorina littorea

The menotactic orientation of the prosobranch mollusc Littorina littorea to a one stripe pattern (Fig. 2) has been investigated under open-loop and closed-loop conditions. Results: 1) Under open-loop conditions the animals try to compensate for an angular deviation of the pattern from the menotactic angular position by turning movements of, on the average, constant angular velocity (Fig. 4). 2) The angular velocity depends on this deviation according to the -characteristic (Fig. 5). The orientation behaviour under closed-loop conditions can be directly derived from the -characteristic. Within experimental limits the snail does not show an optomotor response. 3) To patterns of wedge-shaped intensity distribution the snails orientate at a small angle relative to the edge of the pattern (Fig. 3). The orientation angle of the animals to this pattern is much less variable than the orientation angle to a single light source. The orientation behaviour shows that the intensity gradient of the pattern is important for the orientation of the animal. 4) A normally distributed noise process is superimposed on the average orientation direction. The variance of this noise process is the same for the orientation under open-loop and under closed-loop conditions (Fig. 7). In both cases the power spectrum of the noise process contains pronounced maxima at equally spaced frequencies (Fig. 8).     

Food-attraction conditioning in the snail,Helix pomatia

Adult pulmonate snails (Helix pomatia) were released equidistant between two types of food, carrot and potato, respectively. Naive snails moved in different directions and did not locate either food above chance, although both foods were readily eaten upon direct contact. After a single carrot feeding episode, 75% of the carrot-fed snails moved directly towards the carrot and ate it. Conversely, potato-fed snails located the potato in 67% of the cases. Snails that were fed apple or lettuce behaved like naive animals, with the majority of animals (75% in both cases) locating neither the carrot nor the potato.The ability of snails to locate this particular food after a single feeding episode was maintained for at least 11 days, provided that the snails were not exposed to other foods in the interim. If the animals were fed a different food (but still tested for food-finding ability to the initially conditioned food) their orientation preference decreased gradually over a period of 5 days.Although the snails' orientation is based upon olfactory cues, exposure to food odor alone is not sufficient to enable food-finding; additional feeding related stimuli are necessary.These findings indicate that Helix do not possess a predisposition for the foods tested, and further suggest that processes underlying food-finding and food selection are strongly influenced by learning experiences. The conditioning phenomenon underlying food-finding behavior has been called Food-Attraction Conditioning, and appears to be a crucial link between the ecologies of learning and foraging behaviors. The accessibility of the snail's nervous system should permit neuronal analysis of the mechanisms underlying such a unique and complex learning phenomenon.     

Scorpion lateral eyes: Extremely sensitive receptors of Zeitgeber stimuli

Summary The circadian rhythm of sensitivity in the median eyes ofAndroctonus australis L. can be entrained by exposure of the lateral eyes to a 24-h light-dark rhythm. Presentation of the Zeitgeber to only the anteriormost one of the lateral eyes sufficed (Fig. 1). However, with illumination of an entire group of lateral eyes (Fig. 2), entrainment was obtained at extremely low light intensities — white light at luminance levels of 10^–4cd · m^–2 (=2.5 · 10^–4 lux, cf. Methods).The relatively less marked circadian rhythm of lateral-eye sensitivity is probably controlled via the optic nerve supplying these eyes (Fig. 4).Supported by the Deutsche Forschungsgemeinschaft (F1 77/5-6 and F1 77/7 Schwerpunktprogramm: Biologie der Zeitmessung)     

Plasticity of olfactory orientation to foods in the snailAchatina fulica

Summary Snails were tested in an olfactometer for their orientation to food odours. Measures of odour choice, latency to make a choice and percentage of upwind orientations were obtained after experimental manipulations of dietary experience and hunger motivation. Juvenile snails, given an exclusive diet of a certain food for 12 h or less, oriented preferentially toward the odour of that food when subsequently presented with a choice between it and a novel food odour (Fig. 2). A 48 h period of exposure to a food resulted in a 21 day retention of the odour preference (Fig. 3). There was no evidence for an especially sensitive period for conditioning during the first 50 days of age (Fig. 4); however, adult snails (minimum 1 year old) required longer periods of dietary exposure to establish equivalent food odour memories (Fig. 5). Measures of latency and percentage of upwind orientations confirmed the choice data in demonstrating an effect of dietary experiences on olfactory orientation. Hunger motivation increased the selection for familiar food odours, and reduced the latency (Fig. 6 and Tables 3 and 4). Sensory adaptation appears inadequate to explain the conditioning phenomenon since formation of the preferences was contingent upon ingestion of the foods; exposure to the food odours alone was insufficient (Table 2). The data suggest that orientation preferences derive from a learned association between the odour of a food and its nutritional value.We thank Dr. Donald Kramer for helpful criticism throughout the course of this work. The research was supported financially by the National Research Council of Canada and le Ministère de l'Education du Québec.     

