NATURAL SELECTION IN CEPAEA

Abstract

The remarkable variation in colour and ornamentation of the shell which is shown by certain gastropods has attracted the attention of collectoprs for many years. Recently, several studies of this variation have appeared, which unfortunately lead to very diverse conclusions on its mechanism of mainte- tenance and its significance in evolution. One of the commonest and most strikingly variable snails of Europe is Cepaea nemoralis, which has been studied in considerable detail by several workers, mainly in Europe but also in the U.S.A. where it has been successfully introduced. DIVER (1940) has concluded that its range of variation is wholly random, BOETTGER on the contrary it is determined by natural selection, while LAMOTTE T (1931) that (1951) believes that for banding, at least, it is maintained in each colony primarily by mutation, and SCHILDER (1950) by gene flow. 1952) lead us to the conclusion that variation is maintained by balanced poly- morphism FISHER Our own investigations (CAIN and SHEPPARD 1930a ; FORD 1940), but the proportions of different varie- ties in each colony are strongly affected by selective visual predation. In this paper the principal studies on Cepaea nemoralis are examined, and further evidence for the importance of natural selection is presented