Cytogenetic Study On Hybrid Scallops

Cytogenetic studies were made on several hybrid scallops using the karyotype method. Hybridizations between Chlamys farreri and Patinopecten yessoensis, C. farreri and Chlamys nobilis were studied. Upon the optimization of metaphase chromosome preparation from scallop, analysis and comparison on chromosome number and karyotypes were made between the hybrids and their parents.Method of metaphase chromosome preparation from scallop was optimized. The gill tissue and embryo before the stage of trochophoro larve were proved to be good materials for chromosome preparation, while excellent chromosomes can hardly be prepared from the gonad tissue or embryo after the stage of trochophoro larve. For the gill tissue, the best method is to dip the tissue in Ringers solution for 10 minutes, then 50 minutes in 0.04% colchicines solution, 30 minutes in 0.075M potassium chloride solution, fixation by Carnoy's; for the embryo, it is better to use 0.02% colchicines for 2.5 hours and potassium chloride for 20 minutes. Results also showed that lectins such as PHA did not have distinct influence on increasing of metaphase of scallop.Intergeneric hybridization between Patinopecten yessoensis and Chlamys farreri yielded hybrids which can survive to adult. The karyotypes of hybrids and their parents were analyzed and compared. The Chlamys farreri's diploid chromosome number is 2n=38, karyotype consists of 6m+10sm+22t, NF=54; while the Patinopecten yessoensis's diploid chromosome number is 2n=38, karyotype consists of 6m+10sm+16st+6t, NF=54. Result from analysis on 55 hybrids'metaphase chromosomes showed that the hybrids chromosome number is 38. However, the karyotypes of these hybrids were not uniform. Many kinds of karyotypes were observed from our studies on hybrids. Moreover, some special chromosomes which were obvious in the metaphase chromosomes of the parents scallop did not be observed in hybrids'.The same phenomenon was observed in interspecific hybridization betweenChlamys farreri and Chlamys nobilis . The karyotypes of adult hybrids and their parents were analyzed and compared. The Chlamys nobilis's diploid chromosome number is 2n=32, karyotype consists of 6m+26t, NF=38. The chromosome number of hybrids is 38 other than the expected value 35. Polymorphism in karyotypes of hybrids was also observed.To avoid the negative influence of mass impregnation in former experiments, single pair hybridizations (one male scallop and one female scallop) were carried out. The embryos of the hybridizations were collected for karyotype studies. The results showed that hybrids from hybridization between Chlamys farreri and Chlamys nobilis had 35 chromosomes and uniform karyotype. On the other hand, 1/3 of hybrids from hybridization between Chlamys nobilis and Chlamys farreri had 35 chromosomes, another 1/3 had 38. Results showed polymorphism in karyotypes of hybrids from latter hybridization.This phenomenon of shellfish cytogenetics had not been reported before. Some scientific hypotheses for the phenomenon were listed in the thesis.