Twitching and quivering of the tentacles during snail olfactory orientation

In Helix aspersa the posterior tentacles house a sensitive olfactory organ. We studied two types of tentacular movements, twitch and quiver. A twitch is a brief retraction (mean duration, 4.1 s); a quiver is a rapid lateral movement (350 ms) unaccompanied by retraction. We videotaped the tentacles while snails explored an open field. When an attractive odor source, linalool, was present at one side of the arena, the snails consistently moved towards it. By contrast, if only the carrier substance was present the snails moved in random directions. Twitching was 50 times more frequent during linalool trials than during control trials, while quivering was 1.4 times more frequent. Twitching increased steadily and dramatically as snails approached the linalool source and, in the temporal dimension, the maximum rate of twitching occurred when the snails arrived at the odor source. Quivers occurred at a fairly constant rate. Twitching is interpreted as a mechanism to remove odor molecules trapped in the liquid covering of the olfactory epithelium, thus resulting in better temporal resolution for olfactory perception. Quivering may be a mechanism to increase access of odor molecules to receptors by decreasing the boundary layer at the surface of the tentacle. Accepted: 24 May 1997     

Acoustic orientation in adult, female crickets (Gryllus bimaculatus de Geer) after unilateral foreleg amputation in the larva

Summary InGryllus bimaculatus females one foreleg was amputated at the coxa-trochanter joint in the 2nd, 4th or 8th/9th larval instar. A leg of up to normal length is regenerated (Fig. 1) but it lacks a functional ear. In spite of the, usually shorter, regenerated foreleg, the adult one-eared crickets show no impairments in walking when tested on a locomotion compensator. Without sound they walk erratically and most of them weakly circle towards the intact side (Fig. 2).With calling song presentation three response types can be distinguished:tracking (Fig. 3A), hanging on (Fig. 3B) or continuouscircling towards the intact side (Fig. 3C, D). Turning tendencies in monaurals increase with song intensity and exceed those of intact and bilaterally operated animals (Fig. 4). Course deviations towards the intact side also slightly increase with intensity (Fig. 5). Course stability is reduced compared to that of intact animals but exceeds that of bilaterally operated crickets (Figs. 5, 6). It is best at 60 dB and deteriorates at higher sound intensities (Fig. 6). The percentage of monaurals tracking or hanging on decreases with increasing intensity (Fig. 7B). Tracking is established in most animals but it is limited to a narrow intensity range (Fig. 7A, C). Apart from an increased percentage of tracking after early operations (Fig. 7D), there are no prominent changes in orientational parameters with the date of foreleg amputation.Reamputation of the regenerated leg in the adult monaurals does not significantly impair acoustic orientation (Figs. 8, 9), but occlusion of the ipsilateral prothoracic spiracle does (Figs. 10, 11).An attempt is made to correlate the behavioral performance with the activity of auditory interneurons which have undergone morphological and physiological changes (Fig. 12).     

The role of retinula cell types in fixation behaviour of walkingDrosophila melanogaster

Summary Fixation behaviour of free walking wild typeDrosophila and various retinal mutants was tested in a circular arena. Optomotor response was also measured as a test of the function of R1-6.ora andsev,ora do not fixate a narrow stripe (10° or 20°, Fig. 1) but are able to orient towards broad stripes (110° or 180°, Fig. 1). The behaviour ofsev is not different from wild type. Fixation behaviour ofw rdgB is similar toora (Figs. 5, 6). The mutantora has a maximum optomotor response at low contrast frequencies (Fig. 2), but the threshold for this response is at least one log unit higher than in wild type orsev (Fig. 8). The light intensity threshold at 550 nm of fixation to a broad stripe (110°) is 1–2 log units higher inora than in wildtype, and 4 log units higher insev,ora and the structural brain mutantVam (Fig. 7).The conclusions are that retinula cells R1-6 mediate fixation to a narrow stripe at high and low ambient light intensities, and to a broad stripe at low ambient light levels. R8, possibly in conjunction with R1-6, contributes to orientation towards broad stripes at high light intensities. This hypothesis is supported by evidence that blue-adapted white-eyed flies are able to orient towards a broad stripe at high blue light intensities (Figs. 9 and 12). Blue adaptation totally eliminates the optomotor response (Figs. 10, 11) and so the optomotor response observed inora at low contrast frequencies (Figs. 2 and 8) is most likely due to the small remnants of the rhabdomeres of R1-6 that remain.Abbreviations PDA prolonged depolarising afterpotential - ERG electroretinogram     

