Vickerman K
Institute of Biomedical and Life Sciences, University of Glasgow, U.K.
Int J Parasitol. 1994 Dec;24(8):1317-31. doi: 10.1016/0020-7519(94)90198-8.
The trypanosomatids combine a relatively uniform morphology with ability to parasitise a very diverse range of hosts including animals, plants and other protists. Along with their sister family, the biflagellate bodonids, they are set apart from other eukaryotes by distinctive organisational features, such as the kinetoplast-mitochondrion and RNA editing, isolation of glycolysis enzymes in the glycosome, use of the flagellar pocket for molecular traffic into and out of the cell, a unique method of generating cortical microtubules, and bizarre nuclear organisation. These features testify to the antiquity and isolation of the kinetoplast-bearing flagellates (Kinetoplastida). Molecular sequencing techniques (especially small subunit ribosomal RNA gene sequencing) are now radically reshaping previous ideas on the phylogeny of these organisms. The idea that the monogenetic (MG) trypanosomatids gave rise to the digenetic (DG) genera is losing ground to a view that, after the bodonids, the African trypanosomes (DG) represent the most ancient lineage, followed by Trypanosoma cruzi (DG), then Blastocrithidia (MG), Herpetomonas (MG) and Phytomonas (DG), with Leptomonas (MG), Crithidia (MG), Leishmania (DG) and Endotrypanum (DG) forming the crown of the evolutionary tree. Vast genetic distances (12% divergence) separate T. brucei and T. cruzi, while the Leishmania species are separated by very short distances (less than 1% divergence). These phylogenetic conclusions are supported by studies on RNA editing and on the nature of the parasite surface. The trypanosomatids seem to be able to adapt with ease their energy metabolism to the availability of substrates and oxygen, and this may give them the ability to institute new life cycles if host behaviour patterns allow. Sexual processes, though present in at least some trypanosomatids, may have played only a minor part in generating diversity during trypanosomatid evolution. On the other hand, the development of altruistic behaviour on the part of some life cycle stages may be a hitherto unconsidered way of maximising fitness in this group. It is concluded that, owing to organisational constraints, the trypanosomatids can undergo substantial molecular variation while registering very little in the way of morphological change.
锥虫类原生生物形态相对统一，却能寄生于种类繁多的宿主，包括动物、植物及其他原生生物。与它们的姊妹家族双鞭毛波豆虫科一样，锥虫类原生生物通过独特的组织特征与其他真核生物区分开来，比如动质体 - 线粒体及RNA编辑、糖酵解酶在糖体中的隔离、利用鞭毛袋进行分子进出细胞的运输、产生皮层微管的独特方法以及奇特的核组织。这些特征证明了含动质体鞭毛虫（动质体目）的古老性和隔离性。分子测序技术（尤其是小亚基核糖体RNA基因测序）正在从根本上重塑以往关于这些生物系统发育的观点。单源（MG）锥虫类原生生物产生双源（DG）属的观点正逐渐被另一种观点取代，即继波豆虫科之后，非洲锥虫（DG）代表最古老的谱系，其次是克氏锥虫（DG），然后是巴氏虫属（MG）、细滴虫属（MG）和植生滴虫属（DG），最后是细滴虫属（MG）、短膜虫属（MG）、利什曼原虫属（DG）和内滴虫属（DG）构成进化树顶端。布氏锥虫和克氏锥虫之间存在巨大的遗传距离（12%的差异），而利什曼原虫各物种之间的距离则非常短（差异小于1%）。这些系统发育结论得到了关于RNA编辑和寄生虫表面性质研究的支持。锥虫类原生生物似乎能够轻松地使其能量代谢适应底物和氧气的可利用性，并且如果宿主行为模式允许，这可能使它们有能力建立新的生命周期。虽然至少在某些锥虫类原生生物中存在有性过程，但在锥虫类原生生物进化过程中，有性过程在产生多样性方面可能仅起了很小的作用。另一方面，某些生命周期阶段利他行为的发展可能是该类群中一种迄今为止未被考虑的使适应性最大化的方式。得出的结论是，由于组织限制，锥虫类原生生物能够经历大量分子变异，而形态变化却微乎其微。
