Data from: Thermal plasticity in farmed, wild and hybrid Atlantic salmon during early development: has domestication caused divergence in low temperature tolerance?

Background: In the past three decades, millions of domesticated Atlantic salmon have escaped from farms into the wild. Their offspring display reduced survival in the natural environment, which demonstrates that gene-flow is likely to have a negative effect on wild populations. However, inter-population differences in introgression of farmed salmon have been observed, and the underlying ecological mechanisms remain enigmatic. We hypothesised that domestication-driven divergence in tolerance to low temperatures during early development may contribute to lower survival of farmed salmon offspring in the wild, which in turn, may influence patterns of introgression among populations exposed to different temperature regimes. We reared the offspring of 35 families of wild, farmed and hybrid origin at three temperatures (3.9°C, 5.6°C and 12°C) from the onset of exogenous feeding and throughout their first summer. Thermal reaction norms for growth and survival were investigated along the gradient. Results: The main results of this study, which is based upon the analysis of juvenile salmon from five wild strains, two farmed strains and two hybrid strains, can be summarised as; (i) salmon of all origins were able to successfully initiate feeding at all temperatures and similar survival reaction norms were detected in all strains across the temperature gradient; (ii) deviating growth reaction norms were detected between strains, although this result was most likely due to an overall lack of growth in the lower temperature treatments. Conclusions: This study revealed no evidence of domesticated-driven divergence in low temperature tolerance in Atlantic salmon during early development. Although the potential interaction between low temperature and other river-specific factors cannot be excluded, our results indicate that the reduced survival of farmed offspring in the wild is not explained by farmed salmon displaying impaired abilities to initiate feeding at low temperatures. We therefore suggest that the observed inter-population patterns of introgression are not low-temperature driven and that other ecological or biological factors may explain why detection of farmed salmon in wild rivers is not synonymous with introgression. In general, our results support the literature indicating that phenotypic plasticity instead of thermal adaption has been selected for in Atlantic salmon.

研究背景：近三十年来，数以百万计的养殖大西洋鲑（Atlantic salmon）从水产养殖场逃逸至野生环境中。其后代在自然环境中的存活率显著降低，这表明养殖个体与野生种群间的基因流动（gene-flow）可能对野生种群产生负面影响。然而，已有研究观测到养殖鲑的基因渐渗（introgression）在不同种群间存在差异，但其背后的生态学机制仍尚不明确。本研究提出假说：驯化过程中，大西洋鲑在早期发育阶段对低温耐受能力的驯化驱动分化，可能是导致养殖鲑后代在野生环境中存活率降低的原因，进而可能影响不同温度环境下种群间的基因渐渗模式。我们将35个野生、养殖及杂交起源的家系后代，从外源摄食起始阶段直至首个夏季，分别在3.9℃、5.6℃和12℃三个温度梯度下进行饲养。本研究沿该温度梯度，对生长与存活的热反应规范（thermal reaction norms）进行了分析。研究结果：本研究基于5个野生品系、2个养殖品系及2个杂交品系的幼鲑数据分析，主要结果可总结为：（1）所有起源类型的鲑鱼在所有温度梯度下均能成功启动摄食，且所有种群在该温度梯度下的热反应规范均无显著差异；（2）不同种群间的生长热反应规范存在差异，但该结果极有可能是由于低温处理组整体生长受抑所致。研究结论：本研究未发现大西洋鲑在早期发育阶段存在驯化驱动的低温耐受能力分化的证据。尽管无法排除低温与其他河流特有因素间存在潜在交互作用的可能性，但本研究结果表明，养殖鲑后代在野生环境中存活率降低，并非源于其在低温下启动摄食的能力受损。因此，本研究认为，已观测到的种群间基因渐渗模式并非由低温驱动，其他生态学或生物学因素或可解释为何在野生河流中检测到养殖鲑个体并不等同于发生了基因渐渗。总体而言，本研究结果支持现有文献结论：大西洋鲑的演化所选择的是表型可塑性（phenotypic plasticity）而非热适应性（thermal adaption）。