Temperature-induced plasticity of emergence phenotypes in Chinook salmon (Oncorhynchus tshawytscha)

Abstract

Dams supply services that cultivate and sustain civilization such as flood control, navigation, and electricity. Due to thermal stratification in reservoirs the water released by dams is often a different temperature from environments further upstream on both daily and seasonal time scales. The impacts of flow regulation on temperature are important because of the influence that temperature has on development and distribution of species. Salmon are particularly vulnerable to habitat and temperature changes because their reproductive and early development life phases are spent in freshwater systems. Localized temperature regime changes caused by dams may spur local adaptation. In a common garden laboratory incubation experiment, I measured emergence timing of fry from four Spring Chinook populations originating from Northwest river systems affected by hydropower dams. Four family groups from each of four different populations were created by artificially spawning adult salmon (1 to 1 crosses) during the same week of September, 2012. Each family of eggs was exposed to four different thermal regimes from fertilization to emergence to test the following hypotheses: 1) Altered temperature regimes can cause disparity in development timing between families and across populations. 2) Reaction norms for development timing under different temperature regimes are unique depending on family and population origin. 3) The condition of fry at emergence is regulated by an interaction between genotype and thermal regime. 4) The delivery method of temperature (constant vs. variable) affects emergence phenotypes. We found that fry from warmer thermal regimes emerged earlier both in terms of calendar date and temperature units, and that warmer treatments caused fry to emerge less developed. There was also a significant effect of family on both emergence timing, and development level at emergence. The influence of daily temperature pattern was population specific, with most families from the Willamette Basin showing delayed emergence when incubated in a cold stable thermal regime. By combining measurements of physiological and behavioral traits at emergence, our research provides a better baseline for interpreting results in the context of hatchery, natural, and human-altered environments.