Population Genetic Structure Of Culex Tritaeniorhynchus In Mainland China

Culex tritaeniorhynchus(Insecta: Diptera: Culicidae)distributed throughout China except Xinjiang.C.tritaeniorhynchus is the main vector of Japanese encephalitis(JE).JE is caused by Japanese encephalitis virus(JEV),transmitted to humans through mosquito bites and poses a serious health threat.In this study,the genetic diversity,genetic differentiation,phylogenetic structure,population dynamics and distribution prediction of C.tritaeniorhynchus were described by obtaining mitochondrial gene of different populations from a wide range of samples collected in mainland China.The phylogenetic characteristics of different geographical populations of C.tritaeniorhynchus were correlated with the prevalence of JE,and analysis the risk regionalization of JE in China,to provide a basis for the development of prevention and control measures.The results are as follows:(1)A total of 585 C.tritaeniorhynchus samples were collected from 38 sampling sites in 21 provinces in mainland China.485 COI sequences,525 COII sequences,430 combined sequence of COI and COII genes were obtained,with the length of 658 bp,688bp and 1346 bp respectively.The mitochondrial gene of C.tricaeniorhynchus had the obvious preference.There are many mutation sites and high mutation rate.The COI gene haplotype diversity is 0.980 with 303 haplotypes.The COII gene haplotype diversity is 0.9774 with 262 haplotypes.The genetic diversity was high with higher haplotype and lower nucleotide diversity.(2)The phylogenetic of C.tricaeniorhynchus in mainland China was constructed by neighborhoodjoining,maximum-likelihood and bayesian methods.The results showed that the population genetic structure of C.tricaeniorhynchus was mainly divided into two branches and four branches.Haplotype network analysis had obvious genetic structure corresponds to the phylogenetic results.The genetic structure of C.tricaeniorhynchus in mainland China can be divided into four regions.Region I included southeast of northeast region,east of North China,west of central China,South China and southwest region.region II is mainly Yunnan.region III includes east of central China.Region IV included Inner Mongolia-Xinjiang Region and west of North China.(3)The results of genetic differentiation based on mitochondrial COI gene data showed that South China and Inner Mongolia-Xinjiang Regions had the highest degree of genetic differentiation(Fst=0.14302),while North China and central China regions had the lowest degree(Fst=0.01322).Based on COII gene showed that the genetic differentiation of South China and Inner Mongolia-Xinjiang Region was the highest(Fst=0.19191),and the genetic differentiation degree of northeast and central China region was the lowest(Fst=0.00968).Based on COI and COII genes showed that the highest genetic differentiation was found in Southern China and Mengxin(Fst=0.21704),and the lowest genetic differentiation was in North China and central China(Fst=0.01138).The genetic differentiation of three species of C.tritaeniorhynchus in Chinese mainland was moderately differentiated,and gene exchange was frequent(COI:Fst=0.01203,Nm=20.53;COII:Fst=0.03510,Nm=6.87;COI and COI:Fst=0.07271,Nm=3.19).(4)According to the results of phylogenetic and haplotype network,C.tritaeniorhynchus was grouped into four parts in mainland China.AMOVA analysis showed the population differentiation of C.tritaeniorhynchus mainly came from the population(more than 96%),while the genetic differentiation between regions and within populations was relatively small(less than 7%).Both the neutral test and the Bayesian Skyline Plot showed that the population of C.tritaeniorhynchus had experienced expansion.The Bayesian Skyline Plot showed that the population expansion occurred during the transition time from the Last Glacial Maximum to the middle of Holocene,and the population dynamics tended to be stable after expansion.(5)The results of species distribution prediction showed that during the Last Glacial Maximum,C.tritaeniorhynchus was mainly distributed in the Huaihe River Basin;after the middle Holocene,the population spread to the southwest,west to the central region of China and to the south coast.In 2050 and2070,the suitable distribution area of C.tritaeniorhynchus gradually moved to the north of China,but there was little difference from the present distribution area.From the above results,the genetic structure of C.tritaeniorhynchus in mainland China can be divided into four regions.The population genetic diversity is high,and the level of genetic differentiation is low.The population has expanded after the Last Glacial Maximum.With the climate warming,it will gradually spread to northern China,but was little difference from the present distribution area.According to the correlation between the phylogenetic characteristics of C.tritaeniorhynchus and the risk of JE,although different geographical populations with close phylogenetic relationship are far apart in geographical populations,they may have similar risk of JE transmission.It is suggested that long-term JE monitoring and control should be carried out to ensure the health of Chinese residents.