Data from: Origin, evolution, and population genetics of the selfish Segregation distorter gene duplication in European and African populations of Drosophila melanogaster

Meiotic drive elements are a special class of evolutionarily “selfish genes” that subvert Mendelian segregation to gain preferential transmission at the expense of homologous loci. Many drive elements appear to be maintained in populations as stable polymorphisms, their equilibrium frequencies determined by the balance between drive (increasing frequency) and selection (decreasing frequency). Here we show that a classic, seemingly balanced, drive system is instead characterized by frequent evolutionary turnover giving rise to dynamic, rather than stable, equilibrium frequencies. The autosomal Segregation Distorter (SD) system of the fruitfly Drosophila melanogaster is a selfish coadapted meiotic drive gene complex in which the major driver corresponds to a partial duplication of the gene Ran-GTPase activating protein (RanGAP). SD chromosomes segregate at similar, low frequencies of 1-5% in natural populations worldwide, consistent with a balanced polymorphism. Surprisingly, our population genetic analyses reveal evidence for parallel, independent selective sweeps of different SD chromosomes in populations on different continents. These findings suggest that, rather than persisting at a single stable equilibrium, SD chromosomes turn over frequently within populations.

减数分裂驱动元件（Meiotic drive elements）是一类特殊的进化意义上的「自私基因（selfish genes）」，它们会颠覆孟德尔分离定律（Mendelian segregation），以牺牲同源基因座（homologous loci）为代价获取优先传递优势。诸多此类驱动元件似乎以稳定多态性（stable polymorphisms）的形式存续于种群之中，其平衡频率由驱动效应（提升自身频率）与自然选择（selection）之间的动态平衡所决定。本研究表明，一个曾被认为处于平衡状态的经典驱动系统，实则以频繁的进化更替为特征，最终形成动态而非静态的平衡频率。黑腹果蝇（Drosophila melanogaster）的常染色体分离失调（Segregation Distorter，SD）系统，便是一类自私共适应型减数分裂驱动基因复合体，其核心驱动因子为Ran-GTP酶激活蛋白（Ran-GTPase activating protein，RanGAP）基因的部分复制片段。全球各地自然种群中的SD染色体，其分离频率均维持在1%至5%的较低水平，与平衡多态性的理论预期相符。令人意外的是，本研究的种群遗传学分析发现，不同大陆的种群中，不同SD染色体各自发生了平行且独立的选择性清除（selective sweeps）事件。上述研究结果表明，SD染色体并非长期维持于单一稳定平衡状态，而是在种群内部频繁发生进化更替。