INTRASPECIFIC VARIATION IN RESISTANCE TO DESICCATION AND CLIMATIC GRADIENTS IN THE DISTRIBUTION OF THE BUSH-DWELLING LAND SNAIL TROCHOIDEA-SIMULATA

Resistance to desiccation was examined in six populations of the Israeli bush-dwelling snail Trochoidea simulata, a desert species distributed mainly between the 100-200 mm isohyets. The present study revealed significant intraspecific differences in resistance to desiccation which are correlated with habitat and climatic gradients within the distribution range of the species. Populations from more arid sites were more resistant to desiccation and heat exposure than those from more mesic areas. However, the population from the Rift Valley (an extremely arid region) was surprisingly poorly resistant. Rates of population water loss under the controlled experimental conditions in the laboratory generally matched the calculated water losses during natural summer aestivation.