UBC Theses and Dissertations
Variation in embryonic thermal tolerance among populations of sockeye salmon : offspring survival, growth, and hatch timing in response to elevated incubation temperature Whitney, Charlotte Kathryn
Populations of Pacific salmon are genetically and morphologically distinct across large watersheds, and these differences may reflect long-term adaptation to environmental factors such as temperature. While climate warming is predicted to affect sockeye salmon, it is likely that such impacts will happen differentially across life stages and populations. Given that selective pressures during early development plays an important role in lifetime fitness, and that elevated water temperatures can critically affect embryo success, this thesis focuses on inter-population differences in offspring response to supra-optimal temperatures during incubation. Variation in embryonic thermal tolerance was explored among populations of sockeye salmon using a common garden approach. The gametes of 15-20 families per population (N = 9) were incubated at water temperatures of 10°, 14°, and 16°C. Survival from fertilization to hatch varied significantly by temperature and population, and crossing reaction norms showed an interaction of genotype (population) and environment (incubation temperature). Thermal tolerance within the study was related to historical temperatures during early development in nature. From this correlation it seems that population thermal adaptation may exist, and be driven by elevated spawning ground temperatures. The same fertilization experiment was used to evaluate differences in egg size among populations, and to test the effect of temperature, population, and egg size on offspring size and hatching characteristics. Egg size varied among groups and was not related to hatch timing variation, but was tightly correlated to alevin size. Alevin length but not mass was significantly related to incubation temperature, perhaps due to a theoretical tradeoff between development rate and metabolic rate at high temperatures. Most embryos seemed to compensate for increased growth rates at high temperatures by requiring more thermal units to hatch than at lower temperatures. Overall, I found that populations of sockeye salmon responded differently to thermal stress during embryo development, and populations responded best to temperatures that reflected their historical natal thermal regime. In the context of climate change, these results show that inter-population thermal tolerance may influence future selection among populations, and additionally, that this intraspecific thermal adaptation will be important in ensuring population, and therefore species, persistence.
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