Universidade Federal de São Carlos, Departamento de Genética e Evolução, 13565-905, CP 676, São Carlos-SP, Brazil.
BMC Evol Biol. 2010 Sep 24;10:293. doi: 10.1186/1471-2148-10-293.
Many genes involved in the sex determining cascade have indicated signals of positive selection and rapid evolution across different species. Even though fruitless is an important gene involved mostly in several aspects of male courtship behavior, the few studies so far have explained its high rates of evolution by relaxed selective constraints. This would indicate that a large portion of this gene has evolved neutrally, contrary to what has been observed for other genes in the sex cascade.
Here we test whether the fruitless gene has evolved neutrally or under positive selection in species of Anastrepha (Tephritidae: Diptera) using two different approaches, a long-term evolutionary analysis and a populational genetic data analysis. The first analysis was performed by using sequences of three species of Anastrepha and sequences from several species of Drosophila using the ratio of nonsynonymous to synonymous rates of evolution in PAML, which revealed that the fru region here studied has evolved by positive selection. Using Bayes Empirical Bayes we estimated that 16 sites located in the connecting region of the fruitless gene were evolving under positive selection. We also investigated for signs of this positive selection using populational data from 50 specimens from three species of Anastrepha from different localities in Brazil. The use of standard tests of selection and a new test that compares patterns of differential survival between synonymous and nonsynonymous in evolutionary time also provide evidence of positive selection across species and of a selective sweep for one of the species investigated.
Our data indicate that the high diversification of fru connecting region in Anastrepha flies is due at least in part to positive selection, not merely as a consequence of relaxed selective constraint. These conclusions are based not only on the comparison of distantly related taxa that show long-term divergence time, but also on recently diverged lineages and suggest that episodes of adaptive evolution in fru may be related to sexual selection and/or conflict related to its involvement in male courtship behavior.
许多参与性别决定级联的基因都表明，在不同物种中存在正选择和快速进化的信号。尽管无果基因主要涉及雄性求偶行为的几个方面，但迄今为止的少数研究表明，其进化速度较快的原因是选择压力放松。这表明，该基因的很大一部分是中性进化的，与性别级联中的其他基因观察到的情况相反。
在这里，我们使用两种不同的方法，即长期进化分析和群体遗传数据分析，来检验 Anastrepha 物种中的无果基因是否是中性进化还是受到正选择的影响。第一种分析是使用 Anastrepha 的三个物种的序列和来自几个 Drosophila 物种的序列，使用 PAML 中的非同义与同义进化速率比来进行，结果表明，所研究的 fru 区域是通过正选择进化的。使用贝叶斯经验贝叶斯估计，我们发现位于无果基因连接区的 16 个位点正在受到正选择的影响。我们还使用来自巴西不同地区的 50 个 Anastrepha 物种的群体数据，调查了这种正选择的迹象。标准选择测试和一种比较进化过程中同义与非同义差异存活模式的新测试都提供了证据，表明在物种之间存在正选择，并且在研究的一个物种中存在选择清除。
我们的数据表明，Anastrepha 蝇中 fru 连接区的高度多样化至少部分是由于正选择，而不仅仅是由于选择压力放松的结果。这些结论不仅基于对具有长期分化时间的远缘分类群的比较，还基于最近分化的谱系，并表明 fru 中的适应性进化事件可能与性选择和/或与雄性求偶行为有关的冲突有关。
