Nanney D L, Park C, Preparata R, Simon E M
Department of Ecology, Ethology and Evolution, University of Illinois, Urbana 61801, USA.
J Eukaryot Microbiol. 1998 Jan-Feb;45(1):91-100. doi: 10.1111/j.1550-7408.1998.tb05075.x.
Studies were undertaken to discover the relative molecular distances separating some familiar forms of ciliated protozoa, and the genetic species they include. Sequences of 190 bases of the D2 domain of the large ribosomal nucleic acid molecule were obtained by polymerase chain reaction from protists of three distinctive groups of ciliated protozoa-Colpoda, Paramecium and Tetrahymena. Evolutionary trees were constructed for each set of sequences using the PHYLOGEN 1.0 string programs. All three groups of ciliates manifested large molecular diversity among strains difficult or impossible to distinguish morphologically. The largest single evolutionary distance within a group was the 75 differences separating Tetrahymena paravorax from the other tetrahymenids. The largest mean distance for a group was the 21.2 for the colpodids. In all the protist groups the large molecular diversity is obscured by morphological conservatism associated with constraints of ancient designs. The molecular diversity within morphotypes argues for long evolutionary coexistence of species differentiated from each other in significant physiological, ecological, or nutritional ways.
开展了多项研究，以发现一些常见纤毛原生动物形态之间以及它们所包含的遗传物种之间的相对分子距离。通过聚合酶链反应，从三组不同的纤毛原生动物——肾形虫、草履虫和四膜虫的原生生物中获得了大核糖体核酸分子D2结构域190个碱基的序列。使用PHYLOGEN 1.0字符串程序为每组序列构建进化树。所有三组纤毛虫在形态上难以或无法区分的菌株之间都表现出很大的分子多样性。一组内最大的单一进化距离是将嗜杀四膜虫与其他四膜虫科区分开来的75个差异。一组的最大平均距离是肾形虫的21.2个差异。在所有原生生物群体中，与古老设计的限制相关的形态保守性掩盖了很大的分子多样性。形态型内的分子多样性表明，以显著的生理、生态或营养方式相互分化的物种长期进化共存。
