Molecular evidence of the presence of Dictyota dichotoma (Dictyotales: Phaeophyceae) in Argentina based on sequences from mtDNA and cpDNA and a discussion of its possible origin

Dictyota is a brown algae genus inhabiting tropical to warm temperate environments where it is an important food source, shelter and substrate to several species of invertebrates and other algae. The taxonomy of this genus is troublesome, with poor species delimitation and doubtful records in the literature. Dictyota dichotoma, the type species of the genus, was commonly accepted as a cosmopolitan species because of the inaccurate geographical distributional range as a consequence of misidentification in several parts of the world. Recent studies with molecular data revealed new species and a new understanding of the evolution and biogeography of the genus Dictyota. These studies confined natural populations of D. dichotoma to Europe (Atlantic and Mediterranean coasts) and Macaronesian islands (Azores, Madeira and Canary archipelagos). Also, they confirmed its presence in South Africa, but whether the species was native or introduced in South Africa could not be verified. In the present study two regions of cpDNA (psbA, rbcL) and one region of mtDNA (nad1) from Argentinian samples, identified morphologically as D. dichotoma, were analysed and compared to other Dictyota species. The identity of these samples as D. dichotoma was confirmed. A haplotype network analysis using all available psbA sequences distinguished seven haplotypes divided into two geographic groups: Atlantic–Mediterranean and Canarian. In Argentina and South Africa only the most common haplotype of the Atlantic–Mediterranean group was observed. According to the paleoceanographic currents and the presence of a European haplotype, the introduced nature of D. dichotoma is indicated.网地藻属（Dictyota）是一类褐藻，栖息于热带至暖温带海域，是多种无脊椎动物及其他藻类的重要食物来源、庇护场所与附着基质。该属的分类学研究颇具挑战性，物种界定模糊，且文献记载多存疑。该属的模式种（type species）为叉开网地藻（Dictyota dichotoma），此前因全球多地的误鉴定导致地理分布范围被错误认定，曾被普遍认为是广布种。近期基于分子数据的研究揭示了多个新种，并重塑了人们对网地藻属演化与生物地理学的认知。这些研究将叉开网地藻的自然种群限定在了欧洲（大西洋及地中海沿岸）以及马卡罗尼西亚群岛（亚速尔群岛、马德拉群岛与加那利群岛）。同时，研究证实该种在南非亦有分布，但无法确认该物种在南非究竟是原生分布还是人为引入。本研究对形态学鉴定为叉开网地藻的阿根廷样本的两段叶绿体DNA（cpDNA）区域（psbA、rbcL）以及一段线粒体DNA（mtDNA）区域（nad1）进行了分析，并与其他网地藻属物种进行了比对。研究确认了这批样本确为叉开网地藻。基于所有可用psbA序列构建的单倍型网络（haplotype network）分析共区分出7个单倍型，可划分为两个地理类群：大西洋-地中海类群与加那利群岛类群。在阿根廷与南非仅观测到大西洋-地中海类群中最常见的单倍型。结合古海洋洋流特征以及欧洲单倍型的存在，本研究提示叉开网地藻为外来引入物种。