The establishment of an autotetraploid fish lineage produced by female allotetraploid hybrids × male homodiploid hybrids derived from Cyprinus carpio (♀) × Megalobrama amblycephala (♂)

Abstract

Distant hybridization leads to obvious changes in genotypes and phenotypes, giving rise to species with novel capabilities and adaptabilities. The establishment of autotetraploid lineages is difficult but useful in genetics and breeding. Here, we established a new autotetraploid fish lineage (4n = 200, F1-F4) via hybridization of an allotetraploid hybrid fish (4n = 148) (♀) × a crucian carp-like homodiploid fish (2n = 100) (♂) derived from common carp (Cyprinus carpio, 2n = 100) (♀) × blunt snout bream (Megalobrama amblycephala, 2n = 48) (♂). The results at the chromosome and DNA content levels indicated that the individuals of the autotetraploid fish had 200 chromosomes originating from common carp. The mean erythrocyte nuclear and spermatozoa volumes of these individuals were two times larger than those of common carp. Furthermore, the autotetraploid individuals harboured more DNA types in the 5S rDNA and Hox genes, including the recombination type, maternal-specific type, and paternal-specific type. The establishment of the autotetraploid fish lineage was caused by the fertilization of autotriploid eggs produced by the female allotetraploid fish (4n = 148) and haploid sperm produced by the male crucian carp-like homodiploid fish (2n = 100). The formation of the autotriploid eggs was associated with the mechanism of genomic doubling by premeiotic endoreduplication, endomitosis, or fusion of the oogonia of the female allotetraploid fish. The transmission of DNA variation between successive generations (F1-F3) suggested that the autotetraploid fish lineage is undergoing rapid diploidization to maintain tetraploid stability. The establishment of this new autotetraploid fish lineage provides new germplasm resources for fish genetic breeding and for studies on species evolution.