Department of Integrative Marine Ecology, Stazione Zoologica Anton Dohrn, Villa Comunale, Napoli 80121, Italy.
Department of Integrative Marine Ecology, Stazione Zoologica Anton Dohrn, Villa Comunale, Napoli 80121, Italy.
Mol Phylogenet Evol. 2019 Nov;140:106575. doi: 10.1016/j.ympev.2019.106575. Epub 2019 Jul 27.
The diatom family Chaetocerotaceae (Bacillariophyta) is common in the marine plankton worldwide, especially in coastal areas and upwelling zones. Its defining character constitutes hollow processes, called setae, which emerge from the valves of the vegetative cells. The family comprises two extant genera: Bacteriastrum and Chaetoceros. Current systematics is based on morphological features of vegetative cells and resting spores and is summarised in a classification scheme subdividing Bacteriastrum in two sections, Isomorpha and Sagittata, and Chaetoceros in three subgenera: Hyalochaete, Chaetoceros (Phaeoceros) and Bacteriastroidea, and further into 22 sections. Phylogenies inferred from single molecular markers (18S and partial 28S rDNA) show only partial topological agreement and many poorly or unresolved basal ramifications. Since classification should not only satisfy practical needs but also reflect well-supported evolutionary relationships of the taxa under investigation, we inferred a multigene phylogeny of the family Chaetocerotaceae amplifying five genes of 100 strains encompassing six Bacteriastrum and 60 Chaetoceros species. We also compared the phylogenetic signal of nuclear, plastid and mitochondrial compartments to ascertain if the inferred tree topologies were congruent. Our results provided a robust multigene phylogeny of the family Chaetocerotaceae, offering a solid framework to test the validity of the traditional taxonomical classification. The genera Bacteriastrum and Chaetoceros were resolved as sister clades, whilst the subgenus Hyalochaete was found to be paraphyletic. Consequently, we rejected the subdivision in subgenera and only considered sections. Most of the already recognised sections were found to be monophyletic. We emended one section, rejected seven and erected three new ones. As a consequence of our proposed changes, all the sections investigated are supported by morphological and molecular characters alike. Thus, a natural classification is feasible for this important and very diverse marine planktonic family.
甲藻科（Bacillariophyta）是一种常见的海洋浮游生物，分布广泛，尤其是在沿海地区和上升流区域。其特征是具有中空的突起，称为刚毛，从营养细胞的壳面伸出。该科包括两个现生属：杆形藻属（Bacteriastrum）和角毛藻属（Chaetoceros）。目前的系统分类基于营养细胞和休眠孢子的形态特征，并总结在一个分类方案中，该方案将杆形藻属分为两个节，即等形节和箭形节，角毛藻属分为三个亚属：脆杆藻亚属（Hyalochaete）、角毛藻亚属（Phaeoceros）和杆形藻亚属（Bacteriastroidea），并进一步分为 22 个节。基于单一分子标记（18S 和部分 28S rDNA）推断的系统发育关系仅在拓扑上部分一致，并且许多分支关系较差或未解决。由于分类不仅应满足实际需要，还应反映所研究分类群的良好支持的进化关系，因此我们扩增了来自 100 株菌的 5 个基因（6 个杆形藻属和 60 个角毛藻属物种），推断了甲藻科的多基因系统发育关系。我们还比较了核、质体和线粒体区室的系统发育信号，以确定推断的树拓扑结构是否一致。我们的结果提供了一个强大的甲藻科多基因系统发育关系，为测试传统分类学分类的有效性提供了一个坚实的框架。杆形藻属和角毛藻属被解析为姐妹群，而脆杆藻亚属被发现为并系群。因此，我们拒绝了亚属的划分，仅考虑节。已经识别的大多数节都被发现是单系的。我们修正了一个节，拒绝了七个节，并建立了三个新节。由于我们提出的变化，所有调查的节都得到了形态和分子特征的支持。因此，对于这个重要且非常多样化的海洋浮游生物科，可以采用自然分类法。
