Li Shi-Zhu, Wang Yi-Xiu, Yang Kun, Liu Qin, Wang Qiang, Zhang Yi, Wu Xiao-Hua, Guo Jia-Gang, Bergquist Robert, Zhou Xiao-Nong
National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Shanghai, 200025, China.
Geospat Health. 2009 May;3(2):221-31. doi: 10.4081/gh.2009.222.
Two internal transcribed spacer (ITS1 and ITS2) sequences of the non-coding region of the rDNA and a 16S RNA gene fragment of the mtDNA of Oncomelania hupensis, the intermediate host snail of Schistosoma japonicum in mainland China, have been investigated with a view to illustrate the influence of the environment on genetic differentiation. Thirteen populations of O. hupensis snails, representing four types of ecological settings, were collected to compare genetic and spatial distances. The length of the ITS1-5.8S-ITS2 gene sequence showed a range from 752 to 796 bp with a guanine-cytosine (GC) content of 49.1-50.3%, while that of the 16S sequence ranged from 505 to 508 bp with a GC content of 33.5-35.1%. The 5.8S fragment was shown to be highly conserved and it was therefore removed in the subsequent analysis. In contrast, the ITS flanking sequences and the 16S fragment were found useful for further study as their degree of polymorphism amounted to 13.2% and 8.6%, respectively. The genetic relationship was investigated using tools based on maximum parsimony, minimum evolution and neighbour-joining algorithms. Four branches of O. hupensis were found to be clearly represented on the 16S phylogenetic tree, namely (i) the mountainous region population (from Sichuan and Yunnan provinces); (ii) the Karst region population (from Guangxi autonomous region); (iii) the population representing the region of swamps and lakes along the Yangtze River basin which stretches through the Anhui, Hunan, Hubei, Jiangxi, Jiangsu and Zhejiang provinces; and (iv) the littoral, hilly region population (from Fujian province). These four population branches were found to be correlated to environmental features based on the concept of landscape ecology attributing genetic differentiation to differences in ecological features. However, only three main branches could be found on the ITS1-ITS2 phylogenetic tree. The swamps and lakes population (from the Yangtze River basin) and the littoral, hilly population (from Fujian province) were clustered on the third branch in spite of these two populations not being spatially related, i.e. no firm genetic demarcation between their snail populations was found. Thus, it seems that the Fujian population does not constitute a separate branch but belongs to the third branch. This fact, together with the strong genetic evidence that the subspecies O. hupensis guangxiensis represents a discrete branch, support the hypothesis that genetic differentiation of O. hupensis in mainland China is ultimately structured by landscape ecology.
为阐明环境对遗传分化的影响，对中国大陆日本血吸虫中间宿主钉螺的核糖体DNA（rDNA）非编码区的两个内部转录间隔区（ITS1和ITS2）序列以及线粒体DNA（mtDNA）的16S RNA基因片段进行了研究。采集了代表四种生态环境类型的13个钉螺种群，以比较遗传距离和空间距离。ITS1-5.8S-ITS2基因序列长度在752至796 bp之间，鸟嘌呤-胞嘧啶（GC）含量为49.1-50.3%，而16S序列长度在505至508 bp之间，GC含量为33.5-35.1%。5.8S片段显示高度保守，因此在后续分析中将其去除。相比之下，ITS侧翼序列和16S片段因多态性程度分别达13.2%和8.6%，被认为对进一步研究有用。使用基于最大简约法、最小进化法和邻接法算法的工具研究遗传关系。在16S系统发育树上清晰地呈现出钉螺的四个分支，即：（i）山区种群（来自四川和云南省）；（ii）喀斯特地区种群（来自广西自治区）；（iii）代表长江流域沼泽和湖泊区域的种群（该区域贯穿安徽、湖南、湖北、江西、江苏和浙江省）；以及（iv）沿海丘陵地区种群（来自福建省）。基于景观生态学概念，将遗传分化归因于生态特征差异，发现这四个种群分支与环境特征相关。然而，在ITS1-ITS2系统发育树上仅发现三个主要分支。长江流域的沼泽和湖泊种群与福建沿海丘陵种群虽在空间上不相邻，但却聚类在第三个分支上，即未发现其螺类种群间存在明确的遗传界限。因此，福建种群似乎并不构成一个单独的分支，而是属于第三个分支。这一事实，连同有力的遗传学证据表明广西钉螺亚种代表一个离散分支，支持了中国大陆钉螺遗传分化最终由景观生态学构建的假说。
