SHORT-TERM AND LONG-TERM RESISTANCE TO DESICCATION IN A MINUTE LITTERDWELLING LAND SNAIL LAURIA-CYLINDRACEA (PULMONATA, PUPILLIDAE)

This study examines the water economy and resistance to desiccation in a minute (5 mg snail mass; 3 mm shell height) litter-dwelling land sn ail Lauria cylindracea (Pupillidae). As expected from its small size a nd from its moist habitat, L. cylindracea exposed to normothermic desi ccation lost water at the highest rate revealed so far in our studies of resistance to desiccation in some 30 Israeli species and population s of land snails-22.7% of the whole snail mass within 5 days. This hig h water loss was selectively contributed by the extra-pallial (free) c ompartment while soft body water content was closely maintained, witho ut catabolism of body tissue as a source of metabolic water. Surprisin gly, however, samples of L. cylindracea survived long periods (2-4 mon ths) of aestivation when left undisturbed in the laboratory, sustainin g a mass loss of 25-40%. This long-term aestivation revealed a differe nt pattern of water compartmentalization, as the snails also lost wate r from the soft body tissue. Samples of these snails were rehydrated f or 48 h and then exposed to an identical desiccation regime as the ori ginal, field-collected snails. Most of the water taken up during rehyd ration was lost within the first 24 h of desiccation, after which the rate of water loss dropped sharply. We conclude that short-term water regulatory responses to experimental desiccation differ from long-term responses to aestivation. We suggest that during long-term aestivatio n, a new set-point of water economy is established, in association wit h a metabolic depression, and that an extended period of contact with moisture is needed to change this set-point.