HEAT TOLERANCE AND RECOVERY IN MEDITERRANEAN LAND SNAILS AFTER PRE-EXPOSURE IN THE FIELD

Mediterranean land snails such as Xeropicta derbentina (Hygromiidae) and Theba pisana (Helicidae) are known for their remarkable tolerance to elevated temperatures and desiccation, yet the biochemical and cellular mechanisms underlying this tolerance are relatively unknown. We investigated the effects of increased temperatures and the ability of these snail species to recover from heat stress, examining the condition and amount of different types of hepatopancreatic cells (histopathology) and heat-shock protein 70 (stress protein) levels. Snails were exposed to defined control and increased temperatures and allowed a postheat phase for possible recovery. Results indicate the ability of X. derbentina to recover from natural and experimental temperature stress to some extent within the set time, whereas no such ability was found in T. pisana. Xeropicta derbentina is more heat-tolerant in general and less affected by heat stress than T. pisana. This is probably due to its greater ability to increase size and number of hepatopancreatic calcium cells that are essential for osmoregulation. The hypertrophy and hyperplasia of calcium cells can be regarded as a general response of molluscs to osmotic stressors, e.g. heat, as long as the organism is not overwhelmed by the stressor. Additionally, it can be assumed that the robust stress-protein system of X. derbentina plays a crucial role in this species' high thermotolerance.