Evolutionary patterns of mating systems in the genus Closterium inferred from molecular information.

新月形属植物包含70多种植物，每一种都有变种。一些有性种群在单个无性系内形成合子孢子(同裂)，而另一些有性种群在无性系之间形成合子孢子(异交)。也有无性生殖群体，形成厚壁抗性孢子而没有接合(孤雌生殖)。为了更好地了解该属的物种形成及其生殖类型的进化模式，本研究主要对三个近缘关系较近的种复合体进行了研究：串珠弯孢菌(C.moniliferum-ehrenbergii)、轮孢菌(C.calosporum)和串珠藻(C.peracerosum-strigosum-littrale，PSL)。根据核SSU rDNA和叶绿体编码的rbcL构建的系统发育树通常支持在每个物种复合体中将物种分为三个不同的分支。根据SSU rDNA数据构建的系统发育树表明，在串珠丝虫-埃伦伯格氏菌复合体中，同源串珠丝虫v.moniliferum是该种复合体中所有其他种群的祖先。根据SSU 1506第一组内含子构建的ML树和ITS-2数据表明，埃伦伯格氏菌的种群不是单系进化的。在ITS-2二级结构的螺旋I末端的特征重复可能是无性种群从有性种群进化衍生的重要线索。在C.calosporum复合体中，C.calosporum和C.sposporum都是多系的。在该物种复合体的ITS-2二级结构的螺旋II上，在同源的Calosporum v.Himalayense中发现的一个特征基序在异源的C.calosporum v.Galiciense中复制。由于这两个分类群之间的亲缘关系最密切，对此的一种解释可能是异源的Galiciense是从一个类似于同源的喜马拉雅的祖先进化而来的。遗憾的是，在PSL种复合体中，到目前为止还没有发现它们每种繁殖型的序列和结构特征。

The genus Closterium contains more than 70 species each comprising varieties. Some sexual populations form zygospores within single clones (homothallism), while some others between clones (heterothallism). There are also asexual populations which form thick-walled resistant spores without conjugation (parthenogenesis). In order to get better understanding of speciation of the genus along with evolutionary patterns of their reproductive types, this study has primarily treated with three closely-related species complex : C. moniliferum-ehrenbergii ; C. calosporum and ; C peracerosum-strigosum-littrale (psl). Phylogenetic trees inferred from both nuclear SSU rDNA and chloroplast-encoded rbcL generally supported diversification into three different clades in each of those species complex. In the C moniliferum-ehrenbergii species complex, the phylogenetic tree built from SSU rDNA data has suggested that homothallic C moniliferum v. moniliferum was ancestral to all other populations of this species complex. ML trees constructed from SSU 1506 group I intron and ITS-2 data has shown that populations of C ehrenbergii were not monophyletic. A characteristic duplication at the tip of helix I of their ITS-2 secondary structure may serve as an important clue for evolutionary derivation of asexual populations from sexual ones. In the C. calosporum complex, each of the two species C. calosporum and C. spinosporum has turned out to be polyphyletic. On helix II of their ITS-2 secondary structure of this species complex, a characteristic motif found in homothallic C. calosporum v. himalayense was duplicated in heterothallic C. calosporum v. galiciense. Since these two taxa are most closely related with each other, one explanation for this may be that heterothallic galiciense has been derived from a homothallic himalayense-like ancestor. In the C. psl species complex, unfortunately, neither sequence nor structure characteristic for their each reproductive type was found so far.