Most of our knowledge of insect genomes comes from Holometabolous species, which undergo the complete metamorphosis and have genomes under 2Gb with little signs of DNA methylation. In contrast, Hemiemetabolous insects undergo the ancestral incomplete metamorphosis and have larger genomes with high levels of DNA methylation. Hemimetabolous species from the Orthopteran order (grasshoppers and crickets) have some of the largest insect genomes. What drives the evolution of these unusual insect genome sizes, remains unknown. Here we report the sequencing, assembly and annotation of the 1.66-Gb genome of the Mediterranean field cricket Gryllus bimaculatus, and the annotation of the 1.60-Gb genome of the Hawaiian cricket Laupala kohalensis. We compare these two cricket genomes with those of 14 additional insects, and find evidence that hemimetabolous genomes expanded due to transposable element activity. Based on the ratio of observed to expected CpG sites, we find higher conservation and stronger purifying selection of methylated genes than non-methylated genes. Finally, our analysis suggests an expansion of the pickpocket class V gene family in crickets, which we speculate might play a role in the evolution of cricket courtship, including their characteristic chirping.

中文翻译：

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从基因组洞察昆虫的基因组进化

我们对昆虫基因组的大多数了解都来自全代谢物种，该物种经历了完全的变态，并且基因组在2Gb以下，几乎没有DNA甲基化的迹象。相反，半代谢昆虫经历了祖先不完全变态，并具有较大的基因组和较高的DNA甲基化水平。来自直翅目的半代谢物种（蚱s和）具有一些最大的昆虫基因组。导致这些异常昆虫基因组大小演变的原因仍然未知。在这里，我们报告了地中海田G Gryllus bimaculatus的1.66-Gb基因组的测序，组装和注释，以及夏威夷Laupala kohalensis的1.60-Gb基因组的注释。。我们将这两种的基因组与其他14种昆虫的基因组进行了比较，发现有证据表明半代谢基因组因转座因子的活性而扩展。基于观察到的CpG位点与预期CpG位点的比率，我们发现甲基化基因比非甲基化基因具有更高的保守性和更强的纯化选择。最后，我们的分析表明the中的扒手V类基因家族有所扩展，我们推测这可能在of求爱的演变中起作用，包括including的特征性chi声。