Figure Legends
Figure 1 . Studied hybrid region. A) Map of the 20 sampled populations. Dark blue circles denote allopatric I. elegans , yellow circles denote allopatric I. graellsii . Inside of the Spanish hybrid region, dark blue, yellow and orange circles denote I. elegans dominant, I. graellsii dominant or both species, respectively (1 indicates north-west populations, 2 indicates north-central populations and 3 the Balearic population). B)Zoom of Spain, showing the geographic distribution of I. elegans over time, from 1888-1979 (8 provinces, dark-grey), 1980-1999 (13 provinces, medium grey) and 2000-actuality (12 provinces, light grey). White colour indicates onlyI. graellsii populations (15 provinces).
Figure 2. Strength of mechanical barriers to reach the copula in A ) north-central hybrid region (colonized by I. elegans at least 14 years ago), and B) north-western hybrid region (colonized by I. elegans at least 41 years ago). INTROGRESS estimates of ancestry proportion (HI) and heterospecific ancestry (HET) by using the 381 fixed SNPs for I. elegans , I. graellsii and hybrids fromC ) north-central hybrid region and D ) north-western hybrid region. F1 and F2 hybrids (orange) occupy the apex of the triangle. Backcrosses to I. elegans introgressed I. elegans and pure I. elegans(light blue). Backcrosses to I. graellsii , introgressed I. graellsii and pure I. graellsii (light blue).
Figure 3 . INTROGRESS individual and class proportions estimates of ancestry proportion in A ) north-central hybrid populations, and B) north-west hybrid populations. Populations were assigned to three qualitative measures depending on the frequency distribution of the different hybrid classes: unimodal hybridization pattern, when the distribution spans a range of admixture and backcrosses towards both parental species; bimodal hybridization pattern, when the distribution is deviated to the two parental or parental-like genotypes, and few hybrids (F1 and F2 hybrids); and introgressed hybridization pattern, when the distribution was deviated to one parental-like genotype.
Figure 4. Heterozygosity violin plot by population. A ) I. elegans without hybrids, B ) I. elegans with hybrids, C )I. graellsii with hybrids, D ) I. graellsiiwithout hybrids. Violin width represents the relative frequency of SNPs at each observed heterozygosity value, i.e., wider violin areas show higher number of SNPs at that heterozygosity. The line and the circle at each violin represents the median and the average HO, while the triangle points at the average HE. Finally, the value above each violin shows the percentages of SNPs that showed statistical differences between HO and HE (p < 0.05) to the total number of non-missing-data SNPs.