Genome-wide patterns of divergence and gene flow across a butterfly radiation

The Heliconius butterflies are a diverse recent radiation comprising multiple levels of divergence with on-going gene flow between species. The recently sequenced genome of Heliconius melpomene allowed us to investigate the genomic evolution of this group using dense RAD marker sequencing. Phylogenetic analysis of 54 individuals robustly supported reciprocal monophyly of H. melpomene and H. cydno and refuted previous phylogenetic hypotheses that H. melpomene may be paraphylectic with respect to H. cydno. H. timareta also formed a monophyletic clade closely related but distinct from H. cydno with H. heurippa falling within this clade. We find evidence for pervasive gene flow between sympatric populations of the sister clades H. melpomene and H. cydno/timareta, particularly between H. cydno and H. melpomene from Central America and between H. timareta and H. melpomene from the eastern slopes of the Andes. Between races, divergence is primarily explained by isolation-by-distance; and there...