Journal article

Publication year: 1999

Pages: 355-377

Journal: Malacologia

Volume number: 41

Issue number: 2

ISSN: 0076-2997

URL: https://biodiversitylibrary.org/page/13111770

Publisher: Institute of Malacology

Abstract: 
This paper focuses on two snail-borne helminths in China infecting man, Schistosoma and Paragonimus, but primarily on Schistosoma (Asian caenogastropod-transmitted). Of concern are 1) the direction and timing of the evolution of the snail family Pomatiopsidae and the pattern of coevolution of Schistosoma and Paragonimus with defined clades within the Pomatiopsidae, 2) the question of monophyly of the Pomatiopsidae and its two subfamilies Pomatiopsinae and Triculinae, 3) the amount of genetic diversity within Oncomelania throughout China as revealed by allozymes and DNA sequences, 4) Oncomelania ecology and genetics with regard to different modes of transmission of Schistosoma japonicum, 5) the implications of the Three Gorges dam across the Yangtze River on emerging diseases.Allozyme and COI gene sequence data confirm the monophyly of the Pomatiopsidae with its two subfamilies. The timing and direction of evolution of the Pomatiopsidae in Asia are congruent with area cladograms based on geological-paleontological events and evolving river systems (Yangtze, Mekong, Red) from about the end of the Miocene. The two subfamilies are highly divergent on the basis of morphology and ecology but less so on the basis of molecular genetics. The Pomatiopsidae are in a clade distinctly divergent from the Hydrobiidae, a family that has been used in China to classify the Pomatiopsinae and Triculinae. Figs. 2 and 3 show the relationships of the two parasite genera with the morphology-based clades of those caenogastropod families transmitting Schistosoma and Paragonimus throughout the world (excluding Africa for which too little is known). Two caenogastropod superfamilies are involved (Ceritheacea and Rissoacea); Only Paragonimus has evolved with taxa of the Thiaridae, Pleuroceridae, Hydrobiidae; both parasite genera have evolved with various pomatiopsid taxa of both subfamilies. While all data available (reviewed in Davis, 1980, 1992) show that Schistosoma is tightly linked genetically in a coevolved system with its snail host, such a close linked genetic coevolved system operating at the population to genus level in Paragonimus is in doubt. Erhaia (Pomatiopsinae) and Tricula (Triculinae) were found in sympatry in Fujian Province, both reported transmitting putative Paragonimus skrjabini. P. skrjabini has been reported from at least 22 species of pomatiopsine and triculine snails in China. The evidence suggests that species of Paragonimus can switch hosts between different snail subfamilies and genera. The higher classification of Erhaia is in doubt. Should Erhaia be found not to be a pomatiopsid snail, then host switching can occur between some families (at least of the Rissoacea).Based on COI and allozyme data there are three geographically isolated subspecies of Oncomelania on the mainland of China: O. h robertsoni in Yunnan and Sichuan, O. h. tangi in Fujian Province, O. h. hupensis throughout the Yangtze drainage below the Three Gorges of the Yangtze River as well as parts of Guangxi and Zhejiang Provinces. Within O. h. hupensis there is considerable genetic diversity. Nei's minimum genetic distance among populations is 0.204 +/- 0.085. We conclude, on the basis of allozyme data from Miao River populations of O. h. hupensis in Hubei Province, that ribbed and smooth-shelled populations (shell with varix; shell growth with the same allometry) are the same species. Ribbing is found in populations affected by annual floods, especially the annual flooding of the Yangtze River. Smooth-shelled populations are upstream, above the effects of flooding. Thus, smooth-shelled O. fausti and O. h. guangxiensis, nominal taxa used by some authors, are synonyms of O. h. hupensis.Using allozyme population genetics and COI gene sequence data we have found that there is considerable genetic instability in what one would initially presume to be a population. Duringflooding, snails are swept from flood plains and islands, float down the Yangtze, and are deposited in diverse locations or are swept into canals and become deposited along canals. These aggregates of snails derived from various places do not exhibit Hardy-Weinberg equilibrium for polymorphic loci. Haplotypes of the COI gene are shown to be most useful for demonstrating genetic instability. Data are presented from six "populations" from around Dong Ting Lake of Hunan Province. Sequence data were obtained from 10 individuals taken from each site. In a stable population, one expects 0 to 0.5% nucleotide differences within a population (0-3 nucleotide differences), or one to two haplotypes per 10 individuals. One such population was found at low elevation beyond effects of flooding. The other sites were around the edge of the lake and are flooded annually. Snails from these lowland localities had 6 to 10 haplotypes per 10 individuals (3.5 to 3.9% polymorphic sites), i.e. they were genetically unstable aggregates. The diversity of haplotypes enables us to map gene flow and patterns of intermixing of snails among localities.Four different modes of transmission of Schistosoma japonicum are discussed. Differences are based on genetically differentiated subspecies, whether or not the populations are affected by annual flooding, life expectancy, population genetic stability, biogeography, and whether or not cattle play a dominant role in transmission of the disease. The implications of the Three Gorges Dam across the Yangtze River is discussed both in terms of the potential for snail transport into the vast reservoir but also of the impact on Poyang Lake, the largest lake in China and a major endemic area for schistosomiasis. A remote sensing image is used in conjunction with GIS technology to discuss snail-schistosome interactions and epidemiology on Poyang Lake marshlands.

Harvard Citation style: Davis, G., Wilke, T., Zhang, Y., Xu, X., Qiu, C., Spolsky, C., et al. (1999) Snail-Schistosoma, Paragonimus interactions in China: Population ecology, genetic diversity, coevolution and emerging diseases, Malacologia, 41(2), pp. 355-377. https://biodiversitylibrary.org/page/13111770

APA Citation style: Davis, G., Wilke, T., Zhang, Y., Xu, X., Qiu, C., Spolsky, C., Qiu, D., Li, Y., Xia, M., & Feng, Z. (1999). Snail-Schistosoma, Paragonimus interactions in China: Population ecology, genetic diversity, coevolution and emerging diseases. Malacologia. 41(2), 355-377. https://biodiversitylibrary.org/page/13111770