The genetic structure of a southern peripheral population of the snail Cepaea nemoralis

Abstract

The polymorphic land snail Cepaea nemoralis reaches the southern limit of its range in Yugoslavia. The overall frequency of yellow shells is much higher than in Britain (95% compared to 54%), while the frequencies of the genes controlling the number of bands on the shell do not differ as greatly from those found in British populations. Pink shells are found most commonly in one area which is known to be a frost hollow. The frequencies of the various phenotypes shows a great deal of microgeographical variation which does not appear to be related to topography. The existence of an apparent selective response at the colour locus to gross climatic differences from the north to the south of the species' range suggests that microclimate may be important in affecting local differentiations ('area effects') in shell colour morph frequency found in central populations. It is possible that the absence of such a selective response in the frequency of the banding genes in Yugoslav peripheral populations indicates that climatic selection is also less important in controlling their microgeographical differentiation.