The Taxonomic Status Of Anodonta Woodiana Based On Morphology And Molecular Properties

The Taihu Lake is the third largest freshwater lake in China. So far, the lake has been seriously eutrophicated and the water quality has greatly deteriorated because of the discharge of industrial and domestic wastewater. Therefore, a "Freshwater Mussel Watch’’project in Taihu Lake has been under way first-hand by Freshwater Fisheries Research Center, Chinese Academy of Fishery Sciences, using the bivalve mussels Anodonta woodiana from the Taihu Lake as a unique bioindicator, to document reliable baseline levels of persistent chemical pollutants. Anodonta woodiana is widely distributed across China and commonly used for food and cultivating pearl. This unionid mussel is considered traditionally as being divided into3species, Anodonta woodiana elliptica, Anodonta woodiana pacifica, and Anodonta woodiana woodiana, based on the differences in shell morphology. However, the morphological features are greatly variable under different environmental conditions and hence taxonomic confusion usually exists when we use this mussel. Trying to clarify this problem, we employed the molecular approaches to re-identified the possible taxonomic characteristics of the mussel individuals, studying comparatively with the morphological features. Moreover, the present study is also hoped to provide the further theoretical basis for the above-mentioned "Freshwater Mussel Watch" project.In the present study, multivariate statistical analysis, i.e., Principal Component Analysis, Cluster Analysis, and Discriminate Analysis were used for morphological investigation, while the mitochondrial NADH dehydrogenase subunit1(ND1) gene, the ribosomal DNA internal transcribed spacer1(ITS1), and16S rRNA gene fragment sequences were used for molecular analysis. The main results are as follow:1. Although there are some morphological differences among A. woodiana elliptica, A. woodiana pacifica, and A woodiana woodiana, all multivariate statistical analysis of Principal Component Analysis, Cluster Analysis, and Discriminate Analysis seemed to be unable to accurately identify the above three species each other. The discrimination rates of A. woodiana woodiana, A. woodiana pacifica and A. woodiana elloptica were75.0%,75.6%and84.5%, respectively.2. The comparative analysis of16SrRNA, ITS1, and ND1gene fragment sequences suggested that the16SrRNA gene was more suitable for A. woodiana determination at the genus level, while ITS1、ND1were more suitable for the determination at species-level.3. Genetic distances were calculated based on the Kimura2-parameter model and in turn the neighbor-joining (NJ) phylogenetic tree was constructed. For purpose of comparison, the ND1and ITS1sequences of Cristaria plicata from NCBI GeneBank were co-analyzed with those of the mussels in this study. The largest intraspecific genetic distances among all studied mussels were0.002-0.087by the ITS1gene, and0-0.0082by the NDl gene, and0-0.0065by the16SrRNA gene, respectively, which were much lower than those of the interspecific distances with C. plicata.4. Based on the morphology and molecular properties obtained, the present suggested that A. woodiana woodiana, A. woodiana pacifica and A. woodiana elloptica are likely to be the same species. It will be not necessary to separate them in our future researches of "Freshwater Mussel Watch" project.