Rampant Genome-Wide Admixture across the Heliconius Radiation

Abstract

How frequent is gene flow between species? The pattern of evolution is typically portrayed as a phylogenetic tree, yet gene flow between good speciesmay be an importantmechanismin diversification, spreading adaptive traits and leading to a complex pattern of phylogenetic incongruence. This processhas thus farbeenstudiedmainly amonga fewclosely relatedspecies, or ingeographically restricted areas such as islands, but noton the scale of a continental radiation.Using a genomic representation of40 out of47 species in the genus, we demonstrate that admixture has played a role throughout the evolution of the charismatic Neotropical butterflies Heliconius. Modeling of phylogenetic networks based on the exome uncovers up to 13 instances of interspecific gene flow. Admixture is detected among the relatives of Heliconius erato, as well as between the ancient lineages leading to modern clades. Interspecificgeneflowplayeda role throughout the evolutionof thegenus, althoughtheprocess hasbeenmost frequent inthe clade ofHeliconiusmelpomene and relatives.We identifyHeliconius hecalesia and relatives as putative hybrids, including newevidence for introgression at the loci controlling the mimeticwing patterns.Models accounting for interspecific gene flow yield a more complete picture of the radiation as a network, which will improve our ability to study trait evolution in a realistic comparative framework.