Rapid Evolution of the Mitochondrial Genome in Chalcidoid Wasps (Hymenoptera: Chalcidoidea) Driven by Parasitic Lifestyles

Among the Chalcidoids, hymenopteran parasitic wasps that have diversified lifestyles, a partial mitochondrial genome has been reported only from Nasonia. This genome had many unusual features, especially a dramatic reorganization and a high rate of evolution. Comparisons based on more mitochondrial genomic data from the same superfamily were required to reveal weather these unusual features are peculiar to Nasonia or not. In the present study, we sequenced the nearly complete mitochondrial genomes from the species Philotrypesis. pilosa and Philotrypesis sp., both of which were associated with Ficus hispida. The acquired data included all of the protein-coding genes, rRNAs, and most of the tRNAs, and in P. pilosa the control region. High levels of nucleotide divergence separated the two species. A comparison of all available hymenopteran mitochondrial genomes (including a submitted partial genome from Ceratosolen solmsi) revealed that the Chalcidoids had dramatic mitochondrial gene rearrangments, involved not only the tRNAs, but also several protein-coding genes. The AT-rich control region was translocated and inverted in Philotrypesis. The mitochondrial genomes also exhibited rapid rates of evolution involving elevated nonsynonymous mutations.

小蜂总科（Chalcidoids）是一类生活史多样的膜翅目寄生蜂，此前仅在纳森小蜂属（Nasonia）中报道过其部分线粒体基因组。该基因组存在诸多异常特征，尤其是剧烈的基因重排与极高的进化速率。要明确这些异常特征是否仅为纳森小蜂属所特有，需要基于同总科更多线粒体基因组数据开展比较分析。
本研究中，我们对两种与粗叶榕（Ficus hispida）共生的榕小蜂——毛体榕小蜂（Philotrypesis pilosa）以及未定名榕小蜂（Philotrypesis sp.）的近乎完整线粒体基因组进行了测序。所得基因组数据涵盖全部蛋白编码基因、核糖体RNA（rRNA）以及大部分转运RNA（tRNA），其中毛体榕小蜂的基因组还包含了控制区。两个物种间存在显著的核苷酸序列分化。
对所有已公开的膜翅目线粒体基因组（包括已提交的榕果小蜂（Ceratosolen solmsi）部分线粒体基因组）进行比较后发现，小蜂总科存在剧烈的线粒体基因重排现象，该重排不仅涉及转运RNA，还包含数个蛋白编码基因。
在榕小蜂属（Philotrypesis）类群中，富含AT碱基的控制区发生了易位与倒位。该类群的线粒体基因组同时展现出快速的进化速率，伴随非同义突变（nonsynonymous mutation）水平的显著升高。