Larson A, Kirk M M, Kirk D L
Department of Biology, Washington University, St. Louis, Missouri 63130.
Mol Biol Evol. 1992 Jan;9(1):85-105. doi: 10.1093/oxfordjournals.molbev.a040710.
Phylogenetic studies of approximately 2,000 bases of sequence from the large and small nuclear-encoded ribosomal RNAs are used to investigate the origins of the genus Volvox. The colonial and multicellular genera currently placed in the family Volvocaceae form a monophyletic group that is significantly closer phylogenetically to Chlamydomonas reinhardtii than it is to the other unicellular green flagellates that were tested, including Chlamydomonas eugametos, Chlorella pyrenoidosa, and Haematococcus lacustris. Statistical analysis of 251 phylogenetically informative nucleotide positions rejects the "volvocine lineage" hypothesis, which postulates a monophyletic evolutionary progression from unicellular organisms (such as Chlamydomonas), through colonial organisms (e.g., Gonium, Pandorina, Eudorina, and Pleodorina) demonstrating increasing size, cell number, and tendency toward cellular differentiation, to multicellular organisms having fully differentiated somatic and reproductive cells (in the genus Volvox). The genus Volvox appears not to be monophyletic. Volvox capensis falls outside a lineage containing other representatives of Volvox (V. aureus, V. carteri, and V. obversus), and both of these Volvox lineages are more closely related to certain colonial genera than they are to each other. This implies either a diphyletic origin of Volvox from different colonial volvocacean ancestors, a phylogenetic derivation of some of the colonial genera from a multicellular (i.e., Volvox) ancestor, or both. Considered together with previously published observations, these results suggest that the different levels of organizational and developmental complexity found in the Volvocaceae represent alternative stable states, among which evolutionary transitions have occurred several times during the phylogenetic history of this group.
对大小核编码核糖体RNA约2000个碱基的序列进行系统发育研究，以探究团藻属的起源。目前置于团藻科的群体型和多细胞型属形成了一个单系类群，在系统发育上，它与莱茵衣藻的亲缘关系明显比与其他受试的单细胞绿色鞭毛虫更近，这些受试的单细胞绿色鞭毛虫包括优配衣藻、蛋白核小球藻和湖生血球藻。对251个系统发育信息丰富的核苷酸位点进行统计分析后，否定了“团藻谱系”假说，该假说假定从单细胞生物（如衣藻）开始，经过群体生物（如盘藻、实球藻、空球藻和扁藻），其大小、细胞数量不断增加，细胞分化趋势增强，到具有完全分化的体细胞和生殖细胞的多细胞生物（团藻属）存在单系进化进程。团藻属似乎并非单系类群。卡彭氏团藻不属于包含团藻其他代表物种（金色团藻、卡特氏团藻和反转团藻）的谱系，而且这两个团藻谱系与某些群体型属的亲缘关系比它们彼此之间的关系更密切。这意味着团藻要么起源于不同的群体型团藻科祖先，具有双系起源；要么某些群体型属是从多细胞（即团藻）祖先系统发育而来，或者两者皆有。结合之前发表的观察结果来看，这些结果表明，团藻科中发现的不同组织和发育复杂程度代表了不同的稳定状态，在该类群的系统发育历史中，进化转变在这些稳定状态之间发生了好几次。
