Uplift-associated population structure
PCAs and neighbor joining trees revealed populations in the uplift zone form genetically distinct clusters in both L. segnis and O. neglectus . These findings were further confirmed by sNMF results where the K with the lowest cross entropy value (K = 4) revealed spatial structuring closely associated with the Akatore uplift zone for both species. In the amphipod P. karaka , by contrast, virtually no population structure was detectable along the relevant coastlines (Fig. 2; Fig. S1-S3). Overall, the strong uplift-associated genetic structure in strictly intertidal epifaunal species (L. segnis andO. neglectus ) closely matches that of their intertidal macroalgal hosts (D. antarctica and D. poha ; Fig. 2; Fig. S1-S6). In all four of these strictly intertidal species, a shallow yet distinct genetic cluster is tightly linked to the Akatore Fault boundaries (from Taieri Island in the north to Toko Mouth in the south; Fig. 1). Additionally, in both intertidal hosts and their epifauna, genetic admixture is detectable only at the fringes of the uplifted region (Fig. 2).