BURNAFORD, J.L.; HOFMANN, G.E.: Ecological and Physiological Effects of Thermal Stress on Intertidal Snails

Evaluating the cumulative consequences of repeated exposure to sub-lethal stress on individuals, populations and communities requires integrated studies that assess both stress avoidance and tolerance under ecologically relevant conditions. Using a combination of ecological and physiological techniques, we estimated the relative importance of avoidance (use of thermal refugia) and tolerance (the heat-shock response and cell signaling events) for five species of herbivorous snails from the rocky intertidal zone of the Northern Gulf of California. Animals from this region experience more chronic thermal stress than temperate intertidal organisms, and are therefore ideal for the study of the heat-shock response (HSR), in which a set of ‘chaperone’ proteins (Heat-shock proteins, or Hsps) is produced in response to stressors which are denaturing to the cellular protein pool. We examined Turbo fluctuosus, Tegula mariana, Tegula rugosa, Nerita funiculata and Nerita scabricosta, species with overlapping distributions spanning the zone from the low (lowest stress) to the high intertidal (highest stress). We conducted field surveys and laboratory habitat choice tests to evaluate species’ avoidance of thermal stress. We examined several steps of the HSR (endogenous Hsp70 levels, induction temperatures of Hsp70, and the transcriptional factor HSF1) in autumn field-collected and laboratory cold-acclimated animals in order to make predictions about how the relative species’ responses would change over seasonal time scales. Our results show that integrated studies such as this are essential for understanding how thermal stress affects natural systems.