Molecular phylogenetic analyses of Ulva (Chlorophyta, Ulvophyceae) mats in the Xiangshan Bay of China using high-resolut
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Molecular phylogenetic analyses of Ulva (Chlorophyta, Ulvophyceae) mats in the Xiangshan Bay of China using high-resolution DNA markers Feng Liu & Shaojun Pang & Xiaobo Zhao
Received: 1 August 2012 / Revised and accepted: 22 November 2012 # Springer Science+Business Media Dordrecht 2012
Abstract Intertidal Ulva mats occur annually in winter and spring in the Xiangshan Bay (29°26′–29°34′ N, 121°27′– 121°50′ E) of China. Thousands of tons of Ulva biomass have been harvested as edible seaweeds for human consumption for several decades in this region. This investigation was designed to quantify Ulva microscopic propagules associated with the mat, identify species composition, and to analyze intra-species relationships using three molecular markers. Phylogenetic analysis based on the nuclear encoded rDNA internal transcribed spacer region, the plastid encoded large subunit of the ribulose 1,5-bisphosphate carboxylase gene, and the 5S rDNA spacer region showed that the mat was principally composed of Ulva prolifera and Ulva flexuosa. Their propagules were detected in both the water column and sediment. Based on phylogenetic analyses of the 5S rDNA spacer region, mat samples of U. prolifera and U. flexuosa were genetically distinct from the green tide samples in the Yellow Sea and U. flexuosa samples from Jiangsu coasts, respectively, revealing that isolated geographical position of the Xiangshan Bay might result in the maintenance of a distinct Ulva population. The results demonstrate that high-resolution DNA markers have great potential in identification and discrimination at and below the species level. Keywords Microscopic propagule . Ulva mat . Ulva prolifera . Ulva flexuosa . High-resolution DNA markers F. Liu : S. Pang (*) : X. Zhao Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao 266071, China e-mail: [email protected] URL: www.mbccc.ac.cn
Introduction Species of the green macroalgae genus Ulva (including Enteromorpha; Hayden et al. 2003) show high levels of intraspecific morphological and cytological plasticity in different growth phases, seasons, and environmental conditions (Blomster et al. 2002; O’Kelly et al. 2010), leading to difficulties in morphology-based species identification (Leskinen et al. 2004). Some DNA markers, including the nuclear encoded rDNA internal transcribed spacer (ITS) region, the plastid encoded large subunit of the ribulose 1,5-bisphosphate carboxylase gene (rbcL), and the 5S rDNA spacer region, have been used in species level phylogenetic studies in the order Ulvales (Hayden and Waaland 2002; Pang et al. 2010; Sun et al. 2011). Previous studies found that ITS and rbcL sequences were not effective DNA markers to infer interspecies relationships in the Ulva linza–procera–prolifera (LPP) clade (Leliaert et al. 2009; Liu et al. 2010a, b). Instead, the 5S rDNA spacer region, which is about ten times more variable than the ITS, was found to be a useful marker to delimit species within the LPP clade (Shimada et al.
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