Hamilton Patrick B, Gibson Wendy C, Stevens Jamie R
School of Biosciences, University of Exeter, Exeter, UK.
Mol Phylogenet Evol. 2007 Jul;44(1):15-25. doi: 10.1016/j.ympev.2007.03.023. Epub 2007 Apr 13.
Trypanosomes (genus Trypanosoma) are widespread blood parasites of vertebrates, usually transmitted by arthropod or leech vectors. Most trypanosomes have lifecycles that alternate between a vertebrate host, where they exist in the bloodstream, and an invertebrate host, where they develop in the alimentary tract. This raises the question of whether one type of host has had greater influence on the evolution of the genus. Working from the generally accepted view that trypanosomes are monophyletic, here we examine relationships between trypanosomes using phylogenies based on the genes for the small subunit ribosomal RNA (SSU rRNA) and the glycosomal glyceraldehyde phosphate dehydrogenase (gGAPDH). New analysis of a combined dataset of both these genes provides strong support for many known clades of trypanosomes. It also resolves the deepest split within the genus between the Aquatic clade, which mainly contains trypanosomes of aquatic and amphibious vertebrates, and a clade of trypanosomes from terrestrial vertebrates. There is also strengthened support for two deep clades, one comprising a wide selection of mammalian trypanosomes and a tsetse fly-transmitted reptilian trypanosome, and the other combining two bird trypanosome subclades. Considering the vertebrate and invertebrate hosts of each clade, it is apparent that co-speciation played little role in trypanosome evolution. However most clades are associated with a type of vertebrate or invertebrate host, or both, indicating that 'host fitting' has been the principal mechanism for evolution of trypanosomes.
锥虫（锥虫属）是广泛存在于脊椎动物血液中的寄生虫，通常由节肢动物或水蛭作为传播媒介。大多数锥虫的生命周期在脊椎动物宿主（它们存在于血液中）和无脊椎动物宿主（它们在消化道中发育）之间交替。这就引发了一个问题，即哪种类型的宿主对该属的进化产生了更大的影响。基于锥虫是单系群这一普遍接受的观点，我们在此使用基于小亚基核糖体RNA（SSU rRNA）基因和糖体甘油醛-3-磷酸脱氢酶（gGAPDH）基因构建的系统发育树来研究锥虫之间的关系。对这两个基因的组合数据集进行的新分析为许多已知的锥虫进化枝提供了有力支持。它还解决了该属内最深层次的分化问题，即水生进化枝（主要包含水生和两栖脊椎动物的锥虫）与陆地脊椎动物锥虫进化枝之间的分化。对于两个深层进化枝也有了更强的支持，一个进化枝包含多种哺乳动物锥虫和一种由采采蝇传播的爬行动物锥虫，另一个进化枝则合并了两个鸟类锥虫亚进化枝。考虑到每个进化枝的脊椎动物和无脊椎动物宿主，很明显共物种形成在锥虫进化中作用不大。然而，大多数进化枝与一种类型的脊椎动物或无脊椎动物宿主，或两者都有关联，这表明“宿主适应”是锥虫进化的主要机制。
