Species And Genetic Diversity Of Curculio Spp.in China

Quercus plant is the most widely distributed and the most diverse group in the Fagaceae,which can be found in each provinces of China.It is an important afforestation and landscape tree species,and has important economic and ecological value.Due to the seeds of Quercus are large and rich in starch and other nutrients,they often become the priority prey of rodents,birds and arthropods.Among them,Curculio spp.is the most harmful and widespread pest of Quercus,which seriously affects the fate of seeds and the natural regeneration of Quercus forests.It is difficult to distinguish based on traditional morphological methods,which brings great challenges to the research of pest biology,comprehensive prevention and control technology and the protection of Quercus resources.This study is taking the inter-trophic acorn weevils and their Quercus host plants as the study system,investigated the species diversity,host specificity,and species diversification of acorn weevils based on mitochondrial and nuclear genes.Through the development and utilization of SNP molecular markers,the population structure,genetic diversity and gene flow level of Curculio bimaculatus were analyzed.The main findings are as follows:(1)Acorns were collected in 18 provinces of China during the seed rain from August to October 2019,and the samples of larvae from 11 host plants of Quercus were collected.The sequences of mitochondrial gene COI and nuclear gene EF1-α of 520 samples were analyzed and 119 and 193 haplotypes were obtained.The results of phylogenetic tree based on haplotypes show that all samples of weevils were divided into 11 clades,and the genetic distance between each clades had diverged into species level.After homology comparison,4 species of Curculio were identified,C.sikkimensis、C.dentipes、C.bimaculatus 、C.robustus and other 7 clades may be undescribed species due to their independent phylogenetic locations of known weevils species in phylogenetic tree.(2)Analysis of the genetic diversity of acorn weevils showed that the populations had high haplotype diversity and nucleotide polymorphism,and the overall genetic differentiation was obvious.The genetic diversity of most populations was affected by geographic isolation.The analysis of population dynamics based on the COI gene found that the acorn weevil populations was in a stage of expansion but not significant(COI:Tajimas’ D=0.49,p>0.1;Fu’s Fs=0.90,p>0.1;EF1-α:Tajimas’ D=-1.93,p>0.05;Fu’s Fs=-7.25,p>0.05),no significant expansion had occurred recently,and the status of various population was relatively stable.The analysis of genetic variation of various populations shows that there was a large differentiation among different geographical populations of each clades(Fst>0.15),and there was an obvious geographical isolation phenomenon in the acorn weevil populations.(3)Among the 11 acorn weevil species,7 were generalist and the others are specialist.The most typical one is the C.bimaculatus,which had as many as 7 host plants and had the smallest host specificity among all acorn weevil species.The distribution range of the acorn weevil populations was extremely uneven,and there were 8 wide-area populations.Clade Ⅹ(C.bimaculatus)had the widest distribution,distributed in 10 sampling points,and 3 narrow-region populations,distributed in only 1 sampling point.(4)Based on the simplified genome sequencing technology,SNP data mining was performed on 115 samples of the real population of acorn weevils in China,and a total of 178,467 SNP mutation sites were obtained.There were three subpopulations real population of acorn weevils,which can be divided into two large groups: southeast coast and inland.The genetic diversity among the various populations was obvious,the average observed heterozygosity was 0.0603~0.0729,and the average expected heterozygosity was 0.0459~0.208.Among the geographical populations,the Jiangxi(JX)population has the highest genetic diversity(Pi=0.2206),while in the host population,the highest genetic diversity(Pi=0.2108)exists in the Qurecus dentata(HS)population.The gene flow results showed that the Jiangxi and Castanopsis carlesii populations were the first to be separated from other populations,and extensive gene exchanges existed with multiple populations.