Snail Movement Research Articles

Responses of Invertebrate Herbivores to Stinging Trichomes of Urtica dioica and Laportea canadensis

We investigated whether stinging trichomes of two plant species, Urtica dioica and Laportea canadensis, are effective defenses against four species of invertebrate herbivores (Vanessa atalanta, Popillia japonica, Chortophaga viridifasciata and Anguispira alternata). Feeding was compared on leaf pieces of contrasting stinging trichome density, in petri-dish feeding trials. In addition, a test of snail movement over hairy and shaved L. canadensis stems was carried out. In no case was there significant evidence that stinging trichomes deter or interfere with feeding by these herbivores. Factors of body size and feeding behavior allow them to feed with little interference from nettle stings. Stinging trichomes are known to be effective against mammalian herbivores, and are well-suited to deterrence of large grazers. We therefore hypothesize that stinging has evolved as a defense against mammalian herbivory.

Population estimation of the snail Bithynia tentaculata (Gastropoda: Prosobranchia) using mark-recapture and the examination of snail movement in pools

Population estimation of the snail Bithynia tentaculata (Gastropoda: Prosobranchia) using mark-recapture and the examination of snail movement in pools

Mate‐ and Oviposition‐Influenced Host Preferences in the Coral‐Feeding Snail Cyphoma Gibbosum

Mate—searching has been hypothesized to influence the host preferences of small grazers, yet no previous field data have examined this idea. I examined the host preferences of Cyphoma gibbosum, a generalist gastropod that feeds on gorgonian corals, and tested if mate searching or oviposition preferences contributed to variation in host preferences. I constructed experimental reefs containing three species of gorgonian corals at uniform densities and placed snails on these reefs either alone or in group of four. Half of the groups of snails were single—sexed while the other half contained two snails of each sex. I observed snail movements by conducting daily censuses of three reefs and constructed transition matrices describing the movements of snails in each treatment among the three species of coral. Snails showed preferences for some hosts over others, and these preferences varied due to both mate searching and oviposition. Snails preferred to occupy Briareum asbestinum over Plexaurella dichotoma or Pseudopterogorgia acerosa, but these preferences were strongly influenced by previous experience. Moreover, females tended to move from B. asbestinum to Plexaurella dichotoma to oviposit, and back to B. asbestinum afterwards. Finally, both males and females moved frequently towards members of the opposite sex, in order to copulate, which influence their distribution among hosts. These data reveal that behaviors associated with mating can influence host preferences and need to be considered in understanding host utilization patterns.

Habitat Distribution in the Desert Snail Trochoidea seetzenii

what are the factors that influence the density distribution, among habitats, of the desert snail, Trochoidea seetzenii. This was done by examining the relationship between individual movement, reproductive success and density distribution of a population in two habitats. We studied individual movement in two adjacent habitats, the wadi and the lower slope of the same watershed. The overall experimental design entailed: a) enclosed plots in which the original density distribution was maintained, b) enclosed plots in which all the snails from the wadi were transfered to the slope, c) enclosed plots in which all the snails from the slope were transferred to the wadi, d) unfenced control plots with no limitations on direction of snail movement. We found that in the winter, after the first heavy rains, snails moved from the wadi to the slope until snail density was similar in the two habitats. In the late rainy period we found the opposite trend in movement, resulting in higher density in the wadi relative to the slope. This directional movement was found in the undisturbed as well as in the manipulated plots. We suggest that the temporal changes in the density distribution of T. seetzenii are mainly the effect of the snails moving between habitats so that they seem to maximize reproduction in winters and survival in summers.

