Egg size and emergence timing affect morphology and behavior in juvenile Chinook Salmon,Oncorhynchus tshawytscha

Abstract

Variation in early life history traits often leads to differentially expressed morphological and behavioral phenotypes. We investigated whether variation in egg size and emergence timing influence subsequent morphology associated with migration timing in juvenile spring Chinook Salmon, Oncorhynchus tshawytscha. Based on evidence for a positive relationship between growth rate and migration timing, we predicted that fish from small eggs and fish that emerged earlier would have similar morphology to fall migrants, while fish from large eggs and individuals that emerged later would be more similar to older spring yearling migrants. We sorted eyed embryos within females into two size categories: small and large. We collected early and late‐emerging juveniles from each egg size category. We used landmark‐based geometric morphometrics and found that egg size appears to drive morphological differences. Egg size shows evidence for an absolute rather than relative effect on body morphology. Fish from small eggs were morphologically more similar to fall migrants, while fish from large eggs were morphologically more similar to older spring yearling migrants. Previous research has shown that the body morphology of fish that prefer the surface or bottom location in a tank soon after emergence also correlates with the morphological variations between wild fall and spring migrants, respectively. We found that late‐emerging fish spent more time near the surface. Our study shows that subtle differences in early life history characteristics may correlate with a diversity of future phenotypes.

Gene expression in the phenotypically plastic Arctic charr (Salvelinus alpinus): A focus on growth and ossification at early stages of development

“…Better understanding the causes of phenotypic divergence at early life‐stages and the relationship between egg size and offspring phenotype and fitness − especially under differing dietary/ecological conditions − would shed light both on early stages of divergence along the speciation continuum (e.g., Nosil, ) as well as the evolution of optimal maternal investment in contrasting environments (e.g., Smith & Fretwell, ). The number of studies documenting egg size mediated effects on offspring phenotype in fishes is rapidly growing (Cogliati et al, ; Leblanc et al, ; Leblanc et al, ; Segers et al, ; Self, Schreck, Cogliati, Billman, & Noakes, ; Thorn & Morbey, ). At the same time, our knowledge as to whether egg size can influence evolutionary divergence is limited.…”

“…For instance, egg size variation along such a continuum may decline with increasing diversification due to canalization (Parsons et al, ; Waddington, ), and strong divergence in egg size is also likely in populations inhabiting contrasting environments. Environmental heterogeneity can influence egg size (Koops, Hutchings, & Adams, ), and could therefore be considered a factor in the generation of different phenotypes especially given the potential for egg size mediated differences in gene expression (Segers et al, ), as well as phenotype (e.g., Cogliati et al, ). In general, our findings on gene expression suggest that maternal effects and early developmental changes in gene expression may influence developmental plasticity, yet studies combining both gene expression and phenotypic variation are needed to further our understanding on the mechanisms of early phenotypic divergence.…”

“…In fish, egg size is not only heritable (Kinnison, Unwin, Hendry, & Quinn, ; Su, Liljedahl, & Gall, ), but can vary both within and among females and is also influenced by the environment the mother experiences, as well as maternal age and size (Chambers & Leggett, ; Cogliati, Unrein, Stewart, Schreck, & Noakes, ; Leblanc, Benhaïm, Hansen, Kristjánsson, & Skúlason, ; Segers & Taborsky, ). In turn, egg size can strongly affect behavior and fitness of offspring (Benhaïm, Skúlason, & Hansen, ; Leblanc et al, ; Leblanc, Kristjánsson, & Skúlason, ), with smaller embryos often developing faster than larger embryos (Cogliati et al, ; Leblanc et al, ; Valdimarsson, Skúlason, & Snorrason, ). Despite the widely accepted view that egg size can affect offspring fitness (Bernardo, ; Mousseau & Fox, ), only one study has reported a link between egg size and offspring gene expression in fishes.…”

“…Such egg size-dependent gene expression demonstrates the potential of maternal effects to influence developmental plasticity. Finally, the model of evolution of resource polymorphism (alternative phenotypes utilising different resources; Smith & Skúlason, 1996) proposes that phenotypic plasticity is important during early stages of diversification (e.g., Schneider & Meyer, 2017;Skúlason, Snorrason, & Jonsson, 1999), and this may involve egg size-mediated maternal effects (Benhaïm et al, 2003;Cogliati et al, 2018;Leblanc et al, 2011). Resource polymorphism is common in fishes, such as Arctic charr (Salvelinus alpinus), that inhabit young freshwater systems of the Northern hemisphere − likely due to lack of predation and increased intraspecific competition for habitats and food resources promoting character release (Skúlason & Smith, 1995).…”

Egg size and growth in steelheadOncorhynchus mykiss

“…Cogliati et al . () observed differences in the body morphology of Oncorhynchus tshawytscha (Walbaum 1792) between fish that originated from small or large‐egg‐origin fish.…”