Fig. 1: Ancient versus contemporary hybrids.

Conceptual overview and a comparative summary of genomic patterns expected in ancient hybrids (a) versus contemporary hybrids (b). Histograms show narrow (ancient) versus wide (contemporary) distributions of hybrid indexes. In ancient hybrids, ancestry blocks (gray vs. blue segments) have been broken up by recombination and some have stabilized, that is, fixed within the hybrid lineage. In contemporary hybrids, larger ancestry blocks are expected and these vary more among individuals. Plots show the expected effect of selection on ancestry frequencies and patterns of introgression in ancient and contemporary hybrids, respectively. In ancient hybrids, selection (pink arrows) shifts ancestry frequencies. In contemporary hybrids, selection shifts genomic clines for individual loci relative to the genome-wide average (dashed line). c Diagram represents the hypothesized history of hybridization in Lycaeides. Our results suggest that Jackson Hole Lycaeides are ancient hybrids, with ancestry blocks from L. idas and L. melissa (akin to panel a), whereas Dubois are contemporary hybrids with ancestry blocks from Jackson Hole Lycaeides and L. melissa (akin to panel b with colors denoting Jackson Hole vs. L. melissa ancestry).