| Aedes aegypti is a small black mosquito species,originated in Africa and is mianly distributed in tropical and subtropical regions throught the world.It can breed all year round.Although the flying distance of adult mosquitoes is limited,the average diffusion radius within 100 meters,Ae.aegypti eggs can resist drought and achieve long distance passive diffusion with adult mosquitos and pupae by trade and human activities.The distribution of Ae.aegypti in China is below 22 degree north latitude including Hainan,Qinzhou and Weizhou island of Guangxi,Zhanjiang of Guangdong and Taiwan,revealed by the scale survey in 1980s.There was no Ae.aegypti found in all surveys before 2000 in Yunnan.Ae.aegypti is found in Ruili,Mangshi,Mengla,Menghai,Jinghong,Longchuan,Lushui,has become an important invasive species in Yunnan province since it was foung at the first time in Ruili Jiegao Port.Ae.aegypti is the main vector of Dengue fever.DF is the most rapidly spreading viral disease in the world and there are approximately 50 million new cases of dengue per year and about 2.5 billion people(more than 40%)are at the risk of DF around the world.In recent years,the incidence of DF has increased sharply in the world.Yunnan had its first dengue outbreak with imported cases in 2008.Subsequently,dengue outbreaks have been reported annually in Yunnan,especially after 2013.Prevention of dengue depends entirely on the control of the vector populations because there are currently no licensed vaccines or specific therapeutics available.To explore the origin and pathways of Ae.aegypti invasion and maintain effective vector control strategies,a study on the population genetic structure of the among Ae.aegypti populations are required.In this study,the genetic diversity and genetic structure of 17 populations of Ae.aegypti from Yunnan,Guangdong and Hainan province were studied by two different molecular markers,microsatellite markers and mitochondrial genes.The results are as follow:(1)11 pairs of microsatellite primers were obtained by database search method,and 1 pairs of primers were found in the literature.These primers can be successfully amplified and showed polymorphic results.The number of alleles is between 6 to 16,and the average polymorphic information(PIC)is 0.551.No linkage disequilibrium was found among all loci.These microsatellite primers can be uesd to study on the population genetics of Ae.Megypti.(2)Results based on microsatellite markers showed that the average value of alleles obtained at each site was between 3.083-5.583,and the heterozygosity was between 0.309-0.464,the average value was 0.389,which was slightly lower than the average expected heterozygosity of 0.500.The diversity of CAJ population in Jinghong is the highest.All Ae.aegypti population conforms to the Hardy-Weinberg equilibrium expect those two laboratory populations from Guangdong and Hainan province.The bottleneck effect test shows that all natural populations experiencing bottleneck effects come from Ruili and Jinghong.Cluster analysis of genetic structure by different softwares showed that 17 populations were divided into 3 groups.The first group is Dehong,Ruili,Longchuan County and Gengma County of Lincang City,relatively close to the western region.The second group consisted of Ae.aegypti population from Jinghong and Menghai,Xishuangbanna.The population of Mengla County in Xishuangbanna consists of the third group with population from Guangdong and Hainan province.The results of genetic differentiation showed that there was a certain degree of inbreeding in various areas.The paired Fst values are mostly less than 0.15 indicating that these populations are at low differentiation stage.AMOVA analysis results based on clustering results showed that the percentage of variation between groups was only 8.71%.The genetic differentiation among individuals was the most significant,and the percentage of variation was 63.48%.It also proved that the degree of differentiation among different populations was low.Correlation test showed that there was a significant positive correlation between genetic distance and geographical distance(R2=0.3747,P<0.01).(3)In this study,3 mitochondrial genes COI,ND4 and ND5 were choosed to analyze the genetic diversity of 17 populations.The results showed that COI gene had 11 haplotypes.The haplotype diversity index of the total population was 0.5670,and the nucleotide diversity index was 0.00344.The ND4 gene has 15 haplotypes.The haplotype diversity index of the total populations is 0.5603,and the nucleotide diversity index is 0.02236.The results of population expansion test showed that the P values with negative test values were all less than 0.05,indicating that these populations had not been expanded in history.Based on the haplotype network map of 3 genes,each gene has two dominant haplotypes,one in Jinghong region and the other in Ruili region.But the populations of Mengla are shared by those two haplotypes and the number is not very different.That can not be accurately divided.The results of genetic differentiation showed that the paired Fst values based on mitochondria DNA were higher than microsatellites.That the Fst value between LGD population and other populations is higher indicates this population has higher genetic differentiation.Compared to the value among groups,the paired Fst value within groups is lower.Although differences within individuals still occupy the largest proportion,and the Fsc values between groups are relatively large,showing a state of a high differentiation,indicated by AMOVA results.(4)In conclusion,Ae.aegypti in Yunnan has a multiple independent invasion.The population in Ruili region invaded from north Myanmar.Ae.aegypti invaded Jinghong area by ships on the Lancang river-Meikong river from northeast Myanmar or west Laos.Ae.aegypti in Mengla County invaded through Mohan port from north Laos.Conclusion:(1)microsatellite primers obtained from this study can successfully amplify Ae.aegypti population in China.Their stability and polymorphism are high.(2)The study of microsatellite markers and mitochondrial genes found that 17 groups were divided into 3 groups:the first group centered in Ruili City andLongchuan County of DeHong and Gengma County in Lincang City;the second group was composed of Jinghong City and Menghai County of Xishuangbanna;populations from Mengla County of Yunnan province t,Guangdong and Hainan consisted of the third group.Population clustering and genetic differentiation among populations are consistent with geographical regions. |
PDF Full Text Request