Resistance to desiccation and distribution patterns in bush-dwelling land snails



Bush-dwelling land snails are exposed to desiccating conditions that are more severe than those of snails that seek the shelter of rock crevices, litter or the upper layers of the soil. We studied the resistance to desiccation in four bush-dwelling species of Israeli snails to evaluate a possible relation between their water economy and their distribution pattern. The resistance to desiccation decreased in the following order: Xeropicta vestalis (a widely distributed Mediterranean species), Trochoidea simulata (a desert species), Theba pisana (a Mediterranean species from the sand dunes of the coastal plain), and Monacha haifaensis (a Mediterranean species). Xeropicta vestalis also had the quickest response to the desiccating conditions. It is probably prevented from establishing itself in the desert, in spite of its superior water economy, because it is an annual, semelparous species, and the desert is a highly unpredictable environment. An immediate response to desiccating conditions may be a key factor in the success of desert-inhabiting land snails. Snails from more humid regions take several days to recruit their water preserving mechanisms, a delay which may be crucial to their water balance. The conchiometrics of X. vestalis and T. simulata suggest that the main water preserving mechanisms of these species are located in the mantle, rather than in the shell and epiphragm.