The Genomics of Speciation and Pattern Evolution in (butter)flies. Chris Jiggins. Dept Zoology, University of Cambridge, Cambridge, United Kingdom.

   Heliconius butterflies are a rapidly radiating neotropical genus widely used in studies of ecology, behaviour, mimicry and speciation. Closely related species typically differ in several aspects of their ecology and behaviour, and in particular their mimetic wing patterns. 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. 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. Furthermore, we investigate genome-wide patterns of introgression between hybridising species, H. melpomene and H. cydno by comparing genetic differentiation in sympatry and allopatry, and applying various different tests for introgression. We find a strong signal of introgression throughout the genome, and estimate that at least 25% of the genome has been shared between the Panamanian sub-populations of the two species. Furthermore, we detect patterns divergence and linkage disequalibrium that are consistent with recent or ongoing gene flow in sympatry. Introgression appears to be significantly reduced on the Z chromosome, which is consistent with observed female hybrid sterility between these populations. We also observe numerous narrow islands of divergence, which include wing patterning loci known to be under divergent selection. Overall these results show that these species have diverged and persisted despite pervasive genome sharing.