An organism’s ability to cope with thermal stress is an important predictor of survival in a changing climate. Organisms can respond to increased stress via behavior (e.g., range shifts), acclimatization, and/or genetic adaptation. Because many organisms do not have the ability to migrate or change their behavior, acclimatization and adaptation will play vital roles in organisms’ responses to changing environmental conditions. One way in which organisms may acclimatize to thermal stress in the short-run is through induced thermotolerance, whereby exposure to a sublethal heat shock increases an organism’s tolerance to what might otherwise be a lethal event. The effects of this kind of pre-stress event are not well understood in marine organisms. Furthermore, whether populations of the same species differ in their capacity for induced thermotolerance is unclear. Here, we tested for differences in basal thermotolerance and induced thermotolerance among six populations of Olympia oysters (Ostrea lurida) from three California estuaries. Oysters were raised under common-garden laboratory conditions for a generation and then exposed to two treatments (control or sublethal heat shock) followed by a spectrum of temperatures that bound the likely upper critical temperature in order to determine the population’s LT50 (temperature at which 50% of the population dies).
Results/Conclusions
We found that all oyster populations exhibited inducible thermotolerance by increasing their LT50 to a similar maximum temperature when extreme thermal stress was preceded by a sublethal heat shock. However, the populations differed in their basal thermotolerance and their level of thermal tolerance plasticity. Oyster populations with the highest basal thermotolerance exhibited the least thermal tolerance plasticity while the population with the lowest basal thermotolerance exhibited the greatest plasticity. Our results highlight that populations of the same species may have differing scopes for thermal tolerance plasticity, with implications for vulnerability to environmental change. Specifically, organisms with the highest basal thermal tolerance may be the most vulnerable to warming associated with climate change because they lack the plasticity required to adjust to changes in temperature.