Snail Survival Research Articles

Diminished fitness in an endemic Hawaiian snail in nonnative host plants

Hawaii’s diverse achatinellid tree snails occur almost exclusively in host trees and shrubs that are native to the Hawaiian Archipelago. A few exceptions to this pattern are known, where an arboreal gastropod population has persisted in introduced plants. On Oahu, Hawaii, the last known population of the single-island endemic snail Auriculella diaphana has persisted in nonnative plants for multiple decades, leading to the following question: are there differences in the relative fitness of native gastropods in native versus nonnative host plants? To address this we conducted laboratory trials with A. diaphana in three treatment groups, one with the two dominant nonnative host plants from their current distribution, another group with two primary native host plant species, and a third treatment maintained in cages with a mixture of equal parts of both the nonnative and native plants. Trials were replicated in two 16-week intervals, with 100 snails. Relative fitness was assessed among treatments as survival and reproductive output (number of eggs produced). Results demonstrated that while survival of adult snails was equivalent across treatments (100%), fecundity was significantly higher in cages where native plants were available. Egg production was 20.05-fold and 14.95-fold greater in treatments with 100% and 50% native host plants, respectively, than in treatments with nonnative plants only. These results suggest that native snails persisting in nonnative host plants experience sublethal stress, reflected in a dramatic reduction in reproductive output. Snails in treatments with mixed native and nonnative plants also showed significantly higher reproduction than those in nonnative plant cages. We suggest that the observed decreased fecundity was due to the poor nutritional value of the microbial phyllosphere of nonnative vegetation, and that translocation of this and related species occurring in nonnative habitat to nearby native host plants will be beneficial in terms of relative fitness.

Survival of an invasive aquatic snail to overland translocation in non-aquatic media: Implications for spreading

Invasive species are a threat to aquatic ecosystems worldwide. Aquatic snails have a limited ability for an active dispersal. Therefore, their ability to survive to transport in non-aquatic media may help explain their spread across unconnected habitats. We assessed the ability of New Zealand Mud Snail (NZMS) ( Potamopyrgus antipodarum ) to survive attached to different materials. Two studies were conducted: (1) a laboratory study to assess the tolerance of a laboratory population of NZMS to non-aquatic media attaching snails to leaf litter, sediment and clay and (2) a field-laboratory study to assess the survival of an invasive field population after being left imbedded in clay in the laboratory and subsequently transferred to a new river reach. All laboratory animals died after 3 days in leaf litter, while in the case of sediment and clay all snails died after 5 days. After being imbedded in clay and subsequently transferred to the river, the survival of the field population was lower than that of the laboratory populations. We conclude that NZMS can be dispersed by mechanisms which imply spending some time in non-aquatic media, and that this species has a relatively high tolerance to translocation between reaches with contrasting environmental properties.

Abstract A56: Inhibition of Snail-induced EMT promotes anti-tumor immune response in ovarian cancer.

Abstract Background: Peritoneal dissemination is a common mode of tumor progression in ovarian cancer, and one of the most important unfavorable prognostic factors. Epithelial-mesenchymal transition (EMT) has been indicated to be a key process in tumor invasion and metastasis. Recent studies demonstrate that EMT suppresses anti-tumor immunity in some types of cancer. The aim of the current study is to elucidate the relationship between EMT-related gene Snail and local immunity in ovarian cancer. Methods: The expression of Snail and patient survival was analyzed in two microarray datasets, TCGA, and KOV75 (75 ovarian cancer cases operated in our department). Using mouse ovarian cancer cell line HM-1, the influence of Snail expression on EMT, peritoneal dissemination, survival, and local immunity was analyzed using both in vitro and in vivo models. Snail-silenced cell line, HM1-sh-snail was established, and compared with the control HM-1. Results: Among 4 subtypes of high grade serous ovarian cancer, Mesenchymal subtype, which show marked stromal reaction in histopathology, shows the worst prognosis (TCGA, KOV75). Snail expression was significantly high in Mesenchymal subtype (TCGA, p<0.0001; KOV75, p<0.05). High Snail expression was significantly related to short overall survival in TCGA (p<0.05). In HM1-sh-snail, expression of vimentin and fibronectin was decreased in RT-PCR analysis. Cell migration was inhibited in wound-healing assay (p<0.001), but the cell proliferation was not altered in WST assay. In mouse peritoneal dissemination model, HM1-sh-snail group demonstrated longer survival than the control group (p<0.05). In mouse subcutaneous tumor model, HM-1-sh-snail group revealed smaller tumor than the control group (p<0.05), although there was no difference between two groups in nude mouse model. Flow cytometric analysis of mouse tumors revealed that infiltration of CD4+ T cells and CD8+ T cells were all increased and MDSCs were decreased in HM1-sh-snail group. Conclusion: Snail-induced EMT inhibits local immune reaction and promotes peritoneal dissemination in ovarian cancer. Snail may be a potential therapeutic target in ovarian cancer. Citation Format: Mana Taki, Kaoru Abiko, Noriomi Matsumura, Tsukasa Baba, Junzo Hamanishi, Naoki Horikawa, Ikuo Konishi. Inhibition of Snail-induced EMT promotes anti-tumor immune response in ovarian cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr A56.

