我国沿海双唇形突海链藻的形态学研究

唇形突是海链藻中常见的一类突起, 其形态学特征和排列方式是重要的分类学依据。绝大多数海链藻只有一个唇形突, 两个唇形突的现象仅报道于极少数海链藻种类。我国关于双唇形突海链藻的报道较少。研究利用扫描电镜(SEM)技术, 对采自我国沿海海域的自然水样, 以及分离获得的单克隆培养藻株进行了形态学观察, 针对其中的海链藻属Thalassiosira Cleve种类开展了形态学的专题研究。报道了4个具有双唇形突的海链藻种类, 分别是有翼海链藻T. bipartita (Rattray) Hallegraeff、脆弱海链藻T. fragilis Fryxell、亨氏海链藻T. hendeyi Hasle &; Fryxell和维斯吉思海链藻T. visurgis Hustedt, 其中有3个为我国新记录种类: 脆弱海链藻、亨氏海链藻和维斯吉思海链藻。对每个种类的形态学特征、生活习性和生态分布进行了描述, 提供了扫描电镜照片, 对相似种类的形态学特征进行了比较研究, 分析了唇形突的变化类型及其分类学价值。     

采自广东大亚湾水域的海链藻属一新种——扇形海链藻

为澄清广东大亚湾水域海链藻属的物种多样性, 研究建立了它的单克隆培养株系。结合光镜和扫描电镜下的形态学特征, 以及基于核糖体大、小亚基序列的分子系统发育分析, 报道了中国海链藻属的1个新种, 即扇形海链藻Thalassiosira flabellata sp. nov. X.H. Guo, Y.Q. Guo & Y. Li。该种以短链状群体或单细胞生活, 壳面具有一圈壳缘支持突、一个中央支持突和一个壳缘唇形突。壳面孔纹束状排列, 是此种的典型特征。此种与帕尔海链藻T. partheneia较为相似, 区别特征如下: 此种的壳面支持突和唇形突均具有外管, 而帕尔海链藻的突起没有外管, 只有内管; 其次, 此种的壳面较平, 而帕尔海链藻的壳面隆起呈鼓状; 第三, 此种的中央支持突具有3个围孔, 而帕尔海链藻具有4—5个围孔。     

小字海链藻双卫变种,海链藻属一新变种

采用毛细管复洗技术建立海链藻属(Thalassiosira)物种的单克隆培养株系,结合形态学和分子系统学研究,对小字海链藻原变种(Thalassiosira minuscula var.minuscula Krasske)的形态特征进行观察,并报道了1个新变种:小字海链藻双卫变种(T.minuscula var.bicustodis X.H.Guo,Y.Q.GuoY.Li)。双卫变种与原变种的形态特征基本一致,区别仅在于唇形突的伴生支持突数目不同,双卫变种具有2个,原变种只有1个。基于对多个株系生活史的连续观察,确认其伴生支持突的数目稳定,具有分类学意义。     

我国沿海线形亚属海链藻的形态学研究

壳面孔纹的形态学特征是海链藻的重要分类学依据之一。线形亚属的海链藻种类大多是从圆筛藻属修订而来, 它们之间的区别特征细微, 需电镜下观察才能准确鉴定。我国关于线形亚属海链藻的报道较少。研究利用电镜(EM)技术, 对采自我国沿海海域的自然水样, 以及分离获得的单克隆培养藻株进行了形态学观察, 针对其中的海链藻属Thalassiosira Cleve种类开展了形态分类学的专题研究。报道了6个隶属于线形亚属的海链藻种类, 分别是紧密海链藻T. densannula Hasle &; Fryxell、微小海链藻T. exigua Fryxell &; Hasle、线形海链藻T. lineata Jousé、微线形海链藻T. nanolineata (Mann) Fryxell &; Hasle、结线形海链藻T. nodulolineata (Hendey) Hasle &; Fryxell和柔弱海链藻T. tenera Proschkina-Lavrenko, 其中有4个为我国新记录种类: 紧密海链藻、线形海链藻、微线形海链藻和结线形海链藻。对每个种类的形态学特征、生活习性和生态分布进行了描述, 提供了电镜照片。对相似种类的形态学特征进行了比较研究, 分析了孔纹特征的变化类型及其分类学意义。     

