| 词汇 | example_english_snail |
| 释义 | Examples of snailThese examples are from corpora and from sources on the web. Any opinions in the examples do not represent the opinion of the Cambridge Dictionary editors or of Cambridge University Press or its licensors. In resistant snails, haemocytes infiltrate the tissues surrounding young sporocysts and form multi-layered cellular encapsulations that result in larval destruction within 24-48 hours. Therefore, we only excluded juvenile snails from the analysis to lessen the effects of the dynamics or local heterogeneity of host population on parasite prevalence. The encystation of metacercariae in primary infected snails without the release of cercariae into the environment may also be an artefact of the experimental procedure. The collected snails were then identified by species using an identification key [16]. Trematodes, however, not only modify their immediate habitat (snails), they also can affect the positioning of that habitat in an ecosystem. We then focus on flukes and snails, highlighting important biological traits with regard to population structure. They collected 18 uninfected snails, 162 with single infections (5 species), 134 with double infections (11 combinations), and 65 with triple infections (5 combinations). Of snails examined, 12n57 % carried multiple-species infections, usually involving core species. Potentiation of zinc stress caused by parasitic infections of snails. Only 8.0% of the snails with shell length 15 mm were infected, in contrast to 98.0% of the snails with shell length > 26 mm. Overall, 51n04 % of snails were infected (range across 9 sites l 8n7-100 %) with 1 or more species. In most habitats, infections were recorded in both cattle and snails. Each replicate line was maintained in large (51i31 cm) tanks containing 60 snails of matched compatibility selection status, with no intervention on mating strategy incorporated. However, these have not been fully applied for the detection of infections in snails under field conditions. Ecological factors in schistosome transmission, and an environmentally benign method for controlling snails in a recreational lake with a record of schistosome dermatitis. Results were similar in different batches of snails. Compared to frequencies of tissue lesions in the digestive gland, those recorded in the kidney were more surprising, as most snails showed multifocal epithelial necrosis. Snails, measuring 4 mm in height, were divided into three groups of 100 snails each. The snails were characterized and the prevalence of their infestation by schistosomes was investigated. The debate about whether parasite infracommunities are interactive or isolationist has rarely been centered on larval trematodes in snails. The activity of each molluscicidal product was interrupted after 48 h by placing snails in dechlorinated water. If cercarial production for both lymnaeids is explained by the low number of mature rediae which develop within these snails, another hypothesis cannot be excluded. Uninfected snails were included in the data for the duration of cercariae shedding, while those containing trematodes were excluded. Four snails were excluded from the autocorrelation analysis because of short production period leaving 17 individuals for the analysis. Evolutionary relationships between trematodes and snails emphasizing schistosomes and paragonimids. The breeding system of these snails, by permitting the rapid establishment of evolutionary novelties, allows the group to exploit marginal habitats. If these snails are subsequently exposed to normal miracidia, the parasites are quickly destroyed by amoebocytes near the penetration area in the head-foot. In absence of human infection, a likely explanation is the restricted movement and dispersion of both rodents and snails. To screen for emergence of cercariae, snails were kept separately in test tubes each containing 10 ml filtered habitat water. Measuring currents in the field experienced by snails is difficult because of variations in time and space. Only low intensity shedding by 13.1% of the snails was observed for the 1500- 1700 h period and no shedding was observed thereafter. The snails were examined for emerging cercariae from day 28 following exposure and checked for cercarial shedding until death. The treatment of the death rate of shedding snails is more complicated. Infections appear to be permanent and greater prevalence in older snails might be predicted because they have been longer exposed to infection. The remaining eight species were found infrequently, each in less than 1% of the snails. Each week dead snails were removed from the tank and the number of mortalities recorded. Infections in immature snails do occur, but are seldom recorded, possibly because prevalence is low and such hosts are less frequently examined. In natural populations the parasite's influence is further accentuated by its action on the reproductive rate of shedding snails. Also, the manual collection of snails and cleanup of vegetation zones in the sector in question may be considered [26, 27]. Higher temperatures not only trigger the release of cercariae from snails, but they also accelerate the production of cercariae within snails. All snails were provided with an excess of clean boiled lettuce as food throughout the acclimatization and monitoring periods. Spatial and seasonal heterogenities of infected snails were also analysed to test the effects of these factors on the overall community pattern. Exact location of the cysts in the snails was not determined. Four replicates of 6 infected and 6 uninfected snails were used. A matched number of control snails were exposed to both parasite strains. Finally, a group of unselected snails were included to serve as controls. The