Department of Zoology, University of Oxford, The Tinbergen Building, South Parks Road, Oxford, OX1 3PS, UK.
BMC Genomics. 2009 Dec 14;10:603. doi: 10.1186/1471-2164-10-603.
Strepsiptera are an unusual group of sexually dimorphic, entomophagous parasitoids whose evolutionary origins remain elusive. The lineage leading to Mengenilla australiensis (Family Mengenillidae) is the sister group to all remaining extant strepsipterans. It is unique in that members of this family have retained a less derived condition, where females are free-living from pupation onwards, and are structurally much less simplified. We sequenced almost the entire mitochondrial genome of M. australiensis as an important comparative data point to the already available genome of its distant relative Xenos vesparum (Family Xenidae). This study represents the first in-depth comparative mitochondrial genomic analysis of Strepsiptera.
The partial genome of M. australiensis is presented as a 13421 bp fragment, across which all 13 protein-coding genes (PCGs), 2 ribosomal RNA (rRNA) genes and 18 transfer RNA (tRNA) sequences are identified. Two tRNA translocations disrupt an otherwise ancestral insect mitochondrial genome order. A+T content is measured at 84.3%, C-content is also very skewed. Compared with M. australiensis, codon bias in X. vesparum is more balanced. Interestingly, the size of the protein coding genome is truncated in both strepsipterans, especially in X. vesparum which, uniquely, has 4.3% fewer amino acids than the average holometabolan complement. A revised assessment of mitochondrial rRNA secondary structure based on comparative structural considerations is presented for M. australiensis and X. vesparum.
The mitochondrial genome of X. vesparum has undergone a series of alterations which are probably related to an extremely derived lifestyle. Although M. australiensis shares some of these attributes; it has retained greater signal from the hypothetical most recent common ancestor (MRCA) of Strepsiptera, inviting the possibility that a shift in the mitochondrial selective environment might be related to the specialization accompanying the evolution of a small, morphologically simplified completely host-dependent lifestyle. These results provide useful insights into the nature of the evolutionary transitions that accompanied the emergence of Strepsiptera, but we emphasize the need for adequate sampling across the order in future investigations concerning the extraordinary developmental and evolutionary origins of this group.
双翅目是一组性二态的、食虫寄生的昆虫，其进化起源仍难以捉摸。导致 Mengenilla australiensis（Mengenillidae 科）的谱系是所有现存的双翅目昆虫的姊妹群。它的独特之处在于，这个家族的成员保留了一种不太发达的状态，即雌性从蛹化开始就是自由生活的，并且在结构上简化得更少。我们对 M. australiensis 的几乎整个线粒体基因组进行了测序，作为对其远亲 Xenidae 科的 Xenos vesparum 已有基因组的重要比较数据点。这项研究代表了对双翅目进行的首次深入比较线粒体基因组分析。
M. australiensis 的部分基因组呈现为 13421 bp 片段，其中鉴定出所有 13 个蛋白质编码基因（PCGs）、2 个核糖体 RNA（rRNA）基因和 18 个转移 RNA（tRNA）序列。两个 tRNA 易位破坏了原本的昆虫线粒体基因组排列。A+T 含量为 84.3%，C 含量也非常偏斜。与 M. australiensis 相比，X. vesparum 的密码子偏好性更平衡。有趣的是，双翅目昆虫的蛋白质编码基因组大小都被截断，尤其是 X. vesparum，它的氨基酸数量比平均的完全变态动物少 4.3%。根据比较结构考虑，提出了一种针对 M. australiensis 和 X. vesparum 的线粒体 rRNA 二级结构的修订评估。
X. vesparum 的线粒体基因组经历了一系列的改变，这些改变可能与一种极其特化的生活方式有关。尽管 M. australiensis 具有一些这些特征，但它保留了更多来自双翅目假想的最近共同祖先（MRCA）的信号，这使得线粒体选择环境的变化可能与伴随小而形态简化的完全依赖宿主的生活方式的进化而来的特化有关。这些结果为双翅目出现时所伴随的进化转变的性质提供了有用的见解，但我们强调，在未来的研究中，需要在该目中进行充分的采样，以了解这个群体非凡的发育和进化起源。