我国沿海闭合突海链藻的形态学研究

闭合突是一类特殊的突起, 仅报道于少数海链藻种类, 其形态学特征和排列方式是重要的分类学依据。我国关于闭合突海链藻的报道较少。研究利用扫描电镜(SEM)技术, 对采自我国沿海海域的自然水样, 以及分离获得的单克隆培养藻株进行了形态学观察, 针对其中的海链藻属Thalassiosira Cleve种类开展了形态分类学的专题研究。报道了5个具有闭合突的海链藻种类, 分别是西达礁海链藻T. cedarkeyensis Prasad、偏心海链藻T. eccentrica (Ehrenberg) Cleve、伦德海链藻T. lundiana Fryxell、细孔海链藻T. punctigera (Castracane) Hasle和管状海链藻T. tubifera Fryxell, 其中有3个为我国新记录种类: 西达礁海链藻、细孔海链藻和管状海链藻。对每个种类的形态学特征和生境进行了描述, 提供了扫描电镜照片, 对相似种类的形态学特征进行了比较研究, 分析了突起特征的变化类型及其分类学价值。       

海链藻属一新变种艾伦海链藻肋纹变种

为了澄清海链藻属Thalassiosira的物种多样性, 采用毛细管复洗技术建立了单克隆培养株系。利用光镜和扫描电镜观察形态学特征, 并扩增其核糖体小亚基和大亚基序列, 用于分子系统树的构建。结合形态学和分子系统学数据, 发现艾伦海链藻株系之间存在一定的形态差异和遗传多样性。经过与原始文献的比对, 确认了艾伦海链藻原变种的特征, 并报道了该种的一个新变种艾伦海链藻肋纹变种Thalassiosira allenii var. striata X. H. Guo, Y. Q. Guo & Y. Li。该变种与原变种的形态特征基本相似, 区别在于壳面边缘具有肋纹结构, 原变种则无。基于核糖体小亚基和大亚基的系统树均显示, 肋纹变种与原变种聚在同一个分支上, 形成姐妹支(BPP>0.90), 表明两者之间具有最近的亲缘关系。2个变种的核糖体小亚基序列完全一致, 没有碱基差异。但用于分析的556个核糖体大亚基序列中, 两者存在11个差异碱基, 遗传距离为0.01。     

海链藻(Thalassiosira)与圆筛藻(Coscinodiscus)的形态学比较研究

海链藻属（Thalassiosira）和圆筛藻属（Coscinodiscus）的种类繁多,是硅藻门中的大属和代表属。两者的形态学特征具有较多相似之处,易混淆鉴定。通过光学显微镜和电镜观察,比较研究了海链藻和圆筛藻种类的形态学特征。海链藻种类除了具有1~2个唇形突之外,还具有数量较多的支持突,少数种类具有闭合突;筛膜位于壳面内侧;中孔在壳面外侧。而圆筛藻种类只具有数量众多的唇形突,且其中两个较大;筛膜位于壳面外侧;中孔在壳面内侧。由于两属形态学特征的区别只有在电镜下才能清晰观察到,因此尚有较多的分类修订工作需要进行。     

我国新记录海链藻属物种的形态学和系统学研究

为了廓清我国海链藻属的物种多样性, 并丰富其分子生物学信息, 为后续的系统学研究提供基础数据, 从我国沿海分离并建立了海链藻的单克隆培养株系, 利用光学显微镜和电镜技术进行了形态学研究, 同时还对其核糖体大亚基的高变区序列进行了扩增和测序分析。结合形态学和分子生物学数据, 鉴定了我国海链藻属的2个新记录种: 狭线形海链藻Thalassiosira anguste-lineata (Schmidt) Fryxell & Hasle和碟形海链藻T. minicosmica Lee & Park。对它们的形态学特征进行了较为详尽的描述, 并与相似种进行了比较研究。此外, 还基于核糖体大亚基高变区的碱基序列信息, 分析了它们的分子系统学位置。在分子系统树上, 狭线形海链藻和碟形海链藻均不与该属模式种——诺氏海链藻T. nordenskioeldii 聚在同一分支上, 显示它们与典型海链藻属物种之间具有较大的遗传差异。分子系统树还显示, 目前基于形态学建立的海链藻属并非自然类群, 而是被骨条藻属Skeletonema、小环藻属Cyclotella、漂流藻属Planktoniella等邻近属种分隔成多个分支, 这预示着现存的海链藻属应该是一个并系类群, 在后续的系统学研究中, 或许会有较大的系统学调整, 但目前有限的分子生物学信息是相关研究推进的重要限制。     

