Theba Pisana Research Articles

PLEISTOCENE LANDSNAILS FROM THE COASTAL PLAIN OF ISRAEL

ABSTRACT The landsnail fauna of five fossil layers from two sites in Israel's Coastal Plain, Shefayyim and Netanya, was analyzed. The layers date from about 45,000 years ago to Subrecent. Four species were found: The Jaminia ovularis-sulcidens complex, Trochoidea (Xerocrassa) davidiana, Xeropicta vestalis and Monacha syriaca—all present in the Coastal Plain today. Remarkable is the absence from all fossil layers of Theba pisana, the landsnail most abundant today in the Coastal Plain. As T. pisana has also not been found in any other Pleistocene sites in Israel, it is suggested that this species was introduced into Israel during historic times. Thereafter, competition with Xeropicta vestalis was inevitable, as both occupy a similar habitat. Rich morph diversity occurs in recent Xeropicta as compared with the fossil samples; it is tempting to suggest that this outburst of diversity is related to some ecological displacement into which Xeropicta was perhaps forced, due to competition with Theba. Within Jamin...

Historic data analysis reveals ambient temperature as a source of phenotypic variation in populations of the land snailTheba pisana

Pulmonate land snails are often polymorphic in their shell coloration pattern. To quantify the contribution of environmental parameters to the nondirectional change in phenotypic variation, we used a historic dataset on Theba pisana morph frequencies and climate data for statistical modelling. We found significant correlations of the degree of phenotypic diversity between juveniles and corresponding adult individuals within the same and the subsequent generation. Among climate parameters, the phenotypic diversity of adults correlated significantly and positively with the mean and maximum ambient temperatures in the winter and spring only. There was no correlation between high or low temperatures and the frequency of distinct morphs. Akaike's information criterion-based model selection revealed the particular importance of only parental phenotypic diversity for next generation juvenile phenotypic diversity. By contrast, phenotypic diversity of the juveniles of the preceding year and the mean temperatures in winter and spring were important for the phenotypic diversity of adult snails. Approximately two-thirds of the explicable variation in phenotypic diversity of adults was explained by inheritance and approximately one-third was expained by ambient temperature. The present study shows that genetics and temperature interact to generate nondirectional changes in phenotypic variation within populations, which also can be reflected by changes in the phenotype of individuals

The snail Theba pisana as an indicator of soil contamination by trace elements: potential exposure for animals and humans

The ability of snails to accumulate trace elements is well known. We analysed the snail Theba pisana as an indicator of soil contamination by trace elements after a mine spill accident, to assess the exposure of animal and human consumption. Snails were collected in autumn and spring, when they are most active. In general, trace elements in the soft tissues reached greater concentrations in the contaminated soils than in the non-contaminated soils, although significant differences were only found for As, Cd, Cu Fe and Hg. Cadmium content in tissues, with a maximum value of 10 mg kg⁻¹ (dry matter), was the most worrying result. Trace element concentrations in the snail bodies were still of concern for human consumption; As and Cd concentrations were sometimes higher than the maximum concentration authorised in foodstuffs. Generally, nutritional status of the contaminated snails was not altered; concentrations of the main nutrients (Ca, K, Mg, P and S) were similar to those of the non-contaminated snails. Results reveal a potential risk for animal and human consumption of T. pisana. It seems thus advisable to avoid collecting this species for human consumption in the affected area. Periodic monitoring is recommended to assess the evolution of potential risk for animal consumption.

Shell colour polymorphism, injuries and immune defense in three helicid snail species, Cepaea hortensis, Theba pisana and Cornu aspersum maximum

Shell colour polymorphism is a widespread feature of various land snail species. In our study we aimed at elucidating the question whether there is a correlation between shell colouration and immune defense in three land snail species by comparing phenoloxidase (PO) activity levels of different morphs after immunostimulation via Zymosan A-injection. Since phenoloxidase is involved both in immune defense as well as in melanin production, the PO activity level is particularly interesting when trying to resolve this question. Even though Zymosan A failed to induce PO activity rendering a comparison of inducible PO activity impossible, an interesting difference between pale and dark morphs of all tested species could be observed: dark snails were less affected by hemolymph withdrawal and were able to maintain or regenerate a significantly higher PO activity level after hemolymph withdrawal than pale snails. Possible implications of this observation are discussed.

