Repeated and independent adaptation to specific environmental conditions from standing genetic variation is common. However, if genetic variation is limited, the evolution of similar locally adapted traits may be restricted to genetically different and potentially less optimal solutions or prevented from happening altogether. Using a quantitative trait locus (QTL) mapping approach, we identified the genomic regions responsible for the repeated pelvic reduction (PR) in three crosses between nine‐spined stickleback populations expressing full and reduced pelvic structures. In one cross, PR mapped to linkage group 7 (LG7) containing the gene Pitx1, known to control pelvic reduction also in the three‐spined stickleback. In the two other crosses, PR was polygenic and attributed to 10 novel QTL, of which 90% were unique to specific crosses. When screening the genomes from 27 different populations for deletions in the Pitx1 regulatory element, these were only found in the population in which PR mapped to LG7, even though the morphological data indicated large‐effect QTL for PR in several other populations as well. Consistent with the available theory and simulations parameterized on empirical data, we hypothesize that the observed variability in genetic architecture of PR is due to heterogeneity in the spatial distribution of standing genetic variation caused by >2× stronger population structuring among freshwater populations and >10× stronger genetic isolation by distance in the sea in nine‐spined sticklebacks as compared to three‐spined sticklebacks.

中文翻译：

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遗传种群结构限制了棘背鱼的局部适应

从站立的遗传变异中反复和独立地适应特定的环境条件是很普遍的。但是，如果遗传变异受到限制，则类似的局部适应性状的进化可能仅限于遗传上不同且可能潜在的最佳解决方案，或者完全无法发生。使用定量性状基因座（QTL）定位方法，我们确定了表达完整和减少的骨盆结构的9个棘刺背背种群之间的三个杂交中重复骨盆减少（PR）的基因组区域。在一个杂交中，PR定位到包含基因Pitx1的连锁群7（LG7），它也可以控制三棘背刺控制骨盆的减少。在另外两个杂交中，PR是多基因的，并归因于10个新的QTL，其中90％是特定杂交所特有的。当筛选来自27个不同种群的基因组中Pitx1中的缺失时调节元素，即使形态数据表明在其他几个人群中PR的影响QTL也很大，但仅在PR映射到LG7的人群中才发现。与基于经验数据的可用理论和模拟相一致，我们假设观察到的PR遗传结构变异性是由于站立遗传变异的空间分布存在异质性，这是由淡水种群中的种群结构增强了2倍以上和10倍以上所导致的。与三轴棘背compared相比，九轴棘背stick在海洋中的距离更强。