A Comparative Study on the Food-Locating Ability of Helisoma duryi, Biomphalaria camerunensis and Bulinus truncatus (Pulmonata: Planorbidae)

1. Helisoma duryi, a planorbid snail has been suggested as a biological control agent against the snail intermediate hosts of schistosomes, Biomphalaria and Bulinus species. It has been demonstrated that competition for food resources is involved. The aim of this paper is to compare the ability of these species to locate food sources. 2. The paper compares the accumulation of groups of Helisoma duryi, Biomphalaria camerunensis and Bulinus truncatus on varying amounts of two different artificial food preparations and the movement of individual snails of these three species when approaching a food source by analysing their tracks. 3. There were slight differences in the ability of H. duryi and B. camerunensis to locate food preparations, but both were superior to B. truncatus. The two types of food preparations differed markedly in their attraction of B. truncatus. H. duryi was less attracted to the food preparations with the two lowest amounts of food of both types than to preparations with larger amounts of food, while this was not observed for B. camerunensis and B. truncatus. Medium-sized H. duryi were superior to small and large snails in their ability to locate food, while no significant differences were found among three size groups of B. truncatus. 4. Analysis of snail tracks did not reveal an increased frequency of turning in any of the three species as the food source was approached. The reason for the higher accumulation of H. duryi and B. camerunensis on the food could in part be explained by their higher activity level. Other explanations are also discussed.

Behavior and respiration of the salt marsh periwinkle,Littorina irrorata(Say), during winter

The response of the salt marsh periwinkle (Littorina irrorata) to changing environmental conditions was studied in the field and under controlled laboratory conditions. Similar results were obtained in both studies and showed that maximum daily air temperature was the single most important factor controlling snail activity. With declining (23°C to 13°C) temperatures, snail movement was significantly reduced from more than 40% of the sample at temperatures >15°C to 12% at 14°C. Under an increasing regime (0°C to 18°C) dormancy was broken near 11°C in some trials and at 14°C in others. Oxygen consumption rates of warm‐adapted (23°C) and cold‐adapted (0°C) snails were tested at 6, 16 and 26°C. At 6°C, cold‐adapted snails consumed less oxygen than did warm‐adapted snails, but the reverse was true at 26°C. These results suggest that temperature plays a major role in the activity and dormancy of L. irrorata and that the observed dormancy can be classified as true hibernation. In the temperate extension of L. ir...

Diet Selection and Depression of Prey Abundance by an Intensively Foraging Lizard

Diet of the intensively foraging Puerto Rican lizard Ameiva exsul included most taxa of macroorganisms found in the leaf litter and soil surface at the study site. Nevertheless, certain items, Anolis eggs an extreme example, were overconsumed in relation to their abundance as determined by stratified random sampling of the leaf litter and soil surface where the lizards foraged. Other food items, such as land snails, were important in the diet but underconsumed relative to their high level of abundance in the leaf litter. Millipedes and termites were the only common litter organisms encounterd that were not found in diet samples. Effects of Ameiva predation on abundance of land snails were studied in two experiments with hardware cloth exclosures that permitted free movement of snails through the 1.3 cm x 1.3 cm mesh and entrance of Anolis and birds through the open tops. Adult A. exsul were the only predators known to be excluded. Protection from A. exsul was associated with increased abundance of the low mobility land snails. No consistent changes in other species were detected. Exposure to high quality prey items or high quality patches permits selectivity in the context of a broad diet, a tenet of foraging theory (Stephens and Krebs, 1986). The probing, investigative, energetic behavior of intensive foragers (Anderson and Karasov, 1981; Regal, 1983) may bring them into contact with a great number of potential prey including some items of high quality (Huey and Pianka, 1981). Moreover, the high level of movement of intensive foragers may increase the chance of encounter with rich patches of prey. Intensively foraging lizards obtain broad diets by searching large areas (Schoener, 1971; Regal, 1983). The Puerto Rican teiid Ameiva exsul, for example, has been reported to eat everything from other lizards and lizard eggs to frogs, arthropods, snails, fruit, fungi, and garbage as it probes the leaf litter and soil surface (Wolcott, 1924; Rodriguez-Ramirez, 1985; Lewis, 1986; Lewis and Saliva, 1987). Whereas emphasis sometimes has been placed on diet breadth giving the impression that such relative omnivores forage indiscriminately (Heatwole and Torres, 1967), intensive foragers avoid some potential prey types (Vitt and Cooper, 1986) and probably favor others. Activity of lizards over the spectrum of styles from sit-and-wait foraging to intensive foraging in both Brazil (Magnusson et al., 1985) and Africa (Huey and Pianka, 1981) is positively correlated with the number of termites, a patchy resource, in the diet. Exclosure and enclosure experiments with experimentally amenable aquatic organisms indicate that predators can modify prey abundance and thus, at least potentially, mold community structure (Morin, 1984; Quammen, 1984; Vanni, 1986). Experiments with sit-and-wait iguanids suggest that lizards using this low energy foraging mode are selective feeders that take disproportionate quantities of relatively rare items (Stamps et al., 1981) and influence the structure of arthropod communities in certain microhabitats (Pacala and Roughgarden, 1984). Intensively foraging lizards, particularly when present at high density, may similarly modify relative and absolute abundance of litter dwelling macroorganisms. Evidence is presented here to test hypotheses that 1) Ameiva exsul forages selectively and that 2) foraging by A. exsul has a significant impact on the leaf litter community.

