Microhabitat choice and polymorphism in the land snail theba pisana (Müller)

Abstract

Associations between microhabitat, shell banding and apex colour were examined in the land snail Theba pisana. Snails on their summer aestivation sites were sampled from a transect that included a relatively sheltered Acacia habitat and a more exposed open habitat. The frequencies of fully banded snails and snails with dark apexes, as well as the intensity of banding in fully banded snails, were lower in the open habitat than in the Acacia habitat. No differences in microhabitat relative to shell phenotypes were found in samples from the open habitat. However, significant differences in microhabitat were found between effectively unhanded and fully banded snails in the Acacia habitat, with effectively unhanded snails more common in the exposed Acacia canopy and fully banded snails more common beneath the canopy. Air temperatures in the Acacia canopy were consistently higher than below the canopy, while body temperatures of living fully banded and unbanded snails in sunlight indicated that fully banded snails heat more rapidly than do unhanded snails. These results suggest a potential role for both climatic selection and adaptive plasticity in microhabitat choice in the maintenance of variation in shell banding. © 1990 The Genetical Society of Great Britain.