The complete mitochondrial genome of the Parathyma sulpitia （Lepidoptera, Nymphalidae, Limenitidinae） was determined. The entire mitochondrial DNA （mtDNA） molecule was 15 268 bp in size. Its gene content and organization were the same as those of other lepidopteran species, except for the presence of the 121 bp long intergenic spacer between trnSI（AGN）and trnE. The 13 protein-coding genes （PCGs） started with the typical ATN codon, with the exception of the coxl gene that used CGA as its initial codon. In addition, all protein-coding genes terminated at the common stop codon TAA, except the nad4 gene which used a single T as its terminating codon. All 22 tRNA genes possessed the typical clover leaf secondary structure except for trnSI（AGN）, which had a simple loop with the absence of the DHU stem. Excluding the A＋T-rich region, the mtDNA genome of P. sulpitia harbored 11 intergenic spacers, the longest of which was 121 bp long with the highest A＋T content （100%）, located between trnSI（AGN） and trnE. As in other lepidopteran species, there was an 18-bp poly-T stretch at the 3＇-end of the A＋T-rich region, and there were a few short microsatellite-like repeat regions without conspicuous macro-repeats in the A＋T-rich region. The phylogenetic analyses of the published complete mt genomes from nine Nymphalidae species were conducted using the concatenated sequences of 13 PCGs with maximum likelihood and Bayesian inference methods. The results indicated that Limenitidinae was a sister to the Heliconiinae among the main Nymphalidae lineages in this study, strongly supporting the results of previous molecular data, while contradicting speculations based on morphological characters.
谱系年代学是结合化石记录和分子钟方法计算"生命树"(Tree of Life)上各分歧点时间的一个新兴交叉学术领域。由于化石记录的不完整性,各类生物的起源年代和支系分化时间的确定可借助于部分化石记录和通过计算现生生物类群之间的遗传距离转换得出的相对分歧时间相结合的办法进行讨论。化石记录可代表部分生物类群起源时间的保守估计值,而分子钟方法可为那些不易保存为化石的生物类群与其姊妹群的分化时间提供依据。如果使用得当的话,两者可进行相互验证。在分子谱系年代分析中,正确使用化石校准方案是获得准确分歧时间的关键,这需要:1)正确确定化石物种在谱系树上的位置;2)正确解释化石记录所代表的时间含义(最小值、确定值、最大值及其标准差)。分子钟估算分歧时间的技术在不断改进,目前常用的分子分歧时间估算法(宽松分子钟法,如贝叶斯法、补偿性似然法等)包容分子演化速率在谱系间和随时间的变化。随着谱系年代研究的不断深入,长期困扰人们的化石记录时间与分子钟计算结果悬殊的问题正在逐渐趋于和谐并得到正确诠释。文中还讨论了有关动物起源与早期分化时间以及早期陆生节肢动物的谱系年代学研究进展。我们强调,化石记录和分子钟分析可以优势互补,两者的整合无疑将提高生物演化历史时间格架的准确度和精度,以利更好地将生命演化事件置于地球系统科学及地球环境演化史之中。
