Infection status of females collected in 2011 and 2016, and sex ratios of their offspring from Rapid comeback of males: evolution of male-killer suppression in a green lacewing population

Evolutionary theory predicts that the spread of cytoplasmic sex ratio distorters leads to the evolution of host nuclear suppressors, although there are extremely few empirical observations of this phenomenon. Here, we demonstrate that a nuclear suppressor of a cytoplasmic male killer has spread rapidly in a population of the green lacewing <i>Mallada desjardinsi</i>. An <i>M. desjardinsi</i> population, which was strongly female-biased in 2011 because of a high prevalence of the male-killing <i>Spiroplasma</i> endosymbiont, had a sex ratio near parity in 2016, despite a consistent <i>Spiroplasma</i> prevalence. Most of the offspring derived from individuals collected in 2016 had 1 : 1 sex ratios in subsequent generations. Contrastingly, all-female or female-biased broods appeared frequently from crossings of these female offspring with males derived from a laboratory line founded by individuals collected in 2011. These results suggest near-fixation of a nuclear suppressor against male killing in 2016 and reject the notion that a non-male-killing <i>Spiroplasma</i> variant has spread in the population. Consistently, no significant difference was detected in mitochondrial haplotype variation between 2011 and 2016. These findings, and earlier findings in the butterfly <i>Hypolimnas bolina</i> in Samoa, suggest that these quick events of male recovery occur more commonly than is generally appreciated.

进化理论预测，细胞质性别比例操纵因子的扩散会驱动宿主核抑制因子的演化，但目前针对该现象的实证观测极为匮乏。本研究证实，一种针对细胞质杀雄因子的核抑制因子，已在绿草蛉（Mallada desjardinsi）的种群中快速扩散。2011年，由于杀雄螺原体（Spiroplasma）内共生菌的高感染率，该种群的性别比例严重偏向雌性；而到2016年，尽管螺原体的感染率始终保持稳定，其种群性别比例已接近1:1的均衡状态。2016年采集的个体所产生的多数后代，在后续世代中均呈现1:1的性别比例。与之形成鲜明对比的是，将这些2016年采集的雌性个体与2011年采集个体建立的实验室品系雄性个体进行杂交时，后代中频繁出现全雌性或雌性偏向的子代群。上述结果表明，至2016年时，针对杀雄作用的核抑制因子已接近固定，并否定了"非杀雄螺原体变异株已在种群中扩散"这一假说。一致的是，2011年与2016年的线粒体单倍型变异未检测到显著差异。本研究结果与此前萨摩亚幻紫斑蛱蝶（Hypolimnas bolina）的研究发现相符，表明这类雄性性别比例快速恢复的事件，其发生频率或许远超此前的认知。