Genetics And Diet Traits Of Reciprocal Hybrids Lineage Derived From Hybridization Between Megalobrama Amblycephala And Culter Alburnus

It is commonly believed that distance hybridization is an effective method for new species formation,resulting from two or more sets of divergent genomes merger or doubling instantaneously.Hybridization played critical roles in fish farming,as the hybrid generally combine advantage traits of both parents.Recently,our understanding of gene imprint and maternal effect have been increasing enriched through the data from high-throughput sequencing,and which provide molecular basics for the mechanism of heterosis.In our previous study,we obtained two reciprocal hybrid lineages,BT(F1～F5)and TB(F1～F3),from distance hybridization between blunt snout bream(Megalobrama amblycephala,2n=48,BSB)and topmouth culter(Culter alburnus,2n=48,TC).In the present study,the generation BT-F4 performed self-crossing and successfully obtained generation BT-F5,the morphological characteristics,DNA content,reproductive characteristics,and ratio of genetic differentiation were comparatively analyzed to investigate stability and evolution of the allodiploid populations.Besides,the characteristics of alimentary canal,the content of digestion enzymes,and gut microbiota communities between the two types of hybrids and their parents were comparatively analyzed to investigate the diet traits of hybrids BT-F1 and TB-F1.Finally,liver transcriptome of the two types of hybrids lineage and parent were obtained by using RNA-seq,and the gene structure variation and homoeologs expression patterns were investigated between them.The main research contents are as follows:1.Comparative analysis the populations of hybrids BT lineage,flow cytometry results showed that all the tested BT-F4 and BT-F5 hybrids were diploid;and there no significant difference were detected between hybrids BT-F4～F5 and BT-F1～F3 in the appearance characteristics(quantifiable traits).Interestingly,approximately 15%individuals in hybrids BT-F4 and BT-F5 appeared genotype and phenotype differentiation.In addition,a larger number of halved chromosomes were observed in gonad tissues,indicated that the diverged chromosomes in allodiploid hybrid were able to be matched correctly during the meiosis process.2.To investigate the diet traits of BT and TB lineage,the structure of alimentary canal,enzyme content,and gut microbiota were comparatively analyzed,the result showed that the morphology of body,head,mouth,and pharyngeal bone were in the middle parent level,while the structure of intestinal(relative gut length,relative gut mass,and ZI index)and digestion content(intestinal cellulase and amylase,liver trypsin and amylase)in the reciprocal hybrids were more similar to BSB than to TC.Furthermore,the two types of hybrids showed a higher biodiversity level compared with carnivorous TC(P<0.05).Besides,the shared microbiota taxa(at genus level)in the two types of hybrids and BSB were more than that the microbiota taxa shared with TC.In addition,the composition and abundance of dominant microbiota taxa in the two types of hybrids were more similar to those of BSB than to those of TC,for example,the proportions of cellulase-producing microbes(such as Aeromonas and Clostridium)in hybrid BT-F1(23.53%)and hybrid TB-F1(18.37%)were similar to those in the BSB(20.71%),while showed significantly higher than that TC(4.81%).3.Based on the liver transcriptome from BT and TB lineage,orthologous analysis revealed that more than 7.57%homoeologs were chimera(non-homologous recombination)in BT lineage,while there less than 6.0%chimera in TB lineage.Combined with the results of Sanger sequence,the types of chimera were random polymorphism and can inheritance in different generation hybrids.Global expression level analysis showed approximately 20%genes were BSB-genome expression level dominance.Besides,the expression level of parent-origin homologous in different types of hybrids offspring were asymmetrical,a number of homoeologs were also detected silenced and special expressed in reciprocal hybrids.The results of qPCR showed the direction of homoeologs expression bias were transformed in different tissues and in different development stage.Taken together,we have obtained a stable and bisexual fertility hybrid lineage BT,made it became a precious germplasm resource of fish A large number of halved chromosomes were observed in the gonad tissues of BT lineage,which given insight into the reproductive biology of the allodiploid.The diets traits of BT-F1 and TB-F1 were both bias toward one parent,which provide perspectives in the fish’s diet adaptation and improvement.A proportion of chimera showed a random polymorphism and inherent reveled the two types of hybrid lineage was stay a dynamic evolution stage.The variations of gene regulation mechanism(such as silence,expression level dominance,homoeologs expression bias,and maternal effect),provide molecular basics for the heterosis research and genetic evolution.