Genetic and physiological adaptations of the prosobranch landsnail Pomatias olivieri to microclimatic stresses on Mount Carmel, Israel

Slope orientation in the Mediterranean climate may lead to different adaptations of the faunistic elements to the environment. The south-facing slope (SF) of Lower Nahal Oren (Mount Carmel) is more exposed to solar radiation and therefore is warmer, drier, and has a lower vegetation coverage than the north-facing slope (NF). Resistance to desiccation and genetic diversity of the northeastern Mediterranean prosobranch landsnail Pomatias olivieri, whose southern border is on Mount Carmel, were examined to elucidate potential physiological and genetic adaptations to contrasting microclimatic conditions. The body water content and the extrapallial fluid content were significantly higher in fully-hydrated SF-snails than in those from NF. Similar rates of water loss were found during normothermic and hyperthermic desiccation in SF-snails, whereas in NF-snails water loss increased in hyperthermic conditions. Thus, the snails on the opposite slopes differ in their physiological responses to high ambient temperature. Allozyme polymorphism in 137 specimens (59 from SF and 78 from NF) was examined in 5 subpopulations, 2-3 on each slope, at different altitudes, and compared with a sample of 12 specimens from the Galilee mountains in northern Israel. The polymorphism of the SF population at 20 putative allozymic loci was 50%, whereas that of NF was 45%. Heterozygosity was 0.088 on SF and 0.067 on NF. Genetic distances among all Carmel subpopulations were very small, but there was a conspicuous difference between the Carmel and Galilee populations, which indicates a long isolation of the Carmel population. The subpopulation of the middle collection site in NF contained 11 private alleles, whereas at most, 2 such alleles were found in any other subpopulation. This indicates a patch of unfavorable conditions within the habitat and thus we suggest that the preferred habitat of P. olivieri is the edge of the woodland or cleared spaces on NF. Snails of SF and NF differ in their susceptibility to hyperthermic desiccation and, genetic diversity increases with environmental stress.