Selection Against Late Emergence and Small Offspring in Atlantic Salmon (Salmo Salar)

Abstract

Timing of breeding and offspring size are maternal traits that may influence offspring competitive ability, dispersal, foraging, and vulnerability to predation and climatic conditions. To quantify the extent to which these maternal traits may ultimately affect an organism's fitness, we undertook laboratory and field experiments with Atlantic salmon (Salmo salar). To control for confounding effects caused by correlated traits, manipulations of the timing of fertilization combined with intraclutch comparisons were used. In the wild, a total of 1462 juveniles were marked at emergence from gravel nests. Recapture rates suggest that up to 83.5% mortality occurred during the first four months after emergence from the gravel nests, with the majority (67.5%) occurring during the initial period ending 17 days after median emergence. Moreover, the mortality was selective during this initial period, resulting in a significant phenotypic shift toward an earlier date of and an increased length at emergence. However, no significant selection differentials were detected thereafter, indicating that the critical episode of selection had occurred at emergence. Furthermore, standardized selection gradients indicated that selection was more intense on date of than on body size at emergence. Timing of emergence had additional consequences in terms of juvenile body size. Late-emerging juveniles were smaller than early-emerging ones at subsequent samplings, both in the wild and in parallel experiments conducted in seminatural stream channels, and this may affect success at subsequent size-selective episodes, such as winter mortality and reproduction. Finally, our findings also suggest that egg size had fitness consequences independent of the effects of emergence time that directly affected body size at emergence and, in turn, survival and size at later life stages. The causality of the maternal effects observed in the present study supports the hypothesis that selection on juvenile traits may play an important role in the evolution of maternal traits in natural populations.

Quantitative trait locus analysis of hatch timing, weight, length and growth rate in coho salmon, Oncorhynchus kisutch

“…The QTL analysis offers no evidence to suggest that there would be a molecular basis to any phenotypic correlation with this trait. This result was unexpected in light of previous ecological studies that suggest that hatch timing, as a measure of early development, is correlated with growth as alevin and fry (Beacham et al, 1988;Einum and Fleming, 2000;Sundstrom et al, 2005). In an inbred line of rainbow trout, one major QTL for hatch timing was associated with length at the start of exogenous feeding, suggesting a possible genetic correlation between development rate and later growth (Robison et al, 2001).…”

“…Eggs hatch into alevin that rear in the gravel until they are able to begin exogenous feeding, at which time they emerge into the water column (Quinn, 2005). Rapidly developing embryos may have more access to resources, because they emerge from the gravel first and have more opportunity for feeding early in the season, resulting in larger size as fry (Beacham et al, 1988;Einum and Fleming, 2000). Greater size at the fry stage is positively correlated with freshwater overwintering survival (Quinn and Peterson, 1996).…”

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

“…Saura et al (2010) estimated the h 2 of adult length (and also adult mass) of Atlantic salmon to be 0.32, while Serbezov et al (2010) report h 2 estimates between 0.16 and 0.31 for length-at-age for wild-living juvenile brown trout (Salmo trutta). Body size of salmon juveniles is positively related to their ability to acquire and defend feeding/nursing territories and has previously been shown to be under positive natural selection (Einum and Fleming, 2000). Thus, estimates of the h 2 of size-at-age traits obtained under natural conditions are of evolutionary importance; moreover, these traits are known to vary between farm and wild populations and hence understanding how they are inherited can improve predictions of likely genetic consequences of introgression.…”

Life-history plasticity in female threespine stickleback

“…Thus, there is often found to be a positive correlation between egg size and fry size or capability (Einum and Fleming, 2000a;Segers and Taborsky, 2011). Because even small differences early in life can lead to large variations in fry fitness (Anderson, 1988;Perez and Munch, 2010; JA Baker, unpublished data) plasticity should be a considerable advantage to females.…”