The Genetic Diversity Of The Glyptosternum Maculatum Populations

Glyptosternum maculatum belonged to the order of Siluriformes,Sisoridae,Glyptosternum.It was mainly distributed in the Brahmaputra River basin in Tibet of China and was mainly distributed in the Indus River basin in India.Based on the control region(D-loop)sequence and cytochrome b gene(Cyt b)sequence of the mitochondrial gene,the genetic structure and genetic diversity of G.maculatum populations in different water systems of Glyptosternum in China were explored.It would provide some biological methods for developing and implementing the protective measures of germplasm resources of G.maculatum and provide certain reference value for the study and protection of other plateau fish species.The main results of this study were as follows:(1)Based on the mitochondrial D-loop sequence and Cyt b sequence,the genetic composition of G.maculatum populations in different geographical populations of the Brahmaputra River basin were studied.Results showed that the sequence length of DLoop were 551 bp and sequence length of Cyt b sequence were 1100 bp after sequence analysis and multiple alignment.The average base contents of T,C,A,and G in the D-loop sequence were 30.8%,19.6%,35.3%,and 14.3%,respectively,in which the content of base A was the highest,while the content of base G was the lowest.The total content of base G and C was(33.9%),which was significantly lower than that of base A and T(66.1%).The average base contents of T,C,A,and G in the Cyt b sequence were 27.2%,23.9%,23.9%,and 25.0%,respectively,in which the content of base T was the highest,while the content of base C and A were the lowest.The total content of base G and C was 48.9%,which was significantly lower than that of base A and T(51.1%).The Cyt b sequence also exhibited a base bias similar to that of the D-loop sequence,which reflects the characteristics of the base composition of the mitochondrial gene sequence of G.maculatum.(2)The sequence variation and base substitution of G.maculatum population were analyzed by mitochondrial D-loop sequence and Cyt b sequence,and the genetic variation of G.maculatum in different regions was discussed.Based on the mitochondrial DNA control region,a total of seven sites were found to be mutated,and the ratio of the average transitionsal pairs to the transversional pairs R was six.The transitionsal pairs mainly occured between G-A base pairs,and the transversional pairs occured between T-A base pairs.Moreover,based on Cyt b sequences,G.maculatum sequences were detected,a total of twenty five sites were found to be mutated,and the ratio of the average transitionsal pairs to the transversional pairs R was 2.125.The transitionsal pairs mainly occured between C-T base pairs,and the transversional pairs occured between A-C base pairs.The sequence variation of Cyt b mainly distributed in the third codon.(3)The genetic diversity and genetic distance of different G.maculatum populations were analyzed by mitochondrial D-loop sequence and Cyt b sequence.Ten haplotypes among G.maculatum individuals were detected in the mitochondrial DNA control region,haplotype diversity and nucleotide diversity were 0.678 and 0.0016,respectively.Twenty five haplotypes were detected in the Cyt b markers,haplotype diversity and nucleotide diversity was 0.713 and 0.0010,respectively.Analysis of molecular variance(AMOVA)was performed on the mitochondrial sequences of different populations of G.maculatum.The results showed that the genetic variation based on D-loop sequence occurred mainly within populations was 88.4%,and among populations was 11.6%.The genetic variation based on Cyt b sequence occurred mainly within populations was 87.0%,and among populations was 13.0%.The genetic distance results showed that the genetic distances among populations of D-loop sequences of different G.maculatum geographical populations were relatively obvious,while the differences within populations were relatively small.Among that,the genetic distance between the SG population and the XTM population was the largest,and the genetic distance between the QS population and the LS population was the smallest.The genetic distance analysis result of Cyt b sequence of the different G.maculatum geographical populations was similar to the D-loop sequence,the genetic distances among populations were relatively obvious,but the differences within populations were relatively small.Among that,the genetic distance between the LS population and the BSC population was the largest,and the genetic distance between the QS population and the LZ population was the smallest.(4)The NJ clustering tree was constructed by the haplotype of the D-loop sequence and Cyt b sequence of the different G.maculatum populations.Two kinds of NJ clustering trees showed that the differentiation level among different haplotypes was low.All G.maculatum sequences were clustered into one clade.Haplotypes of the different geographical population crossed each other and cannot be effectively distinguished.There was no obvious correspondence between haplotype clustering and geographical distribution of different populations.