Maternal effects of egg size in brown trout (Salmo trutta): norms of reaction to environmental quality

Abstract

The magnitude of ¢tness variation caused by maternal e¡ects and, thus, the adaptive signi¢cance of maternal traits may depend on environmental quality, generating crossing reaction norms among o¡spring phenotypes that shape life-history evolution. By manipulating intraclutch variation in egg size and comparing siblings we examined the maternal e¡ects of egg size on o¡spring performance and tested for the existence of reaction norms to environmental quality using the brown trout Salmo trutta. When sibling groups of small and large eggs were reared separately in a hatchery environment initial size di¡er-ences disappeared rapidly. However, in semi-natural environments and under direct competition, juveniles from large eggs experienced growth and survival advantages over siblings from small eggs. Moreover, distinct reaction norms existed, with the di¡erences in performance of juveniles from small and large eggs being most pronounced in the poorer growth environments. Our results provide the ¢rst direct evidence, to our knowledge, for a causal relationship between egg size and ¢tness-related traits in ¢shes, independent of potentially confounding genetic e¡ects. Moreover, they indicate that previous studies have been biased by experimental conditions that excluded competitive asymmetries and environmental variability. The existence of reaction norms indicates a shift in optimal egg size across gradients of environmental quality that probably shapes the evolution of this trait.

Fine-scale local adaptation in an invasive freshwater fish has evolved in contemporary time

“…2 populations is necessary to show that differences are unlikely to be explained by population  habitat interactions unrelated to divergent selection (discussed by Kawecki & Ebert [1]). Non-genetic maternal effects can influence offspring performance in nature [48]; however, our results are unlikely to reflect maternal contributions as the beneficial effects of egg size erode quickly with age [32]. We attempted to minimize the influence of any lingering maternal effects by rearing individuals for several months in common-laboratory conditions prior to their release into the wild, and controlled for individual body size and condition on survival.…”

Maternal effects on phenotypic plasticity in larvae of the salamander Hynobius retardatus

“…2). In various taxa, mothers in poor condition produce larger (presumably better provisioned) eggs and better quality offspring that show greater survivorship than mothers in good condition (Fleming and Gross 1990;Sinervo and Doughty 1996;Fox et al 1997;Einum and Fleming 1999). This maternal effect on offspring size and quality is considered an adaptive reproductive strategy (Bernardo 1996;Mousseau and Fox 1998) and is observed in insects (Fox et al 1997), amphibians (Kaplan 1998), and other groups (Price 1998).…”

“…An individual's phenotype is influenced by its own genotype and by the environment that it experiences itself, as well as by the genotype and environmental experience of other individuals, especially its mother (Mousseau and Fox 1998). The level of maternal investment can profoundly influence the development of embryos and the phenotypes and survival of the hatchlings, especially in animals that do not practice parental care (Fleming and Gross 1990;Sinervo and Doughty 1996;Fox et al 1997, Einum andFleming 1999), and the evolutionary fitness of both offspring and parents (Smith and Fretwell 1974;McGinley et al 1987;Fox et al 1997). …”

Quantifying heritable variation in fitness-related traits of wild, farmed and hybrid Atlantic salmon families in a wild river environment

“…The latter was a single value per family (see McGinnity et al, 1997McGinnity et al, , 2003 for details on how this was measured) and was used as an index of maternal effects mediated via egg size (Einum and Fleming, 1999). Dam fork length (L F ) and egg mass were also measured but both were strongly correlated with egg diameter (r40.5 in all cohorts), so to avoid problems with collinearity of explanatory variables, only egg diameter was included in the models.…”