Abstract
Offspring traits are greatly influenced by maternal effects, and these maternal effects may provide an important pathway through which populations can adapt to changing thermal environments. We investigated the effect of egg size on the among‐ and within‐population variation in early life history traits among introduced Great Lakes Chinook salmon (Oncorhynchus tshawytscha) populations under varying thermal conditions. We reared Chinook salmon from three populations in a common‐garden hatchery study at 6.5, 9.4, and 15.2°C and measured a variety of fitness‐related traits during development. We found that most of the among‐population variation in early life history traits was explained by egg size. However, the contribution of egg size to the among‐population variation decreased with an increase in temperature suggesting that other effects, such as genetic, contribute at high temperature. Within populations, egg size explained much of the dam variance and maternal effect for traits in every temperature, whereas egg size generally had little to no influence on the sire variance and heritability. Overall, our results demonstrate the significant contribution egg size makes to shaping early life history phenotypes among and within populations, and suggest that egg size is an important pathway through which offspring phenotypes can evolve on contemporary timescales.
Highlights
Temperature has a direct effect on the rate of biological reactions within the body of ectotherms (Gillooly, Brown, West, Savage, & Charnov, 2001; Huey & Kingsolver, 1989), and alterations to environmental temperature regimes, such as those predicted for climate change, can have a dramatic impact on the development, fitness, and lifespan of these organisms (Andrews & Schwarzkopf, 2012; Clusella- Trullas, Blackburn, & Chown, 2011; Fry, 1967; Munch & Salinas, 2009; Paaijmans et al, 2013; Wood & McDonald, 1997)
We used introduced Great Lakes Chinook salmon populations to test several hypotheses: (i) the divergence in early life history traits among introduced Chinook salmon populations will be largely mediated by variation in egg size; (ii) egg size will influence the estimation of quantitative genetic parameters; and (iii) the variance explained by egg size, both among and within populations, will depend on the rearing temperature of the offspring
Using a common-garden hatchery study, we have shown that the early life history traits of introduced Great Lakes Chinook salmon populations have diverged within ~10 generations and that much of this divergence can be explained by variation in egg size
Summary
Temperature has a direct effect on the rate of biological reactions within the body of ectotherms (Gillooly, Brown, West, Savage, & Charnov, 2001; Huey & Kingsolver, 1989), and alterations to environmental temperature regimes, such as those predicted for climate change, can have a dramatic impact on the development, fitness, and lifespan of these organisms (Andrews & Schwarzkopf, 2012; Clusella- Trullas, Blackburn, & Chown, 2011; Fry, 1967; Munch & Salinas, 2009; Paaijmans et al, 2013; Wood & McDonald, 1997). Quantitative genetic studies of early life history traits have shown that these traits are largely influenced by maternal rather than genetic effects (Falica, Lehnert, Pitcher, Heath, & Higgs, 2016; Heath, Fox, & Heath, 1999; Houde, Wilson, & Neff, 2013; Kinnison, Unwin, Hershberger, & Quinn, 1998; Páez, Morrissey, Bernatchez, & Dodson, 2010; Pitcher & Neff, 2007) Often, these studies quantify the maternal effect as the proportion of phenotypic variation explained by dam identity, which does not provide information on the maternal effect traits that contribute to the overall maternal effect (McAdam, Garant, & Wilson, 2014). We used introduced Great Lakes Chinook salmon populations to test several hypotheses: (i) the divergence in early life history traits among introduced Chinook salmon populations will be largely mediated by variation in egg size; (ii) egg size will influence the estimation of quantitative genetic parameters (i.e., within-population variation); and (iii) the variance explained by egg size, both among and within populations, will depend on the rearing temperature of the offspring. We used a model comparison approach, whereby we compared models before and after including egg size, to quantify the variation among and within populations that is explained by egg size across the three temperature treatments
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