Prey Selection by the Tropical Snail Thais Melones: A Study of Interindividual Variation

I studied the feeding behavior of marked individuals of the carnivorous marine snail Thais melones in a rocky shore habitat along the Pacific coast of Panama. These snails consumed a variety of invertebrate species such as bivalves, limpets, and polychaetes. The population of Thais melones was generalized in overall diet, but individuals varied in degree of specialization. Feeding sequences of 282 marked snails were divided into size classes for the 100 snails observed through five or more sequential feeding attacks. These sequences revealed two interesting patterns. First, diets varied from specialized to generalized even among individuals of similar size foraging adjacent to one another in the same habitat. Second, among individuals that exhibited more specialized diets, the prey species of choice was not always the same. Individual diets of snails were monitored twice daily in the field for time periods ≤3.5 mo. Two of five snails that were observed over longer periods showed consistency of prey choice with more specialized diets for 11 and 13 mo until they were lost. Neither of these patterns appeared to result from biased movements of individual snails among different habitat patches since mapped foraging tacks of individual snails intersected and overlapped extensively. Both of these results do, however, reveal that no single "optimal" pattern of prey selection was exhibited by these size—matched, co—occurring snails. In addition, for medium—sized snails (20—30 mm shell length), rates of spiral shell growth measured over the same time period revealed a statistically significant association with diet diversity: individuals with a less diverse (i.e., more specialized) diet tended to grow more rapidly, yet the relationship was not significant for small (<20 mm) or large (>30 mm) snails. These studies indicate that pattern of prey choice (i.e., specialized or generalized) may be as important as the composition of the diet on correlates of fitness. Superiority of a specialized diet (regardless of specific prey identity) could occur through increased efficiency in prey handling.

Multifactorial analyses of directions of movement of animals

Analyses of the orientations and movements of animals require multifactorial experiments to differentiate among complex, interacting influences. There are no statistical procedures for the analysis of multifactorial sets of angular data. As a result, many studies have inadequate spatial replication, or confound several potential sources of variation. In this paper, methods are described for the analysis of complex multifactorial sets of angular data. Analogues of techniques of analysis of variance are demonstrated that allow partitioning of the resultant vectors of sets of angular data to serve as a basis for tests of significance. Resultants are partitioned into components corresponding to any identifiable or planned source of variation in the experiment, allowing hierarchical, factorial and mixed experimental designs (as with linear models for analyses of variance). Because the statistical properties of these partitions are at present unknown, significance tests are then done by randomization procedures on each set of data. The randomizations produce an empirical distribution of a test statistic (in this case, analogous to F-ratios in linear analyses of variance), against which the calculated statistic for the given set of data can be compared. These techniques are illustrated for experiments on the directions of movement of a small intertidal snail, Littorina unifasciata Gray, on sandstone shores in New South Wales. Various experimental designs are discussed, including two and three experimental factors, in nested and orthogonal analyses. The results revealed that the movements of this species are influenced by many factors, and that the effects of these vary from time to time and place to place on the shore. The complexity of these results is discussed with respect to previous, simpler experiments about movements of gastropods. The potential advantages of multifactorial comparisons using the methods described here are indicated for various aspects of the study of directional movements of intertidal snails.

