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首页> 外文期刊>Marine ecology >Adaptations Of Araphid Pennate Diatoms To A Planktonic Existence
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Adaptations Of Araphid Pennate Diatoms To A Planktonic Existence

机译：Araphid Pennate硅藻适应浮游生物的存在

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Pennate diatoms are monophyletic. Their principal cell wall elements, called valves, are shaped like a ship's hull. Within the pennates, the araphids are para-phyletic; they possess rimoportulae and pore fields located at the valve apices. The pore fields exude mucilage pads with which cells attach to one another to form chains. Many taxa use the pads also for attachment to substrata. Only a few genera are truly planktonic. The main question addressed in this study is whether the planktonic lifestyle is ancestral or derived. Phylogenies inferred from nuclear SSU rDNA gene sequences of diatoms indicated that the attached lifestyle is ancestral among the araphids, whereas a typically planktonic lifestyle seems to have developed at least three times and possibly four times independently. Acquisition of a planktonic lifestyle from benthic ancestry was accompanied by a reduction in the silicification of cell-wall elements, but changes in morphological characters shared by all four clades were not detected. The reason why only three or four araphid pennate clades have adopted a planktonic lifestyle may be related to constraints associated to their sexual reproduction mode. Partner cells of opposite mating type align with one another and produce isogametes. These gametes lack flagella; they move to one another in an amoeboid fashion, which functions well on surfaces, but seems a liability in a turbulent water column. The planktonic lineages must have overcome this constraint, e.g. by sinking to the bottom, or aggregating, to perform sexual reproduction. Members of the four araphid pennate lineages are now common constituents of the plankton, suggesting that they are ecologically successful.
机译：笔形硅藻是单系的。它们的主要细胞壁元件称为阀门，其形状像船的船体。在蓬内，杂草是近亲的；它们具有位于瓣膜顶端的边缘孔和孔道。孔场散发着黏液垫，细胞与黏液垫相互连接形成链。许多分类单元还使用垫板将其连接到底层。只有少数属是真正的浮游生物。这项研究解决的主要问题是浮游生活方式是祖先的还是衍生的。从硅藻的核SSU rDNA基因序列推断出的系统发育史表明，附着的生活方式是阿拉伯动物中的祖先，而典型的浮游生活方式似乎至少独立发展了三倍甚至四倍。从底栖血统获得浮游生活方式的同时，细胞壁元素的硅化作用降低，但未检测到所有四个进化枝共有的形态特征变化。为什么只有三个或四个阿拉伯蚜虫成虫进化枝采取浮游生活方式，可能与它们的有性生殖方式有关。相反交配类型的伴侣细胞相互排列并产生同配子。这些配子缺乏鞭毛。它们以变形虫的形式相互移动，在表面上表现良好，但在湍流的水柱中似乎是一个缺点。浮游血统必须克服这一限制，例如通过下沉或聚合来进行有性生殖。现在，四个阿拉伯phipenate血统的成员是浮游生物的共同组成部分，表明它们在生态上是成功的。

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