Fig. 2: Genomic admixture between H. elevatus and H. pardalinus.

a, Gene flow between species in sympatry is typically significantly greater (f₄ > 0, filled points) than the within-species gene flow between populations across the Amazon basin. Numbers next to the points indicate the population pairs compared (see Fig. 1b). A significant positive correlation indicates that the within-species gene flow between populations X and Y declines with increasing geographical distance relative to between-species gene flow at populations X and/or Y. b, Estimates of effective migration rate (Nm) within and between species using G-PhoCS. In the Amazon, between-species Nm (par_Ama/ele_Ama) is similar to within-species Nm between locations (par_Ama/par_Ama and ele_Ama/ele_Ama). The estimates for par_Ama/ele_Ama are denoted as filled and open circles and correspond to within and between location comparisons, respectively. c, The best supported demographic model based on the site-frequency spectrum analysis supports H. elevatus and H. pardalinus as reciprocally monophyletic (Extended Data Fig. 4). They initially diverged with continuous gene flow (933 to 221 kya) and after splitting into Amazonian and non-Amazonian populations, they came into secondary contact and continued exchanging genes until the present (45 kya to the present). Numbers within the blocks are effective population sizes in thousands. Arrows between groups represent continuous gene flow; numbers above or below arrows indicate 2Nm values.