Atrazine reduces the transmission of an amphibian trematode by altering snail and ostracod host-parasite interactions.

Trematodes are ubiquitous members of aquatic environments, have many functional roles in ecosystems, and can cause diseases in humans, livestock, and wild animals. Despite their importance and reports of parasite population declines, few studies have concurrently assessed the effects of aquatic contaminants on multiple hosts, multiple parasite life cycle stages, and on transmission-related host-parasite interactions. Here, we test the effects of environmentally relevant concentrations of the herbicide atrazine (0, 3, 30 μg/L) on the establishment and development of an amphibian trematode (Halipegus eccentricus) in a first-intermediate snail host (Physa acuta) and in a second-intermediate ostracod host (Cypridopsis sp.). Additionally, we test the interactive effects of atrazine and parasitism on snail and ostracod survival. Our results indicate that atrazine negatively affects trematode transmission by altering snail and ostracod host-parasite interactions. Although atrazine did not affect the survival of uninfected snails alone, atrazine acted synergistically with parasitism to reduce the longevity of infected snails. As a result, the number of cercariae (i.e., larval trematodes) produced by snails was 50.7 % (3 μg/L) and 14.9 % (30 μg/L) relative to controls. Atrazine exhibited direct negative effects on ostracod survival at 30 μg/L. However, when ostracods were also exposed to trematodes, the negative effects of atrazine on survival were diminished. Although infected ostracod survival remained high, trematode development was significantly reduced, resulting in reduced infectivity of metacercariae (i.e., nongravid adult cysts infective to definite host) to 32.2 % (3 μg/L) and 28.6 % (30 μg/L) relative to the controls. The combination of reduced cercaria production and reduced metacercarial infectivity in the 3 and 30 μg/L atrazine treatment groups reduced the net number of infective worms produced to 16.4 and 4.3 % (respectively) relative to the control. These results demonstrate the complex nature of pesticide effects on trematode infections and indicate that trematodes can affect their first- and second-intermediate hosts differently under different pesticide concentrations. Our work has broad implications for parasite transmission and conservation and provides a testable mechanism for understanding trematode population declines in contaminated wetlands.

Survival and Growth of Freshwater Pulmonate and Nonpulmonate Snails in 28-Day Exposures to Copper, Ammonia, and Pentachlorophenol.

We performed toxicity tests with two species of pulmonate snails (Lymnaea stagnalis and Physa gyrina) and four taxa of nonpulmonate snails in the family Hydrobiidae (Pyrgulopsis robusta, Taylorconcha serpenticola, Fluminicola sp., and Fontigens aldrichi). Snails were maintained in static-renewal or recirculating culture systems with adults removed periodically to isolate cohorts of offspring for toxicity testing. This method successfully produced offspring for bothspecies of pulmonate snails and for two hydrobiid species, P. robusta and Fluminicola sp. Toxicity tests were performed for 28days with copper, ammonia, and pentachlorophenol in hard reconstituted water with endpoints of survival and growth. Tests were started with 1-week-old L. stagnalis, 2-week-old P. gyrina, 5- to 13-week-old P. robusta and Fluminicola sp., and older juveniles and adults of several hydrobiid species. For all three chemicals, chronic toxicity values for pulmonate snails were consistently greater than those for hydrobiid snails, and hydrobiids were among the most sensitive taxa in species sensitivity distributions for all three chemicals. These results suggest that the toxicant sensitivity of nonpulmonate snails in the family Hydrobiidae would not be adequately represented by results of toxicity testing with pulmonate snails.