我国3个新记录海链藻种类的形态学研究

利用光镜(LM)和扫描电镜(SEM)技术,对采自我国沿海海域的自然水样,以及分离获得的单克隆培养藻株进行了形态学观察,针对其中的海链藻属Thalassiosira Cleve种类开展了形态分类学的专题研究。报道了3个新记录种类,分别是安达曼海链藻Thalassiosira andamanica Gedde、缢缩海链藻Thalassiosira con-stricta Gaarder和双线海链藻Thalassiosira duostra Pienaar。对每个种类的形态学特征、生活习性和生态分布进行了描述,提供了光镜和电镜照片,并对相似种类的形态学特征进行了比较研究。     

小盘藻属，我国微型硅藻类的一个新记录属

本文描述了我国首次记录的小盘藻属Minidiscus硅藻四种。主要特征是壳缘无环突起,壳面上 的支持突和1个唇形突均远离壳缘。小盘藻M．trioculatus,奇特小盘藻M．comicus和智利小盘藻M．chilensis为我国的新记录;细弱小盘藻M．subtilis为新种。它们的主要区别在于壳面花纹及支持突和唇形突排列方式的不同。     

THALASSIOSIRA ANDAMANICA SP. NOV. (BACILLARIOPHYCEAE), A NEW DIATOM FROM THE ANDAMAN SEA (THAILAND)

A new marine diatom, Thalassiosira andamanica, is described from light and electron microscopy. The specimens were collected in the vicinity of Phuket Marine Biological Center, Thailand, and later brought into clonal culture. Thalassiosira andamanica possess a rimoportula with a pronounced outer extension, one marginal ring of fultoportulae, and three rings of fultoportulae on the valve face. Cells are united into colonies by a single thread secreted through a central fultoportula. Marginal fultoportulae extensions are shortest on the inside of the valve. The areolae are arranged in sectors, and the valve margin is ribbed with approximately 38 ribs in 10 μm. The valvocopula and copula have rows of pores, four to six pores in 1 μm. Apparently, the pleurae are hyaline. Experiments with a clonal culture isolated at Phuket, Thailand, showed that growth (cell divisions·24 h⁻¹) was reduced for cultures grown at 14° C compared to those grown at 19°, 24°, or 30° C. The maximum growth rate (2.2 divisions·24 h⁻¹) was at 30° C. Thalassiosira andamanica is compared with morphologically similar taxa. On the basis of morphological features and the response to different temperature regimens, it is concluded that this taxon must be recognized as a new warm-water species. In addition, T. andamanica does not clearly belong to any of the two subgroups of species of Thalassiosira. To accommodate the morphological characteristics of T. andamanica, the establishment of a possible third subgroup is discussed.     

Morphology and molecular phylogeny of Thalassiosira sinica sp. nov. (Bacillariophyta) with delicate areolae and fultoportulae pattern

