Species diversity and geographical distribution of the Chaetoceros lorenzianus complex along the coast of China

doi:10.17520/biods.2018261

Abstract

Abstract:

The Chaetoceros lorenzianus complex is composed of several planktonic diatom species that share a similar morphology with C. lorenzianus Grunow. The complex has been recorded frequently in coastal waters across the world. Recently, new taxonomic information has enriched the known species diversity of the complex from 3 to 7 taxa. However, the identities of many species comprising the complex in China is still unclear. To clarify the species diversity and provide solid identification criteria for further studies, 332 monoclonal strains belonging to the C. lorenzianus complex were collected from the coast of China. With light microscopy and scanning and transmission electron microscopy, the morphologies of vegetative cells and resting spores were observed. Hypervariable D1-D3 regions of nuclear large subunit ribosomal encoded genes were amplified to construct the phylogenetic relationship. Morphological clustering was consistent with molecular systematics, which indicated that a total of 5 species are present within the C. lorenzianus complex along the coast of China; C. decipiens, C. elegans, C. laevisporus, C. mannaii and C. pauciramosus. The ultrastructure on setae, such as the shape, size and density of the setae pores, can be used as distinguishing features among allied taxa. The morphology of the resting spores also aid in accurate identification. The previous reports identifying the taxa within the C. lorenzianus complex in China need to be reexamined. Chaetoceros decipiens and C. laevisporus are the most widespread taxa along the coast of China, whereas C. pauciramosus has the narrowest distribution, having only been recorded in Taishan and Zhuhai of the Guangdong Province.

http://jtp.cnki.net/bilingual/detail/html/SWDY201902006

Key words: Chaetoceros lorenzianus complex, species diversity, morphology, molecular phylogeny, resting spore, coast of China

Chen Zuoyi, Xu Xiaojing, Zhu Suying, Zhai Mengyi, Li Yang. Species diversity and geographical distribution of the Chaetoceros lorenzianus complex along the coast of China[J]. Biodiv Sci, 2019, 27(2): 149-158.

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URL: https://www.biodiversity-science.net/EN/10.17520/biods.2018261

https://www.biodiversity-science.net/EN/Y2019/V27/I2/149

Figures/Tables 9

Fig. 1 Sampling sites and geographical distribution of the Chaetoceros lorenzianus complex along the coast of China. 〇, Sampling sites; A, Bohai Sea; B, Shandong coast; C, Zhejiang coast; D, Taiwan Strait; E, Guangdong coast; F, Hainan coast.

Fig. 2 Morphology of Chaetoceros decipiens under light microscopy (LM) (A, E), scanning electron microscopy (SEM) (B-D, F, G) and transmission electron microscopy (TEM) (H-J). A-B, Broad girdle views showing fusing sibling setae base present (B, arrowheads) and not (A, arrowheads); C, Internal view of intercalary valve; D, Terminal valve with rimoportula (arrowhead) and U-shaped terminal setae; E-G, Structure of setae; H, Terminal valve with rimoportula (arrow); I, Mantle; J, Girdle bands. Scale bars, 20 μm (A), 10 μm (B, D, E), 6 μm (C), 5 μm (H), 2 μm (F, G, J), 1 μm (I).

Fig. 3 Morphology of Chaetoceros elegans under light microscopy (LM) (A-B), scanning electron microscopy (SEM) (C-D, I-J) and transmission electron microscopy (TEM) (E-H). A, Chain in broad girdle view; B, Resting spores within the mother cells of a chain; C, Sibling intercalary valves showing overlapping silica ear-like structures (arrowhead); D, Released resting spore. E, Terminal valve with external process of rimoportula (arrowhead) and fringe (arrow); F, Parallel rows of poroids on the mantle; G, Central annulus (arrow) on terminal valve; H, Girdle bands; I and J, Seta structure. Scale bars, 20 μm (A, B), 6 μm (D), 4 μm (C), 2 μm (E, F, G, H, I, J).

Fig. 4 Morphology of Chaetoceros laevisporus under light microscopy (LM) (A-B), scanning electron microscopy (SEM) (C-E, I-J) and transmission electron microscopy (TEM) (F-H). A, Chain in broad girdle view; B, Resting spores within the mother cells of a chain; C, Sibling intercalary valves showing overlapping silica wings (broad arrow), silica ridges (arrowhead) and furrow above the basal ring of mantle (arrow); D, A released resting spore; E, Terminal valve with central processes (arrowhead) and silica rib (arrows); F, Mantle; G, Intercalary valve with central annulus (arrow); H, Girdle bands; I and J, Setae structure. Scale bars, 50 μm (A), 20 μm (B), 4 μm (C, E), 2 μm (D, F, G, H, I, J).

