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

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.

与动物成功驯化相关的核心特征之一，是降低其在人类管控环境中对环境胁迫的敏感性。为探究经过约10个世代的大西洋鲑（Salmo salar L.）驯化选择是否会无意间筛选出胁迫响应减弱的个体，我们在标准孵化场养殖条件（对照组）与每日两次降低水位的胁迫环境下，共同饲养了29个野生、杂交与驯化家系，并比较其生长反应规范。本实验持续14周。对照组养殖池中，驯化鲑的生长速率为野生个体的1∶2.93，且三类家系的平均体重无重叠，表明三类群体的反应规范高度存在显著差异。整体而言，胁迫环境下的生长速率较对照组降低约25%；但在此胁迫条件下，驯化个体的生长速率仍为野生个体的1∶3.42。驯化大西洋鲑在胁迫环境中仍能维持较野生个体更高的生长速率，这证明其对胁迫的响应能力更弱。由此可见，驯化群体的反应规范斜率更为平缓，表明在该特定实验条件下，该性状的表型可塑性有所降低。在两种环境的所有生长测量指标中，杂交鲑的体重表型均介于野生与驯化群体之间。野生群体的体重遗传力估计值均高于杂交与驯化群体，这暗示本研究中驯化群体相较于野生群体，其体重相关的遗传变异有所降低。尽管上述结果可能仅与本次研究所涉及的特定家系与种群相关，仍需在其他种群与性状中开展验证，但本实验数据与驯化理论的预测结果相符。