AbstractIn response to rapid environmental change, organisms rely on both genetic adaptation and phenotypic plasticity to adjust key traits that are necessary for survival and reproduction. Given the accelerating rate of climate change, plasticity may be particularly important. For organisms in warming aquatic habitats, upper thermal tolerance is likely to be a key trait, and many organisms express plasticity in this trait in response to developmental or adulthood temperatures. Although plasticity at one life stage may influence plasticity at another life stage, relatively little is known about these interactive effects for thermal tolerance. Here we used locally adapted populations of the intertidal copepod Tigriopus californicus to investigate these interactions in a marine ectotherm. We found that low latitude populations had greater critical thermal maxima (CTmax) than high latitude populations, and variation in developmental temperature altered CTmax plasticity in adulthood. After development at 25°C, CTmax was plastic in adults, whereas no adult plasticity in this trait was observed after 20°C development. This pattern was identical across four populations, suggesting that local thermal adaptation has not shaped this interactive effect. However, differences in the capacities to maintain ATP synthesis rates and to induce heat shock proteins at high temperatures, two likely mechanisms of local adaptation in this species, were consistent with changes in CTmax due to developmental temperatures, suggesting there is mechanistic overlap between plastic interactions and adaptation in general. These results indicate that interactive effects of plasticity across life stages may have substantial impacts on upper thermal tolerance in ectothermic organisms.Summary statementDevelopmental temperatures alter the plasticity of thermal limits in adults of a marine ectotherm, and differences in ATP synthesis rate and heat shock protein expression parallel the changes in tolerance.
Interactions across life stages and thermal tolerance plasticity in Tigriopus californicus
