Lane Christopher E, Lindstrom Sandra C, Saunders Gary W
Centre for Environmental and Molecular Algal Research, Department of Biology, University of New Brunswick, Fredericton, NB, Canada E3B 6E1.
Mol Phylogenet Evol. 2007 Aug;44(2):634-48. doi: 10.1016/j.ympev.2007.03.016. Epub 2007 Apr 4.
Despite their relatively complex morphologies, species in the genus Alaria Greville are notoriously difficult to identify with certainty. Morphological characters, often influenced by environmental factors, make individuals in similar habitats artificially appear related. Species identification would, therefore, benefit greatly from the application of molecular tools. We applied DNA barcoding, using the 5' end of the cytochrome c oxidase I (coxI-5') gene from the mitochondrial genome, to define species limits and relationships in northeast Pacific populations of Alaria. This emerging technique is being employed to catalogue species diversity worldwide, particularly among animals, and it has been shown to be sensitive enough to discriminate between closely related species. However, the utility of this marker for identifying or categorizing the majority of life remains unclear. We compared the resolution obtained with this marker to two other molecular systems commonly used in algal research: the nuclear internal transcribed spacer (ITS) of the ribosomal cistron, and the plastid Rubisco operon spacer (rbcSp). In agreement with previous results, Alaria fistulosa Postels & Ruprecht, with its distinct morphological, ecological and molecular features, stands apart from the other species in the genus and we establish Druehlia gen. nov. to accommodate it. For the remaining isolates, distinct mitochondrial haplotypes resolved with the barcode data indicate a period of genetic isolation for at least three incipient species in the northeast Pacific, whereas unexpected levels and patterns of ITS variation, as well as the extreme morphological plasticity found among these isolates, have most probably resulted from a recent collapse in species barriers. The cloning of ITS amplicons revealed multiple ITS copies in several individuals, further supporting this hypothesis.
尽管阿拉里亚属（Alaria Greville）的物种形态相对复杂，但要确切鉴定它们却极为困难。形态特征常常受到环境因素的影响，使得相似栖息地中的个体在人为看来具有相关性。因此，物种鉴定将极大地受益于分子工具的应用。我们应用DNA条形码技术，利用线粒体基因组中细胞色素c氧化酶I（coxI - 5'）基因的5'端，来界定东北太平洋阿拉里亚种群的物种界限和关系。这项新兴技术正被用于对全球物种多样性进行编目，尤其是在动物中，并且已证明它足够灵敏，能够区分亲缘关系相近的物种。然而，该标记物在识别或分类大多数生物方面的效用仍不明确。我们将使用此标记物获得的分辨率与藻类研究中常用的另外两个分子系统进行了比较：核糖体顺反子的核内转录间隔区（ITS）和质体核酮糖-1,5-二磷酸羧化酶操纵子间隔区（rbcSp）。与先前的结果一致，具有独特形态、生态和分子特征的瘘管阿拉里亚（Alaria fistulosa Postels & Ruprecht）与该属中的其他物种不同，我们建立了新属德鲁埃利亚属（Druehlia gen. nov.）来容纳它。对于其余的分离株，条形码数据解析出的不同线粒体单倍型表明，东北太平洋至少有三个初始物种经历了一段遗传隔离期，而ITS变异的意外水平和模式，以及这些分离株中发现的极端形态可塑性，很可能是近期物种屏障崩溃的结果。ITS扩增子的克隆揭示了几个个体中有多个ITS拷贝，进一步支持了这一假设。
