Non-visual differences between colour morphs of the polymorphic snail Arianta arbustorum

Abstract

Brown shelled morphs of Arianta arbustorum are more frequent in shaded woodland than in open, sunnier habitats. This is thought to be the result of selective visual predation (Parkin, 1971). Yellow shelled morphs have a higher metabolic rate than browns, especially at high temperatures, and remain more exposed to sunlight. These non-visual differences in metabolism and behaviour will offset differences in radiant heat gain which result from the two shell colours in open habitats. Differences in heat gain will seldom occur in shaded habitats. The non-visual differences therefore appear to adjust for differences in energy gain caused by shell colour, rather than to act as component forces generating the polymorphism. They therefore do not have a balancing effect. © The Genetical Society of Great Britain.