Cold hardiness abilities vary with the size of the land snail Cornu aspersum

Seasonal cellular stress phenomena and phenotypic plasticity in land snail Helix lucorum populations from different altitudes

Temperature, a major abiotic environmental factor, regulates various physiological functions in land snails and therefore determines their biogeographical distribution. Thus, species with different distributions may present different thermal tolerance limits. Additionally, the intense reactivation of snail metabolic rate upon arousal from hibernation or estivation may provoke stress. Land snails, Helix lucorum, display a wide altitudinal distribution resulting in populations being exposed to different seasonal temperature variations. The aim of the present study was to investigate the expression of heat shock proteins (Hsps), mitogen activated protein kinases (MAPKs) and proteins that are related to apoptosis (Bcl-2, ubiquitin), that have 'cytoprotective' roles and are also considered to be reliable indicators of stress because of their crucial role in maintaining cellular homeostasis. These proteins were assessed in H. lucorum individuals from two different populations, one at Axios (sea level, 0 m) and the other at Kokkinopilos (Olympus, 1250 m), as well as after mutual population exchanges, in order to find out whether the different responses of these stress-related proteins depend solely on the environmental temperature. The results showed seasonally altered levels in all studied proteins in the hepatopancreas and foot of snails, both among different populations and between the same populations exposed to varying altitudes. However, individuals of the same population in their native habitat or acclimatized to a different habitat showed a relatively similar pattern of expression, supporting the induction of the specific proteins according to the life history of each species.

The "Sandwich" System: A Potential Solution for Protecting Overwintering Cornu aspersum Snails Reared in Semi-Intensive Heliciculture Farms in Colder Climates

Simple Summary

The Italian semi-intensive (ISISF) technology is widely used for rearing the Mediterranean snail, Cornu aspersum. It relies on protecting overwintering specimens with Lutrasil frost cloth (LFC). This approach yielded elevated mortalities in Romanian snail farms. We aimed to develop a simple and effective system for protecting overwintering C. aspersum adults in colder climates. This three-year, three-phase experiment investigated selected behavioral aspects and thermal protection efficiency of different protective structures. Mature gastropods in preparation for hibernation exhibited a significant preference for wood and ridge-tile micro shelters. Soil texture significantly influenced the burrowing behavior, but not the burrowing depth. The structure soil/LFC/straw/10-cm air cushion/high-density polyethylene (HDPE)—the “sandwich” system—was selected to be used as a protective system. Under farm conditions, adult snails tended to hibernate clustered together, attached to the lower surface of micro shelters. The “sandwich” system coupled with using ridge-tile/wood micro shelters resulted in significantly higher survival thanthe sole use of LFC. Predator occurrence appeared to exert a minor effect on snail survival. These data render the “sandwich” system a potential solution for overwintering C. aspersum breeders in colder climates.

Abstract

(1) Background: Hibernation in pens covered with LFC was associated with high mortality of C. aspersum snails in Romanian snail farms. This three-year study aimed to develop a simple, but effective system for protecting breeders in colder climates. (2) Methods: The first phase investigated the (pre)hibernal burrowing behavior and the overwintering habitat choice. Protective structures based on straw, LFC, and/or HDPE were tested at pilot level (no snails). The most suitable system was applied under farm conditions. (3) Results: Wood and ridge-tile micro shelters were significantly preferred to corrugated iron micro shelters. Burrowing specimens acted as shallow-burrowers, and this behaviorwas significantly more common for looser soils. All pilot systems displayed significantly higher thermal protection efficiency compared to the sole use of LFC. The balance between straw moistening and thermal protection favored using structure soil/LFC/straw/10-cm air cushion/HDPE. Its use yielded significantly higher survival compared to the sole use of LFC. Most hibernating snails clustered together in large groups, attached on the lower surface of micro shelters. Predator occurrence appeared to marginally affect overwintering survival. (4) Conclusions: The “sandwich” system could be an effective solution for overwintering mature C. aspersum snails in colder climates.

