CAS Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Science, Guangzhou, China.
PLoS One. 2013 Aug 19;8(8):e71346. doi: 10.1371/journal.pone.0071346. eCollection 2013.
Traditionally Cocholodinium and Gymnodinium sensu lato clade are distinguished based on the cingulum turn number, which has been increasingly recognized to be inadequate for Gymnodiniales genus classification. This has been improved by the combination of the apical groove characteristics and molecular phylogeny, which has led to the erection of several new genera (Takayama, Akashiwo, Karenia, and Karlodinium). Taking the apical groove characteristics and molecular phylogeny combined approach, we reexamined the historically taxonomically uncertain species Cochlodinium geminatum that formed massive blooms in Pearl River Estuary, China, in recent years. Samples were collected from a bloom in 2011 for morphological, characteristic pigment, and molecular analyses. We found that the cingulum in this species wraps around the cell body about 1.2 turns on average but can appear under the light microscopy to be >1.5 turns after the cells have been preserved. The shape of its apical groove, however, was stably an open-ended anticlockwise loop of kidney bean shape, similar to that of Polykrikos. Furthermore, the molecular phylogenetic analysis using 18S rRNA-ITS-28S rRNA gene cistron we obtained in this study also consistently placed this species closest to Polykrikos within the Gymnodinium sensu stricto clade and set it far separated from the clade of Cochlodinium. These results suggest that this species should be transferred to Polykrikos as Polykrikos geminatum. Our results reiterate the need to use the combination of apical groove morphology and molecular phylogeny for the classification of species within the genus of Cochlodinium and other Gymnodiniales lineages.
传统上，Cochlodinium 和 Gymnodinium sensu lato 分支是基于顶环转弯数来区分的，而这一方法已逐渐被认为不足以用于 Gymnodiniales 属的分类。这一方法通过结合顶环特征和分子系统发育得到了改进，从而建立了几个新属（Takayama、Akashiwo、Karenia 和 Karlodinium）。我们采用顶环特征和分子系统发育相结合的方法，重新研究了近年来在中国珠江口形成大规模水华的历史上分类不确定的物种 Cochlodinium geminatum。从 2011 年的一次水华事件中采集了样本，进行了形态学、特征色素和分子分析。我们发现，该物种的顶环平均环绕细胞体约 1.2 圈，但在细胞保存后，在光镜下可能会出现>1.5 圈的情况。然而，它的顶环形状稳定为开放式逆时针环，形状为肾形，类似于 Polykrikos。此外，我们在这项研究中使用 18S rRNA-ITS-28S rRNA 基因顺式获得的分子系统发育分析也一致表明，该物种在 Gymnodinium sensu stricto 分支中与 Polykrikos 最接近，并与 Cochlodinium 分支分离较远。这些结果表明，该物种应被转移到 Polykrikos 中，成为 Polykrikos geminatum。我们的研究结果再次强调，在 Cochlodinium 属和其他 Gymnodiniales 谱系的物种分类中，需要结合顶环形态和分子系统发育。
