Molecular Biological Evidence For The Evolution Of Common Carp Into Crucian Carp Through Distant Hybridization

Natural hybridization can promote gene communication among species,increase genetic diversity,and then evolve new species,which is one of the important driving forces for the speciation and evolution of natural species.Artificial distant hybridization can simulate natural hybridization,which provides efficient ways and materials for exploring the origin of species.In the experiment of distant hybridization between common carp?Cyprinus carpio L.,2nCOC,2n=100,??and blunt snout bream?Megalobrama amblycephala,2n BSB,2n=48,??,it was found that some individuals without a beard in the obtained hybrid offspring were very similar to wild crucian carp in appearance,so they were named as the new homodiploid crucian carp-like species?2nNCRC,2n=100?.The emergence of NCRC provides a new idea for the origin of crucian carp,that is,the species of crucian carp may originate from the hybridization of common carp and blunt snout bream.At present,the hybrid lineage has propagated to the sixth generation with good fertility.The results of fluorescence in situ hybridization tests and 18S rDNA,HoxB5b and other genes showed that NCRC was more inclined to crucian carp than their parents.Based on these,three aspects of DNA barcoding,Hox gene and transcriptome of NCRC were studied.To explore the genetic variation and genomic stability of NCRC in different generations will provide molecular biological evidences for the evolution of common carp into crucian carp by distant hybridization.The results are as follows:1)The COI and CR mitochondrial molecular markers and Tf nuclear gene molecular markers of NCRC,different geographical populations of wild crucian carp,red crucian carp,and HFJ were obtained.The phylogenetic analysis with parents revealed that:with the mitochondrial molecular markers,NCRC had a closer genetic relationship with crucian carp groups in each generation.And NCRC-F₂?NCRC-F₅ had a lower level of genetic diversity and stable genetic variation.With the nuclear gene molecular marker,NCRC had a high level of genetic diversity in each generation,and its relative with common carp and crucian carp in different groups was also shown in NCRC-F₁,which disappeared in following generations.Under the pressure of distant hybridization,the intense interaction between incompatible parental genomes resulted in a highest level of genetic diversity in NCRC-F₁.Subsequent generations tended to stabilize with self-crossing and internal self-protection mechanisms.2)The structure of Hox genes in three generations?F₁,F₂,F₅?of NCRC were analyzed with reference to parents,and the results showed that in the phylogenetic analysis of Hox genes,different genotypes of NCRC were clustered into the branches with common carp,blunt snout bream,and crucian carp,which not only reflected the hybridization characteristic,but also showed the closeness to crucian carp.The genetic types of Hox genes in different generations were divided into five types:mutations,chimerism,inheritance,pseudogene,depseudogene.A large number of mutant and chimeric Hox genes were found in NCRC genomes,which indicated that distant hybridization carried a huge impact on parental gene flow.The Hox genes had the most significant mutation and the highest level of genetic diversity in NCRC-F₁.As the generations continue,some Hox genotypes were retained and inherited stably in following generations,while some Hox genotypes were discarded during the rapid evolution of the species,and a small number of new genotypes were appeared.3)The liver tissues transcriptome analysis of five generations of NCRC showed that the gene expression of NCRC-F₁ was significantly different from other generations.Moreover,there were some gene differential expressions between adjacent generations,the functions were mainly concentrated in endoplasmic reticulum protein processing,protein output and other pathways.At the same time,the number of differentially expressed genes showed a decreasing trend with the generation,which were consistent with the genetic diversity and gene structure differences in two previous studies.In addition,it was found that the three types of genes of common carp,blunt snout bream and crucian carp were expressed in each generation.With successive generations,the gene expression ratio of common carp and blunt snout bream decreased while gene expression ratio of crucian carp increased,and the gene expression level gradually tended to be stable.Existing studies have shown that the new homodiploid crucian carp-like species has both the characteristics of hybridization and obvious biological characteristics of crucian carp.These results efficiently confirmed that common carp and blunt snout bream evolved into the new homodiploid crucian carp-like species through distant hybridization,which provided molecular biological evidence for the evolution of common carp into crucian carp through distant hybridization,and also provided an important reference for exploring the hybridization origin and the formation mechanism of distant hybridization species of crucian carp.