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 a daptations of the faunistic elements to the environment. The south-fac ing slope (SF) of Lower Nahal Oren (Mount Carmel) is more exposed to s olar radiation and therefore is warmer, drier, and has a lower vegetat ion coverage than the north-facing slope (NF). Resistance to desiccati on 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 adapt ations 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-sna ils, whereas in NF-snails water loss increased in hyperthermic conditi ons. Thus, the snails on the opposite slopes differ in their physiolog ical responses to high ambient temperature. Allozyme polymorphism in 1 37 specimens (59 from SF and 78 from NF) was examined in 5 subpopulati ons, 2-3 on each slope, at different altitudes, and compared with a sa mple of 12 specimens from the Galilee mountains in northern Israel. Th e 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 po pulation. The subpopulation of the middle collection site in NF contai ned 11 private alleles, whereas at most, 2 such alleles were found in any other subpopulation. This indicates a patch of unfavorable conditi ons 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. Sn ails of SF and NF differ in their susceptibility to hyperthermic desic cation and, genetic diversity increases with environmental stress.