Leander Brian S, Clopton Richard E, Keeling Patrick J
Canadian Institute for Advanced Research, Program in Evolutionary Biology, Department of Botany, University of British Columbia, Vancouver, BC, Canada V6T 1Z4.
Division of Science and Technology, Peru State College, Peru, NE 68421, USA.
Int J Syst Evol Microbiol. 2003 Jan;53(Pt 1):345-354. doi: 10.1099/ijs.0.02284-0.
Gregarines are thought to be deep-branching apicomplexans. Accordingly, a robust inference of gregarine phylogeny is crucial to any interpretation of apicomplexan evolution, but molecular sequences from gregarines are restricted to a small number of small-subunit (SSU) rDNA sequences from derived taxa. This work examines the usefulness of SSU rDNA and beta-tubulin sequences for inferring gregarine phylogeny. SSU rRNA genes from Lecudina (Mingazzini) sp., Monocystis agilis Stein, Leidyana migrator Clopton and Gregarina polymorpha Dufour, as well as the beta-tubulin gene from Leidyana migrator, were sequenced. The results of phylogenetic analyses of alveolate taxa using both genes were consistent with an early origin of gregarines and the putative 'sister' relationship between gregarines and Cryptosporidium, but neither phylogeny was strongly supported. In addition, two SSU rDNA sequences from unidentified marine eukaryotes were found to branch among the gregarines: one was a sequence derived from the haemolymph parasite of the giant clam, Tridacna crocea, and the other was a sequence misattributed to the foraminiferan Ammonium beccarii. In all of our analyses, the SSU rDNA sequence from Colpodella sp. clustered weakly with the apicomplexans, which is consistent with ultrastructural data. Altogether, the exact position of gregarines with respect to Cryptosporidium and other apicomplexans remains to be confirmed, but the congruence of SSU rDNA and beta-tubulin trees with one another and with morphological data does suggest that further sampling of molecular data will eventually put gregarine diversity into a phylogenetic context.
簇虫被认为是进化分支较深的顶复门生物。因此，对簇虫系统发育进行可靠推断对于理解顶复门生物的进化至关重要，但来自簇虫的分子序列仅限于少数来自衍生类群的小亚基（SSU）核糖体DNA序列。这项工作研究了SSU核糖体DNA和β-微管蛋白序列在推断簇虫系统发育方面的实用性。对来自Lecudina（Mingazzini）属物种、敏捷单囊簇虫（Monocystis agilis Stein）、迁移类莱迪簇虫（Leidyana migrator Clopton）和多形簇虫（Gregarina polymorpha Dufour）的SSU核糖体RNA基因，以及迁移类莱迪簇虫的β-微管蛋白基因进行了测序。使用这两个基因对肺泡类群进行系统发育分析的结果与簇虫的早期起源以及簇虫与隐孢子虫之间假定的“姐妹”关系一致，但两种系统发育关系都没有得到有力支持。此外，发现来自未鉴定海洋真核生物的两个SSU核糖体DNA序列在簇虫中分支：一个是来自大砗磲（Tridacna crocea）血淋巴寄生虫的序列，另一个是错误归因于有孔虫贝氏铵（Ammonium beccarii）的序列。在我们所有的分析中，来自Colpodella属物种（Colpodella sp.）的SSU核糖体DNA序列与顶复门生物的聚类关系较弱，这与超微结构数据一致。总之，簇虫相对于隐孢子虫和其他顶复门生物的确切位置仍有待确定，但SSU核糖体DNA和β-微管蛋白树之间以及与形态学数据的一致性确实表明，进一步的分子数据采样最终将把簇虫的多样性置于系统发育背景中。
