Fig. 2: Population structure.

a Admixture panels showing the best-scoring cluster configurations out of 15 runs produced by NGSadmix for K-values ranging from two to 10. The X axis represents the admixture proportion and the Y axis indicates the sample ID and taxon correspondance. Thick black horizontal lines draw the taxon boundaries according to current classification. Taxa are labeled according to the following abbreviations: ARD: O. t. ardens, NIG: O. t. nigellicauda, ROB: O. t. robinsoni, TRA: O. t. traillii, MEL: O. mellianus. Optimal number of discrete groups returned by DeltaK is 4. B and C: PCA plots showing how samples cluster along continuous axes of variation when including all samples (b) and after excluding island taxa (O. t. ardens and O. t. nigellicauda) (c).