Morphological Variation And Molecular Phylogeny Of Different Geographical Populations

The freshwater snail species Physa acuta which originated from in North America is a cosmopolitan pulmonate and an important intermediate host for many parasites such as Angiostrongylis cantonensis and Echinostoma revolutum. During past three decades, it has been found in Taiwan, Hong Kong, Shenzhen, Lijiang, Taihu, Beijing. As an alien invasive specie with a great power in reproduction and strong adaption to environment, Physa acuta can threaten the biodiversity and human health. By understanding shell moprhologieal and genetic diversity of Physa acuta populations in distribution area, the government department concerned can facilitate the development of the Physa acuta population to strengthen the control and prevention for reducing its impact on the ecosystem in China.Through field survey, specimens collection and identification, samples were collected from Yanzhou, Nansihu, Sihe, Dajiangkou, Chaohu, Xingyunhu, Shenzhen, seven geographic populations of Physa acuta in five provinces based on the research object. Specimens were used to measure anatomic data(shell height, shell width, shell mouth length, shell mouth width, body whorl height, spiral department) with an electronic digital caliper and analysed by using scatter plots, cluster analysis, principal component analysis. CTAB method were adopted to conduct DNA isolation and purification in the test. Cytochrome oxidase subunit I partial sequences of mitochondrial DNA was used as a molecular marker to amplify and sequenced, the conservation genetics and molecular phylogeography of the Physa acuta were discussed, and the phylogenetic relationships of 7 geographic populations from China was also studied. The results are below.There are obvious differences in body whorl height and spiral department between Chaohu population and the other six populations by using scatter plots, cluster analysis, principal component analysis. The results shows that phenotype traits have some similarities and differences in each of the populations. The Physa acuta make use of the plasticity of shells to adapt to the environment.Mitochondrial cytochrome oxidase subunit I gene with 654 base pairs from 7 populations. The base composition of mtDNA COI gene partial sequences was: A 26.13%, C 14.79%, G 18.44%, T 40.64%, the content of T is the largest and C is the smallest. A+T 66.80% is significantly higher than G+C 33.20%. This phenomenon is similar with the other shellfish. 19 kinds of amino acids are coded in Mitochondrial CO I genes and shows strong bias i n amino acids contents.Among the gene fragments of all the individuals, 13 variable nucleotides were detected, and 3 haplotypes shared in 7 populations. The overall haplotype diversity was 0.767±0.071 in the 7 geographic populations, the overall nucleotide diversity was 0.011213±0.009016. The population of haplotype diversity and nucleotide diversity are in a low level. Analysis of molecular variance across all populations showed that there are low levels of genetic divergences among the 7 populations.We established the phylogenetic trees by using Neighbor-Joining, Maximum Parsimony and Maximum Likelihood methods. The 7 populations, American, Canadian, Franch, Netherlandish were located in a group and had a close relationship and weren’t located in the Physa foncinalis which is from the other species in Chinese Physidae.The results showed that the topologies of the three phylogenetic trees are almost identical.