Are the European snails, Theba pisana (Müller, 1774) (Helicidae), Cernuella virgata (da Costa, 1778) and Cochlicella acuta (Müller, 1774) (Hygromiidae) attracted by potential food odours?

White snails, Cernuella virgata and Theba pisana, and the conical snail Cochlicella acuta, are introduced pests of grain crops and pastures throughout much of southern Australia. All are native to Europe and, in particular, widespread throughout the western Mediterranean. The snails are principally regarded as pests in Australia because they foul grain harvests when aestivating on the heads and stalks of crops. Molluscicide baits are commonly used to control the pests. These baits are usually based on a bran or pasta formulation with metaldehyde as the pesticide ingredient. However, the baits are not strongly attractive as food sources for the snails. Their cost-effectiveness could be enhanced if more attractive formulations were developed. We therefore explored the possibility that other potential food sources/attractants could be incorporated into baits to increase their effectiveness against white and conical snails. The snails were assessed for preferential attraction towards odours elicited from 21 potential food attractants offered in olfactometers, with water as a control. The common, brown garden snail (Cornu aspersum), with its known attraction to carrot, was used to verify the validity of the olfactometer design. We were unable to identify any food items that elicited strong preferences in the white and conical snails. A few positive responses, and one negative, were obtained but these could well have occurred by chance, given the large number of tests that were completed. It seems most likely that white and conical snails are not directly attracted to food in their environment, but find it by random encounter.

Shell colouration and antioxidant defence capacity in Theba pisana (O.F. Müller, 1774)

Theba pisana (Müller, 1774), a Mediterranean snail, is known for its heat tolerance and its remarkable shell colour polymorphism ranging from pale white to darkly striped, although darker morphs are considered less vital in hot habitats due to presumably stronger absorption of radiation. Melanin, the black pigment of these snails, is known as an effective antioxidant, and elevated temperatures can increase oxidative stress. By analysing oxidative waste products via the ferrous oxidation xylenol orange (FOX) assay as a marker for the lipid peroxidation level, we aimed at investigating possible links between heat stress, colouration and antioxidant defence capacity in T. pisana. Although we found increasing levels of peroxidation products with increasing heat exposure duration, there was no difference in antioxidant defence capacity observable between different morphs of T. pisana. Hence the avoidance of lipid peroxidation as an environmentally relevant factor for the maintenance of melanistic morphs in strongly illuminated habitats can be considered improbable.

INTEGRATED CONTROL USING DIFFERENT METHODS AGAINST TWO LAND SNAIL SPECIES Theba pisana ( Muller) AND Helicella vestalis ( Pfeiffer) INFESTING Citrus nobilis TREES AT SHARKIA GOVERNORATE

Number of field experiments were conducted to evaluate the efficiency of certain safe and non- safe control methods as components of integrated pest management which help in reducing the population density of two land snail species, Theba pisana and Helicella vestalis infesting mandarin ( Citrus nobilis ) trees in orchards at newly salhyia, Sharkia Governorate during 2010- 2011. The safe methods were agricultural control ( Tillage or plowing process and plant traps ) and mechanical control (hand picking) for six weeks. The non-safe methods were chemical control by some toxicants (glyphosate: Herbicide, carbofuran: Insecticide and nematicide, chlorpyrifos-methyl: Insecticide, methamidophos: Insecticide, paraquate: Herbicide) and biological control by Xentari : Bacillus thuringiensis ( B .T. ) : Biocide and Insecticide.These toxicants were prepared as wheat bran baits for three weeks. The tested IPM components reduced the snail population of both species depending on their efficiency and the time of performance. Tillage, plant traps, toxicants and hand picking were useful to control land snails during December and January 2010, February and March 2011, April, June and July successively. Results revealed that glyphosate was the most effective toxicant giving highest average values of reduction percentage (58.02% and 61.4%) followed by tillage process (53% and 45.5%), plant traps (44.7% and 52.7%) and hand picking (37.9% and 45.2%) for Theba pisana and Helicella vestalis respectively, at the end of experiments. The biocide xentari (Bacillus thuringiensis) was the least effective one (31.9% and 32.02%). Moreover, the descending order of the tested toxicants was, glyphosate, carbofuran, chlorpyrifos-methyl, methamidophos, paraquate and Xentari.

