Data from: The signature of fine scale local adaptation in Atlantic salmon revealed from common garden experiments in nature

Understanding the extent, scale and genetic basis of local adaptation is important for conservation and management. Its relevance in salmonids at microgeographic scales, where dispersal (and hence potential gene flow) can be substantial, has however been questioned. Here we compare the fitness of communally-reared offspring of local and foreign Atlantic salmon Salmo salar from adjacent Irish rivers and reciprocal F1 hybrid crosses between them, in the wild ‘home’ environment of the local population. Experimental groups did not differ in wild smolt output but a catastrophic flood event may have limited our ability to detect freshwater performance differences, which were evident in a previous study. Foreign parr exhibited higher, and hybrids intermediate, emigration rates from the natal stream relative to local parr, consistent with genetically-based behavioural differences. Adult return rates were lower for the foreign compared to the local group. Overall lifetime success of foreigners and hybrids relative to locals was estimated at 31% and 40% (mean of both hybrid groups), respectively. The results imply a genetic basis to fitness differences among populations separated by only 50km, driven largely by variation in smolt to adult return rates. Hence even if supplementary stocking programs obtain broodstock from neighbouring rivers, the risk of extrinsic outbreeding depression may be high.

阐明局域适应的范围、程度及其遗传基础，对于物种保护与资源管理具有重要意义。然而，在微地理尺度下的鲑科鱼类中，这一相关性曾受到质疑——该尺度下个体扩散（进而潜在的基因流）往往较为显著。本研究在当地种群的野生原生境中，对比了来自爱尔兰相邻河流的本地与外来大西洋鲑（Salmo salar）的共同饲养后代，以及二者间的正反交F1杂交组合的适合度。各组的野生银化幼鲑（smolt）产出量并无显著差异，但一场灾难性洪水可能限制了我们检测淡水阶段表现差异的能力——这类差异在既往研究中曾被观测到。相较于本地河川稚鱼（parr），外来稚鱼的出生溪流迁出率更高，杂交组合则介于二者之间，这与基于遗传的行为差异相符。外来组的成鱼回归率低于本地组。据估算，外来组与杂交组相对于本地组的终生繁殖成功率分别为31%和40%（杂交两组的平均值）。研究结果表明，仅相距50公里的种群间存在适合度差异，且该差异具有遗传基础，其主要驱动因素为银化幼鲑至成鱼的回归率变异。因此，即便辅助放流计划的亲鱼群体取自邻近河流，外源远交衰退（outbreeding depression）的风险仍可能较高。