Repeated eye reduction events reveal multiple pathways to degeneration in a family of marine snails

Eye reduction occurs in many troglobitic, fossorial, and deep‐sea animals but there is no clear consensus on its evolutionary mechanism. Given the highly conserved and pleiotropic nature of many genes instrumental to eye development, degeneration might be expected to follow consistent evolutionary trajectories in closely related animals. We tested this in a comparative study of ocular anatomy in solariellid snails from deep and shallow marine habitats using morphological, histological, and tomographic techniques, contextualized phylogenetically. Of 67 species studied, 15 lack retinal pigmentation and at least seven have eyes enveloped by surrounding epithelium. Independent instances of reduction follow numerous different morphological trajectories. We estimate eye loss has evolved at least seven times within Solariellidae, in at least three different ways: characters such as pigmentation loss, obstruction of eye aperture, and “lens” degeneration can occur in any order. In one instance, two morphologically distinct reduction pathways appear within a single genus, Bathymophila. Even amongst closely related animals living at similar depths and presumably with similar selective pressures, the processes leading to eye loss have more evolutionary plasticity than previously realized. Although there is selective pressure driving eye reduction, it is clearly not morphologically or developmentally constrained as has been suggested by previous studies.     

Host-specific performance and host use in the kleptoparasitic marine snail<Emphasis Type="Italic"> Trichotropis cancellata</Emphasis>

Generalist parasites may disproportionately use certain hosts because of different benefits associated with each host species. I measured the growth rate of the marine snail Trichotropis cancellata, a facultative kleptoparasite that can suspension feed and steal food, on different hosts to determine the relative nutritional benefits of each host. The variation in tentacle (feeding structure) area among the hosts studied had the potential to provide parasitic snails with different amounts of nutrition for growth. In field experiments, suspension-feeding snails isolated from potential hosts grew at a similar rate to snails on brachiopods and significantly more slowly than snails on the following polychaete worms: Serpula columbiana (Serpulidae), Pseudopotamilla ocellata (Sabellidae), Schizobranchia insignis (Sabellidae), and Eudistylia vancouveri (Sabellidae). However, choice among worm hosts affected snail growth rates only in the fall, when phytoplankton levels are low. At this time, snails parasitizing the sabellids Schizobranchia and Eudistylia grew more quickly than snails on Serpula. In the spring and summer, with high levels of phytoplankton, Trichotropis grew at similar rates on all worm species tested. Trichotropis spent approximately the same time stealing food from each worm host species, >50% of the time the worms had their tentacles extended (the difference among hosts was not significant). This finding demonstrates that the similarity of snail growth rates on different worm species is not due to the snails compensating for poor hosts (worms that provide food at a slower rate) by spending more time stealing food. Snails in choice experiments preferred live Serpula to empty Serpula tubes, indicating that at least some of the cue(s) snails use to identify hosts are derived from living host tissues. In choice racks containing live Serpula and live Schizobranchia, snails did not choose one host worm significantly more often than the other. Because Trichotropis grows faster on sabellids than serpulids in the fall, I predicted that snails in nature would infect sabellids more often than other species. However, snails were usually distributed randomly among host species. In the few cases where the snails showed a significant preference among host species, proportionally more snails were found on serpulids than on sabellids or sabellarids. This study is the first to quantify under natural conditions the growth benefits of a kleptoparasite across the range of possible hosts, and implies that factors other than growth rate influence host choice specificity in the marine kleptoparasite T. cancellata.     

The structural organization of the snail sensory systems]

In the paper are reviewed the author's data on the structure of peripheral nervous system of the body wall, gravitational organs--statocysts, eyes, and organs of distant chemoreception--ommatophors, or posterior head tentacles, of the snails Helix vulgaris and Helix pomatia. Localization in the CNS of central parts of the main sensory systems is shown and some structural characteristics of them are described. The data on the organization of the procerebrum which takes part in processing of information from the receptors of the head tentacles are presented. By some morphological features the procerebrum may be considered as one of the highest associative centers of the snails. The data under consideration were obtained by means of silver impregnation by Golgi, retro- and anterograde infusion of CoCl2, horseradish peroxidase and Lucifer yellow into the nerves, as well as by means of a number of other classical histological techniques.     

