Rokas Antonis, King Nicole, Finnerty John, Carroll Sean B
Howard Hughes Medical Institute, University of Wisconsin-Madison, 1525 Linden Drive, Madison, WI 53706-1596, USA.
Evol Dev. 2003 Jul-Aug;5(4):346-59. doi: 10.1046/j.1525-142x.2003.03042.x.
A phylogenetic framework is essential for under-standing the origin and evolution of metazoan development. Despite a number of recent molecular studies and a rich fossil record of sponges and cnidarians, the evolutionary relationships of the early branching metazoan groups to each other and to a putative outgroup, the choanoflagellates, remain uncertain. This situation may be the result of the limited amount of phylogenetic information found in single genes and the small number of relevant taxa surveyed. To alleviate the effect of these analytical factors in the phylogenetic recons-truction of early branching metazoan lineages, we cloned multiple protein-coding genes from two choanoflagellates and diverse sponges, cnidarians, and a ctenophore. Comparisons of sequences for alpha-tubulin, beta-tubulin, elongation factor 2, HSP90, and HSP70 robustly support the hypothesis that choanoflagellates are closely affiliated with animals. However, analyses of single and concatenated amino acid sequences fail to resolve the relationships either between early branching metazoan groups or between Metazoa and choano-flagellates. We demonstrate that variable rates of evolution among lineages, sensitivity of the analyses to taxon selection, and conflicts in the phylogenetic signal contained in different amino acid sequences obscure the phylogenetic associations among the early branching Metazoa. These factors raise concerns about the ability to resolve the phylogenetic history of animals with molecular sequences. A consensus view of animal evolution may require investigations of genome-scale characters.
系统发育框架对于理解后生动物发育的起源和进化至关重要。尽管最近有一些分子研究，以及丰富的海绵动物和刺胞动物化石记录，但早期分支后生动物类群之间以及与假定的外类群领鞭毛虫之间的进化关系仍不明确。这种情况可能是由于单个基因中发现的系统发育信息有限，以及所调查的相关分类单元数量较少所致。为了减轻这些分析因素对早期分支后生动物谱系系统发育重建的影响，我们从两种领鞭毛虫、多种海绵动物、刺胞动物和一种栉水母中克隆了多个蛋白质编码基因。对α-微管蛋白、β-微管蛋白、延伸因子2、热休克蛋白90和热休克蛋白70的序列比较有力地支持了领鞭毛虫与动物密切相关的假说。然而，对单个和串联氨基酸序列的分析未能解决早期分支后生动物类群之间或后生动物与领鞭毛虫之间的关系。我们证明，谱系间不同的进化速率、分析对分类单元选择的敏感性，以及不同氨基酸序列中系统发育信号的冲突，模糊了早期分支后生动物之间的系统发育关联。这些因素引发了对用分子序列解析动物系统发育历史能力的担忧。动物进化的共识观点可能需要对基因组规模特征进行研究。
