3.3 Population genomic structure
The PCA identified significant population structure across the sampled range of P. auritus . PC1 explained 25.89% of the variation and separated the three northern sites (EF, ND, TM) from the remaining six sites (CM, MC, MK, LP, KS, GC). PC2 explained 9.26% of variation and separated GC, the southernmost coastal site, from all other sites (Fig. 1b). FastStructure analyses also revealed a pattern of population structure that is organized latitudinally into five distinct populations: 1) EF, ND, and TM, 2) CM, 3) MC and MK, 4) KS and LP, and 5) GC.
Pairwise FST values between sites ranged from 0.017 to 0.450 (mean = 0.234; Appendix 3), indicating low to moderate levels of genomic differentiation between sites. We found a significant correlation between pairwise FST and geographic distances between the sites (Mantel r = 0.6642; mantel simulated p-value = 0.001), suggesting a strong pattern of IBD.