Contrasting patterns of X-chromosome divergence underlie multiple sex-ratio polymorphisms in stalk-eyed flies

Sex-linked segregation distorters cause offspring sex ratios to differ from equality. Theory predicts that such selfish alleles may either go to fixation and cause extinction, reach a stable polymorphism, or initiate an evolutionary arms race with genetic modifiers. The extent to which a sex ratio distorter follows any of these trajectories in nature is poorly known. Here we used X-linked sequence and simple tandem repeat data for three sympatric species of stalk-eyed flies (Teleopsis whitei and two cryptic species of T. dalmanni) to infer the evolution of distorting X chromosomes. By screening large numbers of field and recently lab-bred flies we found no evidence of males with strongly female-biased sex ratio phenotypes (SR) in one species but high frequencies of SR males in the other two species. In the two species with SR males, we find contrasting patterns of X chromosome evolution. T. dalmanni - 1 shows chromosome-wide differences between sex-ratio (XSR) and standard (XST) X ch...性连锁分离扭曲因子（sex-linked segregation distorter）会导致子代性比偏离均等。理论预测，这类自私等位基因（selfish allele）或可发生固定并引发种群灭绝，或达到稳定多态性（stable polymorphism），亦或是与遗传修饰因子（genetic modifier）展开进化军备竞赛。目前学界对自然环境中性比扭曲因子（sex ratio distorter）遵循上述何种演化轨迹的认知仍较为匮乏。本研究借助3种同域分布的眼柄蝇（stalk-eyed fly）的X连锁序列（X-linked sequence）与简单串联重复序列（simple tandem repeat）数据，涵盖泰氏眼柄蝇（Teleopsis whitei）以及达氏眼柄蝇（T. dalmanni）的两个隐存种，以推断扭曲型X染色体的演化历程。通过对大量野外采集与新近室内繁育的蝇类个体进行筛查，我们在其中一个物种中未发现携带显著雌性偏向性表型（sex ratio，SR）的雄性个体，而在另外两个物种中则检测到高频次的SR雄性。在这两个携带SR雄性的物种中，我们观察到X染色体演化模式存在显著差异。达氏眼柄蝇（T. dalmanni）-1品系的性比扭曲型X染色体（XSR）与标准型X染色体（XST）之间呈现全染色体水平的差异……