mitochondrial genomes

Total genomic DNA was extracted using the Ezup Column Animal Genomic DNA Extraction Kit (B518251; Sangon Biotech, Shanghai, China) according to its instruction. A second-generation sequencing library was constructed for each sample with a starting DNA material of 300-1000 ng according to Meyer and Kircher and Li et al. Briefly, the DNA samples were sheared to about 250 bp using a Covaris M220 ultrasonicator (Covaris, Inc., MA, USA). The fragmented DNA samples were checked using electrophoresis with a 1.5% agarose gel. The library construction process include end repair, ligation and fillin Meyer and Kircher (2010) and Li et al. (Li et al. 2013). After amplification, the library products of all samples were mixed in equimolar, and DNA fragments larger than 1 kb were removed by gel extration. The recovered samples were sequenced on an Illumina HiSeq platform with 2x150 paired-end configuation at Genewiz (Suzhou, China).采用Ezup柱式动物基因组DNA提取试剂盒（Ezup Column Animal Genomic DNA Extraction Kit，货号B518251；上海生工生物工程股份有限公司，Sangon Biotech，中国上海），严格依照产品说明书提取总基因组DNA。参照Meyer与Kircher以及Li等团队的实验方法，以300~1000 ng的起始DNA投入量为基准，为每个样本构建第二代测序（second-generation sequencing）文库。具体操作如下：首先使用Covaris M220超声波破碎仪（Covaris, Inc., 美国马萨诸塞州科瓦里斯公司）将DNA样本破碎至约250 bp；随后采用1.5%琼脂糖凝胶电泳对破碎后的DNA样本进行质检。文库构建流程涵盖末端修复、接头连接与末端补平步骤，具体方法参照Meyer和Kircher（2010）以及Li等（2013）的公开报道。扩增完成后，将所有样本的文库产物按摩尔浓度等量混合，并通过凝胶切胶回收去除长度大于1 kb的DNA片段。回收所得的样本委托苏州金唯智生物科技有限公司（Genewiz，中国苏州）在Illumina HiSeq测序平台上，采用2×150 bp双端测序配置完成测序。