Fig. 3: Past introgression among tropical eels.

a Likelihood support of individual RAD loci for different relationships of A. interioris: as sister to A. marmorata and A. luzonensis (bottom left), as sister to A. obscura and A. bicolor (bottom right), and as sister to a clade formed by those four species (top). The position of each dot shows the relative likelihood support of one RAD locus for each of the three tested relationships, with a distance corresponding to a log-likelihood difference of 10 indicated by the scale bar. The central triangle connects the mean relative likelihood support for each relationship. A black dot inside that triangle marks the central position corresponding to equal support for all three relationships. Sample sizes (n) report the number of loci that support each of the two competing relationships connected by that edge. b Heatmap indicating maximum pairwise D (above diagonal) and f₄ (below diagonal) statistics (see Table 1). Combinations marked with “x” symbols indicate sister taxa; introgression between these could not be assessed. Asterisks indicate the significance of f₄ values (*p < 0.05; **p < 0.01; ***p < 0.001; not adjusted for multiple comparisons; see Table 1 for precise values), determined through one-sided comparison with coalescent simulations with the F4 software⁵². The cladogram on the left summarizes the species-tree topology according to a and the significant signals of introgression according to b. c, d Comparisons of the maximum D value per species with the species' geographic range or population mutation rate Θ. Geographic range was measured as the number of geographic hexagons (see Fig. 1) in which the species is present, and Watterson’s estimator¹²³ was used for the population mutation rate Θ. n.s. not significant. e Genomic patterns of phylogenetic relationships among A. marmorata, A. obscura, and A. megastoma, based on WGS reads mapped to the 11 largest scaffolds (those longer than 5 Mbp) of the A. anguilla reference genome. Blocks in light gray show 20,000-bp regions (incremented by 10,000 bp) in which A. marmorata and A. obscura appear as sister species, in agreement with the inferred species tree; in other blocks, A. megastoma appears closer to either A. obscura (gray) or A. marmorata (dark gray).