Conifers make up about one third of global forests but are threatened by seed parasitoid wasp species. Many of these wasps belong to the genus Megastigmus, yet little is known about their genomic background. In this study, we provide chromosome-level genome assemblies for two oligophagous conifer parasitoid species of Megastigmus, which represent the first two chromosome-level genomes of the genus. The assembled genomes of Megastigmus duclouxiana and M. sabinae are 878.48 Mb (scaffold N50 of 215.60 Mb) and 812.98 Mb (scaffold N50 of 139.16 Mb), respectively, which are larger than the genome size of most hymenopterans due to the expansion of transposable elements. Expanded gene families highlight the difference in sensory-related genes between the two species, reflecting the difference in their hosts. We further found that these two species have fewer family members but more single-gene duplications than polyphagous congeners in the gene families of ATP-binding cassette transporter (ABC), cytochrome P450 (P450) and olfactory receptors (OR). These findings shed light on the pattern of adaptation to a narrow spectrum of hosts in oligophagous parasitoids. Our findings suggest potential drivers underlying genome evolution and parasitism adaptation, and provide valuable resources for understanding the ecology, genetics and evolution of Megastigmus, as well as for the research and biological control of global conifer forest pests.

中文翻译：

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两种针叶树寄生蜂 Megastigmus duclouxiana 和 Megastigmus sabinae 的染色体水平从头基因组组装揭示了适应宿主的基因组印记

针叶树约占全球森林的三分之一，但受到种子寄生蜂物种的威胁。许多这些黄蜂属于巨柱属，但对其基因组背景知之甚少。在这项研究中，我们为Megastigmus的两种寡食性针叶树寄生蜂提供了染色体水平的基因组组装，它们代表了该属的前两个染色体水平基因组。Megastigmus duclouxiana和M. sabinae的组装基因组分别为 878.48 Mb（支架 N50 为 215.60 Mb）和 812.98 Mb（支架 N50 为 139.16 Mb），由于转座因子的扩展，它们比大多数膜翅目动物的基因组大小都大。扩展的基因家族突出了两个物种之间感官相关基因的差异，反映了它们宿主的差异。我们进一步发现，这两个物种在 ATP 结合盒转运蛋白 (ABC)、细胞色素 P450 (P450) 和嗅觉受体 (OR) 基因家族中的家族成员较少，但单基因重复比杂食性同系物多。这些发现揭示了寡食寄生蜂适应窄谱宿主的模式。我们的研究结果揭示了基因组进化和寄生适应的潜在驱动因素，并为了解生态学提供了宝贵的资源，Megastigmus，以及全球针叶林害虫的研究和生物防治。