Genetic Diversity Of Haemaphysalis Tibetensis And Haemaphysalis Flava Based On Partial Mitochondrial Genes

Both Haemaphysalis tibetensis and Haemaphysalis flava belong to the genus Haemaphysalis of Ixodidae,which can spread a variety of pathogens and harm the health of human and animal.H.tibetensis is distributed in the Qinghai-Tibet region of China,and the H.flava is widely distributed in China,Japan and South Korea.Through the comparative study on the genetic diversity of the two species populations,it is value to study the species formation,evolution,and geographical distribution of ticks.The aim of this study was to analyze H.tibetensis and H.flava populations using mitochondrial COI,Cytb,ND5 and 16 S rRNA genes.1.In this study,H.tibetensis was collected in Lhasa,Tibet Autonomous Region and obtained 74 COI gene sequences,802 bp in length.Cytb,ND5 and 16 S rRNA genes were obtained from 57,66 and 56 sequences,respectively.The lengths of the sequences were 336 bp,476 bp and 406 bp respectively.H.flava was collected in Xinyang City,Henan Province,Wuxi City,Jiangsu Province and Yueyang City,Hunan Province.COI,Cytb,ND5 and 16 S rRNA genes were obtained from 60,62,62 and 54 sequences,respectively.The lengths of the sequences were 802 bp,336 bp,476 bp and 407 bp.2.The mitochondrial genes of H.tibetensis and H.flava all had obvious AT deviation.The AT content of mitochondrial genes in H.tibetensis was lower than that of H.flava,indicating that mitochondrial genes of H.tibetensis were more susceptible to natural selection and mutate.The transition of 16 S rRNA gene in these two species of ticks was less than that of transversion.After analysis of base saturation substitution,the two mitochondrial genes of ticks did not reach saturation.3.The genetic diversity parameters of each mitochondrial gene in H.tibetensis were higher than those in H.flava,indicating that H.tibetensis adapted easily to environment and survivability.The evolution of H.tibetensis was relatively stable.The results of the 16 S rRNA gene of mitochondria only showed that the population was rapidly expanding after being bottlenecked.Mitochondrial Cytb and ND5 gene of H.flava results showed the population experienced a bottleneck effect.The mitochondrial COI and 16 S rRNA genes showed that the population experienced a bottleneck effect and then experienced expansion.4.The codon preference of mitochondrial genes in H.tibetensis and H.flava was low,but the codon preference of each mitochondrial gene in the latter was higher than that in the former.The ENC mapping analysis revealed that the the cause of the codon bias in the two ticks was mainly selection,not mutation.By comparing the amino acid contents of the proteins encoded by the two mitochondrial genes,the contents of glutamic acid,valine,arginine content in H.tibetensis were significantly higher than that of H.flava.5.In selective pressure analysis,it was found that the H.tibetensis COI,Cytb gene and H.flava COI gene was positively selected of evolutionary process,and the remaining mitochondrial genes were purified.The positive selection sites of mitochondrial genes from H.tibetensis and H.flava were detected using PAML software.Positive selection sites were detected in both COI and Cytb genes.This result was the same as the result of selective pressure analysis.6.In the joint sequence analysis,the mitochondrial genes of H.tibetensis showed greater variation,the genetic diversity parameters were higher than that of the H.flava,and H.tibetensis had evolved steadily,whereas H.flava experienced a bottleneck and then experienced population expansion.The results of the selective pressure showed that the Ka/Ks values of the combined sequence of the two species of ticks was less than 1,indicating that the evolution of the two species of ticks was restricted by the purification.