Albert Arianne Y K, Sawaya Sterling, Vines Timothy H, Knecht Anne K, Miller Craig T, Summers Brian R, Balabhadra Sarita, Kingsley David M, Schluter Dolph
Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada.
Evolution. 2008 Jan;62(1):76-85. doi: 10.1111/j.1558-5646.2007.00259.x. Epub 2007 Nov 12.
The distribution of effect sizes of genes underlying adaptation is unknown (Orr 2005). Are suites of traits that diverged under natural selection controlled by a few pleiotropic genes of large effect (major genes model), by many independently acting genes of small effect (infinitesimal model), or by a combination, with frequency inversely related to effect size (geometric model)? To address this we carried out a quantitative trait loci (QTL) study of a suite of 54 position traits describing body shapes of two threespine stickleback species: an ancestral Pacific marine form and a highly derived benthic species inhabiting a geologically young lake. About half of the 26 detected QTL affected just one coordinate and had small net effects, but several genomic regions affected multiple aspects of shape and had large net effects. The distribution of effect sizes followed the gamma distribution, as predicted by the geometric model of adaptation when detection limits are taken into account. The sex-determining chromosome region had the largest effect of any QTL. Ancestral sexual dimorphism was similar to the direction of divergence, and was largely eliminated during freshwater adaptation, suggesting that sex differences may provide variation upon which selection can act. Several shape QTL are linked to Eda, a major gene responsible for reduction of lateral body armor in freshwater. Our results are consistent with predictions of the geometric model of adaptation. Shape evolution in stickleback results from a few genes with large and possibly widespread effects and multiple genes of smaller effect.
适应相关基因的效应大小分布尚不清楚（奥尔 2005 年）。在自然选择下发生分化的性状组合是由少数具有大效应的多效基因控制（主基因模型）、由许多具有小效应的独立作用基因控制（微效基因模型），还是由两者结合控制，且频率与效应大小呈反比（几何模型）？为了解决这个问题，我们对一套描述两种三刺鱼身体形状的 54 个位置性状进行了数量性状基因座（QTL）研究：一种是祖先太平洋海洋形态，另一种是高度特化的底栖物种，栖息在一个地质年代较新的湖泊中。在检测到的 26 个 QTL 中，约一半仅影响一个坐标且净效应较小，但有几个基因组区域影响形状的多个方面且净效应较大。考虑到检测限后，效应大小的分布遵循伽马分布，这与适应的几何模型预测一致。性别决定染色体区域的效应在所有 QTL 中最大。祖先的两性异形与分化方向相似，在淡水适应过程中基本消失，这表明性别差异可能提供了可供选择作用的变异。几个形状 QTL 与 Eda 基因相连，Eda 是负责减少淡水鱼体侧盔甲的一个主要基因。我们的结果与适应几何模型的预测一致。三刺鱼的形状进化是由少数具有大的、可能广泛效应的基因以及多个效应较小的基因共同作用的结果。
