Genomics of Neotropical biodiversity indicators: two butterfly radiations with rampant chromosomal rearrangements and hybridisation

A major question in evolutionary biology is what drives the diversification of lineages. Rapid, recent radiations are ideal systems for addressing how new species arise because they may preserve key morphological and ecological adaptations associated with speciation. Melinaea and Mechanitis are two classic examples of rapidly radiating Neotropical butterfly genera of the tribe Ithomiini. They were models for early studies of Amazonian biogeography and colour pattern mimicry and have been proposed as biodiversity indicators. We generated reference genomes for five species of each genus, and whole-genome resequencing data of most species and subspecies covering a wide geographic range to assess phylogeographic relationships, patterns of hybridisation and chromosomal rearrangements. We find rampant evidence of hybridisation within both radiations, which may have facilitated their rapid diversification. Our data also provide evidence for a putative hybrid species that combines traits of both parental species. Moreover, many chromosomal fusions and fissions were identified, even between sister species. Our data also help resolve the classification of these notoriously taxonomically challenging butterflies. We conclude that interactions between geography, hybridisation and chromosomal rearrangements have contributed to these two rapid radiations in the highly diverse Neotropical region.