long lifespan of the host must be coupled with the slow rate at which trematodes colonize snails. The snails were transferred to 1.7 ml microcentrifuge tubes. In one zone, snails harboured six species of trematodes but in an adjacent zone, only two trematodes were present. Perhaps miracidia colonize snails at higher rates in freshwater. The experiment was run until all snails had died, which turned out to be 67 days. Cercarial production varied between days but was not cyclic, probably because of the physiology of the sporocysts within snails. Nine of the 17 snails (52.9 %) showed significant autocorrelations in cercarial production. They compared the susceptibility of snails from 6 sites to trematode infection. Another factor that could bring about increased larval digenean prevalence in polluted sites is the possible increased susceptibility of snails to miracidial attack. The concentration of dissolved salts limits the distribution of pulmonate snails when it is unusually high or low. A noteworthy outcome was that freshwater snails seemed much more likely to display gigantism than marine snails. In both of these studies, the snails were grouped together. The majority of exposed snails were either of second or third generation. The pools represent more extreme conditions and snails colonising them require considerable powers of aestivation to survive for many months when they dry out. The application of catalytic models to schistosomiasis in snails. The snails used in the present study were in the size class 3-5 mm, unless otherwise stated. Routine co-occurrence of trematodes in snails is thus unlikely. Snails gain infections and infected snails shed cercariae, which infect bird hosts. Marked snails were located and shell height changes noted through summers and autumns of both release years. Individual snails were thus scored as positive or negative for cercarial production. Potentiation of zinc stress caused by parasitic infection of snails. The death rates may be due to infectivity of the parasites or possibly to the condition of the snails at the time of exposure. Except for a few collection sites where snails were rare, the sample size varied from 15 to 50 individuals. The density of infected snails was reduced from more than 10 000 to less than 1000 individuals m-# over a mere five weeks. All snails were randomly assigned to 1 of the 4 experimental groups. A comparative approach stands to inform our perspective on what drives the ecological phenomena associated with marine snails and trematodes. Humans contract the disease when the infective larvae of the parasites, the cercariae, having emerged from intermediate host snails in fresh water, penetrate their skin. In a literature review of the last 30 years, we found 41 publications examining various life history characteristics of trematode-infected snails. Interestingly, data collected from field studies also show gigantism occurring more frequently among rediaeinfected snails than among those bearing sporocysts ; however, this difference is slight. Although laboratory studies offered a more refined view of tendencies over time, there were limitations in the diversity of snails used. In these clonal lines, the genotypes for resistance in the snails are inextricably linked with their multilocal allozyme genotypes. The patient isolates were obtained by hatching miracidia from faecal samples and these miracidia were used to infect lab-reared snails. Evidence from two planorbid snails of a complex and dedicated response to digenean (echinostome) infection. A total infection rate of 40n9 % (90\\220) occurred among the snails that received a single miracidium. As mentioned above, selfing may not be less common than random-mating in flukes and snails. Thus, it appears that gigantism may be as evident in the field as it is in the laboratory for trematode-infected freshwater snails. Perhaps adult snails shunt energy from growth towards early reproduction when parasitized ; consequently adults hosts grow less than uninfected individuals. Considerable attention has been given to identifying these snails but few studies have demonstrated the relationships among the species of this genus. A way out of this design limitation is offered by molluscs, whose best-known land-living forms include slugs and snails. As a result, it progressed at a snail's pace. In this respect, the movement of snails is essentially due to human activities. The negatively phototactic phase could be expected to enhance the probability of contact with benthic second intermediate host snails. All snails used were in the 0.3-0.5 cm size range. The same method was used for naturally co-infected snails. Each experimental group consisted of 100 snails at miracidial exposure. Only snails measuring 3 mm or more in height were searched visually and collected. An explanation might be that mates were larger than experimental snails, especially during the first weeks of the experiment. Numbers within the graph are the numbers of snails examined. Laboratory snails provided convenient packaging of known numbers of cysts. Metacercarial cysts from wild and laboratory snails were then used to attempt infection of definitive host candidates. The results originated from snails with 2-sporocyst infections and normal development of redial generations. Large and heavily infected snails are more frequently observed on the floating vegetation in the stream. Adult snails were reared under laboratory conditions to provide the 4-mm high snails used in this experiment. These examples are from corpora and from sources on the web. Any opinions in the examples do not represent the opinion of the Cambridge Dictionary editors or of Cambridge University Press or its licensors. |
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