Climate gradients, and patterns of biodiversity and biotic homogenization in urban residential yards

Residential yards constitute a substantive biodiverse greenspace within urban areas. This biodiversity results from a combination of native and non-native species and can contribute to biotic homogenization. Geographical climatic patterns affect the distribution of native species and may differently affect non-native species. In this study, we examined biodiversity and biotic homogenization patterns of yard-dwelling land snails across 12 towns in Oklahoma and Kansas (USA). The 3 x 4 array of towns incorporated a N-S winter temperature gradient (mean low January temperature range = -8.4 to 0.1°C) and an E-W annual rainfall gradient (annual rainfall range = 113.8 to 61.3 cm/yr). Ten yards per town were surveyed. We hypothesized that mild winter temperatures and greater annual rainfall would be associated with greater snail abundance and richness, and that the presence of non-native species would contribute to biotic homogenization. Non-native snails were present and often abundant in all towns. Snail communities varied with both rainfall and cold temperature. Contrary to our prediction, snail abundance was inversely related to annual rainfall–likely because drier conditions resulted in greater yard watering that both augmented rainfall and maintained moist conditions. Sørensen similarity between towns for the entire land snail community and for only non-native species both showed distance-decay patterns, with snail composition becoming less similar with increasing distance—patterns resulting from species turnover. The biotic homogenization index also showed a distance-related pattern, such that closer towns were more likely to have biotic homogenization whereas more distant towns tended to have biotic differentiation. These results support the concept that biotic homogenization is more likely regionally and that climatic changes over distance result in species turnover and can reduce spatially broad biotic homogenization.

Life-history changes in the cold tolerance of the two-spot spider mite Tetranychus urticae: applications in pest control and establishment risk assessment

Lethal time50 (LTime50) and lethal temp (LTemp50) are commonly used laboratory indices of arthropod cold tolerance, with the former often being employed to predict winter survival in the field. In the present study, we compare the cold tolerance of different life-history stages (nondiapausing and diapausing females, as well as males and juveniles) of a major agricultural pest: the two-spot spider mite Tetranychus urticae Koch (Acarina: Tetranychidae). Diapausing females from European populations of this species are shown to be freeze avoiding, supercooling to -23.6 ± 0.37  °C and with an LTemp50 of -23.2 °C. However, nondiapausing females [supercooling point (SCP) -19.1 ± 0.49 °C, LTemp50 -14.32 °C], males (SCP -21.27 ± 0.52  °C, LTemp50 -16 °C) and juveniles (SCP -25.34 ± 0.29 °C, LTemp50 -18.3 °C) are subclassified as strongly chill tolerant juveniles. LTime50 is 148.3 days for non-acclimated diapausing females, whereas nondiapausing females, males and juveniles reach 50% mortality by 21.7 days. When individuals are acclimated at 10 °C for a period of 7 days, no effect is found. Cold tolerance is suggested to be a major contributor to the successful spread of T. urticae across temperate countries, although it is dependent on a diapause trait, suggesting a potential target for control. Winter field trial data from diapausing females indicate that LTime50 is a reliable indicator of winter survival even within diapause, supporting the use of these indices as a valuable component within environmental niche models for the prediction of future pest invasions.

Brachylaimiasis: Brachylaima spp. (Digenea: Brachylaimidae) Metacercariae Parasitizing the Edible Snail Cornu aspersum (Helicidae) in Spanish Public Marketplaces and Health-Associated Risk Factors

The edible land snail Cornu aspersum (Pulmonata: Stylommatophora) acts as a second intermediate host in the terrestrial life cycle of Brachylaima spp. trematodes, harboring unencysted metacercariae in its kidney. The ingestion of undercooked infected snails by humans may allow metacercariae to potentially develop to adult stage in the intestine, causing brachylaimiasis, as already seen in Australia. The prevalence and dynamics of C. aspersum parasitization by Brachylaima spp. metacercariae in specimens intended for human consumption in Spanish marketplaces were studied. In total, 3,710 C. aspersum specimens were analyzed over 5 yr, which were obtained from public marketplaces in the Spanish cities of Barcelona, Bilbao, Madrid, Tudela, Valencia, and Zaragoza. The overall prevalence was 41.97% (95% CI: 40.38-45.56%). The Tudela marketplace had the highest values for both the seasonal prevalence and abundance in all studies during autumn (93.57% and 3.09, respectively). This market also gave the highest individual metacercarial burden recorded, 212 metacercariae in a single specimen. Overall, the highest prevalence of Brachylaima spp. occurred in autumn (58.65%) and the lowest in winter (22.64%). There was a seasonal effect on prevalence, which increased from summer to autumn and then decreased in winter. In total, 96 experimental Brachylaima adults were obtained from the metacercariae parasitizing the analyzed snails. These were identified through morphometric tools (principal component analysis) as Brachylaima mascomai (56 in Barcelona, 1 in Bilbao, 7 in Tudela, and 3 in Valencia), and Brachylaima llobregatensis (17 in Barcelona, 8 in Bilbao, 1 in Valencia, and 3 in Zaragoza). Logistic regression modeling, conducted to predict the probability of purchasing parasitized snails using city and season as predictors showed a correct prediction overall of 79.0%, with a significant (p = 0.001) risk effect in the Barcelona-autumn interaction (2.551-38.442), a significant (p = 0.049) protection effect in the Tudela-spring interaction (0.076-0.997), a significant (p < 0.001) risk effect in the Tudela-autumn interaction (4.330-78.584), and a significant (p = 0.014) protection effect in the Valencia-spring interaction (0.033-0.687). The high overall prevalence of Brachylaima spp. metacercariae should be a matter of concern for public health authorities, mainly in countries where C. aspersum is consumed.

