Does Domestication Cause Changes in Growth Reaction Norms? A Study of Farmed, Wild and Hybrid Atlantic Salmon Families Exposed to Environmental Stress

Abstract

One of the most important traits linked with the successful domestication of animals is reducing their sensitivity to environmental stressors in the human controlled environment. In order to examine whether domestication selection in Atlantic salmon Salmo salar L., over approximately ten generations, has inadvertently selected for reduced responsiveness to stress, we compared the growth reaction norms of 29 wild, hybrid and domesticated families reared together under standard hatchery conditions (control) and in the presence of a stressor (reduced water level twice daily). The experiment was conducted for a 14 week period. Farmed salmon outgrew wild salmon 1∶2.93 in the control tanks, and no overlap in mean weight was displayed between families representing the three groups. Thus, the elevation of the reaction norms differed among the groups. Overall, growth was approximately 25% lower in the stressed tanksl; however, farmed salmon outgrew wild salmon 1∶3.42 under these conditions. That farmed salmon maintained a relatively higher growth rate than the wild salmon in the stressed tanks demonstrates a lower responsiveness to stress in the farmed salmon. Thus, flatter reaction norm slopes were displayed in the farmed salmon, demonstrating reduced plasticity for this trait under these specific experimental conditions. For all growth measurements, hybrid salmon displayed intermediate values. Wild salmon displayed higher heritability estimates for body weight than the hybrid and farmed salmon in both environments. This suggests reduced genetic variation for body weight in the farmed contra wild salmon studied here. While these results may be linked to the specific families and stocks investigated, and verification in other stocks and traits is needed, these data are consistent with the theoretical predictions of domestication.

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

“…However, these growth rate differences seem to be less pronounced in wild stream environments and in hatchery conditions simulating a semi-natural environment with restricted food (Solberg et al, 2013a). In our experiments, size-at-age differences between wild and farm offspring measured in the wild were statistically significant but moderate in magnitude (Table 2), with electrofished farm parr being in the order of 5-20% larger and heavier than wild parr, consistent with the findings of these previous studies.…”

“…In the other five samples, the residual variance was either highest in the WW group (for example, mass of 1994 cohort electrofished 1+ parr sample) or the FF group (for example, L F and mass of pre-smolts in 1993 cohort hatchery controls). Intriguingly, found that within-family variation in body size of Atlantic salmon (measured in a hatchery setting) diminished with increasing generations of domestication (see also Solberg et al, 2013a). Under fully wild conditions, variance differences between wild, farmed and hybrid families may be largely unpredictable and context dependent, given that our findings did not match those of Skaala et al (2012) despite very similar study designs (but different genetic backgrounds).…”

Multigenerational hybridisation and its consequences for maternal effects in Atlantic salmon

“…This may have introduced a bias in all DD dam offspring data by, for example, their very small variation in egg size relative to other dam crosses. We cannot determine whether the small variation is a result of the domestication process (as suggested for variation in growth; Solberg et al, 2013) or of the close kinship among dams. However, it was not possible to account in our analyses for dam cross-specific variances (except for egg size) because of nonestimable DD dam cross variances.…”

Genetic introgression of farmed salmon in native populations: quantifying the relative influence of population size and frequency of escapees

“…For example, they out-grow wild salmon under hatchery conditions (Glover et al 2009, Solberg et al 2013a. Wild salmon populations are regarded as potentially adapted to their natal rivers (Garcia de Leaniz et al 2007, Fraser et al 2011, and the survival of farmed salmon offspring in the wild is lower than for native salmon (McGinnity et al 1997, 2003, Fleming et al 2000.…”