TOMANEK, L.: The heat-shock response and patterns of vertical zonation in intertidal Tegula congeners

What enables a marine invertebrate species to cope with the heat stress it experiences in the intertidal zone? Which biochemical and molecular assays are useful indicators for heat stress? Studies on marine gastropods of the genus Tegula, which occupy widely differing thermal habitats along the transition from the sub- to the intertidal zone have provided some insights. The mid-intertidal T. funebralis shows, in comparison to the subtidal T. brunnea and T. montereyi, (i) greater heat tolerance, (ii) higher induction, peak, and inactivation temperatures of hsp synthesis, as well as (iii) higher endogenous levels of a heat-shock protein of 72 kDa (hsp72) and (iv) of heat-shock transcription factor 1 (HSF1), following acclimation to a common temperature. Induction temperatures suggest that T. funebralis induces the heat-shock response more frequently under the variable thermal conditions characteristic for the intertidal, compared to the subtidal congeners. This may illustrate a general correlation between the thermal variability of the environment and the temperature at (and frequency with) which the stress response is activated. We attempted to explain interspecific and acclimation-induced intraspecific variation in the heat-shock responses by testing predictions of the cellular thermometer model (CTM) for the transcriptional regulation of hsp expression. Higher endogenous levels of hsp72 and HSF1 in T. funebralis suggest that a simple version of the CTM cannot explain interspecific differences in induction temperature, but may explain higher rates of hsp synthesis following heat-shock observed for this species. Predictions made by the CTM can, however, explain acclimation-induced changes in the induction temperature found for the subtidal species.