Genomic mapping of the loci associated with phenotypic evolution has revealed genomic “hotspots,” or regions of the genome that control multiple phenotypic traits. This clustering of loci has important implications for the speed and maintenance of adaptation and could be due to pleiotropic effects of a single mutation or tight genetic linkage of multiple causative mutations affecting different traits. The threespine stickleback (Gasterosteus aculeatus) is a powerful model for the study of adaptive evolution because the marine ecotype has repeatedly adapted to freshwater environments across the northern hemisphere in the last 12,000 years. Freshwater ecotypes have repeatedly fixed a 16 kilobase haplotype on chromosome IV that contains Ectodysplasin (Eda), a gene known to affect multiple traits, including defensive armor plates, lateral line sensory hair cells, and schooling behavior. Many additional traits have previously been mapped to a larger region of chromosome IV that encompasses the Eda freshwater haplotype. To identify which of these traits specifically map to this adaptive haplotype, we made crosses of rare marine fish heterozygous for the freshwater haplotype in an otherwise marine genetic background. Further, we performed fine‐scale association mapping in a fully interbreeding, polymorphic population of freshwater stickleback to disentangle the effects of pleiotropy and linkage on the phenotypes affected by this haplotype. Although we find evidence that linked mutations have small effects on a few phenotypes, a small 1.4‐kb region within the first intron of Eda has large effects on three phenotypic traits: lateral plate count, and both the number and patterning of the posterior lateral line neuromasts. Thus, the Eda haplotype is a hotspot of adaptation in stickleback due to both a small, pleiotropic region affecting multiple traits as well as multiple linked mutations affecting additional traits.

中文翻译：

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通过多效性和连锁来适应：关联图谱揭示了棘背Eda基因座内的复杂遗传结构。

与表型进化有关的基因座的基因组图谱揭示了基因组“热点”，即控制多个表型性状的基因组区域。基因座的这种聚集对于适应的速度和维持具有重要意义，并且可能是由于单个突变的多效性效应或影响不同性状的多个致病突变的紧密遗传连锁。三脊背棘背（（Gasterosteus aculeatus）是研究适应性进化的强大模型，因为在过去的12,000年中，海洋生态型已反复适应北半球的淡水环境。淡水生态型已经反复地在包含Ectodysplasin（Eda），一种已知会影响多种性状的基因，包括防御性盔甲，侧线感觉毛细胞和上学行为。先前已将许多其他特征映射到涵盖Eda的IV号染色体的较大区域淡水单倍型。为了确定这些特征中的哪些特异地映射到该适应性单倍型，我们在其他海洋遗传背景下将淡水单倍型的稀有海鱼杂交。此外，我们在完全杂交的淡水water形多态种群中进行了精细的关联映射，以消除多效性和连锁对受此单倍型影响的表型的影响。尽管我们发现有证据表明连锁突变对某些表型影响较小，但Eda第一个内含子内的一个1.4kb小区域对三种表型特征有较大影响：侧板数以及后侧线的数量和样式神经质。因此，埃达 单倍型是棘背动物适应的热点，这是因为一个小的多效性区域会影响多个性状，以及多个连锁的突变会影响其他性状。