Genetic Structure Of Coilia Ectenes And Myxocyprinus Asiaticus In Yangtze River And Phylogeny Of Engraulidae And Catostomidae Fishes Based On Mitochondrial DNA Sequences

Because of overfishing, worsening environment, and construction of large water conservancy project, abundance of Coilia ectenes and Myxocyprinus asiaticus population had decreased obviously in recent years. Genetic diversity level of species concerns their capacity of adaptation, viability and potential of evolution. Therefore, the study of genetic diversity has important theoretical significance and application value for species conservation and sustainable utilization. C. ectences is an important commercial fish and M. asiaticus is an endangered fish in China. In the study, we analyzed genetic diversity of the two species by D-loop and Cytb sequences using molecular biology and bioinformatics methods. Meanwhile, genome characteristics of family Engraulidae and phylogeny of family Catostomidae were discussed. The results are as follows:1) We analysed genome characteristics, selection pattern and phylogenetic information included in different regions of mitochondrial genomes of10Engraulidae fishes. The results were as follows:Lengths of mitochondrial genomes were from16660bp to17069bp. Mitochondrial genome composition and gene order was consistent with other teleost fishes. After alignment,15704base pairs of consensus sequences were obtained. In which,5570were variable sites, accounting for35.5%of total sites. Among all genes, the ND6had the highest sequence divergence (47.5%) and kimura-2-p genetic distance (0.276); whereas the concatenated tRNA had the lowest sequence divergence (18.7%) and K-2-P distance (0.072). Protein coding genes were mainly acted by purifying selection which detected by Z test and Tajima’s D test. Most of the genes, except ND6, were influenced by purifying selection (Ka/Ks<1). ND4, ND2and Cytb genes were suitable molecular markers for phylogenetic study of Engraulidae fishes.2) We obtained mtDNA D-loop region sequences of61C. ectenes individuals in Yangtze River estuary and analyzed their genetic diversity. Results:1) obtained complete sequence of control region for1214-1290bp, showed length heteroplasmy.2)47distinct haplotypes were detected, and the five populations exhibited high haplotype diversity and low nucleotide diversity.3) Genetic differentiation index (Fst) was0.00097to0.09932; genetic distance was between0.000and0.009; the genetic variation among populations accounts for only4.21%of total variation.4) Mismatch distributions, Tajima’s D test and Fu’s Fs test suggested that C. ectenes in the Yangtze River estuary had not experienced a rapid population expansion in the recent past. The results showed that genetic diversity level of C. ectenes in the Yangtze River estuary was high. The five populations had not been formed geographic differentiation obviously and panmixis would occur between them.3) The Mitochondrial cytochrome b (mtDNA cytb) gene of three individuals of Myxocyprinus asiaticus were sequenced and analysed along with five sequences of Catostomidae from GenBank. The results were as follows:1144base pairs of consensus sequence of these three individuals of M. asiaticus were obtained, and these three sequences were identical without variation. Phylogenetic tree showed that genus Xyrauchen and Moxostoma formed a monophyletic clade, and genus Myxocyprinus, Cycleptus and Ictiobus formed the other clade. MtDNA cytb gene of Catostomidae fishes were mainly acted by purifying selection. The divergence time between genus Myxocyprinus and genus Ictiobus was about3.725million years, and that between genus Xyrauchen and Cycleptus was nearly5.375million years.