highly significantP <0.001
As could have been expected from the significant among-population differentiation, there was a strong, highly significant isolation by distance observed both at the level of the entire species (Mantel test, r = 0.89, P <0.001) and within genetic clusters (North: r = 0.78, P <0.001; South: r = 0.78, P <0.001) ( Fig.