The Mechanism Research Reproduction Isolation In Pinctada:Chromosome And RDNA Repetitive Elements Dynamic Evolution Analysis

Self-crossing test and hybrid test through artificial fertilization were conducted among P. martensii, P. chemnitzi, P. maculata and P. nigra. The average fertilization rate of self-crossed in P. martensii, P. nigra and P. maculata is78.56%,46.94%and44.70%, respectively; while the average fertilization rate of P. martensii(♀)xP. chemnitzi (♂) is19.27%; P. chemnitzi (♀)xP. martensii (♂) is18.29%; P. martensii(♀)xP nigra (♂) is36.43%; P. martensii(♀)xP. maculata (♂) is18.32%, respectively. The result shows that the fertilization rate of hybrid is lower than self-crossed. The zygote between P. martensiixP. chemnitzi can only develop to trochosphere, and then the larvae die; the fertilized eggs of P. martensii(♀)xP. nigra (♂) and P. martensii(♀)xP. maculata (♂) can develop to D-larvae, but terminate before reaching the umbo-stages. The results show that there is postzygotic isolation among miniature pearl oysters of Pinctada. Karyotype study of P. martensii(♀)xP. nigra (♂) shows that the chromosome number is2n=24and the karyotype formula is2n=10m+2m+16t.The GC content of ITS segments is higher than AT contents in seven kinds of pearl oyster, the GC content of P. maxima is highest, while that of P. chemnitzi is lowest. The GC content of P. teria is higher than four miniature pearl oysters, but lower than the two large-scale pearl oysters. There are310variable sites,81parsim-info sites and227Singleton sites in whole ITS sequence of P. chemnitzi; in P. maxima, that is247variable sites,66parsim-info sites and175Singleton sites. The variable sites of P. maculata and P. nigra are almost the same, but there are no parsim-info sites and Singleton sites, which differ from others. The r-value>1within P. martensii, P. maculate, P. nigra and P. margaritifera, while within P. chemnitzi, P. maxima and Pteria penguin, the r-value<1. There were highest occurrence frequency of double bases TT, CC, AA, GG in seven kinds of pearl oysters. Based on Kimura's2-parameter model, the distances between the sequences of P. maculata, P. nigra and P. martensii is0.10, the distances of P. martensii and P. chemnitzi is0.21,and between P.maxima and P.margaritifera, that is0.10. As an outgroup, Pteria penguin has a distant relationship of0.33-0.43with Pinctada. It shows the same topology in four kinds of phylogenetic Tree constructed by neighbor-joining method, maximum parsimony, maximum likelihood method, and minimum evolution method. P. maxima and P. margaritifera populations cluster in a clade solely, while other pearl oysters grouped together. Pteria penguin is an outgroup and form a sole branch.The homogenization proportion between natural populations of P. maxima and P. margaritifera is of greatest difference, it is6.4%and95.7%, respectively; between P.martensii and P. chemnitzi, it is31.9%and53.2%, they all show three peaks. There is single peak in Pteria penguin natural population, presented completely homogenization. The polymorphisms site of ITS sequence were AA,CA,CC,T, TTA in P. martensii natural population. There is a lot of single base in polymorphisms site of P. maxima and P. chemnitzi, indicates that the sequences have great divergence.