Paternal Genetic Effects on Offspring Swimming Performance Vary with Age of Juvenile Chinook Salmon, Oncorhynchus tshawytscha

While fish swimming behaviour has been extensively studied, the parental genetic basis of this critical behaviour has been rarely examined, especially past the earliest stages of development. We used a quantitative genetic breeding design to measure the critical swimming speed (U-crit) of offspring (15 and 18 weeks post-hatch) from 36 families of Chinook salmon (Oncorhynchus tshawytscha), a species with a nonresource-based mating system. We investigated the roles of dam, sire, and dam x sire on offspring U-crit, and estimated contributions of additive and nonadditive genetic effects and maternal effects to phenotypic variation in U-crit at both ages. We also used existing 'high-survival' and 'low-survival' lines of Chinook to determine if these two lines show differences in U-crit. At 15 weeks, there were no significant genetic effects, but at 18 weeks there were significant sire effects. Furthermore, additive genetic effects increased from 26 to 100 % from 15 to 18 weeks post-hatch. The two survival lines also showed differences in U-crit at 18 weeks post-hatch, with higher U-crit associated with "high-survival" sires. Collectively, the present study provides evidence for increasing importance of paternal identity (additive genetic variation) on swimming as juvenile offspring age. Given that mortality is high in young Pacific salmon and swimming ability is crucial, the sire effects could potentially shape survival though subsequent developmental stages. The change in the magnitude of effects in the present study indicates that future research should investigate genetic effects across multiple stages for better understanding of how phenotypic traits could respond to selection.