Studies oncepaea,V. Sand-dune populations ofcepaea nemoralis(L.)

Abstract

A survey of duneland populations of the polymorphic snailCepaea nemoralis, based on 170 samples from 53 localities on the British and Irish coasts, shows an overall distribution of morph frequencies consistent with the action of visual selection. Some geographical trends of variation can be discerned, but there is great variation, often over short distances within one group of dunes. A detailed investigation of this has been made at Point of Air, Flintshire. Here and at several other dune systems there is an association of the occurrence of dark browns with complex topography which suggests that they are favoured by very local climatic effects caused by the accumulation of cold air. If local temperature or other climatic factors is effective, the apparent agreement of duneland populations with what is expected as a result of visual selection may be misleading.