State Key Laboratory of Rice Biology, Zhejiang University, Hangzhou, China.
BMC Genomics. 2010 Jun 11;11:371. doi: 10.1186/1471-2164-11-371.
Animal mitochondrial genomes are potential models for molecular evolution and markers for phylogenetic and population studies. Previous research has shown interesting features in hymenopteran mitochondrial genomes. Here, we conducted a comparative study of mitochondrial genomes of the family Braconidae, one of the largest families of Hymenoptera, and assessed the utility of mitochondrial genomic data for phylogenetic inference at three different hierarchical levels, i.e., Braconidae, Hymenoptera, and Holometabola.
Seven mitochondrial genomes from seven subfamilies of Braconidae were sequenced. Three of the four sequenced A+T-rich regions are shown to be inverted. Furthermore, all species showed reversal of strand asymmetry, suggesting that inversion of the A+T-rich region might be a synapomorphy of the Braconidae. Gene rearrangement events occurred in all braconid species, but gene rearrangement rates were not taxonomically correlated. Most rearranged genes were tRNAs, except those of Cotesia vestalis, in which 13 protein-coding genes and 14 tRNA genes changed positions or/and directions through three kinds of gene rearrangement events. Remote inversion is posited to be the result of two independent recombination events. Evolutionary rates were lower in species of the cyclostome group than those of noncyclostomes. Phylogenetic analyses based on complete mitochondrial genomes and secondary structure of rrnS supported a sister-group relationship between Aphidiinae and cyclostomes. Many well accepted relationships within Hymenoptera, such as paraphyly of Symphyta and Evaniomorpha, a sister-group relationship between Orussoidea and Apocrita, and monophyly of Proctotrupomorpha, Ichneumonoidea and Aculeata were robustly confirmed. New hypotheses, such as a sister-group relationship between Evanioidea and Aculeata, were generated. Among holometabolous insects, Hymenoptera was shown to be the sister to all other orders. Mecoptera was recovered as the sister-group of Diptera. Neuropterida (Neuroptera + Megaloptera), and a sister-group relationship with (Diptera + Mecoptera) were supported across all analyses.
Our comparative studies indicate that mitochondrial genomes are a useful phylogenetic tool at the ordinal level within Holometabola, at the superfamily within Hymenoptera and at the subfamily level within Braconidae. Variation at all of these hierarchical levels suggests that the utility of mitochondrial genomes is likely to be a valuable tool for systematics in other groups of arthropods.
动物线粒体基因组是分子进化的潜在模型，也是系统发育和种群研究的分子标记。先前的研究表明膜翅目昆虫的线粒体基因组具有有趣的特征。在这里，我们对膜翅目最大的科之一的 Braconidae 科的线粒体基因组进行了比较研究，并评估了线粒体基因组数据在三个不同层次的系统发育推断中的实用性，即 Braconidae 科、膜翅目和全变态目。
从 Braconidae 的七个亚科中测序了七个线粒体基因组。已显示出四个测序的 A+T 丰富区中的三个发生了反转。此外，所有物种均显示出链不对称性的逆转，表明 A+T 丰富区的反转可能是 Braconidae 的一个 synapomorphy。所有 Braconid 物种都发生了基因重排事件，但基因重排率与分类无关。大多数重排的基因是 tRNA，除了 Cotesia vestalis 中的 13 个蛋白质编码基因和 14 个 tRNA 基因通过三种基因重排事件改变了位置或/和方向。远程反转被假定为两个独立的重组事件的结果。环口组的物种进化速度低于非环口组的物种。基于完整的线粒体基因组和 rrnS 的二级结构的系统发育分析支持 Aphidiinae 和环口组之间的姐妹群关系。膜翅目内许多被广泛接受的关系，例如 Symphyta 的并系和 Evaniomorpha 的姐妹群关系、Orussoidea 和 Apocrita 的姐妹群关系以及 Proctotrupomorpha、Ichneumonoidea 和 Aculeata 的单系性都得到了稳健的证实。生成了新的假说，例如 Evanioidea 和 Aculeata 之间的姐妹群关系。在完全变态的昆虫中，膜翅目被认为是所有其他目的姐妹群。长翅目被回收为双翅目和鞘翅目的姐妹群。所有分析均支持神经翅目（神经翅目+巨翅目）和与（双翅目+长翅目）的姐妹群关系。
我们的比较研究表明，线粒体基因组在完全变态目中是一个有用的系统发育工具，在膜翅目超级科中是一个有用的系统发育工具，在 Braconidae 科中是一个有用的系统发育工具。在所有这些层次上的变异性表明，线粒体基因组的实用性可能是节肢动物其他类群系统发育的一个有价值的工具。
