Comparison of mitochondrial (A) and nuclear (B-D) cline concordance using Barton's concordance analysis. Plots show the individual per-locus hybrid index plotted against the hybrid index calculated over all loci. The equal-introgression expectation lies on the diagonal. Per locus fits can deviate toward either genetic background (α) and by having more or less abrupt change (β) (see text). The nuclear clines are concordant with each other (and the consensus nuclear cline), while the mitochondrial cline is not; individuals are more likely to have klauberi mtDNA than expected under equal introgression across loci (α = 0.753).