Fig. 4

Population genomic analysis of red turpentine beetles in the original and invaded regions. a Neighbor-joining phylogeny of all Dendroctonus valens individuals constructed from genome-wide SNP data using the PHYLIP software based on distance data. Abbreviations for sampling sites are as follows: AZ, Arizona; CO, Colorado; CA, California; MT, Montana; WI, Wisconsin; MN, Minnesota; LN, Liaoning; NM, Inner Mongolia; HB, Hebei; SX, Shanxi; SHX, Shaanxi. b Principal component analysis (PCA) of resequencing individuals based on the first two principal components. American population was divided into three subpopulations based on top two components PC1 and PC2. PC1 could separate WIMN from China and other two American subpopulations, while the second axis could distinguish three American subpopulations. c Population genetic structure of individuals sampled from geographic locations in China and North America revealed by the ADMIXTURE software. The cross-validation error was the lowest when K = 3, suggesting three ancestral populations were best supported by the data. Notably, American population could be divided into three sub-groups based on the population structure. d Population genetic metrics in China and three American subpopulations. Genome-wide median pairwise fixation index (F_ST) was calculated for three contrast groups between China and American subpopulations, and genome-wide median nucleotide diversity (Pi) was computed for each population. e Genome-wide distribution of F_ST in three contrast groups between China population and three American subpopulations. Notably, CAMT vs. CHN group displayed the smallest variation among three contrast groups. Wilcoxon rank sum test was used for determination of statistical significance between groups. f Gene flow analysis across different geographical subpopulations in native and invaded regions. The possible gene flow events across geographic subpopulations were inferred using TreeMix when assuming the occurrence of four gene flow events