Colour polymorphism and thermal capacities in Theba pisana (O.F. Müller 1774)

Several land snail species are highly polymorphic regarding their shell colouration. This polymorphism has been related to predatory effects as well as climatic reasons, assuming that dark morphs benefit from being more cryptic and therefore less prone to predation, whereas pale morphs are at an advantage under solar radiation, as they are suspected to heat up less. However, the assumption of different thermal capacities of these morphs is based on experiments with little standardisation or little environmental relevance. In this study, we aimed at measuring thermal capacities of two different morphs (pale versus dark-brown banded) of the Mediterranean land snail Theba pisana, applying a standardised and environmentally relevant test set-up, in order to prove whether darker morphs indeed do heat up more than lighter coloured morphs. We did not find any differences in the thermal capacity of the different morphs and conclude that thermal capacity of the shell is predominantly defined by its material rather than its coloration. These results are discussed with regard to previous studies on thermal characteristics of different land snail morphs and correlations between climate and morph distribution.

Phylogeography of an invasive land snail: natural range expansion versus anthropogenic dispersal in Theba pisana pisana

The invasive land snail Theba pisana pisana has been widely dispersed through human activities. The Mediterranean and adjacent Atlantic coasts are considered as natural range of this species, which also occurs northwards to the Netherlands, the British Islands and in Ireland. In addition, T. p. pisana has been introduced to some Macaronesian Islands as well as to Argentina, Australia, South Africa, and the United States. One important part of understanding biological invasions is the history of the processes including the routes of spread and introduction. Reconstructing the phylogeography based on COI sequences, we asked to which extent it may still be possible to trace natural as opposed to human causes for the current distribution. In addition, we attempted to infer the origins of the apparently recent human-mediated introductions. Tree reconstructions and demographic analyses showed that apart from the origin in NW-Africa, where T. p. pisana already underwent considerable differentiation, and an initial spread to the Iberian Peninsula, the phylogeographic signal was largely blurred. All available evidence indicated that primarily human activities rather than natural causes have shaped and still shape the current distribution. Already the spread through the Mediterranean basin may be anthropogenic and even the origins of our samples from South Africa and Australia could not unambiguously be traced. One clade was geographically particularly diverse suggesting that different lineages differ in their adaptive and invasive potential.

Scrutinising snail shells

Scrutinising snail shells

Epistasis, phenotypic disequilibrium and contrasting associations with climate in the land snail Theba pisana.

Hotter conditions favour effectively unbanded (EUB) shells in the snail Theba pisana. T. pisana is also polymorphic for colour of the shell's apex, determined by a pair of alleles at a locus linked to the banding locus. Apex colour is epistatic to shell banding, such that banded snails with a dark apex have darker bands. Annual censuses over 22 years across an ecotone between a sheltered Acacia thicket and open dune vegetation showed a persistent association of both EUB shells and pale apex with the Open habitat. The parallel variation was due partly to strong phenotypic disequilibrium, as the combination of EUB with dark apex was rare. Nevertheless, in fully banded shells the frequency of pale apex was also higher in the Open habitat, confirming independent, parallel associations of the two contributors to paleness. Within the Acacia habitat, temporal variation of the frequencies of banding morphs was much greater than for apex colour, and EUB shells were associated with hotter summers. Consistent with its primary effect only on the very small snails, apex colour did not vary with summer conditions, but instead, higher frequencies of pale apices were associated with sunnier winters. The intensity of selection was lower on apex colour than shell banding, due partly to the constraint of phenotypic disequilibrium. The shell traits in T. pisana are an example of complex responses to climatic variation, in which phenotypic disequilibrium constrains evolution of apex colour, but separate mechanisms of selection are evident.

