Abstract
Goldfish (Carassius auratus var., GF; 2n = 100) is the most popular ornamental fish in the world. It is assumed that GF evolved from red crucian carp (C. auratus red var., RCC; 2n = 100). However, this hypothesis lacks direct evidence. Furthermore, our knowledge of the role of hybridization in the formation of new species is sparse. In this study, goldfish-like fish with twin tails (GF-L; 2n = 100) was produced by self-mating red crucian carp-like fish (RCC-L; 2n = 100) derived from the distant crossing of koi carp (Cyprinus carpio haematopterus, KOC; 2n = 100; ♀) with blunt snout bream (Megalobrama amblycephala, BSB; 2n = 48; ♂). The phenotypes and genotypes of GF-L and RCC-L were very similar to those of GF and RCC, respectively. Microsatellite DNA and 5S rDNA analyses revealed that GF-L and RCC-L were closely related to GF and RCC, respectively. The presence of a twin tail of GF-L was related to a base mutation in chordinA from G in RCC-L to T in GF-L, indicating that the lineage of RCC-L and GF-L can be used to study gene variation and function. The sequences of 5S rDNA in GF-L and RCC-L were mapped to the genomes of CC and BSB, which revealed that the average similarities of both GF-L and RCC-L to CC were obviously higher than those to BSB, supporting that the genomes of both RCC-L and GF-L were mainly inherited from KOC. GF-L and RCC-L were homodiploids that were mainly derived from the genome of KOC with some DNA fragments from BSB. The reproductive traits of GF-L and RCC-L were quite different from those of their parents, but were the same as those of GF and RCC. RCC-L easily diversified into GF-L, suggesting that RCC and GF evolved within the same period in their evolutionary pathway. This study provided direct evidence of the KOC–RCC–GF evolutionary pathway that was triggered by distant hybridization, which had important significance in evolutionary biology and genetic breeding.
Highlights
Goldfish (Carassius auratus var.,GF; 2n = 100) and red crucian carp (C. auratus red var., RCC; 2n = 100), are the most prevalent ornamental fish in the world, and these species belong to Cyprinidae, Cyprininae, and Carassius (Luo et al, 1999; Wang et al, 2014)
The self-mating of RCCL produced 98% red crucian carp-like fish (RCC-L)-F2 and 2% goldfish-like fish (GF-L) with twin tails
As for RCC-L, CC, and BSB, the nucleotide similarities of the sequences of 5S rDNA (203, 340, and 479 bp) of RCC-L to CC were 98.03, 99.41, and 19.42%, respectively, whereas those similarities of RCC-L to BSB were 48.28, 27.94, and 19.42%, respectively, showing that the average similarity (72.29%) of RCC-L to CC was obviously higher than that (31.88%) of RCC-L to BSB
Summary
Goldfish (Carassius auratus var.,GF; 2n = 100) and red crucian carp (C. auratus red var., RCC; 2n = 100), are the most prevalent ornamental fish in the world, and these species belong to Cyprinidae (family), Cyprininae (subfamily), and Carassius (genus) (Luo et al, 1999; Wang et al, 2014). Some homodiploid hybrid species have been reported, e.g., in Helianthus (Rieseberg et al, 1995, 2003; Ungerer et al, 1998), Vigna (Takahashi et al, 2015), Iris (Arnold et al, 2012), and Pinus (Mao and Wang, 2011). There have been few reports on the formation of homoploid in animals; for example, the formation of a homodiploid crucian carp (Wang et al, 2017). Our knowledge of the role of hybridization in the formation of new animal species is sparse
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