Population structure and recruitment mechanism of Muraenesox cinereus leptocephali using otolith microsturucture and mitochondrial DNA sequences

根据1999年和2000年在宫崎县野冈县、熊本县矢津村县、广岛县尾道县、神奈川县镰仓县和后户群岛（东海）采集的细头鲸矢状耳石的生长增量，研究了Muraenesox cinereus的生长历史和招募情况。增量形成的周期性是通过用茜素络合物治疗头跖骨并在一段时间后检查耳石来证实的。细头期耳石增量的形成节律约为0.13/d，变质期为0.5/d，幼期为1/d。耳石检查表明，在Nobeoka湾招募的头鲸分为两个年龄组，150-200天和250-300天。回归计算的孵化日期分布在全年大部分时间，夏季和冬季为孵化高峰。我们测定了包含细胞色素b基因部分至控制区域前半部分的线粒体DNA序列，以评估该物种的种群结构。从野冈、矢津hiro、镰仓和东海的标本中，共测序了591个核苷酸位点，其中细胞色素b基因位于控制区的前半部分。在对照区396个核苷酸位点中，发现31个（7.8%）可变，16个单倍型。核苷酸序列差异在0.25 ~ 4.55%之间，平均差异为1.88%，表明该物种线粒体DNA控制区具有高变异性的特点。用邻接法构建的系统发育树没有显示出明显的地理聚类。这一结果表明，目前的标本可能来自一个单一的种群。

The growth history and recruitment of Muraenesox cinereus were studied, based on growth increments in sagittal otoliths of leptocephali collected from Nobeoka (Miyazaki Pref.), Yatsushiro (Kumamoto Pref.), Onomichi (Hlroshima Pref.), Kamakura (Kanagawa Pref.) and off Goto Islands (East China Sea) in 1999 and in 2000. The periodicity of increment formation was confirmed by treating leptocephali with alizarin complexon and examining otoliths after a known time period. The formation rhythm of otolith increment was about 0.13/day in leptocephalus stage, 0.5/day in metamorphic stage and 1/day in juvenile stage, respectively. Examination of otoliths showed that leptocephali recruiting to Nobeoka Bay devided into two age groups, 150-200 and 250-300 days old. Back calculated hatching dates were distributed throughout most of the year, with a peak in summer and winter.Mitochondrial DNA sequences that include a part of the cytochrome b gene to the first half of the control region of Muraenesox cinereus leptocephali were determined to evaluate the population structure of the species. A total of 591 nucleotide site, including cytochrome b gene to the first half of the control region, was sequenced from specimens from Nobeoka, Yatsushiro, Kamakura and East China Sea. Out of 396 nucleotide sites on the control region, 31 (7.8%) variable, 16 haplotypes being found. Differences between nucleotide sequences ranged between 0.25 and 4.55% with average of 1.88%, indicating that the control region of the mitochondrial DNA in the species is characterized be high variability. The phylogenetic tree constructed by the neighbor-joining method shows neither significant geographic clusters. This result indicate that the present specimen might come from a single population.