Comparative Investigation Of The Genetic Diversity Between C.a. Gibelio And C.a. Auratus

The silver crucian carp (Carassius auratus gibelio Bloch, triploidy) from northern China is well known for its gynogenesis and its bisexual population. Surprisingly, it might as well have gonochoristic reproduction when inseminated by homologous sperm. But there still has no experimental proof for it. Owing to its identical morphology with Carassius auratus auratus (diploidy) and its specific genetic background, the genetic relationship between triploid and diploid from the same places may be the key to investigate the origin of Carassius auratus gibelio Bloch and its specific reproductive mode.By comparing several levels of polymorphism between wildly diploid individuals and wild triploidies amplified by primers from CDS sequences~ gene sequences and microsatellite loci, we found there were no difference between C. a. gibelio and Carassius auratus auratus in low polymorphic loci. In moderately diverse loci, such as some microsatellites, the wild triploidies and the wild diploidies shared the same band patterns or genotypes; while in highly polymorphic microsatellite loci, both shared the vast majority of the DNA fragments and some of the band patterns. The individuals of the triploid and the diploid overlapped in the phylogenetic tree and formed many small clusters by the UPGMA analysis of SSLP band.patterns. From the band patterns and their phylogenetic tree, we know that the triploid have as much diversity as the diploid, which showed C. a. gibelio didn at all appear to be the typical characteristics of pure clones. The single strand conformational polymorphism (SSCP) of mtDNA D-loop region showed the same phenomenon between the triploid and the diploid, too.The very special polymorphic information helped us construct the reproductive relationship model and evolutionary model between and among the triploid and diploid. The model showed C. a. gibelio Bloch originated from the diploid in certain environment such as cold and evolved the ability of anoxia tolerance in ice-covered water through intraspecific polyploidization. The triploid might evolve from the extant diploid in certain circumstances or have gene exchanges with the diploid. Once the triploid formed, two kinds of reproductive modes existed in them: gynogenesis and gonochoristic reproduction. It the gonochoristic reproduction that directly resulted in the male triploid individuals and clonal diversity. From the very close genetic relationship of both and the functiOnal diploidization of2the triploid, we postulated that the triploid males might be still determined by XY sexual mechanism as the diploid do. Half of the probability of homologous pronucleus fusion might be the ratio of the triploidy male production.