Climatic selection on body colour in the land snail theba pisana (Pulmonata: Helicidae)

Abstract

Eighty-one samples of the land snail Theba pisana were collected from 34 localities throughout its natural Mediterranean, western European and north African coastal distribution and from introduced populations in Western Australia and California. The colour intensity (a score of relative darkness) of the mantle collar, which is visible while the snail is retracted into its shell, was scored by matching to a colour atlas. Despite much within-population variation, among-population variation was significantly related to mean daily maximum temperature of the hottest month, as recorded at nearby meteorological stations. Climatic selection favouring pale colour in hot places is probably responsible for the association. © 1990 The Genetical Society of Great Britain.