Light versus temperature: An intersensitivity conflict in a gastropod (Lymnaea auricularia)

Mean preferred temperature and light were determined in groups of 20 Lymea auricularia (several hundreds of them altogether) placed in gradients of temperature and of light. The preferred temperature, 19.4 °C and light, 300 lx, were independent of the steepness of the gradients.The snails were placed in situations where a light of 300 lx was located over the various loci in water temperature gradients. In the reverse situation a water temperature of 20 °C was produced over the various loci of light gradients. The results of these conflict experiments showed that the shape of the histogram of loci selected by the snails around their preferendum, reflects the magnitude of their need for that variable. In a situation of conflict between two needs, the variable producing the narrower spatial distribution should be chosen over another variable with a broader tolerance range.