Abstract

The evolutionary transition from outcrossing to selfing can have important genomic consequences. Decreased effective population size and the reduced efficacy of selection are predicted to play an important role in the molecular evolution of the genomes of selfing species. We investigated evidence for molecular signatures of the genomic selfing syndrome using 66 species of Primula including distylous (outcrossing) and derived homostylous (selfing) taxa. We complemented our comparative analysis with a microevolutionary study of P. chungensis, which is polymorphic for mating system and consists of both distylous and homostylous populations. We generated chloroplast and nuclear genomic data sets for distylous, homostylous, and distylous–homostylous species and identified patterns of nonsynonymous to synonymous divergence (d_N/d_S) and polymorphism (π_N/π_S) in species or lineages with contrasting mating systems. Our analysis of coding sequence divergence and polymorphism detected strongly reduced genetic diversity and heterozygosity, decreased efficacy of purifying selection, purging of large-effect deleterious mutations, and lower rates of adaptive evolution in samples from homostylous compared with distylous populations, consistent with theoretical expectations of the genomic selfing syndrome. Our results demonstrate that self-fertilization is a major driver of molecular evolutionary processes with genomic signatures of selfing evident in both old and relatively young homostylous populations.

中文翻译：

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基因组自交综合征伴随异质性的进化崩溃。

摘要

从异型到自交的进化过渡可能会产生重要的基因组后果。减少有效种群大小和降低选择效率预计在自交物种基因组的分子进化中起重要作用。我们调查了使用66种报春属植物的基因组自交综合征的分子特征的证据，其中报春属包括二齿（异交）和衍生的同型（交配）类群。我们通过对中华绒螯蟹的微进化研究来补充我们的比较分析。，对交配系统而言是多态的，同时由杂散和同质种群组成。我们产生和叶绿体基因组的核数据集distylous，homostylous，和distylous-homostylous物种鉴定的非同义图案同义发散（d _ñ / d_小号）和多态性（π _ñ / π_小号）的物种或血统，而交配系统却相反。我们对编码序列差异性和多态性的分析检测到，与杂散种群相比，同型种群的样本大大降低了遗传多样性和杂合性，降低了纯化选择的效率，清除了大面积有害突变，并且适应性进化的速率降低，与基因组自交综合征。我们的研究结果表明，自我受精是分子进化过程的主要驱动力，自发的基因组特征在老年人和相对年轻的同型群体中均很明显。