Thermal advantage of pale coloured morphs of the snail Arianta arbustorum (Helicidae, Pulmonata) in alpine habitats

In alpine grasslands pale colour morphs of the snail Arianta arbustorum are more frequent than dark ones As pale morphs absorb less solar radiation, they may forage for longer in sunlight and/or have a lower mortality risk from overheating This hypothesis was tested Equal numbers of pale and dark morphs were kept in enclosures in an alpine meadow During the day, more pale morphs were seen than dark ones, the latter obviously remaining hidden The difference was not significant in enclosures set up in a nearby forest, confirming that the inequality in behaviour depends on the amount of sunlight Dark snails are on average warmer than pale ones Experiments were also conducted in grassland on a mountain slope at altitudes between 1200 and 2000 m Snails were marked with a paint which fades in light, and released When recaptured several days later, the marks were more faded in pale morphs than in dark, suggesting that they had been more exposed to sunlight, supporting our hypothesis The difference in fading was more pronounced at high than at low altitude