Smallpox and Dracunculiasis: The Scientific Value of Infectious Diseases That Have Been Eradicated or Targeted for Eradication. Is Schistosomiasis Next?

Smallpox and Dracunculiasis: The Scientific Value of Infectious Diseases That Have Been Eradicated or Targeted for Eradication. Is Schistosomiasis Next?

Kelp in hot water: II. Effects of warming seawater temperature on kelp quality as a food source and settlement substrate

ABSTRACT: Predicting the effect of climate change on communities requires an understanding ofthe effects of environmental conditions on species and their interactions. We investigated thepotential for warming seawater temperature to modify the interactions of the gastropod meso-grazer Lacuna vincta and the invasive bryozoan Membranipora membranacea with kelps in NovaScotia. The nutritional content (C/N) of the kelps Saccharina latissima, Laminaria digitata andAgarum clathratum were unaffected by temperature (11, 18 and 21°C), and chemical defenses(phlorotannins) were reduced only in A. clathratum after 1 wk exposure to 21°C. C/N and phloro-tannin content increased over the season in S. latissima collected monthly in summer 2013 and2014. The effect of temperature-induced changes in kelp on the grazing of L. vincta was assessedusing feeding experiments with S. latissima pretreated at 11 or 21°C. Snails consumed more kelppretreated at 21°C only when grazing rate was high. The quality of S. latissima as a food sourcefor L. vincta was not affected by temperature, as diets of kelp pretreated at 11 and 21°C supportedsimilar growth, reproduction, and survival of snails. Temperature also did not affect the quality ofkelp as a substrate for M. membranacea, since settlement rates were not different betweenS. latissima pretreated at ambient temperature (9 to 14) and 21°C. The absence of temperature-induced changes in kelp quality suggests that the effects of L. vincta and M. membranacea will actadditively with the direct effects of temperature and cause increased biomass loss from kelp beds.KEY WORDS: Kelp · Climate change · Temperature · Saccharina latissima · Lacuna vincta ·Herbivory · Membranipora membranacea · Bryozoans

Snails from heavy-metal polluted environments have reduced sensitivity to carbon dioxide-induced acidity.

Anthropogenic atmospheric CO2 reacts with water to form carbonic acid (H2CO3) which increases water acidity. While marine acidification has received recent consideration, less attention has been paid to the effects of atmospheric carbon dioxide on freshwater systems—systems that often have low buffering potential. Since many aquatic systems are already impacted by pollutants such as heavy metals, we wondered about the added effect of rising atmospheric CO2 on freshwater organisms. We studied aquatic pulmonate snails (Physella columbiana) from both a heavy-metal polluted watershed and snails from a reference watershed that has not experienced mining pollution. We used gaseous CO2 to increase water acidity and we then measured changes in antipredatory behavior and also survival. We predicted a simple negative additive effect of low pH. We hypothesized that snails from metal-polluted environments would be physiologically stressed and impaired due to defense responses against heavy metals. Instead, snails from populations that acclimated or evolved in the presence of heavy metal mining pollution were more robust to acidic conditions than were snails from reference habitats. Snails from mining polluted sites seemed to be preadapted to a low pH environment. Their short-term survival in acidic conditions was better than snails from reference sites that lacked metal pollution. In fact, the 48 h survival of snails from polluted sites was so high that it did not significantly differ from the 24 h survival of snails from control sites. This suggests that the response of organisms to a world with rising anthropogenic carbon dioxide levels may be complex and difficult to predict. Snails had a weaker behavioral response to stressful stimuli if kept for 1 month at a pH that differed from their lake of origin. We found that snails raised at a pH of 5.5 had a weaker response (less of a decrease in activity) to concentrated heavy metals than did snails raised at their natal pH of 6.5. Furthermore, snails raised a pH of 5.5, 6.0, and 7.0 all had a weaker antipredatory response to an extract of crushed snail cells than did the pH 6.5 treatment snails.

