Nonfertilizing sperm in Lepidoptera show little evidence for recurrent positive selection
Nonfertilizing sperm in Lepidoptera show little evidence for recurrent positive selection
复制标题
DOI：
10.1111/mec.15096
复制
发表时间：
2019-05
影响因子：
4.9
通讯作者：
Andrew J. Mongue;Megan E. Hansen;Liuqi Gu;Clyde E Sorenson;James R Walters
中科院分区：
文献类型：
--
作者：
Andrew J. Mongue;Megan E. Hansen;Liuqi Gu;Clyde E Sorenson;James R Walters
精子是自然界中最易变的细胞之一。这种变化的结果在精子发生的非适应性错误，但许多物种始终产生多种精子形态，适应性的意义仍然未知。在这里，我们调查的双形精子在鳞翅目，蝴蝶和蛾的进化。这一目的雄性既产生双精子，又产生一种缺乏DNA的次级非双精子。以前的生物学研究表明，非精子在精子竞争中发挥作用，但这一假设从未从分子框架中得到评估。我们将两个物种的已发表数据集与新测序相结合，一雄的卡罗莱纳狮身人面蛾和高度一雄多雄的帝王蝶。基于种群遗传分析，我们看到了在多雄配子中增加适应性进化的证据，但仅限于一雄多雄的物种。该信号主要来自于与基因组的其余部分相比，精子蛋白中的非同义多态性的减少，这表明更强的纯化选择，与通过精子竞争进行的选择一致。与此相反，非同源精子蛋白没有表现出交配系统的影响，似乎也没有从两个物种的背景基因组不同的演变，反对非同源精子参与直接精子竞争。根据我们的研究结果和以前的工作，我们认为，nonprostaglandin精子可能被用来延迟女性在这些昆虫的再交配，降低精子竞争的风险，而不是直接影响其结果。
Sperm are among the most variable cells in nature. Some of this variation results from nonadaptive errors in spermatogenesis, but many species consistently produce multiple sperm morphs, the adaptive significance of which remains unknown. Here, we investigate the evolution of dimorphic sperm in Lepidoptera, the butterflies and moths. Males of this order produce both fertilizing sperm and a secondary, nonfertilizing type that lacks DNA. Previous organismal studies suggested a role for nonfertilizing sperm in sperm competition, but this hypothesis has never been evaluated from a molecular framework. We combined published data sets with new sequencing in two species, the monandrous Carolina sphinx moth and the highly polyandrous monarch butterfly. Based on population genetic analyses, we see evidence for increased adaptive evolution in fertilizing sperm, but only in the polyandrous species. This signal comes primarily from a decrease in nonsynonymous polymorphism in sperm proteins compared to the rest of the genome, suggesting stronger purifying selection, consistent with selection via sperm competition. Nonfertilizing sperm proteins, in contrast, do not show an effect of mating system and do not appear to evolve differently from the background genome in either species, arguing against the involvement of nonfertilizing sperm in direct sperm competition. Based on our results and previous work, we suggest that nonfertilizing sperm may be used to delay female remating in these insects and decrease the risk of sperm competition rather than directly affect its outcome.