The polymorphism of shell colouration in helicoid snails is a well-known phenomenon attributed to different factors such as predation and climatic effects. Another aspect contributing to this polymorphism could be the interplay of melanin production and phenoloxidase-related immunity. Therefore, in this study we aimed at answering the questions whether there is a differential sensitivity of different snail shell colour morphs to nematode infection, and whether this can be related to differences in phenoloxidase (PO) activity levels using the two helicoid, polymorphic snail species Cepaea hortensis and Cernuella virgata. Snails of both species were artificially infected with the parasitic nematode Phasmarhabditis hermaphrodita, and analysed for mortality and PO activity levels. We found C. virgata to be more severely affected by P. hermaphrodita infection than C. hortensis, and the dark C. virgata morphs to be more resistant to lethal effects of this infection than pale morphs. However, these differences in sensitivity to the parasite could not clearly be related to different PO activity levels.

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.

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.(c) 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109, 241256.

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.

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.

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.