The effects of the herbicide atrazine on freshwater snails.

Atrazine has been shown to affect freshwater snails from the subcellular to community level. However, most studies have used different snail species, methods, endpoints, and atrazine exposure concentrations, resulting in some conflicting results and limiting our understanding. The goal of this study was to address these concerns by (1) investigating the acute and chronic effects of atrazine on four species of freshwater snails (Biomphalaria glabrata, Helisoma trivolvis, Physa acuta, and Stagnicola elodes) using the same methods, endpoints, and concentrations, and (2) summarizing the current literature pertaining to the effects of atrazine on freshwater snails. We conducted a 48 h acute toxicity test with an atrazine concentration higher than what typically occurs in aquatic environments (1000 µg/L). Additionally, we exposed snails to environmentally relevant atrazine concentrations (0, 0.3, 3, and 30 µg/L) for 28 days and assessed snail survival, growth, and reproduction. We also summarized all known literature pertaining to atrazine effects on freshwater snails. The literature summary suggests snails are often affected by environmentally relevant atrazine concentrations at the subcellular and cellular levels. These effects are typically not transitive to effects on survival, growth, or reproduction at the same concentrations. Our acute exposures corroborate the general trend of no direct effect on snail populations as atrazine did not directly affect the survival of any of the four snail species. Similarly, environmentally relevant concentrations did not significantly affect the survival, growth, or reproduction of any snail species. These results indicate that, in the absence of other possible stressors, the direct effects of environmentally relevant atrazine concentrations may not be realized at the snail population level.

Size-dependent shell growth and survival in natural populations of the rock-dwelling land snail Chondrina clienta

Rock-dwelling land snails, feeding on algae and lichens that grow on stone surfaces, may influence the structure and function of these ecosystems. Yet, little is known about the life history of rock-dwelling snails. We performed a 30-month mark–release–resight study in four populations of Chondrina clienta (Westerlund, 1883) inhabiting vertical walls of abandoned limestone quarries on the Baltic island of Öland, Sweden, to assess growth rate and survival of juvenile snails and determine age at maturity. We marked 800 individuals ranging in shell height from 1.4 to 4.9 mm, released them in their original habitat, and remeasured their shell height at intervals of 6 months. Shell growth of juvenile C. clienta was affected by the site (quarry wall) and the size of the individual, being highest in medium-sized snails. Shell growth occurred during both summer and winter. Annual apparent survival rates of C. clienta were size-dependent and ranged from 58.6% to 96.3%. Sexual maturity was reached at an age of 5 years, which is later than in most large snail species. Our study extends current knowledge on life history of land snails to a rarely studied group dwelling on rock surfaces.

Impact of soil cadmium on land snails: a two-stage exposure approach under semi-field conditions using bioaccumulative and conchological end-points of exposure.

Land snails are highly tolerant to cadmium exposure and are able to accumulate soil cadmium independently of food ingestion. However, little information exists on the kinetics of cadmium retention in terrestrial gastropods exposed to an increase in the soil cadmium content, over time. There is also little knowledge about how exposure to cadmium-polluted soils influences shell growth and architecture. In this context, we examined cadmium accumulation in the hepatopancreas and shell of juvenile Cantareus aspersus exposed to elevating high levels of cadmium in soil. Also, the toxicity of cadmium to snails was assessed using a range of conchological endpoints, including shell height, width, volume, allometry and integrity. Test snails, aged three months, were reared under semi-field conditions, fed an uncontaminated diet and exposed first, for a period of 30 days, to a series of soil cadmium concentrations, and then, for a second period of 30 days, to soils with higher cadmium content. Cadmium showed a dose-dependent accumulation in both the hepatopancreas and shell. The kinetics of cadmium retention in the hepatopancreas of snails previously exposed to cadmium-spiked soils was significantly influenced by a new exposure event. The shell was not a relevant bioaccumulator for soil cadmium. Under the present experimental conditions, only high cadmium exposure significantly affected either the shell growth or snail survival. There was no consistent effect on shell allometry, but the shell integrity, especially in rapidly growing parts, appeared to be affected by high cadmium exposure. Our results attest to the value of hepatopancreas for describing cadmium retention in land snails and to the difficulty of using conchological parameters in field surveys for estimating the environmental hazard of soil cadmium.

