INTRASPECIFIC VARIATION IN RESISTANCE TO DESICCATION IN THE LAND SNAIL THEBA-PISANA

Theba pisana is a bush-dwelling snail with a circum-Mediterranean dist ribution. In Israel it is limited to a narrow coastal strip, along whi ch there is a north-to-south gradient in mean annual rainfall (700-300 mm per year). In this study We found significant intraspecific differ ences among populations of T. pisana in resistance to desiccation alon g this gradient, and in a population from Greece, which may be grossly correlated with the climatic gradient. The Greek population was the l east resistant to desiccation with an extremely high rate of water los s. The differences in total mass loss were mainly determined by the ra te of water loss during the first 4 days of desiccation. A general phe nomenon during desiccation was the close regulation of the soft body w ater content at the expense of the extra-pallial fluid compartment.