Atkins M S, McArthur A G, Teske A P
Biology Department MS 33, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
J Mol Evol. 2000 Sep;51(3):278-85. doi: 10.1007/s002390010089.
Molecular and morphological evidence points to the ancyromonad Ancyromonas as a plausible candidate for the closest relative to the common ancestor of metazoans, fungi, and choanoflagellates (the Opisthokonta). Using 18S rDNA sequences from most of the major eukaryotic lineages, maximum-likelihood, minimum-evolution, and maximum-parsimony analyses yielded congruent phylogenies supporting this hypothesis. Combined with ultrastructural similarities between Ancyromonas and opisthokonts, the evidence presented here suggests that Ancyromonas may form an independent lineage, the Ancyromonadida Cavalier-Smith 1997, closer in its relationship to the opisthokonts than is its nearest protist relatives, the Apusomonadida. However, the very low bootstrap support for deep nodes and hypothesis testing indicate that the resolving power of 18S rDNA sequences is limited for examining this aspect of eukaryotic phylogeny. Alternate branching positions for the Ancyromonas lineage cannot be robustly rejected, revealing the importance of ultrastructure when examining the origins of multicellularity. The future use of a multigene approach may additionally be needed to resolve this aspect of eukaryotic phylogeny.
分子和形态学证据表明，锚定单胞菌属的锚定单胞菌是后生动物、真菌和领鞭毛虫（后鞭毛生物）共同祖先最亲近的可能候选者。利用来自大多数主要真核生物谱系的18S rDNA序列，最大似然法、最小进化法和最大简约法分析得出了一致的系统发育树，支持这一假说。结合锚定单胞菌与后鞭毛生物之间的超微结构相似性，此处提供的证据表明，锚定单胞菌可能形成一个独立的谱系，即1997年卡瓦利埃-史密斯提出的锚定单胞菌目，它与后鞭毛生物的关系比其最近的原生生物亲属——无尾鞭毛虫目更为密切。然而，对深层节点的极低自展支持率和假设检验表明，18S rDNA序列在研究真核生物系统发育的这一方面时分辨能力有限。锚定单胞菌谱系的其他分支位置无法被有力排除，这揭示了在研究多细胞起源时超微结构的重要性。未来可能还需要采用多基因方法来解决真核生物系统发育的这一方面问题。