Characterizing the effects of temperature on behavioral periodicity in golden apple snails (Pomacea canaliculata)

The golden apple snail (Pomacea canaliculata), an invasive freshwater species in Asia, has become a serious agricultural pest. Water temperature is one of the most important environmental factors influencing the survival, growth rate, reproduction and behavior of freshwater snails. For this reason, the behavioral periodicity of golden apple snails was examined at different water temperatures (15°C, 20°C, 25°C, and 30°C). We classified the snails' behaviors into 12 pre-defined categories each minute for 2days at each temperature. Five dominant behavioral categories (clinging to the side of the aquarium [clinging], clinging with sprawling out its antennae [clinging-NM], crawling on the bottom of the aquarium, crawling on the side of the aquarium and feeding) were selected for further analyses. Spectral analysis and cross-spectral analysis were applied to determine the periodicity of these behaviors. Snails spent less time in moving during photophase than scotophase at all temperatures. Behavioral periodicity was much longer at lower temperatures, for both motion and motionless behaviors except clinging-NM. Detrended correspondence analysis based on periodogram values clearly characterized the differences in behavior at the various temperatures. Behavioral turnover, assessed by cross-spectral analysis, was faster at higher temperatures, and Markov chain analysis supported this result by finding a lower probability of maintaining the current behavior at higher temperatures.

Necropsy findings in 62 opportunistically collected free-ranging moose (Alces alces) from Minnesota, USA (2003-13).

The Minnesota, US moose population has declined dramatically since the 1990s. All 54 carcasses of moose that died of unknown cause or were euthanized by gun shot by tribal or Department of Natural Resources personnel because of perceived signs of illness between 2003 and 2013 and eight carcasses of moose that died from vehicular accidents between 2009 and 2013 were submitted to the Minnesota Veterinary Diagnostic Laboratory and included in our study. The majority of the animals were underweight or cachectic (n = 53; 85%). Neural migration presumably by Parelaphostrongylus tenuis was a common finding (n = 28; 45%). Moderate to marked Dermacentor albipictus ("winter tick") ectoparasitism with widespread alopecia was the cause or a contributing cause of death in 14 (23%) cases in which grossly apparent anemia was associated with exhaustion of hepatic iron stores. Hepatic lesions associated with Fascioloides magna were common (n = 37; 60%) but were unlikely to be the cause of death. Environmental factors favoring winter tick survival, habitat expansion of white-tailed deer (Odocoileus virginianus), and the survival of terrestrial and aquatic snails (serving as intermediate hosts for P. tenuis and F. magna), might contribute to the seemingly severe parasitic burden in Minnesota's moose population.

Field-derived Schistosoma mansoni and Biomphalaria pfeifferi in Kenya: a compatible association characterized by lack of strong local adaptation, and presence of some snails able to persistently produce cercariae for over a year.

BackgroundSchistosoma mansoni is widely distributed in sub-Saharan Africa with Biomphalaria pfeifferi being its most widespread and important snail intermediate host. Few studies have examined the compatibility of field-derived B. pfeifferi snails with S. mansoni miracidia derived from human hosts. We investigated compatibility (as defined by shedding of cercariae following exposure to miracidia) of two isolates of S. mansoni from school children from Asao (western Kenya) and Mwea (central Kenya) with B. pfeifferi collected directly from Asao stream or the Mwea rice fields.MethodsWe exposed snails from both regions to four different doses of miracidia (1, 5, 10 and 25) from sympatric or allopatric S. mansoni, and maintained them in a shaded, screened out-of-doors rearing facility in Kisian, in western Kenya. Both snail survival and the number of snails that became infected were monitored weekly. This was done for 25 weeks post-exposure (PE). Those infected snails which survived beyond this period were monitored until they all died.ResultsAlthough overall survival of Mwea snails maintained in western Kenya was generally low, both sympatric and allopatric combinations of parasites and snails exhibited high compatibility (approximately 50% at a dose of one miracidium per snail), with an increase in infection rates as the miracidial dose was increased (P < 0.002). Schistosomes were no more compatible with sympatric than allopatric snails, nor were snails less compatible with sympatric than allopatric schistosomes. Snail mortality increased significantly with dose of miracidia (P < 0.05). Approximately 3% of Asao snails exposed to a low dose of sympatric miracidia (1 or 5) continued to shed cercariae for as long as 58 weeks post exposure.ConclusionsThere were no significant local adaptation effects for either schistosomes or snails. Also, the existence of “super-survivor” snails is noteworthy for its implications for current control initiatives that mostly rely on mass drug administration (MDA). Long-term shedders could provide an ongoing source of cercariae to initiate human infections for many months, suggesting care is required in considering how human MDA treatments are timed. Future control programs should incorporate means to eliminate infected snails to complement chemotherapy interventions in controlling schistosomiasis.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-014-0533-3) contains supplementary material, which is available to authorized users.