Local and Latitudinal Variation in Predation on an Herbivorous Marine Snail

Intertidal grazing molluscs show striking local and geographic variation in distribution and body size. Their density is generally greatest in the upper and mid—intertidal zones on rocky shores of the Pacific coastal of North America, and least in the low intertidal zone. However, the elevation of the lower limits of their shore—level distribution varies considerably among sites. In addition, the lower limits are generally higher south of central California than in the north, and the average body size is usually smaller in the south than farther north. This is exemplified by the commonest molluscan grazer in the mid—intertidal region of many rocky shores on this coast, the trochid snail Tegula funebralis. A hypothesis to explain these patterns, that they are due to variation in predation, was tested. At sites where predator density was high, regardless of latitude, the lower limit of Tegula's intertidal range was higher on the shore, compared with areas containing few predators. Shell width was usually smaller, and increased with elevation wherever predators were abundant. Predators were more abundant at southern than at northern sites. The primary predators of Tegula are octopuses (Octopus bimaculoides and O. bimaculatus), the starfish Pisaster ochraceus, and crabs of the genus Cancer. The octopuses occur only at the southern sites, whereas Pisaster and Cancer are found throughout the geographic range of the study. Reciprocal transplants of marked Tegula, done between several southern and northern sites, showed that the lower limit of distribution of adult Tegula on the shore at a given site is influenced by the snails' defensive behavior. Where predators were abundant, both southern and northern Tegula placed low on the shore rapidly climbed to higher levels than in locations where predators were scarce. The probable cause of this upward migration is an avoidance response to chemical exudates from predators. Southern Tegula also have an inherently different response than northern Tegula; southern snails always climbed upwards sooner and reached higher levels than northern snails. This resulted in predators killing more of the northern snails in these experiments. The behavioral difference between southern and northern Tegula may be the result of long—term differences in the intensity of predation by octopuses, which are much rarer in the intertidal north of central California than south of there. Young—of—the—year Tegula were found mainly in the mid—intertidal region. The shift in the direction of shore—level size gradients of Tegula populations between high and low predation sites may be caused by movements of adult snails to levels above or below the less mobile juveniles. The relative scarcity of Tegula and other grazing molluscs in the low intertidal zone is probably due both to upward migration and high mortality rates, with predation being a major cause of both.

Maintenance of the shore-level size gradient in the marine snail Tegula funebralis (A. Adams): Importance of behavioral responses to light and sea star predators

The intertidal gastropod, Tegula funebralis (A. Adams) exhibits a shore-level size gradient with mean shell size increasing in a down-shore direction. Snails transferred to zones where they do not usually occur migrated back towards their original zone, thus re-establishing a size gradient and implying differential movement among size classes. Both large (≥2.1 cm shell width) and small (≤ 1.77 cm) snails were photonegative on a horizontal surface and geonegative in the laboratory; there were no statistical differences between size classes. Light, however, inhibited upward, or caused downward, movement of large snails on vertical surfaces. Small snails were unaffected, ranging higher on illuminated vertical surfaces than large snails. Both sizes exhibited similar distributions in the dark. In an experimental chamber providing both emersed and immersed surfaces, T. funebralis established vertical size gradients when the chamber was illuminated from above. It is suggested that light is an important factor in the formation and maintenance of Tegula's shore-level size gradient. In response to water-borne chemicals derived from the sea star Pisaster ochraceus (Brandt), large snails moved up vertical surfaces in greater proportion than small. In response to contact with the predator, large snails moved away faster than small and individuals collected from crevices in the field moved away slower than those collected from open rock faces. Although predation may select for a size gradient in Tegula funebralis, it is unlikely that responses to predatory sea stars directly and proximally cause or maintain them over the short term.

