Climate change is leading to altered temperature regimes which are impacting aquatic life, particularly for ectothermic fish. The impacts of environmental stress can be translated across generations through maternally-derived glucocorticoids, leading to altered offspring phenotypes. Although these maternal stress effects are often considered negative, recent studies suggest this maternal stress signal may prepare offspring for a similarly stressful environment (environmental match). We applied the environmental match hypothesis to examine whether a prenatal stress signal can dampen the effects of elevated water temperatures on body size, condition, and survival during early development in Chinook salmon Oncorhynchus tshawytscha from Lake Ontario, Canada. We exposed fertilized eggs to prenatal exogenous egg cortisol (1000ng*mL^-1 cortisol or 0ng*mL^-1 control) and then reared these dosed groups at temperatures indicative of current (+0°C) and future (+3°C) temperature conditions. Offspring reared in elevated temperatures were smaller and had a lower survival at the hatchling developmental stage. Overall, we found that our exogenous cortisol dose did not dampen effects of elevated rearing temperatures (environmental match) on body size or early survival. Instead, our eyed stage survival indicates that our prenatal cortisol dose may be detrimental, as cortisol-dosed offspring raised in elevated temperatures had lower survival than cortisol-dosed and control reared in current temperatures. Our results suggest that a maternal stress signal may not be able to ameliorate the effects of thermal stress during early development. However, we highlight the importance of interpreting the fitness impacts of maternal stress within an environmentally relevant context.

Egg cortisol data shows the results from ELISA, including three replicates. Using dilution and egg mass, it was used to calculate the cortisol concentration per gram of egg. bcEggCortisol is the egg cortisol data transformed using Box-cox transformation (lambda=0.242), which was used for statistical tests.

Fertilization success shows data used in the model (output after data went throught buildBinary function in the fullfact r package). Status indicates whether egg was fertilized (coded as 1) or unfertilized (coded as 0). Includes maternal identity, tray, cell ID which were used as random effects. Under cortisol treatment: Cortisol=1000ng/mL, Control=0ng/mL

Early Survival shows data used in the model (output after data went throught buildBinary function in the fullfact r package). Status indicates whether individual was alive (coded as 1) or dead (coded as 0) at each development stage (fertilized, eyed, hatch, & fry). Includes maternal identity, tray, cell ID which were used as random effects. Under cortisol treatment: Cortisol=1000ng/mL, Control=0ng/mL

Fry Morphology shows measurements of mass and ImageJ measurements. Each parameter was scaled prior to input into PCA, this scaled value is under 'parameter_scaled' (e.g., 'ForkedLength_scaled'). Scores for each rotated (Varimax) PCA component that had eigenvalues above 1 were included for each individual. Under cortisol treatment: Cortisol=1000ng/mL, Control=0ng/mL Individuals that had incomplete values (i.e., did not have all morphology characteristics) are not included in this dataset.