Molecular phylogenetics and population genetics of pearl oysters in pinctada Röding, 1798.

• Other Authors: Yu, Dahui.
• Format: Others
• Language: English; Chinese
• Published: 2005
• Subjects: Molecular genetics; Pearl oysters > Phylogeny > Molecular aspects; Population genetics
• Online Access: http://library.cuhk.edu.hk/record=b6074094; http://repository.lib.cuhk.edu.hk/en/item/cuhk-343723

Pearl oysters of the genus Pinctada include some economically important species. The taxonomy of some of the species is problematic. Phylogenetic relationship of the species in the genus is also poorly studied. In the present study, phylogenetic relationships of P. chemnitzi, P. fucata, P. margaritifera, P. maxima, P. nigra, P. radiata (from China), P. fucata martensii (from Japan), P. albina and P. imbricata (from Australia) were studied with Pteria penguin as an outgroup, and genetic variation of Chinese P. fucata, Japanese P. fucata martensii and Australian P. imbricata populations were investigated (1) to address the taxonomic confusion and phylogeny of pearl oysters, (2) to understand the genetic connections between the Chinese P. fucata, Japanese P. fucata martensii and Australian P. imbricata in west Pacific and (3) to provide information for the genetic improvement program initiated in China. === Since P. fucata, P. fucata martensii and P. imbricata are synonymous, to study the genetic differentiation and genetic variation of such widely distributed populations is helpful in understanding their genetic connections. For this purpose, five populations, three from China (Daya Bay, Sanya Bay and Beibu Bay), one from Japan (Mie Prefecture) and one from Australia (Port Stephens) were studied using AFLP technique. Three primer pairs generated 184 loci among which 91.8-97.3% is polymorphic. An overall genetic among populations and an average of 0.37 within populations (ranging from 0.35 in Japanese population to 0.39 in Beibu Bay population) were observed. Genetic differentiation among the five populations is low but significant as indicated by pairwise GST (0.0079-0.0404). AMOVA further shows that differentiation is significant among the five populations but is not significant at a broader geographical scale, among the three groups of Chinese. Japanese and Australian populations or among the two groups of Australian and north Pacific populations. The low level of genetic differentiation indicated that P. fucata populations in the west Pacific are genetically linked. Among the five populations, the Australian one is more differentiated from the others, based on both pairwise AMOVA and GST analyses, and is genetically isolated by distance as indicated by Mantel test. However, genetic differences among the three Chinese populations are not correlated with the geographic distances, suggesting that Hainan Island and Leizhou Peninsula may act as barriers blocking gene flow. === The above three wild Chinese populations in southern China were compared with the three adjacent cultured populations using AFLP markers. Three pairs of primers generated 184 loci among 179 individuals in populations from Beibu Bay, Daya Bay and Sanya Bay. A high level of genetic diversity, ranging from 0.363 in a wild population in Sanya Bay to 0.388 in a wild population in Beibu Bay, was observed within both wild and cultured populations, indicating an absence of strong bottleneck effects in the history of cultured P. fucata populations. Yet cultured populations in Sanya Bay and Beibu Bay had more fixed loci than the corresponding wild populations. Genetic differentiation in most pairwise comparisons of populations was significant. AMOVA indicated that genetic variation among populations were very low (1.77%) though significant, while more than 98% variation resided among individuals within population. These findings provide no evidence to show that hatchery practice of pearl oyster in China to date has significantly affected the genetic diversity of the cultured populations, and suggest that all populations are competent for selection. Yet the significant genetic differentiation among populations implies that any translocation of individuals for genetic improvement program should be managed with caution for the preservation of genetic diversity in natural populations. === The internal transcribed spacers (ITS1 and ITS2) of nuclear ribosomal DNA were compared among the above nine taxa, based on sequences determined by the present study and those available from Genl3ank. The phylogenetic analysis indicates that the pearl oysters studied constitute three clades: clade I with the small oysters P. fucata, P. fucata martensii and P. imbricata, clade II with P. albina, P. nigra, P. chemnitzi and P. radiata, and clade III and clade III with the big pearl oysters P. margaritifera and P. maxima forming the basal clade. Clade II is made up two subclades: clade IIA consisting of P. albina and P. nigra and clade IIB consisting of P. chemnitzi and P. radiata. The topology of the phylogenetic tree and substitution pattern of ITS sequences suggest that P. margaritifera and P. maxima are primitive species and P. chemnitzi is a recent species. The genetic divergences between clades ranged from 28% to 76.5%, and between subclades, 8.7-10.2%. In clade I, the interspecific genetic divergences ranged from 0.6% to 1.4%, and overlapped with interspecific divergences (0.6-1.1%), indicating that P. fucata, P. fucata martensii and P. imbricata may be conspecific. Based on amplified fragment length polymorphism (AFLP) markers and ITS sequences from more individuals, analyses of the populations of these three taxa also support the conclusion that Chinese P. fucata, Japanese P. fucata martensii and Australian P. imbricata are the same species, with P. fucata being the correct name. The genetic divergence between P. albina and P. nigra was also very low (1.2%), suggesting that they may represent two subspecies that can only be distinguished by shell color. The genetic divergences between P. maxima and P. margaritifera, and between clade IIA and clade IIB ranged from 8.3% to 10.2%, suggesting that they are closely related, respectively. The ITS1 sequence of P. radiata from GenBank is almost identical to that of P. chemnitzi determined in the present study, suggesting that the specimen used for the P. radiata sequence was possibly misidentified. === Yu Dahui. === "August 2005." === Adviser: Ka Hou Chu. === Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6125. === Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. === Includes bibliographical references (p. 100-124). === Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. === Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. === Abstracts in English and Chinese. === School code: 1307.