Conservation at a slow pace: terrestrial gastropods facing fast-changing climate

The climate is changing rapidly, and terrestrial ectotherms are expected to be particularly vulnerable to changes in temperature and water regime, but also to an increase in extreme weather events in temperate regions. Physiological responses of terrestrial gastropods to climate change are poorly studied. This is surprising, because they are of biodiversity significance among litter-dwelling species, playing important roles in ecosystem function, with numerous species being listed as endangered and requiring efficient conservation management. Through a summary of our ecophysiological work on snail and slug species, we gained some insights into physiological and behavioural responses to climate change that we can organize into the following four threat categories. (i) Winter temperature and snow cover. Terrestrial gastropods use different strategies to survive sub-zero temperatures in buffered refuges, such as the litter or the soil. Absence of the insulating snow cover exposes species to high variability in temperature. The extent of specific cold tolerance might influence the potential of local extinction, but also of invasion. (ii) Drought and high temperature. Physiological responses involve high-cost processes that protect against heat and dehydration. Some species decrease activity periods, thereby reducing foraging and reproduction time. Related costs and physiological limits are expected to increase mortality. (iii) Extreme events. Although some terrestrial gastropod communities can have a good resilience to fire, storms and flooding, an increase in the frequency of those events might lead to community impoverishment. (iv) Habitat loss and fragmentation. Given that terrestrial gastropods are poorly mobile, landscape alteration generally results in an increased risk of local extinction, but responses are highly variable between species, requiring studies at the population level. There is a great need for studies involving non-invasive methods on the plasticity of physiological and behavioural responses and the ability for local adaptation, considering the spatiotemporally heterogeneous climatic landscape, to allow efficient management of ecosystems and conservation of biodiversity.

Laboratory studies on the thermal tolerance and response of enzymes of intermediate metabolism in different land snail species

Land snails species occur in a range of habitats from humid to semi-arid and arid ones and seasonal variations in their physiology and biochemical composition have been linked to annual cycles of photoperiod, temperature, humidity and water availability. In an effort to understand the thermal tolerance and the impact of temperature elevation on tissue metabolism of land snails we determined the mortality, heamolymph PO₂ and the activities of enzymes of intermediary metabolism in three land snail species (Helix lucorum, Helix pomatia and Cornu aspersum) differing in their geographical distribution and inhabiting areas with different climatic characteristics. No mortality was observed in both population of Cornu aspersum, while Helix pomatia exhibited higher mortality than Helix lucorum. PO₂ dropped within the first 10days of exposure to elevated temperature in all species, although in Cornu aspersum this decrease was significantly lower. No significant reduction in the enzymatic activities of all glycolytic enzymes studied, as well as of citrate synthase (CS) and 3-hydroxyacyl-CoA dehydrogenase (HOAD) was observed in the more thermal tolerant species C. aspersum from both populations studied. Significant reductions of enzymatic activity of the glycolytic enzymes phosphofructokinase (PFK), pyruvate kinase (PK) and d-Lactate dehydrogenase (d-LDH) was observed in Helix lucorum and Helix pomatia. The observed inter-specific differences seem to be in accordance with the life cycle characteristics of each species and may be attributed to climatic differences among habitats within their distribution range.

Lack of supercooling evolution related to winter severity in a lizard

As organisms move into higher latitudes, they may evolve physiological mechanisms to survive in harsher climates. One such mechanism is supercooling, the capacity to survive at subzero temperatures without freezing. While interspecific comparisons reveal greater thermal tolerances at higher latitudes in insects and vertebrates, evidence for intraspecific evolution in supercooling related to latitude is only evident in insects. We measured the supercooling points of lizards from 12 populations reared from hatch in common laboratory conditions to test for evolved differences in supercooling related to winter. Results indicate that winter harshness (depth or length) cannot explain supercooling points regardless of how data are analyzed, which suggests that populations have not evolved greater supercooling capacity. While our results are consistent with the idea that thermal physiology is evolutionarily conserved in vertebrates, we cannot reject several alternatives including the possibility that lizards are able to behaviorally avoid the extreme temperatures that would select for thermal evolution.