The maintenance of shore-level size gradients in an intertidal snail (Littorina sitkana).

The size of many intertidal animals varies with tidal height. These size gradients could be produced by growth or survival varying with tidal height, or by animals moving to a preferred tidal level. The body size of the snail, Littorina sitkana, increases steadily with tidal height in rocky high intertidal habitats of British Columbia. To determine how size gradients were maintained in L. sitkana, I quantified how growth, survival, and snail movement varied with tidal height. I studied populations of L. sitkana found on sheltered pebble beach and exposed basaltic shelf habitats. Mark-recapture studies and experimental transplants showed that growth could not have produced the size gradients because snail growth rates in both habitats were as fast or faster at low tidal levels (where the snails were the smallest) than at high tidal levels. However, survival rates were lowest at low tidal levels. On pebble beaches, this was due to size selective predation on large snails by the pile perch, Rhacochilus vacca. On basaltic shelves, heavy wave action at low tidal levels may have caused the poor survival rates. Transplanted snails moved homeward on pebble beaches, but not on basaltic shelves. Reduced survival rates at low tidal levels cause size gradients in both habitats, and snail movement helps to maintain size gradients on pebble beaches.

Social behavior in the freshwater pulmonate snail Biomphalaria glabrata (Say)

A novel approach, involving the use of a mathematical model and a time-lapse cinematographic device for monitoring snail movements, has been developed to provide a quantitative measure of the degree of sociability of a species of aquatic snails and the extent of the active space around individual snails. The latter is defined as the area surrounding the snail within which a behavioral response can be elicitated from a conspecific. The results indicate that Biomphalaria glabrata (Say) is highly social despite the small size of the active space. It is concluded that aggregate formation is to a large extent determined by random collisions. Although the mean free path decreases as snail density increases, compensating mechanisms which may include a reduction in mean time spent in contact with other snails or in the size of the active space appear to prevent the mean size of the aggregate from increasing.

Expanding Balloons and the Movement of Snails

Expanding Balloons and the Movement of Snails

Effect of ion combinations on protoplasm, amoeboid movement, tissue formation in experimental amoebocyte tissue

In former investigations we have shown that the consistency and state of contraction of the protoplasm determines various functions and transformations in amœbocytes and in the experimental amœbocyte-tissue, such as: (1) The character of the amœboid movements and pseudopods. The greater the consistency, the more rounded are the cells, the sharper are the pseudopods, the slower is the movement of the granuloplasm. At certain stages the movement of the granuloplasm is entirely or almost entirely prevented, while the ectoplasm of the pseudopods may still actively move. Then the cell in toto may move in a snail-like manner, the whole cell being pulled along by the extension and contraction of the pseudopods. However, snail movement may also be produced under other conditions. The other extreme is represented by the circus movement and paripassu movement. In the former, the pseudopod has the shape of a drop or balloon, and moves along the periphery of the cell; the granuloplasm pours into it like a liquid mass. Subsequently the cell as a whole rounds off, and the same cycle begins again after a period of latency. In the latter form of movement, the protoplasm is so soft that the pseudopod is rounded off, and the granuloplasm moves into the pseudopod as soon as it develops, so that the pseudopod is from the beginning filled with granuloplasm. (2) The consistency of the protoplasm influences the extension of the cell. The greater the consistency, the less is the cell liable to extend in contact with solid surfaces; conversely, the softer the cell, the more liable it is to extend. Associated with the extension are usually solution processes in the cell, in particular, solution of the cell granules.