Fig. 1: Summary of key findings, geographical distributions of species and evidence that H. elevatus has a hybrid genome.

a, Evolutionary relationships and main introgression events described in this study. We test the hypothesis that introgression of major pre-mating and post-mating ecological isolating traits from H. melpomene led to the establishment of H. elevatus as a new stable hybrid species. Mya, million years ago. b, Geographical distributions of major clades. Locations at which both H. elevatus and H. pardalinus were sampled are numbered. c, Distance-based network using genome-wide independent SNPs. This concatenated tree shows the existence of two distinct clusters, Amazonian versus non-Amazonian, in both H. elevatus and H. pardalinus. d, Topology weighting analysis (TWISST) showing the percentage of the 11,509 non-overlapping genomic windows of 1,000 SNPs in which the majority of subtrees (that is, topology weighting ≥ 0.5) clusters H. elevatus (ele) with either H. pardalinus (par) (93.2%; top) or H. melpomene (mel) (0.52%; bottom). Note that although H. elevatus groups with H. pardalinus in 93.2% of windows, only 1.61% of those trees yield the two species as reciprocally monophyletic. By contrast, all three species are monophyletic in 81% of the windows for which H. elevatus groups with H. melpomene. Subscripts indicate geographical distributions for H. elevatus and H. pardalinus (Ama, Amazon; And, Andes; Gui, Guianas) and subspecies for H. melpomene (Agl, aglaope; Ams, amaryllis). e, A multispecies coalescent model with introgression supports a hybrid origin of H. elevatus, with the introgression time coinciding closely with the origin of the species (the 95% HPD intervals are given within parenthesis). Images of butterfly wings are copyright of the authors and Michel Cast.