Praziquantel efficacy against Brachylaima sp. metacercariae (Trematoda: Brachylaimidae) parasitizing the edible landsnail Cornu aspersum and its HPLC-MS/MS residue determination

Cornu aspersum is a terrestrial edible snail, often parasitized by Brachylaima (Trematoda) metacercariae. Ingestion of undercooked snails by humans allows metacercariae to develop to adult in the intestine causing brachylaimiasis (expected mortality rate 5-10%). The cosmopolitan character of the trematode and of its vector, enhanced in a future climate change scenario, and the absence of adequate sanitary controls of the snails in marketplaces clearly increase the risk of human brachylaimiasis. The treatment of farmed snails with praziquatel (PZQ) would be a tool to control this food-borne disease. The objectives of this study were: to report the prevalence of Brachylaima metacercariae parasitizing C. aspersum in marketplaces, to assess the efficacy and tolerance of PZQ in C. aspersum and to develop an HPLC-MS/MS analytical method to quantify PZQ residue in the edible snail (the acceptable daily intake of PZQ is 0.17 mg/kg bw in humans). Prevalence of parasitization of C. aspersum by Brachylaima metacercariae in public marketplaces reached the 80%. PZQ was orally administered to snails, mixed with the usual snail food. In dose determination assays three doses were individually tested (10 days): 1.2 mg PZQ/snail, 1.8 mg PZQ/snail (efficacy 97.3%, p < 0.001) and 2.4 mg PZQ/snail (efficacy 98.7%, p < 0.001). In dose confirmation tests (n = 200) the 2.4 mg PZQ/snail dose was group tested (10 snails/box, 7 days): 2 g of PZQ supplemented snail food were disposed daily in the treatment group boxes and 2 g of snail food (placebo) in the control boxes (efficacy 94.6%, p < 0.001; prevalence dropped from 68.7% in control group to 10.1% in treatment group, p < 0.001). Received dose was 220.2 mg PZQ/kg snail with shell. In the analytical method, linearity, lower limit of quantification (0.05 μg/ml), selectivity, carry over, accuracy, precision, dilution integrity, matrix effect and stability were tested. Sixty snails were treated (11 mg PZQ/g snail food) and analyzed. PZQ was detected and quantified (0.093 mg PZQ/g snail). PZQ treatment of C. aspersum is effective, well tolerated by the snail, affordable and easy to reproduce in snail farms.

Soil calcium availability influences shell ecophenotype formation in the sub-antarctic land snail, Notodiscus hookeri

Ecophenotypes reflect local matches between organisms and their environment, and show plasticity across generations in response to current living conditions. Plastic responses in shell morphology and shell growth have been widely studied in gastropods and are often related to environmental calcium availability, which influences shell biomineralisation. To date, all of these studies have overlooked micro-scale structure of the shell, in addition to how it is related to species responses in the context of environmental pressure. This study is the first to demonstrate that environmental factors induce a bi-modal variation in the shell micro-scale structure of a land gastropod. Notodiscus hookeri is the only native land snail present in the Crozet Archipelago (sub-Antarctic region). The adults have evolved into two ecophenotypes, which are referred to here as MS (mineral shell) and OS (organic shell). The MS-ecophenotype is characterised by a thick mineralised shell. It is primarily distributed along the coastline, and could be associated to the presence of exchangeable calcium in the clay minerals of the soils. The Os-ecophenotype is characterised by a thin organic shell. It is primarily distributed at high altitudes in the mesic and xeric fell-fields in soils with large particles that lack clay and exchangeable calcium. Snails of the Os-ecophenotype are characterised by thinner and larger shell sizes compared to snails of the MS-ecophenotype, indicating a trade-off between mineral thickness and shell size. This pattern increased along a temporal scale; whereby, older adult snails were more clearly separated into two clusters compared to the younger adult snails. The prevalence of glycine-rich proteins in the organic shell layer of N. hookeri, along with the absence of chitin, differs to the organic scaffolds of molluscan biominerals. The present study provides new insights for testing the adaptive value of phenotypic plasticity in response to spatial and temporal environmental variations.