Fig. 5 Morphology of Chaetoceros mannaii under light microscopy (LM) (A, I), scanning electron microscopy (SEM) (B-E, J) and transmission electron microscopy (TEM) (F-H). A, Chain in broad girdle view; B, Sibling intercalary valves showing aperture; C, Terminal valve view with external process of rimoportula (arrowhead); D, Intercalary cells with overlapping silica wings (broad arrow), silica ridges (arrowhead) and furrow above the basal ring of mantle (arrow); E, F, Internal view of an intercalary valves, showing central annulus (F, arrow); G, Mantle; H, Girdle bands; I and J: Setae structure. Scale bars, 50 μm (A), 10 μm (B, D, I), 5 μm (F), 4 μm (C, E, J), 2 μm (G, H).

Fig. 6 Morphology of Chaetoceros pauciramosus under light microscopy (LM) (A-B), scanning electron microscopy (SEM) (C-D, I-J) and transmission electron microscopy (TEM) (E-H). A, Chain in broad girdle view; B, Resting spores within the mother cells of a chain; C, Sibling intercalary valves showing overlapping silica ear-like structures (arrows) and furrow above the basal ring of mantle (arrowhead); D, Released resting spore; E, Terminal valve with short external tubes of rimoportulae (arrowhead) and silica rib (arrows); F, Mantle; G, Intercalary valve, showing central annulus (arrow); H, Girdle bands; I and J, Seta structure. Scale bars, 20 μm (A), 10 μm (D), 4 μm (C, D, E), 2 μm (F), 1 μm (G, H, I, J).

Fig. 7 Molecular phylogenetic tree inferred from LSU rDNA, with Chaetoceros diadema as outgroup. Supporting values on each nodule are from Bayesian and Maximum Likelihood analysis.

Table 1 Genetic distance among allied taxa within the Chaetoceros lorenzianus complex (data in the brackets are numbers of different base pairs)

	平孢角毛藻 C. laevisporus	密特拉角毛藻 C. mitra	曼纳角毛藻 C. mannaii	并基角毛藻 C. decipiens	优美角毛藻 C. elegans
密特拉角毛藻 C. mitra	0.081 (52)
曼纳角毛藻 C. mannaii	0.105 (69)	0.047 (33)
并基角毛藻 C. decipiens	0.089 (58)	0.028 (20)	0.057 (38)
优美角毛藻 C. elegans	0.083 (53)	0.036 (25)	0.067 (44)	0.027 (17)
稀树角毛藻 C. pauciramosus	0.092 (60)	0.040 (26)	0.059 (39)	0.028 (18)	0.028 (21)

Table 2 Morphological comparison among allied taxa within Chaetoceros lorenzianus complex

特征 Character	并基角毛藻 C. decipiens	优美角毛藻 C. elegans	平孢角毛藻 C. laevisporus	曼纳角毛藻 C. mannaii	稀树角毛藻 C. pauciramosus	密特拉角毛藻 C. mitra	洛氏角毛藻 C. lorenzianus type material
角毛孔纹形状 Seta poroid shape	椭圆形 Oval	水滴状 Drop-shaped	椭圆形 Oval	椭圆形 Oval	细长形 Elongated	圆形或椭圆形 Round or oval	圆形 Oval
角毛孔纹大小 Seta poroid size (μm)	0.3-0.6 (0.4 ± 0.1)	0.3-1.6 (0.7 ± 0.3)	0.3-0.9 (0.6 ± 0.1)	0.8-1.5 (1.1 ± 0.1)	0.1-0.6 (0.3 ± 0.1)	0.1-0.3 (0.2 ± 0.1)	Nd Nd
角毛孔纹密度 Seta poroid number in 10 μm	14-25 (20.2 ± 3.6)	6-27 (18.7 ± 5.0)	11-17 (14.1 ± 1.9)	6-10 (7.9 ± 1.0)	18-44 (31.7 ± 5.4)	30-56 (39.8 ± 7.4)	5-9 (7.2 ± 1.7)
Brunel 型 Brunel group	I I	I I	I I	I I	I I	II II	I I
角毛基部并行融合Fusion of seta bases	有或无 Present/absent	无 Absent	无 Absent	无 Absent	短或无 Short/absent	无 Absent	有 Present
休眠孢子 Resting spore	未发现 Unknown	有二叉分支 Two branching processes	壳面平滑 Smooth	未发现 Unknown	有二叉分支 Two branching processes	有二叉分支 Two branching processes	有二叉分支? Two branching processes?
窗孔形状 Aperture shape	椭圆形 Oval	圆形或四边形 Rounded or quadrangular	椭圆形 Oval	六边形 Hexagonal	六边形或花生形 Hexagonal or peanut shaped	六边形或花生形Hexagonal or peanut shaped	圆形或六边形 Oval or hexagonal
角毛基部 Basal part of setae	无 Lacking	有且明显 Distinct	无 Lacking	短 Short	短 Short	无 Lacking	无 Lacking
壳面及壳套孔纹 Poroids on valve face and mantle	有 Yes	有 Yes	无 No	无 No	有 Yes	无 No	nd nd

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