并基角毛藻若干分类学疑问的初步探讨

并基角毛藻是硅藻门角毛藻属的典型种类, 以“相邻角毛基部并行融合”作为标志性特征, 但该特征是否稳定, 及如何赋予其分类学价值?尚存较多争议。研究以符合现存并基角毛藻分类标准的藻株作为目标藻株, 采用毛细管显微操作技术从我国沿海代表水域分离藻株, 建立了目标藻株的单克隆培养株系, 利用光学显微镜、扫描电镜和透射电镜分别对其形态学特征进行观察, 同时还扩增了核糖体大亚基编码基因的D1-D3区序列, 并构建系统进化树。综合分析形态学特征和分子系统学数据, 初步得到以下结论: (1)具有相同遗传特征的并基角毛藻株系在“相邻角毛基部并行融合”特征上具有不稳定性, 即“相邻角毛基部并行融合”不能作为并基角毛藻种类的标志性特征; (2)并基角毛藻和洛氏角毛藻作为相似种类, 均显示出较高的物种多样性, 高于目前的认知, 预示着或许存在隐形种或拟隐形种; (3)推测并基角毛藻单胞变型只是并基角毛藻原种的一个生活史阶段, 是并基角毛藻的同种异名, 不宜继续保留其独立的分类学地位。

PRELIMINARY STUDY ON SOME TAXONOMIC PUZZLES OF CHAETOCEROS DECIPIENS CLEVE

As one of the largest marine planktonic diatom genera,Chaetoceros Ehrenberg has a very wide biogeographi-cal distribution from polar to tropical waters.C. decipiens Cleve is a representative species of the genusChaetoceros characterized by the regular chains and stiff setae. The fusing part on the sibling setae bases was the unique characters forC. decipiens in the present taxonomy system that mainly built on morphology, which has been accepted and used by some diatom taxonomists. However, some other researchers hold different opinion, in which the fusing on the sibling setae bases was a variable morphological structure that could not give much significant taxonomic value. Meanwhile, some questions remain about the taxonomic position of the intraspecific units ofC. decipiens, which is difficult to an-swer whether these intraspecific units are independent taxonomic units or just a living stage of life cycle ofC. decipi-ens. To answer this question, the monoclonal stains and the combination of morphology features and molecular analy-sis will be required. To do this, several monoclonal strains were established from several Chinese representative sites using glass micropipette under invert microscopy according with the present taxonomic morphology ofC. decipiens. The morphology was studied by light microscopy, scanning electron microscopy and transmission electron microscopy. Meanwhile, the hypervariable region (D1-D3) of nucleic large subunit ribosomal rRNA encoding gene was amplified and sequenced as molecular evidence. The result indicated that the fusing of sibling setae base was not a steady struc-ture, which could not be considered as significant morphological feature for the accurate identification ofC. decipiens, and that some similar species without fusing of sibling setae base could be the trueC. decipiens. Moreover, according to the molecular phylogenetic analysis, high diversity was hidden in the morphologically-identifiedC. decipiens andC. lorenzianus, which might show the presence of cryptic and pseudo-cryptic species. Inaddition,C. decipiens f.singula-ris Gran was confirmed as a temporary stage of whole life cycle ofC. decipiens based on the continuous observation during cultures maintainance. Finally, they totally shared the same LSU sequences. Thus,C. decipiens f.singularis Gran was proposed as the synonym ofC. decipiens.