High cold tolerance through four seasons and all free-living stages in an ectoparasite

Off-host stages of temperate parasites must cope with low temperatures. Cold tolerance is often highest in winter, as a result of diapause and cold acclimation, and low during the active summer stages. In some blood-feeding ectoparasites, offspring provisioning determines cold tolerance through all the non-feeding, off-host stages. Large size increases survival in the cold, but so far seasonal variation in within-female offspring size has not been associated with offspring cold tolerance. The deer ked (Lipoptena cervi) reproduces on cervids from autumn to spring. Newborn pupae drop off the host, facing frosts without any acclimation. We examined cold tolerance through 4 seasons and from birth to adulthood by means of short- and long-term frost exposure. We expected females to produce more tolerant offspring in winter than in spring. Large spring pupae survived prolonged frosts better than did small winter pupae. Thus more tolerant offspring were not produced when the temperature outside the host is at its lowest. Unexpectedly, the freezing points were −20°C or below all year round. We showed that high cold tolerance is possible without acclimation regardless of life stage, which presumably correlates with other survival characteristics, such as the starvation resistance of free-living ectoparasites.

Physiological response to low temperature in the freshwater apple snail, Pomacea canaliculata (Gastropoda: Ampullariidae)

Cold hardiness of the freshwater apple snail, Pomacea canaliculata, varies seasonally. We investigated lethal factors and physiological changes arising from exposure of P. canaliculata to low temperatures. Snails did not survive freezing. The supercooling point of cold-acclimated (cold tolerant) snails (-6.6+/-0.8 degrees C) did not differ significantly from that of non-acclimated ones (-7.1+/-1.5 degrees C) under laboratory conditions. Furthermore, snails died even under more moderately low temperatures approaching 0 degrees C. These results indicate that indirect chilling injury is a factor in the death of P. canaliculata at low temperatures. Regardless of whether the snails were acclimated to low temperatures, all of the dead, and even some of the snails still alive at 0 degrees C, had injured mantles, indicating that the mantle may be the organ most susceptible to the effects of low temperatures. The concentration of glucose in the posterior chamber of the kidney and concentration of glycerol in the digestive gland were significantly higher in cold-acclimated snails than in non-acclimated ones, suggesting carbohydrate metabolic pathways are altered in snails during cold acclimation.

Physiological ecology of overwintering in hatchling turtles

Temperate species of turtles hatch from eggs in late summer. The hatchlings of some species leave their natal nest to hibernate elsewhere on land or under water, whereas others usually remain inside the nest until spring; thus, post-hatching behavior strongly influences the hibernation ecology and physiology of this age class. Little is known about the habitats of and environmental conditions affecting aquatic hibernators, although laboratory studies suggest that chronically hypoxic sites are inhospitable to hatchlings. Field biologists have long been intrigued by the environmental conditions survived by hatchlings using terrestrial hibernacula, especially nests that ultimately serve as winter refugia. Hatchlings are unable to feed, although as metabolism is greatly reduced in hibernation, they are not at risk of starvation. Dehydration and injury from cold are more formidable challenges. Differential tolerances to these stressors may explain variation in hatchling overwintering habits among turtle taxa. Much study has been devoted to the cold-hardiness adaptations exhibited by terrestrial hibernators. All tolerate a degree of chilling, but survival of frost exposure depends on either freeze avoidance through supercooling or freeze tolerance. Freeze avoidance is promoted by behavioral, anatomical, and physiological features that minimize risk of inoculation by ice and ice-nucleating agents. Freeze tolerance is promoted by a complex suite of molecular, biochemical, and physiological responses enabling certain organisms to survive the freezing and thawing of extracellular fluids. Some species apparently can switch between freeze avoidance or freeze tolerance, the mode utilized in a particular instance of chilling depending on prevailing physiological and environmental conditions.

Freeze tolerance in Aporrectodea caliginosa and other earthworms from Finland

Earthworms that live in subarctic and cold temperate areas must deal with frost even though winter temperatures in the soil are often more moderate than air temperatures. Most lumbricid earthworms can survive temperatures down to the melting point of their body fluids but only few species are freeze tolerant, i.e. tolerate internal ice formation. In the present study, earthworms from Finland were tested for freeze tolerance, and the glycogen reserves and glucose mobilization (as a cryoprotectant) was investigated. Freeze tolerance was observed in Aporrectodea caliginosa, Dendrobaena octaedra, and Dendrodrilus rubidus, but not in Lumbricus rubellus. A. caliginosa tolerated freezing at -5 degrees C with about 40% survival. Some individuals of D. octaedra tolerated freezing even at -20 degrees C. Glycogen storage was largest in D. octaedra where up to 13% of dry weight consisted of this carbohydrate, whereas the other species had only 3-4% glycogen of tissue dry weight. Also glucose accumulation was largest in D. octaedra which was the most freeze-tolerant species, but occurred in all four species upon freezing. It is discussed that freeze tolerance may be a more common phenomenon in earthworms than previously thought.