Geographic distribution, mtDNA haplotype distribution, and autosomal AFLP based admixture proportions of glaucous gull (L. hyperboreus) and American herring gull (L. smithsonianus) populations. The breeding ranges (blue for smithsonianus, grey for hyperboreus), and sampling locations (yellow for smithsonianus, red for hyperboreus). For each of the 12 colonies a boxed area contains all individuals that we used for the analyses of 230 AFLP loci and HVR1 and cytB mtDNA sequencing. Colony name abbreviations above the top-left corner of each box correspond with those in Table 1. Genotypes were analysed by STRUCTURE and revealed the presence of three distinct ancestral populations among present day smithsonianus and hyperboreus. In this figure these are represented by three different colours (pale yellow, pale blue, and red). Each individual is represented by a single (multi) coloured bar, on top of which there is either black-filled square (indicating that this individual displayed an mtDNA clade 1 haplotype), or a white square (representing clade 2 mtDNA haplotypes). The proportion of each colour within a single bar indicates the relative contribution of one of these three ancestral populations to the genome of that gull. For instance, the bottom left panel represents nine smithsonianus from a Nearctic population (PEI). They all display a clade 2 mtDNA haplotype (white squares). Among the nine birds, the leftmost three display a nearly 100% fixed autosomal contribution of the ancestral population coded by pale yellow to their genomes. The rightmost three individuals show a near 100% fixed contribution of another (red) ancestral population. The remaining three individuals display various degrees of admixed contributions of the three ancestral populations.