Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210046, China.
Gene. 2012 Aug 15;505(1):57-65. doi: 10.1016/j.gene.2012.05.049. Epub 2012 Jun 1.
Myriapods are among the earliest arthropods and may have evolved to become part of the terrestrial biota more than 400 million years ago. A noticeable lack of mitochondrial genome data from Pauropoda hampers phylogenetic and evolutionary studies within the subphylum Myriapoda. We sequenced the first complete mitochondrial genome of a microscopic pauropod, Pauropus longiramus (Arthropoda: Myriapoda), and conducted comprehensive mitogenomic analyses across the Myriapoda. The pauropod mitochondrial genome is a circular molecule of 14,487 bp long and contains the entire set of thirty-seven genes. Frequent intergenic overlaps occurred between adjacent tRNAs, and between tRNA and protein-coding genes. This is the first example of a mitochondrial genome with multiple intergenic overlaps and reveals a strategy for arthropods to effectively compact the mitochondrial genome by overlapping and truncating tRNA genes with neighbor genes, instead of only truncating tRNAs. Phylogenetic analyses based on protein-coding genes provide strong evidence that the sister group of Pauropoda is Symphyla. Additionally, approximately unbiased (AU) tests strongly support the Progoneata and confirm the basal position of Chilopoda in Myriapoda. This study provides an estimation of myriapod origins around 555 Ma (95% CI: 444-704 Ma) and this date is comparable with that of the Cambrian explosion and candidate myriapod-like fossils. A new time-scale suggests that deep radiations during early myriapod diversification occurred at least three times, not once as previously proposed. A Carboniferous origin of pauropods is congruent with the idea that these taxa are derived, rather than basal, progoneatans.
多足动物是最早的节肢动物之一，可能在 4 亿多年前就进化成为陆地生物群的一部分。由于缺少来自倍足纲的线粒体基因组数据，这阻碍了在多足亚门内进行系统发育和进化研究。我们对一种微小的倍足纲动物——长足长足虫（节肢动物：多足动物）进行了首次完整的线粒体基因组测序，并对多足动物的整个线粒体基因组进行了综合分析。倍足纲的线粒体基因组是一个 14487bp 的圆形分子，包含了所有 37 个基因。相邻的 tRNA 之间以及 tRNA 和蛋白质编码基因之间经常发生基因间重叠。这是第一个具有多个基因间重叠的线粒体基因组的例子，揭示了节肢动物通过重叠和截断与相邻基因的 tRNA 基因，而不是仅截断 tRNA，从而有效地压缩线粒体基因组的策略。基于蛋白质编码基因的系统发育分析为倍足纲的姐妹群是唇足纲提供了强有力的证据。此外，无偏估计（AU）检验强烈支持原气管亚门，并确认了在多足动物中，唇足纲的基部位置。本研究提供了多足动物起源于大约 5.55 亿年前（95%置信区间：4.44-7.04 百万年前）的估计，这个日期与寒武纪大爆发和候选多足类化石的日期相当。一个新的时间尺度表明，早期多足动物多样化的深层辐射至少发生了三次，而不是像以前提出的那样只有一次。倍足纲的石炭纪起源与这些类群是衍生的，而不是基干的原气管亚门的观点一致。
