Departamento de Genética e Evolução, Universidade Federal de São Carlos, São Carlos, Brazil.
PLoS One. 2012;7(3):e33446. doi: 10.1371/journal.pone.0033446. Epub 2012 Mar 13.
The gene doublesex (dsx) is considered to be under strong selective constraint along its evolutionary history because of its central role in somatic sex differentiation in insects. However, previous studies of dsx used global estimates of evolutionary rates to investigate its molecular evolution, which potentially miss signals of adaptive changes in generally conserved genes. In this work, we investigated the molecular evolution of dsx in the Anastrepha fraterculus species group (Diptera, Tephritidae), and test the hypothesis that this gene evolved solely by purifying selection using divergence-based and population-based methods. In the first approach, we compared sequences from Anastrepha and other Tephritidae with other Muscomorpha species, analyzed variation in nonsynonymous to synonymous rate ratios (dN/dS) in the Tephritidae, and investigated radical and conservative changes in amino acid physicochemical properties. We show a general selective constraint on dsx, but with signs of positive selection mainly in the common region. Such changes were localized in alpha-helices previously reported to be involved in dimer formation in the OD2 domain and near the C-terminal of the OD1 domain. In the population-based approach, we amplified a region of 540 bp that spanned almost all of the region common to both sexes from 32 different sites in Brazil. We investigated patterns of selection using neutrality tests based on the frequency spectrum and locations of synonymous and nonsynonymous mutations in a haplotype network. As in the divergence-based approach, these analyses showed that dsx has evolved under an overall selective constraint, but with some events of positive selection. In contrast to previous studies, our analyses indicate that even though dsx has indeed evolved as a conserved gene, the common region of dsx has also experienced bouts of positive selection, perhaps driven by sexual selection, during its evolution.
性别基因 doublesex（dsx）在其进化历史中被认为受到强烈的选择约束，因为它在昆虫的体性别分化中起着核心作用。然而，以前对 dsx 的研究使用了进化率的全局估计来研究其分子进化，这可能会错过通常保守基因中适应性变化的信号。在这项工作中，我们研究了 Anastrepha fraterculus 物种群（双翅目，瘿蚊科）中 dsx 的分子进化，并测试了该基因仅通过净化选择进化的假设，使用基于分歧和基于种群的方法。在第一种方法中，我们比较了 Anastrepha 和其他瘿蚊科与其他 Muscomorpha 物种的序列，分析了瘿蚊科中非同义到同义比率（dN/dS）的变异，并研究了氨基酸物理化学性质的激进和保守变化。我们显示 dsx 受到普遍的选择约束，但在共同区域主要有正选择的迹象。这些变化定位在以前报道的 OD2 结构域中参与二聚体形成和 OD1 结构域的 C 末端附近的α-螺旋中。在基于种群的方法中，我们从巴西的 32 个不同地点扩增了一个跨越两性共同区域的 540bp 区域。我们使用基于频率谱和同义突变和非同义突变位置的中性测试来研究选择模式。与基于分歧的方法一样，这些分析表明 dsx 在整体选择约束下进化，但也有一些正选择事件。与以前的研究不同，我们的分析表明，尽管 dsx 确实作为一个保守基因进化，但 dsx 的共同区域也经历了一些正选择事件，这可能是由性选择驱动的。
