Ribosomal DNA (rDNA) loci are essential for cellular metabolism due to their participation in ribosome biogenesis. Although these genes have been widely cytogenetically mapped, the evolutionary mechanisms behind their variability in number and chromosomal location remain elusive, even in well-known biological groups, such as ants, bees and wasps (Insecta: Hymenoptera). To address this question in Hymenoptera and therefore advance the understanding of rDNA evolution in insects in general, we integrated molecular cytogenetic data, a phylogenomic framework, model-based predictions and genome sequencing. Hence, we assessed the main evolutionary trends shaping the chromosomal distribution of rDNA loci in Hymenoptera. We noticed the conservation of one site of rDNA per haploid genome, suggesting that a single 45S rDNA locus is the putative ancestral pattern for aculeate Hymenoptera. Moreover, our results highlighted a nonrandom distribution of rDNA in Hymenoptera karyotypes, as well as a lineage-specific preferential location. The proximal location of rDNA is favoured in species with multiple loci and in the two families of Hymenoptera that show the highest range of chromosome numbers: Formicidae and Vespidae. We propose that chromosome fissions have played a crucial role in the distribution pattern of rDNA loci through the evolutionary diversification of Hymenoptera. Moreover, our genomic analysis of two species, one with a single locus of rDNA and one with multiple loci, supported that loci multiplication is followed by sequence divergence. Our results provide detailed information about the number and chromosomal position of rDNA in Hymenoptera and, therefore, broaden our knowledge regarding rDNA evolutionary dynamics in insects.

中文翻译：

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染色体裂变与膜翅目昆虫主要核糖体 DNA 分散的相关性。

由于参与核糖体生物发生，核糖体 DNA (rDNA) 基因座对细胞代谢至关重要。尽管这些基因已被广泛地进行细胞遗传学定位，但其数量和染色体位置可变性背后的进化机制仍然难以捉摸，即使在蚂蚁、蜜蜂和黄蜂等众所周知的生物群体中也是如此（昆虫纲：膜翅目）。为了解决膜翅目中的这个问题，从而促进对昆虫 rDNA 进化的总体理解，我们整合了分子细胞遗传学数据、系统发育框架、基于模型的预测和基因组测序。因此，我们评估了影响膜翅目 rDNA 基因座染色体分布的主要进化趋势。我们注意到每个单倍体基因组的一个 rDNA 位点的保守性，表明单个 45S rDNA 基因座是有刺膜翅目假定的祖先模式。此外，我们的结果强调了膜翅目核型中 rDNA 的非随机分布，以及谱系特定的优先位置。rDNA 的近端位置有利于具有多个基因座的物种和膜翅目的两个家族，它们显示出最高的染色体数量范围：蚁科和胡蜂科。我们提出，通过膜翅目的进化多样化，染色体裂变在 rDNA 基因座的分布模式中发挥了至关重要的作用。此外，我们对两种物种的基因组分析，一种具有单个 rDNA 基因座，另一种具有多个基因座，支持基因座增殖之后是序列差异。