Shell colouration and different introductions of the land snail Cepaea hortensis (Gastropoda: Helicidae) into Western Ukraine

Abstract

The primary introduction of C. hortensis into Western Ukraine, most likely in the second half of the 20th century, led to the formation of many populations characterised not only by a reduced phenotypic composition, but also by a peculiar phenotypic marker (absence of banded shells with a non-white ground colour). White banded shells, common in Western Ukraine, are also found in different parts of the present species range, but less frequently than yellow banded ones. When studying the shell colour and banding polymorphism in C. hortensis, white shells are often combined into one group with yellow ones. Therefore, the findings of these two phenotypes as well as white unbanded shells in Europe were mapped based on the analysis of more than 7 thousand photographs from citizen science database iNaturalist. The results of later introductions of C. hortensis to Western Ukraine, which may occur through different garden centres, are easily distinguished by the presence of yellow banded and/or pink shells. And the presence of a dark lip in all pink shells can be a phenotypic marker of snails, whose ancestors were introduced to the west of Ukraine through the garden centre “Club of Plants” near Lviv. Only near this garden centre were also found three brown-shelled snails not known for other introduced Eastern European populations of C. hortensis.