Effects of contrasting habitats and weather on abundance of the land snail Theba pisana (O. F. Muller, 1774): a 34-year study

The effects of climate on abundance depend on local environments. A predicted interaction was tested in the land snail Theba pisana, in contrasting habitats of dense Acacia thickets and adjacent areas of low open vegetation, in introduced populations in Western Australia. The snails aestivate on vegetation over summer and mortality is higher in the Open habitat than in the Acacia. Growth experiments in winter showed that this advantage of the Acacia habitat in summer is countered by more rapid growth and higher survival of juvenile snails in the Open habitat. Thirty-four successive annual censuses of adult and subadult T. pisana were analysed, to test (1) the prediction that harsher summers would reduce abundance in the Open habitat, with less impact in the sheltered Acacia, and (2) the relative importance of summer (survival during aestivation) and winter (reproduction and growth) for abundance. As predicted, abundance in the Open habitat was lower following hotter, drier and sunnier summers. More surprising, abundance in the Acacia habitat showed the reverse association. Correlations with individual weather variables indicate that, while summer temperature and sunshine are important in the Open habitat, low summer rainfall, rather than high temperatures, is associated with higher abundance in the Acacia habitat. Winter conditions do not predict subsequent abundance of adults in either habitat, indicating the greater importance of summer mortality in determining abundance, but in different ways in the two habitats. This contrast is an example of the importance of considering specific habitats in the search for effects of changing climate on abundance.

Heat tolerance and recovery in Mediterranean land snails after pre-exposure in the field

Mediterranean land snails such as Xeropicta derbentina (Hygromiidae) and Theba pisana (Helicidae) are known for their remarkable tolerance to elevated temperatures and desiccation, yet the biochemical and cellular mechanisms underlying this tolerance are relatively unknown. We investigated the effects of increased temperatures and the ability of these snail species to recover from heat stress, examining the condition and amount of different types of hepatopancreatic cells (histopathology) and heat-shock protein 70 (stress protein) levels. Snails were exposed to defined control and increased temperatures and allowed a postheat phase for possible recovery. Results indicate the ability of X. derbentina to recover from natural and experimental temperature stress to some extent within the set time, whereas no such ability was found in T. pisana. Xeropicta derbentina is more heat-tolerant in general and less affected by heat stress than T. pisana. This is probably due to its greater ability to increase size and number of hepatopancreatic calcium cells that are essential for osmoregulation. The hypertrophy and hyperplasia of calcium cells can be regarded as a general response of molluscs to osmotic stressors, e.g. heat, as long as the organism is not overwhelmed by the stressor. Additionally, it can be assumed that the robust stress-protein system of X. derbentina plays a crucial role in this species’ high thermotolerance.

Thirty-four years of climatic selection in the land snail Theba pisana

Few continuous, long-term studies have measured the intensity and variability of natural selection within a framework of clear adaptive hypotheses. In the snail Theba pisana, the proportion of effectively unbanded shells is higher in exposed habitats than in adjacent acacia thickets, which has been explained by microclimatic selection. Comparisons across an ecotone for 34 consecutive years determined the combined effects on morph frequencies of habitat and changes in weather conditions during summer. The long-term average (±s.e.) frequency of effectively unbanded shells was 0.577±0.011 in the open habitat when compared with 0.353±0.005 in the acacia. The persistent association of shell banding with habitat accounted for 34% of the variation in morph frequencies. Differences among years were also large, representing 23% of the variation. Higher proportions of effectively unbanded snails were associated with hotter, sunnier summers. Thus, temporal variation supports the hypothesis of microclimatic selection, consistent with the spatial association with habitat. Based on observed rates of change, the mean annual selection on this polymorphism was about 0.13, but with a large variance: s was as high as 0.5, but 0.05 in about 40% of the years. The large variance and frequent reversals in direction of selection indicate a potential for rapid genetic change, but with little net change in morph frequencies over three decades, highlighting the value of long-term continuous studies of populations facing natural environmental variation.