Neural pathways and innervation of cnidocytes in tentacles of sea anemones

Our previously published studies are here reviewed detailing neuro-cnidocyte synapses, demonstrating putative neurotransmitter substances, and identifying complex neural pathways in sea anemones. Synapses were traced to their contacts on nematocytes and spirocytes by transmission electron microscopy of serial thin sections of tentacles. In five animals, cells containing microbasic p-mastigophores had synapses with clear vesicles, whereas cells containing basitrichous isorhizas had synapses with dense-cored vesicles, providing preliminary evidence for a selectivity of neurotransmitter types for different nematocysts. Either clear or dense-cored synaptic vesicles were also present at neuro-spirocyte contacts. Antho-RFamide immunoreactivity occurred in some anthozoan synaptic vesicles and immunogold labeling of serotonin was found at a neuro-spirocyte synapse. Neural pathways included direct innervation of spirocytes by sensory cells, sequential neuro-neuro-spirocyte and neuro-neuro-nematocyte synapses and reciprocal synapses involving axons of both sensory cells and ganglion cells. Such synaptic patterns resemble neuro-effector pathways found in higher animals and lay to rest the independent effector hypothesis for cnidocyte discharge in tentacles of sea anemones.     

Parasite-induced alteration of diurnal rhythms in a freshwater snail

The trematode Microphallus sp. alters the behavior of its snail intermediate host, Potamopyrgus antipodarum, in ways that seem to increase transmission to its final host, e.g., waterfowl, and decrease the probability of being eaten by other predators, e.g., fish. The parasite seems to cause the snail to move from the top to the bottom of rocks at about 0900 hr. Waterfowl feed predominantly before 0900 hr, and fish feed predominantly after 0900 hr. In the present study, we tested the hypothesis that Microphallus sp.-infected snails exhibit a change in behavior at around 0900 hr by examining their response to light and vertical orientation before and after 0900 hr. Results demonstrated that uninfected snails generally move toward light, oriented downward, and move a greater distance in the light compared with the dark at all times of day. Microphallus sp.-infected snails behaved differently from uninfected snails in the early morning but similarly to uninfected snails in the late morning with regard to downward orientation and distance moved in response to light. Snails infected with parasites other than Microphallus sp. behaved similarly to uninfected snails during both time periods. These results suggest that Microphallus sp. manipulates the behavior of Potamopyrgus sp. by altering rates of movement in response to light and vertical orientation in a manner consistent with the hypothesized 0900-hr shift.     

Action spectra for photogrowth and phototropism in protonemata of the moss Physcomitrium turbinatum

Summary Protonemata of Physcomitrium were grown in a sucrose-mineral nutrient, liquid medium. Even in this medium containing organic nutrient, the growth rate of lateral branch, chloronemal filaments showed a light dependence which was linear with log intensity. Intensities necessary to give a constant growth rate (45 /1.75 hrs.) were determined at selected wavelengths. The resulting action spectrum paralleled the in-vivo absorption spectrum of a single filament in the red region, showing a major peak at 680 nm. Growth rate and absorption approached zero in the far-red (730 nm). However, significant growth activity occurred at 365–400 nm where absorption was low, and negligible growth was found at 440–500 nm where absorption was high.The action spectrum for the positive, directional photo-orientation of growth was determined by the null-point method in which the effectiveness of each selected wavelength was compared to a 665-nm standard in simultaneous, bilateral irradiation. In contrast to growth, the major peak of phototropic activity was found at 730 nm with significant activity extending to 800 nm. A minor peak was at 680 nm. There was some activity in near ultraviolet but not at longer blue wavelengths.It is concluded that the blue-absorbing system responsible for phototropism in virtually all other groups of plants is inactive or absent in Physcomitrium. Instead growth and orientation seem to be dependent upon an interaction between the photosynthetic and phytochrome systems. Further, the data suggest that the physiological activity of phytochrome in photo-orientation of growth does not derive from a certain amount of P_fr or P_fr/P_r ratio but rather it derives from the simultaneous excitation and consequent cycling of P_r and P_fr.Published with the approval of the Secretary of the Smithsonian Institution.This work was carried out under partial support by the U.S. Atomic Energy Commission under Contract AT(30-1)2373.     

