Evolution and Cytological Diversification of the Green Seaweeds (Ulvophyceae)
Evolution and Cytological Diversification of the Green Seaweeds (Ulvophyceae)
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DOI：
10.1093/molbev/msq091
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发表时间：
2010-09-01
影响因子：
10.7
通讯作者：
De Clerck, Olivier
中科院分区：
文献类型：
--
作者：
Cocquyt, Ellen;Verbruggen, Heroen;De Clerck, Olivier
石莼纲是绿藻门的四个纲之一，由于其具有无与伦比的形态学和细胞学多样性而具有特别的进化意义。形态类型从单细胞和简单的多细胞丝状体到片状和复杂的皮层状菌体。细胞学布局的范围从典型的包含单个细胞核和叶绿体的小细胞到包含数百万个细胞核和叶绿体的巨细胞。为了了解这些形态和细胞学类型的演化，本文旨在评估是否石莼科是单系的，并阐明其订单之间的古老关系。我们的方法包括系统发育分析（最大似然和贝叶斯推断）的7个核基因，小亚基核核糖体DNA和两个质体标记，精心选择的分区策略，和模型的序列进化。我们介绍了一个程序快速网站删除（网站剥离），旨在提高系统发育信号在一个特定的时代的利益和评估的特异性快速网站删除保留信号有关古老的关系。从我们的系统发育分析中，我们得出结论，祖先石腐植物可能是一种单细胞单核生物，宏观生长是在涉及根本不同机制的各种谱系中独立实现的：或者通过伴随有丝分裂和胞质分裂的多细胞进化（石莼目-丝藻目和Trentepohliales），通过获得多核管胞组织，其中每个核提供其自身的胞质结构域，（Cladophorales和Blastophysa），或通过发展一个以一个大核或数百万个小核和细胞质流为特征的管形组织（Bryopteriales和Dasycladales）。我们比较了不同的进化方案产生的管和管枝细胞学，并认为这些并不一定是从多细胞甚至多核状态，而是可以独立地从一个单细胞的祖先进化。
The Ulvophyceae, one of the four classes of the Chlorophyta, is of particular evolutionary interest because it features an unrivaled morphological and cytological diversity. Morphological types range from unicells and simple multicellular filaments to sheet-like and complex corticated thalli. Cytological layouts range from typical small cells containing a single nucleus and chloroplast to giant cells containing millions of nuclei and chloroplasts. In order to understand the evolution of these morphological and cytological types, the present paper aims to assess whether the Ulvophyceae are monophyletic and elucidate the ancient relationships among its orders. Our approach consists of phylogenetic analyses (maximum likelihood and Bayesian inference) of seven nuclear genes, small subunit nuclear ribosomal DNA and two plastid markers with carefully chosen partitioning strategies, and models of sequence evolution. We introduce a procedure for fast site removal (site stripping) targeted at improving phylogenetic signal in a particular epoch of interest and evaluate the specificity of fast site removal to retain signal about ancient relationships. From our phylogenetic analyses, we conclude that the ancestral ulvophyte likely was a unicellular uninucleate organism and that macroscopic growth was achieved independently in various lineages involving radically different mechanisms: either by evolving multicellularity with coupled mitosis and cytokinesis (Ulvales-Ulotrichales and Trentepohliales), by obtaining a multinucleate siphonocladous organization where every nucleus provides for its own cytoplasmic domain (Cladophorales and Blastophysa), or by developing a siphonous organization characterized by either one macronucleus or millions of small nuclei and cytoplasmic streaming (Bryopsidales and Dasycladales). We compare different evolutionary scenarios giving rise to siphonous and siphonocladous cytologies and argue that these did not necessarily evolve from a multicellular or even multinucleate state but instead could have evolved independently from a unicellular ancestor.