Figure 1.

Genetic diversity in NZ populations of Argentine stem weevil. (A) Weevil sampling locations. We collected Argentine stem weevils from 4 locations in the North Island and 6 locations in the South Island of New Zealand. Greymouth is in the South Island, but North of the Main Divide, which runs along the Southern Alps and partitions the South Island. The number of weevils genotyped (after filtering) from each location is shown on the map. Map tiles by Stamen Design under CC BY 3.0, with data by OpenStreetMap under ODbL. (B) Mean observed heterozygosity for each population. (C) Pairwise F_ST values between populations. (D) Principal components analysis (PCA) describing total variability and (E) discriminant analysis of principle components (DAPC) describing between-population variability of 116 individuals genotyped at 18,715 biallelic sites. In the PCA (D), populations overlap on the first two principal components (PC1 and PC2), but weevils sampled from higher latitudes have lower scores on PC1. PC1 and PC2 together explain 9.2% of variance in the dataset, indicating a high level of unstructured genetic variation in weevil populations. In the DAPC (E), the major linear discriminant (LD1) explains 96.7% of between-group variability. LD1 splits individuals from North and South of the Main Divide. LD2 separates Lincoln individuals from other individuals. (F) Posterior probability of group assignment for each individual. All populations contain individuals with high posterior probabilities of membership to other populations. This is consistent with gene flow between populations. We did not detect evidence of gene flow between populations from North and South of the Main Divide. Individuals sampled from Lincoln had the lowest posterior probabilities of membership to other populations.