Resistance to desiccation and distribution patterns in the land snail Sphincterochila

The land snail Sphincterochila is represented in Israel by five species that replace one another along a climatic gradient that ranges from the Mediterranean areas receiving up to 1000 mm down to arid areas receiving only 70 mm of rain per year.
The resistance to three weeks of desiccation was studied in all five species. Total water loss was lowest in the desert-dwelling species S. zonata and highest in the Mediterranean S. aharonii and the desert-dwelling S. prophetarum , while the steppe-dwelling S. cariosa and S. fimbriata were intermediate. Sphincterochila zonata had a significantly thicker epiphragm, the lowest area specific water vapour conductance, the quickest response to desiccation (secretion of epiphragm), and a favourable surface-to-volume ratio compared to all other species. The Mediterranean-type water economy of S. prophetarum , despite its desert distribution, is related to its being an under-rock-dweller while S. zonata , which has the best adaptions to desiccating conditions, thrives in exposed areas. It is concluded that the differences in resistance to desiccation among the five species of one genus correspond to the gross distribution patterns and reflect the abiotic regime and the microhabitat of each species.