The evolutionary importance of hybridization and introgression has long been debated. Hybrids are usually rare and unfit, but even infrequent hybridization can aid adaptation by transferring beneficial traits between species. Here we use genomic tools to investigate introgression in Heliconius, a rapidly radiating genus of neotropical butterflies widely used in studies of ecology, behaviour, mimicry and speciation. We sequenced the genome of Heliconius melpomene and compared it with other taxa to investigate chromosomal evolution in Lepidoptera and gene flow among multiple Heliconius species and races. Among 12, 669 predicted genes, biologically important expansions of families of chemosensory and Hox genes are particularly noteworthy. Chromosomal organization has remained broadly conserved since the Cretaceous period, when butterflies split from the Bombyx (silkmoth) lineage. Using genomic resequencing, we show hybrid exchange of genes between three co-mimics, Heliconius melpomene, Heliconius timareta and Heliconius elevatus, especially at two genomic regions that control mimicry pattern. We infer that closely related Heliconius species exchange protective colour-pattern genes promiscuously, implying that hybridization has an important role in adaptive radiation.
Bibliographical noteFunding Information:
Acknowledgements We thank the governments of Colombia, Peru and Panama for permission to collect the butterflies. Sequencing was funded by contributions from consortium members. We thank M. Abanto for assistance in raising the inbred line. Individuallaboratorieswere fundedbythe LeverhulmeTrust (C.D.J.),the JohnFellFund and Christ Church College, Oxford (L.C.F.), The Royal Society (M.J., C.D.J.), the NSF (W.O.M., M.R.K., R.D.R., S.M., A.D.B.), the NIH (M.R.K., S.L.S., J.A.Y.), the CNRS (M.J.), the ERC (M.J.,P.W.H.H.), the Banco delaRepública andCOLCIENCAS(M.L.) and the BBSRC (J.M., C.D.J., M.L.B. and R.H.f.-C.).