Visual selection in the land snail Arianta arbustorum

Abstract

1. Arianta arbustorum, a British land snail, is polymorphic for colour and banding. The banded condition is usually associated with brown shell colour; unbanded individuals are yellow. There is variation in the shade of brown from pale to dark. 2. Among populations of A. arbustorum inhabiting the Wye valley in Derbyshire, yellow individuals are common in non-woodlands. Pale brown shelled snails are similarly commoner than dark brown in non-woodlands. Dark brown is the predominant form in woodland areas. 3. The frequency of predated shells within a colour class shows a higher proportion among the yellow shells than the browns in woodland. The converse is found in non-woodland habitats for four of the five areas considered. 4. It is argued that visually discriminating predators are selectively removing yellow snails from the woodland populations, resulting in the differences in distribution of the morphs found in the two habitat classes. 5. The results are compared with those obtained in studies of Cepaea nemoralis and C. hortensis and their significance discussed. © 1971 The Genetical Society of Great Britain.