title: Coexistence of diploid, triploid and tetraploid crucian carp (Carassius auratus) in natural waters.
abstract: BACKGROUND
  Crucian carp (abbreviated CC) belongs to the genus of Carassius within the family of Cyprinidae. It has been one of the most important freshwater species for Chinese aquaculture and is especially abundant in the Dongting water system of Hunan province. CC used to be considered as all diploid forms. However, coexistence of diploid (abbreviated 2nCC), triploid (abbreviated 3nCC) and tetraploid crucian carp (abbreviated 4nCC) population of the Dongting water system was first found by our recently researches.
  
  
  RESULTS
  We examined the ploidy level and compared biological characteristics in different ploidy CC. In reproductive mode, 2nCC was bisexual generative and 4nCC generated all-female offspring by gynogenesis. However, 3nCC generated progenies in two different ways. 3nCC produced bisexual triploid offspring fertilized with 3nCC spermatozoa, while it produced all-female triploid offspring by gynogenesis when its ova were activated by heterogenous spermatozoa. The complete mitochondrial DNA of three different ploidy fishes was sequenced and analyzed, suggesting no significant differences. Interestingly, microchromosomes were found only in 3nCC, which were concluded to be the result of hybridization. Allogenetic DNA fragments of Sox genes were obtained in 3nCC and 4nCC, which were absent in 2nCC. Phylogenetics analysis based on Sox4 gene indicated 3nCC and 4nCC formed a separate group from 2nCC.
  
  
  CONCLUSIONS
  In summary, this is the first report of the co-existence of three types of different ploidy crucian carps in natural waters in China. It was proved that the coexistence of different ploidy CC was reproductively maintained. We further hypothesized that 3nCC and 4nCC were allopolyploids that resulted from hybridization. The different ploidy CC population we obtained in this study possesses great significance for the study of polyploidization and the evolution of vertebrates.
authors.affiliation: Key Laboratory of Protein Chemistry and Fish Developmental Biology of Education Ministry of China, College of Life Sciences, Hunan Normal University, Changsha 410081, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Xiao
authors.forename: Tuomi
authors.initials: T
authors.lastname: Zou
authors.forename: Yubao
authors.initials: Y
authors.lastname: Chen
authors.forename: Lin
authors.initials: L
authors.lastname: Chen
authors.forename: Shaojun
authors.initials: S
authors.lastname: Liu
authors.forename: Min
authors.initials: M
authors.lastname: Tao
authors.forename: Chun
authors.initials: C
authors.lastname: Zhang
authors.forename: Rurong
authors.initials: R
authors.lastname: Zhao
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhou
authors.forename: Yu
authors.initials: Y
authors.lastname: Long
authors.forename: Cuiping
authors.initials: C
authors.lastname: You
authors.forename: Jinpeng
authors.initials: J
authors.lastname: Yan
authors.forename: Yun
authors.initials: Y
authors.lastname: Liu
mesh_terms: D000818:Animals; D002347:Carps / Q000235:genetics*; D005260:Female; D005618:Fresh Water; D008297:Male; D012098:Reproduction; D057891:Tetraploidy; D057885:Triploidy