Verbruggen Heroen, Leliaert Frederik, Maggs Christine A, Shimada Satoshi, Schils Tom, Provan Jim, Booth David, Murphy Sue, De Clerck Olivier, Littler Diane S, Littler Mark M, Coppejans Eric
Phycology Research Group and Center for Molecular Phylogenetics and Evolution, Ghent University, Gent, Belgium.
Mol Phylogenet Evol. 2007 Jul;44(1):240-54. doi: 10.1016/j.ympev.2007.01.009. Epub 2007 Jan 31.
Despite the potential model role of the green algal genus Codium for studies of marine speciation and evolution, there have been difficulties with species delimitation and a molecular phylogenetic framework was lacking. In the present study, 74 evolutionarily significant units (ESUs) are delimited using 227 rbcL exon 1 sequences obtained from specimens collected throughout the genus' range. Several morpho-species were shown to be poorly defined, with some clearly in need of lumping and others containing pseudo-cryptic diversity. A phylogenetic hypothesis of 72 Codium ESUs is inferred from rbcL exon 1 and rps3-rpl16 sequence data using a conventional nucleotide substitution model (GTR+Gamma+I), a codon position model and a covariotide (covarion) model, and the fit of a multitude of substitution models and alignment partitioning strategies to the sequence data is reported. Molecular clock tree rooting was carried out because outgroup rooting was probably affected by phylogenetic bias. Several aspects of the evolution of morphological features of Codium are discussed and the inferred phylogenetic hypothesis is used as a framework to study the biogeography of the genus, both at a global scale and within the Indian Ocean.
尽管绿藻属团扇藻在海洋物种形成和进化研究中具有潜在的模式作用，但在物种界定方面存在困难，且缺乏分子系统发育框架。在本研究中，利用从整个团扇藻属分布范围内采集的标本获得的227个rbcL外显子1序列，界定了74个具有进化意义的单元（ESU）。研究表明，几个形态物种的定义不明确，有些明显需要合并，而另一些则包含假隐存多样性。利用传统核苷酸替换模型（GTR+Gamma+I）、密码子位置模型和协变核苷酸（covarion）模型，从rbcL外显子1和rps3-rpl16序列数据推断出72个团扇藻ESU的系统发育假说，并报告了多种替换模型和比对划分策略对序列数据的拟合情况。由于外类群定根可能受到系统发育偏差的影响，因此进行了分子钟树定根。讨论了团扇藻形态特征进化的几个方面，并将推断出的系统发育假说作为研究该属生物地理学的框架，包括全球尺度和印度洋范围内的生物地理学。
