Effects of maternal size, reproductive investment and habitat conditions on juvenile life history in Pacific salmon

Background/Question/Methods

Maternal effects on offspring life history and survival are driven by trade-offs and environmental conditions. We studied sockeye salmon (Oncorhynchus nerka) populations in the Fraser Basin of BC to examine how maternal phenotype and habitat conditions interact to influence reproductive investment and subsequent fitness-related juvenile traits. We used a 20-year time series for three populations to relate annual variation in maternal length and migration conditions to reproductive investment, including egg size, fecundity, and total gonad investment. We then examined how egg size and incubation temperature influence juvenile length and weight, which we interpret as metrics of survival. Finally, we tested the hypothesis that maternal length and incubation temperatures explain patterns in egg size among populations and consequently juvenile survival.

Results/Conclusions

Larger fish had heavier eggs, were more fecund, and had heavier gonads. Migration difficulty negatively correlated with egg size but had little effect on other reproductive traits. Juvenile size was explained by egg size and incubation temperature suggesting that the smallest juveniles result from a combination of small eggs and higher temperatures. In our comparison among populations, egg size scaled positively with both length and water temperature indicating warmer incubation temperatures select for larger eggs. Our findings reveal that variation in maternal length and habitat conditions can be expressed through reproductive investment and subsequent fitness-related juvenile traits.