The apparent rarity of sex in many fungal species has raised questions about how much sex is needed to purge deleterious mutations and how differences in frequency of sex impact fungal evolution. We sought to determine how differences in the extent of recombination between populations of Aspergillus flavus impact the evolution of genes associated with the synthesis of aflatoxin, a notoriously potent carcinogen. We sequenced the genomes of, and quantified aflatoxin production in, 94 isolates of A. flavus sampled from seven states in eastern and central latitudinal transects of the United States. The overall population is subdivided into three genetically differentiated populations (A, B, and C) that differ greatly in their extent of recombination, diversity, and aflatoxin-producing ability. Estimates of the number of recombination events and linkage disequilibrium decay suggest relatively frequent sex only in population A. Population B is sympatric with population A but produces significantly less aflatoxin and is the only population where the inability of nonaflatoxigenic isolates to produce aflatoxin was explained by multiple gene deletions. Population expansion evident in population B suggests a recent introduction or range expansion. Population C is largely nonaflatoxigenic and restricted mainly to northern sampling locations through restricted migration and/or selection. Despite differences in the number and type of mutations in the aflatoxin gene cluster, codon optimization and site frequency differences in synonymous and nonsynonymous mutations suggest that low levels of recombination in some A. flavus populations are sufficient to purge deleterious mutations.

中文翻译：

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性别的频率：群体基因组学揭示了产生黄曲霉毒素的真菌黄曲霉的重组和群体结构的差异。

许多真菌物种中性的明显稀有性引发了关于清除有害突变需要多少性行为以及性频率差异如何影响真菌进化的问题。我们试图确定黄曲霉种群之间重组程度的差异如何影响与黄曲霉毒素合成相关的基因进化，黄曲霉毒素是一种众所周知的强致癌物质。我们对 94 个A. flavus分离株的基因组进行了测序并量化了黄曲霉毒素的产生从美国东部和中部纬度样带的七个州采样。整个种群被细分为三个基因分化种群（A、B 和 C），它们的重组程度、多样性和黄曲霉毒素产生能力差异很大。对重组事件数量和连锁不平衡衰减的估计表明，仅在群体 A 中发生性行为相对频繁。群体 B 与群体 A 同域，但产生的黄曲霉毒素明显较少，并且是唯一一个非黄曲霉毒素分离株无法产生黄曲霉毒素的群体可以通过多种解释基因缺失。种群 B 中明显的种群扩张表明最近的引入或范围扩大。种群 C 主要是非黄曲霉毒素产生的，并且主要通过限制迁移和/或选择限制在北部采样地点。尽管黄曲霉毒素基因簇中突变的数量和类型存在差异，但同义和非同义突变的密码子优化和位点频率差异表明，某些基因簇的重组水平较低。A. flavus种群足以清除有害突变。