From Individual-Based Research on Linking Maternal Experience to Maternal Condition to Offspring Performance/Fitness to Implications for Cross-Generational Population Dynamics

Energetically demanding spawning migrations of sockeye salmon (Oncorhynchus nerka) can have a negative influence on maternal condition. Individual-based research has focused on examining the impact of adverse spawning migration conditions on female survival, reproductive development (e.g. egg size, number, spawn timing, retention), egg viability, and to a lesser extent offspring performance. This latter research is hampered by the severe logistical constraints associated with manipulating environmental conditions in experiments with adult females and directly tracing offspring performance. However, this gap can be bridged by examining complimentary work that highlights the importance of maternal identity in influencing offspring size, development rates, thermal tolerance, metabolic capacity, swim performance, schooling ability, and ultimately survival. Therefore, the degree to which maternal identity, both phenotype and genotype, is a function of maternal migration experience will determine the cross-generational impact on offspring performance/fitness. The next challenge is to apply the results from individual-based research to the population level. Processes that change the maternal condition of individuals, such as age of maturity, gender ratios, egg retention rates, fecundity, and gamete viability, all have the potential for conspicuous impacts on population dynamics. Prior research on one such process, high river temperatures, has focused on the direct changes in adult salmon survival as a function of climate induced shifts in thermal exposure. The consequences of a changing thermal regime on condition of maternal traits in relation to population dynamics are rarely modeled explicitly. An even more difficult consideration is trying to understand the population implications associated with changes in maternal condition that influence offspring performance measures. Based on the individual research, we will present a few examples of the sensitivity of changes in maternal condition factors associated with adverse migration conditions on population dynamics in Fraser sockeye salmon. Future research will explore the cross-generational link between maternal exposure to other sub-lethal stressors (e.g. disease, contaminants, and cumulative stress) and offspring fitness in Pacific salmon.