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

新月藻属包含70多个物种，每个物种包括变种。有些有性群体在单克隆内形成接合孢子（同宗配合），而另一些则在克隆间形成接合孢子（异宗配合）。也有形成厚壁抗性孢子而不接合（单性生殖）的无性种群。为了更好地了解该属沿着的物种形成及其生殖类型的进化模式，本研究主要对三个关系密切的种复合体进行了研究：C.念珠藻C. Calosporum和C peracerosum-strigosum-littrale（psl.）从核SSU rDNA和叶绿体编码的rbcL推断的系统发育树一般支持在这些物种复合体中的每一个到三个不同的分支的多样化。在C moniliferum-ehrenbercyclop物种复合体中，从SSU rDNA数据构建的系统发育树表明，同宗配合的C moniliferum v. moniliferum是该物种复合体的所有其他种群的祖先。根据SSU 1506 Ⅰ组内含子和ITS-2数据构建的ML树表明，胡枝子种群不是单系的。ITS-2二级结构螺旋Ⅰ顶端的特征性重复可能是无性群体从有性群体进化的重要线索。在C. calosporum complex，C. calosporum和C.刺孢菌是多系的。在ITS-2二级结构的螺旋II上，发现了同宗配合的C. calosporum v. himalayense在异宗配合C. [医]盖孢霉由于这两个分类群是最密切相关的彼此，一个解释，这可能是异宗配合的galiciense已来自同宗配合的喜马拉雅山一样的祖先。在C. PSL物种复杂，不幸的是，迄今为止，既没有发现它们每个繁殖类型的序列特征，也没有发现它们每个繁殖类型的结构特征。

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.