Ecological genetics of a population of the snail cepaea nemoraus at the northern limit of its range

Abstract

The importance of environmental selection in controlling the distribution of genes in natural populations of the polymorphic snail Cepaea nemoralis is a matter of controversy. Populations of this species have been sampled at the northern limit of their range in Scotland. There were local differences in gene frequency (“area effects”) for shell colour and banding in the study area, none of which could be related to an environmental variable. No dark brown shells were collected. The frequency of yellow shells was lower than in central populations of this species, and much lower than in southern peripheral populations in Yugoslavia. There are no such regular dines throughout C. nemoralis’ range in the frequencies of the genes controlling the number of bands on the shell. The low frequency of yellow shells in northern peripheral populations is likely to be due to the relatively decreased absorption of solar energy by the more light-coloured yellow shells. The absence of a clinal response to gross climatic differences at the loci controlling shell banding might be due to the frequency of these genes in natural populations being determined primarily by co-adaptation. © 1973 The Genetical Society of Great Britain.