Genetic Diversity And Vector Competence For DENV-2 In Aedes Albopictus Populations From Different Regions Of China

Background:Aedes(Stegomyia)albopictus(Skuse,1894)has spread from Southeast Asia to all continents except Antarctica,and has become one of the fastest spreading and most threatening invasive species in the world.It is also the main vector of Aedes-borne virus in China,including strongly pathogenic and transmissible dengue virus(DENV).To understand the genetic diversity,gene flow and susceptibility to DENY of Ae.albopictus population is of guiding significance for mosquito monitoring and the prevention and control of mosquito-borne diseases in China.Methods:A set of polymorphic microsatellite markers were used to amplify the genomic DNA of Ae.albopictus from 34 populations in China,then sequence and analyze the population genetic structure,to understand the overall genetic structure,clustering and differentiation of Ae.albopictus populations in China.Genomic DNA of eight Ae.albopictus populations from different clustering groups in China were sequenced to identify genome-wide SNP loci based on restriction site-associated DNA sequencing(RAD-seq).The spatial genetic structure was analyzed and compared to those exhibited by genome-wide SNP,mitochondrial cytochrome c oxidase subunit 1(cox1)and microsatellites in the populations.Eight Ae.albopictus populations from different clustering groups in China were fed fresh sheep blood containing DENV-2.The heads,salivary glands and midguts of the mosquitoes were dissected at 14 days post infection.The infection status and DENV-2 loads of these tissues were detected by RT-qPCR.Quantification of Wolbachia and immune-associated gene expression in mosquitoes were also detected by RT-qPCR to explore their impact on the vector competence.Results:A total of 153 distinct alleles were identified at the 13 microsatellite loci in 977 mosquito samples from 34 Ae.albopictus populations in China.Genetic parameters such as polymorphism information content,heterozygosity,allele richness and fixation index revealed highly polymorphic markers,high genetic diversity,and low population genetic differentiation.Based on Bayesian analysis,the 34 populations were divided into five different clusters:southern,western,central,eastern and northern.Genetic structure analysis showed that Ae.albopictus populations in China were regionally clustered.The Mantel test indicated a positive correlation between genetic distance and geographical distance(R2=0.245,P=0.01).A total of 9,968 genome-wide SNP loci in 105 specimens and 32 haplotypes of cox1 in 231 specimens were identified in the eight Ae.albopictus populations from different clustering groups in China.Based on the genome-wide SNP data,asymmetric gene flow was detected among the five Ae.albopictus clustering groups,and it was higher from south to north and west to east regions than the opposite directions.The genome-wide SNPs provided a better resolution and strong signals of novel spatial population genetic structures than those from the cox1 data and a set of previously genotyped microsatellites.In addition,there was no significant difference in infection rate,dissemination rate and potential transmission rate among the eight Ae.albopictus populations from different clustering groups in China at 14 days after DENV-2 infection.The amount of DENV-2 in the mosquito midguts,heads and salivary glands from southern-western China were slightly lower than those from eastern-central-northern China.The DENV-2 loads in whole mosquitoes showed a negative correlation with the expressions of Rell gene(r=-0.285,P=0.011)and STAT gene(r=-0.289,P=0.009).The density of the wA1bB strain was significantly higher than that of wAlbA in the eight Ae.albopictus populations.The relative density of the wA1bB strains showed a negative correlation with the mean loads of DENV-2 in heads(r=-0.729,P=0.040),in salivary glands(r=-0.785,P=0.021)and in whole mosquitoes(r=-0.909,P=0.002).Conclusion:Strong gene flow probably inhibited population differentiation and promoted genetic diversity among populations of Ae.albopictus from different regions of China.The gene flow from south to north and west to east may represent a potential risk of dengue outbreaks in non-dengue endemic areas.The data on the spatial genetic structure of Ae.albopictus population in China and their susceptibility to DENV-2 have important implications for understanding the epidemiology,prevention,and control of vector-borne diseases.