Invasion Genetics Of Fall Webworm (Hyphantria Cunea) In China Based On Microsatellite Markers

The fall webworm (FWW), Hyphantria cunea (Dury) (Lepidoptera:Arctiidae), is a destructive invader of forestry plantations and horticultural plants. In this study, we developed the first set of microsatellite markers for FWW, investigated the records of introduction and dispersal of FWW in China, sampled 24 natural populations spanning the distribution range of FWW in China and analysed the genetic population structures based on microsatellite loci and mitochondrial genes. The results and conclusions were as follows:Here, we developed 48 microsatellite markers for FWW from SSR enrichment libraries. Sequences isolated from libraries were sorted into four categories, Unique, UnBLASTable, Grouped and Redundant. Our results suggest that sequences classified as Grouped should not be used for microsatellite primer design. The genetic diversity of microsatellite loci was assessed in 72 individuals from three populations. The number of alleles per locus ranged from 2 to 5 with an average of 3. The observed and expected heterozygosities of loci ranged from 0 to 0.958 and 0 to 0.773, respectively. A total of 18 out of 153 locus /population combinations deviated significantly from Hardy-Weinberg equilibrium. Moreover, significant linkage disequilibrium was detected in one pair of loci. In the neutral test, two loci were grouped into the candidate category for positive selection and the remainder into the neutral category. In addition, a complex mutation pattern was observed for these loci, and FST performed better than did Rsr for the estimation of population differentiation in different mutation patterns. The results of the present study can be used for population genetic studies of FWW.We analysed the number, spatial distribution and area of sites affected by FWW changing with time, by literature investigation. FWW showed low spread rates in the initial 25 years since invasion, and a lag phase between 1999 and 2003, but the rate increased abruptly in the decade that followed. Preliminary analysis suggested that the dispersal of FWW was likely affected by anthropogenic activity, control campaigns, geographical barriers and climates. The results provide opportunities to investigate and test evolutionary biology or population genetics issues.In this study, we aimed to establish patterns of genetic variation associated with the well-documented history of invasion and expansion of the FWW, into China. Patterns are expected to be affected by geographical and environmental factors as well as a history of control campaigns. We genotyped 18 polymorphic microsatellite loci derived from 657 individuals (25 populations) collected from across the distribution range of FWW in China and a native population in USA, and we also sequenced mitochondrial DNA from a subset of 70 individuals. Population genetic structure was analysed by using three Bayesian cluster methods (STRUCTURE, GENELAND and TESS) and a multivariate principal component analysis (PCA). The scenarios of invasion history were tested using an approximate Bayesian computation (ABC) approach. A multiple matrix regression was performed to assess the relative contributions of geographical and environmental isolation. The average allelic richness and mitochondrial haplotype diversity of the FWW populations in China was very low compared to native populations from USA, pointing to a significant bottleneck during colonization. Based on the nuclear markers, two genetically separated groups were identified along with a contact zone between them. ABC analyses suggested a single introduction into the east with subsequent westward expansion. Geographic distance was more important than environmental distance in contributing to genetic differentiation, and geographical barriers were likely to have restricted gene flow, with the contact zone occurring in a mountainous area. The combination of genetic data and historical records of the expansion suggests that geographical barriers and control campaigns have affected the formation and persistence of the two genetic groups. Our study points to ways in which genetic differentiation can develop rapidly in an invasive species after its introduction.