Feeding and Growth Responses of the Snail Theba pisana to Dietary Metal Exposure

The effects of dietary exposure to copper (Cu), lead (Pb), and zinc (Zn) on feeding activities, growth response, and mortality of Theba pisana snails were studied in 5-week feeding tests. Snails were fed on an artificial diet containing the following Cu, Pb, or Zn concentrations: 0, 50, 100, 500, 1000, 5000, 10,000, and 15,000 μg/g dry food. At the end of 5 weeks, the food consumption rate was decreased with increasinges in both metal concentrations and time of exposure. The estimated concentrations of metals that reduces food consumption to 50% (EC₅₀) after 5 weeks were 56, 118, and 18 μg/g dry food for Cu, Pb, and Zn, respectively. All tested metals in the diet were found to inhibit growth of the snails in a dose-dependent manner. The toxic effect on growth of the tested metals could be arranged in the order Cu > Zn > Pb. The cumulative percentage mortality among snails fed a Cu- or Zn-contaminated diet was 73.3% and the respective value for a Pb-contaminated diet was 13.3%. There was a positive correlation between growth coefficient and food consumption for all tested metals.

Biomarkers of oxidative stress in the land snail, Theba pisana for assessing ecotoxicological effects of urban metal pollution

This study investigates the biomarkers of oxidative stress and heavy metal accumulation for assessing ecotoxicological effects of urban metal pollution in Alexandria city, Egypt. This investigation was performed in the digestive gland of roadside Theba pisana snails obtained from six different sites in the city. Relationships between heavy metal (Zn, Cu, Pb and Cd) concentrations and oxidative stress indicators were also examined. The results showed that mean concentrations of the measured elements (μg g −1 dry weight) were higher in polluted sites when compared to the background levels of the reference site. The pattern of metals accumulation at all sites was Zn > Cu > Pb > Cd. In the metal polluted sites, snails displayed higher mean of catalase (CAT), glutathione peroxidase (GPx) and glutathione S-transferase (GST) activities, lower reduced glutathione (GSH) content and higher levels of lipid peroxidation (LPO) compared to snails from the reference site. All oxidative stress parameters were positively correlated to heavy metal concentrations except GSH content which exhibits negative correlation with the concentrations of these metals. Our results suggest that the tested antioxidant defenses are sensitive parameters that could be useful as oxidative stress biomarkers in snails exposed to the actual metals in the environment. These biomarkers when complemented with metal accumulation in the digestive gland of snails may provide a powerful biomonitor for the assessment of environmental metal pollution.

Molluscicidal and insecticidal potential of monoterpenes on the white garden snail, Theba pisana (Muller) and the cotton leafworm, Spodoptera littoralis (Boisduval)

The present article reports the fumigant and contact toxicities of eleven monoterpenes against adults of Theba pisana and third instar larvae of Spodoptera littoralis. The majority of the tested compounds were found to be toxic to both pests with variable degrees of potency. Among the tested monoterpenes, (L)-fenchone showed the highest fumigant toxicity against T. pisana and S. littoralis with LC50 values of 2.51 and 2.27 mg/l, respectively. Myrcene and 1-8-cineole exhibited strong fumigant toxicity against T. pisana, while cuminaldehyde, geraniol and (−)-menthol were not active. On the other hand, 1-8-cineole and (+)-camphor revealed potent fumigant toxicity against S. littoralis. In the contact assay, the tested monoterpenes were more toxic against T. pisana than S. littoralis. Cuminaldehyde (LD50=28.37 μg/snail) was significantly the most effective compound against T. pisana, followed by geraniol and (−)-limonene. Interestingly, eight of the tested monoterpenes were more toxic to adults of T. pisana than methiocarb. The results of the present study suggested that cuminaldehyde, geraniol, (−)-limonene and (+)-camphor could be used as alternative control agents for T. pisana. In addition, (L)-fenchone and 1-8-cineole could be useful as fumigants for control T. pisana and S. littoralis.