A study of the nannoplankton flagellate Pedinella hexacostata vysotskii by light and electron microscopy

A strain of Pedinella hexacostata Vysotskii (Chrysophyceae, or Chrysomonadida) was grown in culture and examined by light and electron microscopy. Behaviour, phagotrophy and division have been observed and salinity tolerance tested experimentally. Pedinella is discussed with relation to Pseudopedinella and other members of the Pedinellaceae. The fine structure of the tentacles is compared with that of tentacles in some other Protozoa.     

Crcadian pacemaker in theBursatella eye: Properties of the rhythm and its effect on locomotor behavior

Summary The eye of the frilled sea hare,Bursatella leachi plei, expresses a circadian rhythm in the frequency of spontaneously occurring optic nerve impulses. The rhythm will free-run for at least 3 cycles in vitro (Fig. 2) and can be entrained by light cycles provided in vivo (Fig. 4 A). While bothBursatella andAplysia eyes contain circadian pacemakers the two rhythms differ in several respects: (1) the peak impulse frequency forBursatella eyes is only 96/h (±36 SD) compared with 247/h (±61 SD) forAplysia. (2) The ocular waveform of theBursatella rhythm exhibits a steep rise and fall from peak frequencies and lacks the delayed falling phase which creates a shoulder on the ocular waveform inAplysia (Fig. 2). (3) The in vitro free-running period of theBursatella ocular rhythm is 21.2 h (±0.6 SD) compared with 24.3 h (±0.9 SD) for theAplysia rhythm (Fig. 2). (4) The steady state phase angle for entrainment differs withBursatella eyes showing a median activity peak at +3 Z.T. compared with a medianAplysia peak at –1 Z.T. (Fig. 4).We also investigated the locomotor rhythm.Bursatella were found to be predominantly diurnal when exposed to LD, 1212 (Fig. 5A) and to exhibit anticipatory locomotor activity when maintained on LD), 915 (Fig. 6). The eyes appear to play a minor role, if any, in timing the locomotor rhythm. EyelessBursatella remained diurnal on LD, 915 and most animals continued to exhibit anticipatory behavior (Fig. 6). These results suggest that theBursatella eye plays a less prominent role than theAplysia eye in controlling locomotor behavior.Abbreviations DD constant darkness - LD 1212 24 h light cycles 12 h light, 12 h dark - EST Eastern Standard Time - Z.T. Zeitgeber Time We would like to thank L. Baird, W. Kilmartin and S. Wallace for help with animal maintenance, data presentation and photography. We also thank T. Breeden for our computer programs. This work was supported by NIH grant NS-15264 to G. Block.     

Morphology and odor sensitivity of regenerated snail tentacles

This study examined certain structural and functional aspects of the olfactory system in regenerated posterior tentacles of the terrestrial snail Achatina fulica. Regeneration of the epithelial sensory pad occurs with accurate size regulation. All five neuronal cell types which are normally revealed by horseradish peroxidase backfilling are also regenerated. The sensory cells attain normal numbers at about 20 weeks postlesion. The organization of neuronal elements within the tentacle is chaotic, however, at early stages of regeneration. Even later, the digitlike extensions of the ganglion, which are characteristic of intact tentacles, fail to appear. The recovery of odor sensitivity was evaluated using a tentacular olfactormeter and a behavioral assay that involved locomotor orientation towards the odor stimulus. Thresholds and concentration-dependent response rates were equivalent for regenerated and intact tentacles, tested in the same animals, at 10 weeks post-lesion.     

Interaction of photoperiod and nutritive state in female reproduction of Lymnaea stagnalis

Summary

A study was made of the interaction of the photoperiod and the availability of food in influencing egg laying of the freshwater snail Lymnaea stagnalis. At a long day photoperiod (LD = 16 h light/8 h dark) egg laying of fed snails had increased compared with that of fed animals kept at a medium day photoperiod (MD = 12 h light/12 h dark). In MD snails oviposition ceased within a week of the beginning of a starvation period. This is most probably due to a reduction in the activities of the neuroendocrine caudodorsal cells which secrete an ovulation hormone. In contrast, in starved LD snails a low rate of ovipository activity continued, indicating that a lowered frequency of caudodorsal cell release cycles occurred under these conditions. The decreased mean size (number of eggs) of the egg masses in starved LD snails indicates that the activities of the endocrine dorsal bodies, which control vitellogenesis and synthetic activities in the female accessory sex organs, had decreased.

All MD snails survived, but nearly all LD snails died during the course of the experiment. Determinations of the mantle glycogen stores of LD snails suggest that the high mortality of LD snails is due to exhaustion of the animal's energy reserves.