Fig. 2. Signatures of historical introgression across a modified Colias species-tree phylogeny where the placement of C. phicomone and C. palaeno has been changed according to their placement in the SNAPP tree.

Each cell in the grid indicates the f-branch statistic f_b, identifying excess sharing of derived alleles between branch nodes on the y axis (blue dotted lines) and individual species on the x axis. A darker color in the heatmap indicates higher f_b, suggesting gene flow between that branch and species. Results indicate a strong signal of introgression between C. phicomone with Eurasian taxa, as well as between an ancestor of the C. nastes clade and both Eurasian and North American taxa. There is also a strong signal of introgression between C. interior and C. pelidne. Species and internal nodes are colored by the species’ current distribution where purple = South America, blue = North America, orange = Holarctic, and green = Eurasia and Northern Africa.