Thalassiosira Cleve is one of the most species-rich marine diatom genera. Previous studies have mainly focused on polar and temperate areas, but recent studies on material from Asian waters suggested that a high and undescribed species diversity of Thalassiosira occurs in Asia. On the basis of plankton samples collected from the South China Sea, a new species, T. sinica sp. nov. Y. Li & Y. Q. Guo is described. The morphology of the cells was examined by light and scanning electron microscopy. The hypervariable region of the nuclear large-subunit ribosomal DNA and the relatively conserved region of the nuclear small-subunit ribosomal DNA were sequenced for information on phylogenetic relationships. The living cells are usually solitary and drum-shaped. The areolae on the valve are delicate, small and arranged in fascicles. In addition to a regular ring of marginal fultoportulae on the valve edge, T. sinica possesses one central fultoportula and a number of fultoportulae arranged into 2–3 irregular rings on the valve face. A rimoportula located inside the ring of marginal fultoportulae possesses a long and strong external tube. The valvocopula and the copulae have rows of pores, but the pores on the valvocopula are larger than those on the copulae. Thalassiosira sinica appears to be included in subgroup C sensu Gedde because of a rimoportula with a distinct external tube located on the valve face. The molecular phylogeny, inferred from both SSU and LSU sequences, does, however, not support the validity of subgroup C, as the closest allies of T. sinica here turned out to be T. diporocyclus and T. lundiana, species in which the rimoportulae are located on the valve margin.     

Three extant genera of freshwater thalassiosiroid diatoms from Middle Eocene sediments in northern Canada

The evolutionary history of diatoms is only constrained partially by the fossil record. The timing of several key events, such as initial colonization of freshwater habitats by marine taxa, remains poorly resolved. Numerous specimens of the genera Cyclotella, Discostella, and Puncticulata (Ochrophyta: Thalassiosirales) have been recovered in Middle Eocene lacustrine sediments from the Giraffe Pipe locality in the Northwest Territories, Canada. These diatoms extend the fossil record of the family Stephanodiscaceae to at least 40 million years before present (Ma) and thus provide a new evolutionary milepost for the thalassiosiroid diatoms, an important clade of centric diatoms with global representation in both marine and freshwater environments. The quality of the fossil material enables detailed investigations of areolae, fultoportulae, and rimoportulae, revealing direct morphological affinities with a number of extant taxa. These observations extend the antiquity of several characters of phylogenetic importance within the thalassiosiroid diatoms, including the fultoportula, and imply that the entire lineage is considerably older than prior constraints from the fossil record, as suggested independently by several recent molecular phylogenies.     

Changes in the Lipid Composition of Thalassiosira pseudonana during Its Life Cycle

The lipid and fatty acid (FA) compositions of a marine diatom alga Thalassiosira pseudonana grown in culture were investigated. The relative content of separate lipid classes and their FA composition varied during of the life cycle. During the periods of active cell division and resting cell production, the proportion of polar lipids, as the structural components of cell membranes, increased. Changes in the proportion of lipid classes resulted in shifts in the FA composition of total lipids. It is suggested that the structural components of photosynthetic and cells membranes accumulate in the resting cells. Thereby, a rapid cell growth and an extensive development of the species under favorable environmental conditions is provided.     

Long-term seasonal variation in the biological traits of benthic-macroinvertebrates in two Mediterranean-climate streams in California, U.S.A.

1. We investigated the seasonal variation of biological traits and the influence of interannual rainfall variability on this pattern. Using long‐term survey data (6–19 years) from an intermittent and a perennial stream in the Mediterranean‐climate region of northern California, we examined 16 fuzzy‐coded biological traits (e.g. maximum size, life cycle duration, and mode of respiration). 2. Seasonal habitat variability is higher in the intermittent stream than in the perennial stream. During the winter and spring wet‐season both streams flood; however, during the summer dry‐season, the intermittent stream forms isolated pools in (occasionally drying completely). 3. Seasonal habitat variability influenced both taxonomic and biological trait composition. Distinct taxonomic communities were present in each season, particularly in the intermittent stream. The intermittent stream also exhibited more seasonal variation in biological traits than the perennial stream. 4. Despite statistically significant seasonal variation, trait composition was relatively stable among seasons in comparison with taxonomic composition and abundance. Taxonomic composition varied considerably between seasons, because of high seasonal and interannual replacement of taxa resulting from seasonal habitat changes. 5. The seasonality of taxonomic composition and abundance was sensitive to interannual rainfall variability. In dry years, the taxonomic composition of communities was more similar between seasons than in wet years, while trait composition was relatively insensitive to rainfall variability. 6. Despite high seasonal variation in abundance and taxonomic composition, biological traits of aquatic macroinvertebrates varied less and exhibited seasonal stability, which may be a result of the unpredictability and harshness of stream environments.