Bioecology and management of giant African snail, Achatina fulica (Bowdich)

Giant African snail ( Achatina fulica Bowdich) belongs to the Phylum-Mollusca and Class- Gastropoda. It is known for its destructive nature on cultivated crops wherever it occurs and is one of the world's largest and most damaging land snail pests. The pest is an East African origin, has spread in recent times by travel and trade to many countries. They now widely distributed and no longer limited to their region of origin due to several factors viz., high reproductive capacity, voracious feeding habit, inadequate quarantine management and human aided dispersal. A. fulica can cause serious economic damage on different crops and extensive rasping (scrapping), defoliation, slime trials, or ribbon like excrement is signs of infestation. In recent times, severe outbreak of this pest has been noticed due to some desirable agricultural and gardening practices like minimum tillage practices and straw retention techniques which help in survival of snails and make seedlings more susceptible to damage. This review paper aims to enlighten on taxonomy, distribution, extent of damage, morphology, biology, ecology, homing behaviour, seasonal incidence, nature of damage, host plants of A. fulica and its ecofriendly management strategies.

Development and validation of an OECD reproductive toxicity test guideline with the pond snail Lymnaea stagnalis (Mollusca, Gastropoda)

The OECD test guideline development program has been extended in 2011 to establish a partial life-cycle protocol for assessing the reproductive toxicity of chemicals to several mollusk species, including the great pond snail Lymnaea stagnalis. In this paper, we summarize the standard draft protocol for a reproduction test with this species, and present inter-comparison results obtained in a 56-day prevalidation ring-test using this protocol.Seven European laboratories performed semi-static tests with cultured snails of the strain Renilys® exposed to nominal concentrations of cadmium chloride (from 53 to 608μgCdL−1). Cd concentrations in test solutions were analytically determined to confirm accuracy in the metal exposure concentrations in all laboratories. Physico-chemical and biological validity criteria (namely dissolved oxygen content >60% ASV, water temperature 20±1°C, control snail survival >80% and control snail fecundity >8 egg-masses per snail over the test period) were met in all laboratories which consistently demonstrated the reproductive toxicity of Cd in snails using the proposed draft protocol. Effect concentrations for fecundity after 56days were reproducible between laboratories (68<EC50–56d<124μgL−1) and were consistent with literature data. EC50–56d and EC10–56d values were comprised within a factor of 1.8 and 3.6, respectively, which is in the range of acceptable variation defined for reference chemicals in OECD test guidelines for invertebrates. The inter-laboratory reproducibility coefficient of variation (CV) for the Cd LC50–56d values was 8.19%. The inter-laboratory comparison of fecundity within the controls gave a CV of 29.12%, while exposure to Cd gave a CV of 25.49% based on the EC50–56d values. The OECD has acknowledged the success of this prevalidation exercise and a validation ring-test involving 14 laboratories in Europe, North- and South-America is currently being implemented using four chemicals (Cd, prochloraz, trenbolone and tributyltin).

Effects of single, binary and tertiary combinations with Jatropha gossypifolia and other plant-derived molluscicides on reproduction and survival of the snail Lymnaea acuminata.

The effect of sub-lethal doses (40% and 80% of LC50/24h) of plant derived molluscicides of singly, binary (1:1) and tertiary (1:1:1) combinations of the Rutin, Ellagic acid, Betulin and taraxerol with J. gossypifolia latex, leaf and stem bark powder extracts and their active component on the reproduction of freshwater snail Lymnaea acuminata have been studied. It was observed that the J. gossypifolia latex, stem bark, individual leaf and their combinations with other plant derived active molluscicidal components caused a significant reduction in fecundity, hatchability and survival of young snails. It is believed that sub-lethal exposure of these molluscicides on snail reproduction is a complex process involving more than one factor in reducing the reproductive capacity.

