Data from: Neutral and selection-driven decay of sexual traits in asexual stick insects

Environmental shifts and lifestyle changes may result in formerly adaptive traits becoming non-functional or maladaptive. The subsequent decay of such traits highlights the importance of natural selection for adaptations, yet its causes have rarely been investigated. To study the fate of formerly adaptive traits after lifestyle changes, we evaluated sexual traits in five independently derived asexual lineages, including traits that are specific to males and therefore not exposed to selection. At least four of the asexual lineages retained the capacity to produce males that display normal courtship behaviours and are able to fertilize eggs of females from related sexual species. The maintenance of male traits may stem from pleiotropy, or from these traits only regressing via drift, which may require millions of years to generate phenotypic effects. By contrast, we found parallel decay of sexual traits in females. Asexual females produced altered airborne and contact signals, had modified sperm storage organs, and lost the ability to fertilize their eggs, impeding reversals to sexual reproduction. Female sexual traits were decayed even in recently derived asexuals, suggesting that trait changes following the evolution of asexuality, when they occur, proceed rapidly and are driven by selective processes rather than drift.环境变迁与生活方式改变，可能令原本具有适应性的性状丧失功能，甚至变为适应不良的性状。这类性状随后的退化，凸显了自然选择对适应性演化的重要意义，但其背后的成因却鲜有研究。为探究生活方式改变后原适应性性状的演化命运，我们对5个独立起源的无性繁殖谱系开展了有性相关性状的评估，其中包括雄性特异性性状——这类性状原本不会经受选择压力。至少有4个无性谱系仍保留了产生雄性的能力，这些雄性可表现出正常的求偶行为，且能使相关有性物种雌性的卵完成受精。雄性性状的维持，可能源于基因多效性（pleiotropy），或是这类性状仅通过遗传漂变发生退化——而遗传漂变产生表型效应往往需要数百万年的时间。与之形成鲜明对比的是，我们在雌性的有性相关性状中发现了同步退化的现象。无性繁殖雌性产生的空气传播与接触性信号发生了改变，其精子储存器官出现结构修饰，同时丧失了卵受精的能力，这阻碍了无性繁殖向有性繁殖的逆转。即便在新近起源的无性繁殖类群中，雌性的有性相关性状也已发生退化，这表明：无性繁殖演化后出现的性状改变，一旦发生便会快速推进，且其驱动因素是选择过程而非遗传漂变。