Electronic Thesis and Dissertation Repository


Doctor of Philosophy



Collaborative Specialization

Environment and Sustainability


Morbey, Yolanda E.


Pacific salmon (Oncorhynchus spp.) populations are under increasing threat due to habitat degradation, over fishing, invasive pathogens, and climate change. The early life history stage (fertilization – free feeding) is one of the most vulnerable developmental phases and performance at this stage may be a critical factor affecting population persistence. Offspring traits and performance are often greatly influenced by maternal effects, which have the potential to alter patterns of inheritance and selection, and environmental factors such as temperature. However, the contribution of maternal effects to the evolution of offspring traits under varying environmental conditions is still poorly understood in salmon. To address this research gap, I assessed the contribution of egg size, a primary maternal effect trait, to the within and among population variation in offspring traits in Chinook salmon (Oncorhynchus tshawytscha) under different rearing temperatures. I found that egg size explained most of the within and among population variation in offspring traits, which suggests that egg size has the capacity to significantly influence the adaptive response of early life phenotypes. I also assessed the effect of egg nutrient composition, which is a transgenerational maternal effect, on the expression of offspring phenotypes and determined that both the fatty acid and proximate composition of eggs influenced offspring phenotypes above and beyond the effect of egg size. Importantly, the effects of both egg size and nutrient composition were temperature dependent. A primary concern for many studies of maternal effects is the lack of in-situ studies. Therefore, I reared Chinook salmon embryos in-situ and found that egg size had a linear, non-linear, or no effect on early life survival depending on the habitat characteristics of the nest. Based on the in-situ egg size - survival relationships, I showed how variation in egg size could increase or decrease offspring production in a population depending on the match between the population egg size distribution and the egg size selection regime using a simulation model. Overall, this work demonstrates the significant contribution maternal effects make to the expression and evolution of offspring phenotypes in salmon.