Chemical analysis of mucus from certain land snails under Egyptian conditions

The present investigation was carried out to study the chemical analysis of the mucus of three common land snails, Eobania vermiculata, Theba pisana and Monacha obstructa, and identification of the chemical compositions by using GC-MS. Results revealed that several variations in composition were observed between all species. Oxime, methoxy-phenyl and cyclotrisiloxane, hexamethyl were major components found that in three species, the total areas detected were 86.23, 76.83 and 70.83, respectively. This different composition of mucus may be due to differences from one species to another; different mechanical properties (function) are influenced by external factors such as temperature, humidity, light intensity, soil conditions and food supply.

In vivo evaluation of oxidative stress biomarkers in the land snail, Theba pisana exposed to copper-based pesticides

The in vivo evaluation of oxidative stress biomarkers in the digestive gland of Theba pisana exposed to sublethal doses (40% and 80% of LD 50 after 48 h) of copper-based pesticides; copper oxychloride, copper hydroxide and copper sulphate was examined. Oxidative individual perturbations were assessed by measuring non-enzymatic (glutathione; GSH) and enzymatic (catalase; CAT, glutathione peroxidase; GPx and glutathione S-transferase; GST) antioxidants in digestive gland of the snails. Lipid peroxidation (LPO) was also evaluated as marker of cell damage. The results indicated that copper sulphate was the most potent compound against this snail followed by copper hydroxide and copper oxychloride where their corresponding LD 50 values were 26.54, 334.54 and 582.18 μg snail −1, respectively. Copper-based compounds resulted in a significant increase in the level of LPO whereas a significant decline of GSH content in the digestive gland of snails was observed when compared with untreated controls. The CAT, GPx and GST activities of treated snails were significantly higher than those of untreated controls. In general, the activation power of these compounds was in the following order: copper sulphate > copper hydroxide > copper oxychloride. This study suggests that up-regulation of the antioxidant enzyme activities, elevation of LPO and the reduction of GSH content is related to oxidative stress in this species that they could be used as potential biomarkers of copper-based pesticides exposure.

TOXICITY OF CERTAIN COPPER FUNGICIDES AND OTHER PESTICIDES TO TERRESTRIAL SNAILS

Toxicity of certain copper fungicides to the small garden snail, Theba pisana was evaluated fed on sprayed cabbage leaves at the concentrations of 0.5% , 0.25% and 0.125% . According to LT50 values. The obtained LT50 values were 4.67, 5.18 and 8.41 day, with copral; 5.62, 6.39. and 7.54 days for Kocide 2000. 5.47, 5.59 and 9.40 days for Galbin copper, respectively. Besides, molluscicidal efficacy of the copper fungicides, against the small garden snail, Theba pisana fed on sprayed lettuce leaves was carried out. The LT50 values expressed in were 2.67 for copper Acrobate (5% Cu, as copper oxychloride), 3.50 for Kocide 2000 (5% Cu, as copper hydroxide) and 2.17 for Galbine copper (5% Cu, as copper oxychloride + benalxyl). On the other hand, the toxicity of poisoned baits against the brown garden snail, Eobonia vermiculata was assessed. Baits of methomyl (2% a.i.), cadusafos (2% a.i.), carbendazim (2% a.i.), Copral (5% Cu), Kocide 2000 (5% Cu) and imidichlopride (2% a.i), gave LT50 values of 1.54, 6.19, 7.00, 4.39, 4.94 and 6.52 days, respectively. Toxicity of poison baits to the white sand snail, Helicella vestalis was assessed by baits of Lannate (methomyl) 2% a.i., Rugby (cadusafos) 2% a.i., Kocide 2000 Copper oxychloride (2% Cu), kemazed (carbendazim)., 2% a.i, and Confidor (imidichlopride) 2% a.i. The obtained LT50 values were 3.40, 6.48, 10.62, 6.10 and 8.73 days, respectively.