Tradeoff between establishing an infection and killing the host: response of snails ( Physa acuta) to a gradient of trematode (Halipegus eccentricus) exposures.

Pond snails ( Physa acuta ) were exposed to a gradient (0, 1, 3, 5, 10, 15, 20, 25, 30, 35, 40, and 50) of trematode (Halipegus eccentricus) eggs and observed to determine egg dose effects on the survival of snails through the prepatent period, snail reproduction, and the production of cercariae. The probability of snail survival through the prepatent period significantly decreased with increasing egg exposures, where the odds of snail survival was 0.94 per trematode egg. Similarly, the probability of snail reproduction significantly decreased with increasing egg exposures, where the odds of snail reproduction was 0.85 per trematode egg. In contrast, the probability of a snail shedding cercariae significantly increased with increasing egg exposures, where the odds of reaching a patent infection were 1.64 per trematode egg. However, snails shedding cercariae that were exposed to higher doses of trematode eggs tended to die sooner. Thus, there appears to be a tradeoff between infecting a snail and killing the host.

After the burn: factors affecting land snail survival in post-prescribed-burn woodlands

Prescribed burning is commonly used for vegetation management. Whereas effects on vegetation are apparent, effects of these burns on ground-dwelling invertebrates are not. Land snails are especially susceptible to burns. Snail loss occurs directly from burns, but may also occur post-burn because of altered habitat conditions, although post-burn loss has not previously been tested. We used a field experiment to investigate snail survival and factors affecting survival in post-burn habitats. We exposed snails (Discidae: Anguispira alternata) to combinations of intact leaf litter, wood shelters, burned leaf litter, charred wood and ash added to leaf litter, to simulate a variety of post-burn conditions. Half of the replicates were watered every 3 d, which allowed detection of desiccation effects in comparison to ambient water conditions. The on-going drought resulted in high snail mortality. Watering increased survival and, as a consequence, growth. Snail mortality was higher in habitats with burned leaves and/or wood than in unburned habitats. Higher temperatures and rapid initial mortality in burned habitats, and increased survival with watering, indicated that the major cause of post-fire mortality was desiccation, rather than starvation. Contrary to expectations, snails in burned-leaf habitats grew more than snails in unburned habitats, and this greater growth was associated with higher soil pH. Snails surviving fires in burned woodland areas likely have high post-burn mortality. Our experiment highlights the negative impacts of burned woodland habitats on some nontarget organisms and indicates that prescribed burns should be avoided during exceptionally dry conditions.

Effects of fertiliser applications on survival and recruitment of the apple snail, Pomacea canaliculata (Lamarck)

Since its introduction to Asia in the 1980s, the golden apple snail, Pomacea canaliculata (Lamarck), has represented a major constraint to the profitability of rice (Oryza sativa L.) farming by damaging rice seedlings during crop establishment. This study describes a series of experiments designed to determine the effects of nitrogenous fertilisers on snail fitness. We examined the possibility of a two-phase model of snail response to nitrogen, whereby fertilisers initially increase snail mortality through toxicity, but once assimilated into the rice ecosystem, eventually favour snail reproduction and survival. In experimental arenas, fertiliser had lethal effects: Complete fertiliser (14:14:14), urea, ammonium sulphate and organic fertilisers were associated with snail mortality, generally affecting adult snails more than juvenile snails, and with greater effects when applied to saturated soil that was subsequently flooded (as opposed to direct application to flooded soil). Snail mortality was found to decline considerably when snails were added to arenas one day after fertiliser application – this occurred in arenas with soil and water, but not in arenas with water only, suggesting that soil can reduce the toxic effects of fertilisers. In a field experiment, snail numbers declined in both fertilised and non-fertilised plots at the time of crop establishment. Numbers increased in all plots after rice tillering, with significantly more recruitment in plots with high nitrogen. Although the responses were generally weak in the field experiment, they did support the two-phase model. The consequences of fertiliser applications for snail management and ecosystem health are discussed.