The dependence of thermopreferendum in Helix pomatia L. on air temperature

Behavioural tests with 192 specimen of the roman garden snail Helix pomatia L. were performed in order to clarify whether the thermopreferendum of this pulmonate is influenced not only by the temperature of the substratum but also by air temperature. For this purpose, the snails were exposed to a horizontal temperature gradient of the substratum at different air temperatures between 10 and 30 degrees C. The results show that the selection of substratum temperature depends on the air temperature: the lower the air temperature, the lower is the temperature of the substratum preferred by the snails. Obviously, the animals tend to keep the difference between air temperature and temperature of the substratum as small as possible. This behaviour might be a mechanism to reduce the temperature gradient in the snail's body and to adjust the metabolic rate to cardiac output.