干旱区生态环境知识资源中心

This study examines the water economy and resistance to desiccation in a minute (5 mg snail mass; 3 mm shell height) litter-dwelling land snail Lauria cylindracea (Pupillidae). As expected from its small size and from its moist habitat, L. cylindracea exposed to normothermic desiccation lost water at the highest rate revealed so far in our studies of resistance to desiccation in some 30 Israeli species and populations of land snails-22.7% of the whole snail mass within 5 days. This high water loss was selectively contributed by the extra-pallial (free) compartment while soft body water content was closely maintained, without catabolism of body tissue as a source of metabolic water. Surprisingly, however, samples of L. cylindracea survived long periods (2-4 months) of aestivation when left undisturbed in the laboratory, sustaining a mass loss of 25-40%. This long-term aestivation revealed a different pattern of water compartmentalization, as the snails also lost water from the soft body tissue. Samples of these snails were rehydrated for 48 h and then exposed to an identical desiccation regime as the original, field-collected snails. Most of the water taken up during rehydration 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 aestivation, a new set-point of water economy is established, in association with a metabolic depression, and that an extended period of contact with moisture is needed to change this set-point.