Analyse einer bemerkenswerten Population der Schnirkelschnecke Cepaea hortensis Müller

1. Cepaea hortensis Müll. is more susceptible to irradiation by the sun than Cepaea nemoralis L. On sand dunes of the sea-shore in Germany the former species is commonly found only along the Baltic coast eastward from about the eastern 12° as well as it is the case in the north of Europe along the coast of Scotland. Such a sand dune population of Cepaea hortensis Müll., rather isolated, has been studied in the southeast of Rügen, an island at the south coast of the Baltic Sea, Germany. 2. Three groups of characters appear within this population: a) Animals with shells without band or with five bands, b) Pigmented animals and albinos, c) Fusion of shell bands in a varying degree in some of the snails. 3. The distribution of the variants within the population and the breeding experiments demonstrated that the three groups of characters appear independently in individual animals and that the characters are not linked hereditary units. 4. Absence of bands is dominant over five bands, as it already had been shown by A. Lang in his classical experiments. 5. Absence of pigment is recessive to presence of pigment. 6. The fusion of the bands is controlled by more than one factor. This problem is not yet clear in every detail. a) The patterns, (12345), (123)(45), (12)3(45), (12)345, 12345, are an allelic series. Each of the different alleles is dominant over the following in the sequence indicated. b) Independent of the type of fusion of the different bands is the ability of the snails to have the bands separated or fused at different periods of growth. A series is indicated by the following variants which are dominant in the sequence given: early fusion of bands, late fusion of bands, no fusion of bands. c) According to experiments which were not quite completed, the quantity of pigment can be influenced phenotypically, but not the arrangement of pigment which is only controlled genotypically. In case of poor deposit of pigment, fused bands in their marginal zone may not be completely homogenous. 7. In the free-Iiving population on Rügen, which has been studied, the number of albinos and of animals with fused bands is relatively small. The total of all variants with five bands is 25% of the population. The remaining 75% is without bands. It is concluded that one-half the population is homozygous, banded and unbanded in equal parts, and the other half heterozygous with absence of bands dominant. In spite of the different appearance, unbanded and five-banded snails seem to respond identically to environment. This population appears to be balanced.