Variation in the shell colour and banding polymorphism of <i>Cepaea nemoralis</i> (L.) in rural areas around Wrocław

Comparative analysis of phenotypic variability of introduced land snail Cepaea nemoralis (Gastropoda: Helicidae) in two large Eastern European cities

Variation in the shell colour and banding polymorphism of Cepaea nemoralis was recorded in 20 sites in Minsk, Belarus (a total of 3965 adults collected in 2014–2021). This variation was compared with that in 16 sites from Lviv, Western Ukraine (total 3235 adults collected in 2019–2021). Unlike in Lviv, a remarkable spatial differentiation of the phenotypic composition was found in Minsk. The samples collected in the north-eastern part of Minsk were characterized by a greater degree of phenotypic diversity and by higher frequencies of unbanded and brown shells. Samples from the southern and eastern parts of the city were generally lighter and characterised by high frequencies of shells with a single central band (mid-banded). Differences between the two parts of Minsk were greater than those between Minsk and Lviv. This may be related to the history of colonization of Minsk by C. nemoralis. The Lviv samples were, on average, darker, they contained less frequently mid-banded shells and more frequently unbanded shells, especially pink unbanded ones. The Fst values characterizing the level of phenotypic variability and calculated for Minsk and Lviv are quite high and comparable with those for other urban areas recently colonized by C. nemoralis.

Cepaea nemoralis (L.) On Öland, Sweden: recent invasion and unexpected variation

Cepaea nemoralis is a recently introduced species on Öland. Discounting an early and debateable record, the species has been recorded only in the 21st century, despite intensive earlier faunistic surveys. A recent survey has yielded records from the whole length of the island (137 km), but the majority of known populations are in its southern half, most particularly around the settlements of Mörbylånga, Gräsgård and Färjestaden. Populations are usually in anthropogenic habitats. Most appear small and isolated by less disturbed areas. Nearly all samples are polymorphic for both colour and banding morphs, and the variation among populations is low when compared with similar sets from other places where recent colonisation has occurred. There is no latitudinal variation in morph frequencies, nor is any spatial autocorrelation apparent. While a relatively uniform and rigorous selection regime could account for the patterns seen, a single initial introduction followed by transport of propagules large enough to minimise founder effects is also possible.

Shell colour, temperature, (micro)habitat structure and predator pressure affect the behaviour of Cepaea nemoralis

Although shell colour polymorphism of the land snail Cepaea nemoralis is a well-known phenomenon, proximate and ultimate factors driving its evolution remain uncertain. Polymorphic species show variation in behavioural responses to selective forces. Therefore, we estimated effects of various environmental factors (temperature, humidity, food availability, (micro)habitat structure and predatory pressure) on behavioural response (frequency of locomotion, climbing and hiding) of C. nemoralis morphs, in experimental and natural conditions. In the experimental part of study, the frequency of locomotion was negatively affected by temperature and the presence of food and positively influenced by the presence of light. Morphs significantly differed in behavioural responses to environmental variability. Pink mid-banded and yellow five-banded morphs climbed less often and hide in shelter more often than yellow and pink unbanded individuals when temperature was low and food was absent. Snails fed most often at moderate temperature compared to low and high temperatures. Field investigations partially confirmed differences among morphs in frequency of climbing, but not in terms of probability of hiding in sheltered sites. In natural colonies, temperature and (micro)habitat structure significantly affected frequency of climbing as well as hiding in shelter. Snails more often hid in sheltered sites where thrushes preyed on Cepaea. Tendency of unbanded morphs to climb trees may have evolved under avian predatory pressure as thrushes forage on a ground. Tendency of banded morphs to hide in sheltered sites may reflect prey preferences for cryptic background. The results implicate that differential behaviour of C. nemoralis morphs compensate for their morphological and physiological limitations of adaptation to habitat.

Differential shell strength of Cepaea nemoralis colour morphs--implications for their anti-predator defence

One of the most spectacular evolutionary forces is predation, evidenced to stimulate polymorphism in many prey species. Shell colour polymorphism of the land snail Cepaea nemoralis is a well-known model in evolutionary research. Nevertheless, the knowledge on the ecological causes driving its evolution remains incomplete and proximal factors shaping predatory pressure on C. nemoralis morphs are unknown. We evaluated shell crushing resistance and thickness, constituting crucial snail anti-predator defences in two shell areas (the apex and labium) of eight C. nemoralis morphotypes differing in shell colour and banding pattern. A GLM showed a significant effect of shell colour, banding pattern and shell thickness on shell strength. Pink shells were stronger than yellow ones, and banded forms had stronger shells than unbanded snails. The labium (usually attacked by mice) was generally thicker and more resistant than the apex (usually crushed by birds). Thicker shells were more resistant to crushing, and the rate of shell strength increase per unit of shell thickness was greater in pink and banded individuals compared to yellow and unbanded ones. Yellow and unbanded morphs have been found to be preferred by mice in the previous studies, which suggests that shell strength may be an important trait used in prey selection by these shell-crushing predators. The differences in potential anti-predator defences among snail morphs, found in the present study, justify future research on direct effect of C. nemoralis morphs shell strength on predator selectivity.